. -Forestry. Main Library

•b\°l

STUDIES IN FORESTRY

NISBET

HENRY FROWDE

OXFORD UNIVERSITY PRESS WAREHOUSE

AMEN CORNER, E.G.

MACMILLAN & CO., 66 FIFTH AVENUE

STUDIES IN FORESTRY

BEING

A SHORT COURSE OF LECTURES

ON THE

PRINCIPLES OF SYLVICULTURE

DELIVERED AT

THE BOTANIC GARDEN, OXFORD

During the Hilary and Michaelmas Terms, 1893

BY

JOHN NISBET, D.OEC.

OF THE INDIAN FOREST SERVICE

AUTHOR OF 'BRITISH FOREST TREES'

EDITOR OF THE SIXTH EDITION OF BROWN'S 'THE FORESTER'

TRANSLATOR OF KAUSCHINGER AND FURST'S 'PROTECTION OF WOODLANDS,'

AND OF HARTIG'S 'ANATOMY AND PHYSIOLOGY OF PLANTS,' ETC.

AT THE CLARENDON PRESS
1894

SD37-3
N/fc .«

Arric.-Ft>r*Btrv. Main Librar?

PRINTED AT THE CLARENDON PRESS

BY HORACE HART, PRINTER TO THE UNIVERSITY

PREFACE

THE various chapters of the present work formed two short
courses of lectures on the Principles of Sylviculture, which
were delivered, during the Lent and Michaelmas Terms of last
year (1893), at tne Botanic Garden in Oxford, where Professor
Vines, F.R.S., was good enough to arrange for their delivery
in his class-room. I am further indebted to him for kind
assistance given during the revision of the proofs, and gladly
take this opportunity of tendering my thanks to him on both
accounts.

With the permission of the Secretary of State for India,
I have been enabled to make several of the chapters more
complete than they might otherwise have been, by utilizing
freely the greater portion of a series of six Essays on Sylvi-
cultural Subjects, which were written by me in Bavaria during
1892, and were published in 1893 by the Government of India
for distribution among their Forest Officers.

As will be apparent throughout every chapter, my convictions
regarding economic Forestry, i. e. Sylviculture, have been formed
in a Teutonic school. But Science is Truth ; and in acquiring
information with regard to the growth of Forest Trees, or
concerning any other branch of natural knowledge, it ought
to be a matter of perfect indifference from what well this may

78M6O

viii Preface

be drawn. I have therefore had no hesitation in boldly
acknowledging the German sources from which many of the
lessons I am trying to teach have been learned.

With regard to Forestry, Britain stands in a very peculiar
position. Although she has now only a very insignificant area
under woodlands in comparison with any other great European
power, yet all her national and commercial prosperity is
mainly due to her forest wealth — first of all, in the time of
the formation of the coal-measures, and later on again in the
days of the ' wooden walls of England.' For what could the
' Hearts of Oak ' have achieved in the way of naval supremacy
without the ships of home-grown Oak? It is not because
Germany has a forest area fully eleven times as large as the
woodlands and nurseries of Great Britain and Ireland that we
must look mainly to that country for instruction and guidance
with regard to Forestry; it is because at Universities,
Academies, Institutes, and Forest Schools, many Professors of
high scientific attainments are engaged not only in teaching
the Science of Forestry and the Art of Sylviculture, but also
in individual and conjoint efforts and investigations for
ascertaining the natural laws which regulate the growth of
timber-crops.

In Britain, however, nothing of this sort is going on. There
is no body of men of anything like good scientific attainments
who are known to be carrying on investigations that have for
their object the improvement of our natural knowledge regard-
ing the growth of timber. Times have changed since one
of the oldest and most remarkable of the English works on
Forestry, John Evelyn's classic Silva or a Discourse of fores I
Trees, was read by him in its first form as a paper before
the Royal Society in October, 1664; for at that time we
were certainly abreast of continental knowledge. But, with the

Preface ix

subsequent decrease in the woodland area throughout Britain,
we have lagged far behind continental countries with regard
to the improvement of our knowledge of Forestry. With the
present shrinkage in the agricultural and pastural value of land,
however, there certainly is now scope for applying a knowledge
of economic and purely financial Forestry, i. e. Sylviculture, to
considerable tracts that are now lying waste and unproductive.
It may perhaps be convenient, for the sake of ready refer-
ence, to give a short list of the chief works that have been
frequently quoted throughout the various chapters of this
book. These are : —

GREBE, Die Betriebs- und Ertragsregelung der Forste, and edit., 1879.

NEY, Die Lehre vom Waldbau, 1885.

WEBER, Die Aufgaben der Forstwirthschaft, in Lorey's Handbuch der

Forstwissenschaft, vol. i. 1886.
WILLKOMM, Die Forstliche Flora von Deutschland und Oesterreich, 2nd

edit., 1887.

HESS, Der Forstschutz, and edit., vol. i. 1887 ; vol. ii. 1890.
GAYER, Die Forstbenutzung, 7th edit., 1888.

— Der Waldbau, 3rd edit., 1889.
R. HARTIG, Lehrbuch der Baumkrankheiten, and edit. 1889.

Anatomic und Physiologic der Pflanzen, 1891.

C. HEYER, Der Waldbau, 4th edit., vol. i. 1891 ; vol. ii. 1893.
RAMANN, Forstliche Bodenkunde und Klimatologie , 1893.

J. NlSBET.

145 NORWICH ROAD, IPSWICH :
March, 1894.

CONTENTS

CHAPTER I.
FORESTRY IN BRITAIN

CHAPTER II.
THE BRITISH SYLVA, AND THE GROWTH OF WOODLAND CROPS

IN GENERAL .......... 29

CHAPTER III.
THE CHIEF SYLVICULTURAL CHARACTERISTICS OF OUR WOOD-

LAND TREES *. ....... 46

CHAPTER IV.
THE NUTRITION AND FOOD-SUPPLIES OF WOODLAND CROPS . 67

CHAPTER V.
SOIL AND SITUATION IN RELATION TO WOODLAND GROWTH . 90

CHAPTER VI.
ON THE ADVANTAGES OF MIXED TIMBER-CROPS OVER PURE

WOODS ........... 115

CHAPTER VII.
CONCERNING THE FORMATION AND GENERAL TREATMENT OF

MIXED WOODS . . ..... .. .138

CHAPTER VIII.
CONCERNING THE FORMATION AND REGENERATION OF WOOD-

LAND CROPS .......... 158

xii Contents

CHAPTER IX.

PAGE

THE TENDING OF WOODS . . . * , . . .179

CHAPTER X.
METHODS OF STIMULATING THE INCREMENT IN TIMBER-CROPS

WHEN APPROACHING MATURITY . . . • • . 2IO

CHAPTER XL
THE PRACTICAL EFFECTS OF UNDERPLANTING . . . .230

CHAPTER XII.

THE CONSERVATION OF THE PRODUCTIVE CAPACITY OF WOOD-
LAND SOILS . . 253

CHAPTER XIII.

THE FUNGOID DISEASES OF FOREST TREES, AND THEIR PRE-
VENTION » 276

CHAPTER XIV.
THE PROTECTION OF WOODLANDS AGAINST INSECT ENEMIES . 307

INDEX . 333

STUDIES IN FORESTRY

CHAPTER I

V

FORESTRY IN BRITAIN

IN the Agricultural Returns of Great Britain, published for
1892 by the Board of Agriculture, it is shown that, whilst the
total area of the United Kingdom is 77,642,099 acres, the
extent to which it is utilized agriculturally and sylviculturally
is as follows : —

Total Area of Land and Water

77,642,099 acres

Percentage
of Total Area

Arable Land ....
Permanent Pasture .
Woodlands (and Nurseries)

2<M44>577 »
27,533,326 „
3,005,670 „

25-5
35-5
3-8

Though the acreage covered with forest is undoubtedly
extensive, amounting as it does to 470 square miles, or 3-8 %
of the total area of land and water, yet it does not at first
glance convey the full extent of the important interests repre-
sented by it. On arable land, and in fact on all land utilized
agriculturally, the sowing of the seed is followed within one
year by the reaping of the harvest; but in woodlands such
can never be the case. With the exception of willow-beds
cut over annually when once the stools are in vigorous bearing,
and coppice-hags of Oak for tanning-bark, or of various woods
for other purposes, long periods must necessarily elapse before
the timber-crops reach their highest material, technical, and
financial value ; hence the advantageous time of maturity may be

Studies in Forestry [CHAP. i.

•*

4<Yf *:3

.'-•. ;

said roughly to vary from about 60 to 80 years with conifers,
up to about 150 years for Oak. But taking a rotation of about
90 years as the average, — and that would certainly not be too
high a one, — this would mean that the present market value
of the timber-crops on these three millions of acres of woods
(assuming that they range normally from o to 90 years of age)
is equal to 3,000,000, multiplied by the average quantity of
timber contained in crops 45 years of age, or equal to 1,500,000
acres multiplied by the average quantity of timber yielded by
a mature crop of 90 years in age.

Without entering into detailed figures, which of course vary
essentially according as the crops may be of Scots Pine,
Spruce, Silver Fir, Oak, Beech, &c., or mixed woods, it will be
at once intelligible that the monetary value represented by the
timber standing on our three million acres of woodland is of
sufficient amount to be decidedly of national importance.

At the very lowest computation, the actual cost of production
of the timber-crops, which, even under management of an
unsatisfactory economic nature only, must be far below their
true market value, equals

( (annual rental of 3,000,000 acres)

. M

+ costs of forming or regenerating 3,000,000 acres J i'o r 2

where 7-=the rate per cent, at which the proprietor is content
to lock up his capital represented by soil plus growing-stock.
If the sylvicultural soil were of equal productive power with that
utilized agriculturally, then it would be necessary to estimate r
at a higher rate than is permissible in actuarial calculations
relating to farming, owing to the greater risk run by forest crops
from wind, fire, insects, &c., before attaining their financial
maturity. Thus, in central Germany1, whilst the rate of
interest for ordinary investments is about 3^ to 4^ %, that for
actuarial calculations referring to agricultural soil ranges from

1 See G. Heyer, Ankitung zur Waldwerthrechnung, 4th edit. 1892'
p. 15.

CHAP, i.] Forestry in Britain 3

2 to 3 %, and for State Forest land it may be put at 2 to 2\ % ;
but rates varying from 2,\ to 3J% are laid down in laws
referring to expropriation of forest areas, whilst Pressler1
insists that it should be 3 \ % for State Forests, 4 % for large
land-owners, and 4 to 5 % for smaller proprietors working on
more purely financial principles. Owing, however, to the
extrinsic appreciation in the value of broad acres, as conferring
a certain degree of social elevation among the moneyed classes
in Britain, so low a rate as 2\ % may perhaps be taken for the
purpose of determining the actual minimum cost of production
of our growing-stock of timber 2. Taking the annual average
rental of the land at about 5^. an acre, and the cost of forming
or regenerating the crop at £2 an acre (which was the sum
named by Mr. Macgregor in his evidence before the Com-
mittee on Forestry on June 28, 1887, as the cost of planting
Scots Pine in the Athole forests in Perthshire), the actual
cost of production of our woodlands at the present time will
therefore be

(3,005,670 x £2 5^.) I-02546 = £20,544,571.
This does not take into consideration intermediate returns
from thinning, &c. ; but, per contra, it omits all annual charges
for administration, protection, and rates chargeable. And this
is only the actual cost of production, whilst ^^prospective value of
the mature crops is in reality a very much greater sum. Thus
the forests of Germany aggregate 34,353,743 acres3, in regard
to which Professor Gayer, in his rectorial address before the
University of Munich in 1889, stated4 that their annual
outturn in timber amounted to about 60,000,000 cubic metres
worth from £20,000,000 to £22,500,000 sterling, 'so that,
reckoning 2 % as the rate of interest yielded, the capital value, of

1 Rationeller Waldwirth, vol. i. 1858, p. 10.

2 According to Prof. Endres the present returns from forestry in Germany
lie between 2 and 3 %. (Conrad, Elster, Lexis, and Loening's Handworter-
buck der Staatsivissenschaften, 1892, vol. iii. p. 602.)

3 Agricultural Returns for 1892 (Board of Agriculture), p. 167.

4 Der Wald im Wechselder Zeiten, 1889, p. 15.

B 2

4 Studies in Forestry [CHAP. i.

all the German forests may be assessed at about £1,000,000,000
sterling.1

Professor Weber also states ' that, in addition to £4,150,000
annually spent in the management, reproduction, and protec-
tion of the forests, and in the felling, preparing, and handling of
the produce before it is delivered into the hands of the buyer,
the timber and other produce of the woodlands directly affords
employment to 583,000 persons, or 9 % of all the industrial
classes throughout the empire, who are engaged in industries
dependent on the forests for the raw material requisite for
their various trades. These 583,000 bread-winners probably
represent about 3,000,000 of the population. And in addition
thereto, there must also be taken into account the enormous
sums whose outlay is necessitated for transport by land and water
after the raw produce has come into the hands of the buyer.

It therefore follows that, if our woodlands were as economi-
cally and as well managed as the German forests, they would
annually yield very nearly £2,000,000, and have a capital value
of £90,000,000, adopting 2 % as the rate of interest yielded, or
at any rate about £50,000,000, even adopting only twenty-five
years' purchase as their value, and presuming that they yielded
as much as 4 % per annum on their capital value of soil plus
growing-stock.

Our woodland tracts are by no means equally distributed
over the length and breadth of the land ; for, as Major Craigie
reports in the Board of Agriculture's Returns for 1891
(page x.) :—

' The county of Hants now stands in the Returns as possessing the
largest area of woodland in England, or 122,574 acres. Sussex, with
122,073, comes second, while it may be worth noting that the four counties
of Hants, Sussex, Surrey, and Kent, forming the south-eastern corner of
England, possess between them nearly a fourth of the English woods and
plantations, showing over n % of their surface thus occupied, in contrast
with 4 % as the mean of the rest of the country.

1 Die Aufgaben der Forstwirthschaft in Lorey's Handbuch der Forst-
wissenschaft, 1886, vol. i. p. 85.

CHAP, i.] Forestry in Britain 5

' In Scotland the county of Inverness accounts for 169,000 acres of
woodland. This area is far the largest in Great Britain. It is consider-
ably in excess of the surface returned as under all forms of crops or grass in
that county, and nearly equal to a fifth part of the whole Scottish woodlands.''

To look at Scotland alone somewhat more closely, the area
under woods and nurseries amounted to 876,250 acres out of
a total of 19,453,843 for land and water, or in other words we
find-
nearly one-fourth as much woodland as arable land (3,550,095 acres) ;
nearly two-thirds as much woodland as permanent pasture (1,338,249
acres) ;

more than two-thirds as much woodland as land under corn crops
(1,297,231 acres);

and nearly forty % more woodland than arable land under green
crops (638,794 acres).

The timber and minor produce produced on this area by
home growth is, however, entirely inadequate to supply our
actual requirements, as may be seen at a glance from the
statement of Imports into and Exports from the United
Kingdom during the last three years, compiled from the
Customs Returns for 1892 * (see next page).

Although from these Returns it is hardly possible to
eliminate all the classes of timber which it would be physically
impossible to grow in our climate, as, for example, the Teak
timber imported from Burma for the lining of iron ships, and
the Australian hardwoods used for street-pavement in London,
there have been left out of account the imports of Mahogany
(amounting in 1892 to 56,315 tons = £501,203) of Cutch and
Gambier (25,192 tons = £548,395), of Caoutchouc and Gutta
Percha (317,660 cwts. = £3,5oi, 923), &c., the supplies of which
must, under all circumstances, be drawn from across the sea.

It would of course be absurd to throw out any broad casual
statement that, if the treatment accorded to our woodlands
were such as might be dictated by a better knowledge of the
laws governing tree-growth, and of the principles underlying

1 Accounts relating to Trade and Navigation of the United Kingdom,
December, 1892.

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CHAP, i.] Forestry in Britain 7

sylviculture (i. e. when forestry is conducted scientifically), we
could supply a great many of these requirements by home-grown
timber ; but the argument will be strictly pertinent if it be shown
in what respects our woodland owners can, and should, strive
to compete with foreign importers. Taking the countries in
which identically the same species of trees are grown as may
be produced in forests in Britain, there still remain the fol-
lowing imports that may be regarded as utilized by us, and not
exported again : —

Imported from Russia, Sweden, Norway, and Germany
during 1892.

Timber in the Rough
Converted Timber .

Loads.
1,400,927
3.362,425

Value.
£2,257,401
^6,950,504

Total

4,763,352

£9,207,905

It may be unhesitatingly maintained that, if due attention were
given to the selection of proper species for given soils and
situations, and if the principles relating to the most favourable
density of plantations, or sowings, or natural reproductions,
and to the operations of tending (clearing, thinning, &c.) were
properly understood and practised throughout Britain, there
would be not the slightest necessity for the insertion (as at
present obtains) of any clauses into Government contracts
stipulating for the use of foreign wood in preference to home-
grown timber. But if woods are allowed to grow up so that
a considerable portion of the energy of growth of the indi-
vidual trees forming the crop is dissipated in branch develop-
ment, in place of being concentrated in the formation of a
clean, smooth, full-wooded bole of high technical quality, then
no one need be surprised at every person concerned in its utiliza-
tion giving a solid preference to foreign timber grown under more
rational conditions, and consequently of higher technical value,
owing to its comparative freedom from branches and knots.

One economic point of great importance may here be noted,

8 Studies in Forestry [CHAP. i.

viz. the steady appreciation of forest produce during the past '.
And this is bound to become accentuated in the future • for
whilst population and the demands for timber, &c., are con-
stantly increasing, the woodland area, and consequently the
possibility of satisfying these demands, are constantly decreas-
ing over the whole surface of the globe.

On this point Professor Weber remarks 2, in speaking of the
increasing demands for forest produce, and the ever-growing
utilization of timber as a raw product for various mechanical
and chemical industries, that : —

*A proof of the strength of those influences is yielded in
the fact, shown by the statistics of prices for the different
dimensions of wood, that the mean annual increase in the price
of timber during the last fifty years has been from 2 to 2 \ %
throughout Germany.'

This consideration is one that should most certainly not be
lost sight of when we are face to face with the fact 3 that in
fifty years' time the forests of America will have become
exhausted, even if the rate of timber extraction does not
increase at all beyond its present dimensions. The natural
consequences of this must not only be that America will, long
before the close of that period, not have any surplus timber to
export for the supply of our requirements, but also that she
must be a competitor with us for any surplus timber that may
then be available, in any other part of the world, for export
beyond the limits of the countries where it is grown.

It is not contended that any considerable portion of the
£1,365,075 paid away in 1892 for wood-pulp and rosin could
have been retained in exchange for the produce of our own
coniferous woods ; for the manufacture of cellulose, and the
collection of rosin, are usually conducted in localities where

1 See G. Heyer, Anleitung zur Waldiverthrechnung, 3rd edit. 1883,
p. 9.

2 Lehrbuch der Forsteinrichtung, 1891, p. 37.

3 See Article on American Forests in the Journal of the Society of Arts
for February, 1893.

CHAP, i.] Forestry in Britain 9

wood and labour are comparatively very cheap. But surely what-
ever oak-bark is required by tanners might quite easily be grown
at home on vacant land along the railway lines in the vicinity
of the centres consuming it, so as to undersell foreign imports
which incur costs of repeated handling and transport before
reaching us. New sources of employment might ftius easily
be created and developed for many thousands of people,
especially during the early spring, and partly also in the winter
months.

To confine this statement to the practically useful, there is
little doubt that if any encouragement were given to the dis-
semination of sound knowledge concerning forestry through-
out Great Britain, we should not only be able to obtain better
returns — materially, technically, and financially — from the exist-
ing woodlands, but should also in other respects be in a much
better position for profitably utilizing some of the existing waste
lands for the purpose of entering into direct competition later
on with these foreign imports, consisting chiefly of coniferous
species of timber ; for these trees can attain as fine development
as on the continent of Europe, and often finer, especially in
Scotland. There is indeed no climatic reason why a very con-
siderable portion of the timber now annually imported from
Russia, Scandinavia, and Germany, should not in future be
supplied of home growth, when once the crops raised have
been subjected to rational treatment from the time of their
formation onwards until their maturity. This latter condition
is essential ; for woods that are crowded at thirty, forty, or fifty
years of age, may not have been of sufficient or normal
density at ten or fifteen years of age, but may have become
crowded in canopy through excessive and uneconomical rami-
fication and coronal development.

From the Minutes of Evidence (pp. 4, 5, and 42) accom-
panying the Report of the Select Committee on the Adminis-
tration of the Department of Woods and Forests and Land
Revenues of the Crown, submitted to the House of Commons

io Studies in Forestry [CHAP. i.

on July 26, 1889, it appears that the total area classifiable
legally as Crown forests is only 109,139 acres, of which merely
57,304 acres are actually under timber crops, i.e. only 2 % of
our three million acres of woodlands are owned by the State,
whilst 98 % belong to private landowners. Comparatively
slight though this Crown ownership may appear in amount,
Yet 57>3°4 acres, or ninety square miles, represent a very
considerable monetary capital invested in soil and timber
crops.

Over two hundred years ago John Evelyn, whose classic
work Sylva, or a Discourse of Forest Trees, was read by him
before the Royal Society of London in 1664, bemoaned the great
decadence and destruction of the woodlands, or as he termed
it * the impolitic diminution of our timber j that had been handed
down to us from primeval times, and ' which our more prudent
ancestors left standing for the ornament and service of their country?
But he probably little suspected that the very same causes,
which had led to what he considered excessive clearance of
the remnants of the aboriginal forests, would ultimately lead to
their being partially restored by re-planting, that is to say, the
desire to get the best possible monetary returns from the soil.

The effect of the gradual depression of agriculture that has
been making itself felt during the last fifteen to seventeen
years has, of course, first affected the area under the plough.
As Major Craigie remarks (Agricultural Returns for 1891,
p. io) :—

' Turning to the details of the cultivated area, it is again necessary to
note the remarkable changes which have been taking place in the ratio
of arable to pasture land in Great Britain. The two great divisions of
arable and pasture now claim, for the first time, an almost exactly equal share
of the surface. Twenty years ago the arable land was to the grass as 3 is to a.
It exceeded by 6,000,000 acres the surface of permanent grass, there
being 18,403,000 acres returned as arable to 12,435,000 acres of pasture.'

Again, in the Returns for 1892 (pp. 10, u, 21) he has the
same sad tale to tell : —

CHAP. I.]

Forestry in Britain

ii

' The arable land, as has been the case in mery year but two since 1872,
again shows a reduction. The surface appearing in this category is
157,000 acres less than in 1891. The permanent pasture in 1892 is also less
than that returned in 1891 by 76,000 acres. This is a change in an
opposite direction to those recorded for a considerable period, but it is
wholly explained by a stricter definition of the term Permanent Grass
now enforced in certain mountainous counties, where some of the
additions made in 1891 to this category were found on closer inquiry
not to have been fully justified, the areas in question being again
relegated to the class to which they properly belonged, of uncultivated
hill grass

' Between 1872 and 1882 about 936,000 acres were apparently with-
drawn from arable tillage and reappeared in the opposite category of the
cultivated area in the form of permanent pasture.

* In the later ten years a similar process has continued. Between 1882
and 1892 the arable area has again diminished, and this time by
1,165,000 acres. . . . The more important alterations between 1891 and
1892, occurring in the entire United Kingdom, may be summarized in
the accompanying Table : —

Acreage.

1892.

1891.

1892 compared with
1891.

Increase.

Decrease.

Total Cultivated Area . .

Acres.
47»977,9°3

Acres.
48*1 79,473

Acres.

Acres.
201,570

Total of Permanent Pasture
Total of Arable Land . .

27,533,326
20,444,577

27,567,128
20,612,345

. .

33,802
167,768

Owing to the gradual agricultural depression, the poorer
classes of arable soil have during the last twenty years gone
out of plough cultivation, and have been transformed into
pastures; and the immediate consequences of the past year
or two must inevitably result in the poorer classes of pasture
being ultimately planted up again, thus reverting into some-
thing of their original state, as sylviculture will probably hold
out better hope of some profitable return from the land than
any agricultural or pastoral utilization of the soil \

1 During September 1893 the Board of Agriculture drew the attention of
landowners to the increased facilities for the planting of woods and trees in

12 Studies in Forestry [CHAP. i.

Of course, in such an enlightened country as Great Britain,
it might reasonably be expected that everything has already
been done by Government to provide for the due instruction
of those to whom are confided the responsible task of ad-
ministering or working these woodlands. That would certainly
be the natural inference when one looks abroad at other
countries, and at the same time thinks of the many tens of
thousands of pounds spent on, and in connexion with, the fine
collections of stuffed birds, fishes, reptiles, &c., palatially
housed in the magnificent building forming the Natural History
Museum at South Kensington, and on the other vast sums
of national money originally and annually disbursed for the
housing and maintenance of aesthetic and other technical edu-
cation. But one would be vastly mistaken in making any such
common-sense assumption. When Governments are badgered
about any subject in an inconvenient manner, they seem to
have a stereotyped way of gravely appointing a committee for
the purpose of reporting on this, that, or the other subject ; and
after such report has been submitted, there is often practically
an end of the business in the meantime, until they are worried
again on the subject. This solemn farce has been twice recently
enacted with regard to Forestry in Great Britain. During
1885 a committee was appointed for the purpose of considering
' whether by the establishment of a Forest School^ or otherwise,
our woodlands could be rendered more remunerative] and on
August 3, 1887, they delivered themselves of a report, from
which the following excerpts contain the principal conclusions
arrived at : —

Scotland afforded by the Improvement of Land (Scotland) Act, 1893, which
received the Royal assent on August 24, 1893. Hitherto owners of land
in Scotland have been able, with the sanction of the Board of Agri-
culture, to charge their estates for the planting of woods and trees, only in
cases where the planting is for the purpose of providing shelter. By the Act
in question, this limitation has been removed, and applications may now be
made to the Board for sanction to charge estates under the provisions of the
Improvement of Land Act, 1864, with the cost of planting whether for
shelter or otherwise.

CHAP, i.] Forestry in Britain 13

' The woodlands belonging to the State are comparatively small, though
even, as regards them, the difference between skilled and unskilled
management would itself more than repay the cost of a forest school.

' Your Committee are satisfied that, so far as Great Britain and Ireland
are concerned, the management of our woodlands might be materially
improved. Moreover, the present depressed values render economical
and skilful management even more important than if the range of prices
were higher, though it is probable that, with the waste of forests
elsewhere, a brighter future is in store for home forestry, and that some
considerable proportion of the timber now imported, to the value of£ 16,000,000,
might, under more skilful management, be raised at home.

1 Nearly every other civilized State possesses one or more forest schools.
In this country, on the contrary, no organized system of forestry instruc-
tion is in existence excepting in connexion with the Indian service.

' Your Committee recommend the establishment of a forest board.
They are also satisfied by the evidence that the establishment of forest
schools, or at any rate of a course of instruction and examination in
forestry, would be desirable, and they think that the consideration of
the best mode of carrying this into effect might be one of the functions
entrusted to such a forest board.'

As regards the outlay connected with so flimsy a scheme
for the improvement of the natural knowledge of forestry in
general, it was also stated that —

' The expense of secretarial staff and examiners need not, in the
opinion of the Committee, exceed £500 a year, and the cost might be
considerably reduced by fees for diplomas?

I believe I am correct in stating that, up to date, all that has
been done by Government for the advancement of forestry in
Britain has been to pay £100 a year to Edinburgh University
for a lectureship during the last two years, to provide half of
the annual stipend of £500 a year to the Professor of Agri-
culture and Forestry at the Durham College of Science,
Newcastle, for the chair founded there in 1890, to pay (tem-
porarily) £ 150 a year to the free class for foresters, wood-reeves,
and gardeners, now being conducted experimentally at the
Royal Botanic Gardens, Edinburgh, and to give an equal sum
for the elementary course of instruction begun in 1892 at the
Glasgow Technical Institute.

14 * Studies in Forestry [CHAP. i.

The second Committee was appointed in 1889 ( to inquire
into the Administration of the Department of the Woods and
Forests and Land Revenues of the Crown] and duly delivered
itself of a somewhat lengthy report on July 30, 1890, which
terminated as follows : —

' The Committee are of opinion that on the whole the estates are carefully
administered, and that the Commissioners discharge their duties faith-
fully and efficiently.'

This certainly does not tally with the previous finding of the
Forestry Committee, that —

' The woodlands belonging to the State are comparatively small, though
even, as regards them, the difference between skilful and unskilled manage-
ment would itself more than repay the cost of a forest school?

From the evidence adduced before the Forestry Committee
it is impossible to deny the truth of the latter statement, and
therefore we must look for some explanation of this glaring
discrepancy. It is to be found in the fact that the inquiry
into the administration of the Crown Woods and Forests and
Land Revenues was not at all a satisfactory one, so far as the
national Woods and Forests were concerned.

The chief Crown appointments with regard to the adminis-
tration of the actual Woods and Forests are the following : —

Salaries. Allowances. Total.

One of the two Commissioners of Woods £1200 £1200

Deputy Surveyor, New Forest, &c. . . 680 £369 £1049

„ „ Dean Forest, &c. . . 550 304 854

( Windsor Parks and )

I Woods I • 5°° 340 840

Surely the manner in which appointments are made to these
chief administrative and executive posts must have enormous
influence on the administration itself? Had any body of
purely business-men been put to the task of satisfying them-
selves as to the real nature of the administration of these
valuable public estates, they would undoubtedly have asked
each of these fortunate public servants what professional educa-
tion or qualifications he had obtained previous to receiving

CHAP, i.] Forestry in Britain 15

his appointment ; for no private landowner would entrust the
management of his estates to any steward or agent without
knowing something about the qualifications and capacity of
the latter. Yet no inquiries of this description were made by
the Committee ; and appointments to the Department of
Woods and Forests still continue to remain in the patronage
of the First Lord of the Treasury, under Acts 14 and 15
Victoria, chapter 42, section 7, and are in practice more often
filled by the appointment of those having influence with
politicians, than of men having the best qualifications for the
work required of the officers.

Whether or not our three million acres of woodlands can,
by better general knowledge of the natural laws governing
tree-growth, be made to yield \, or f , or i % beyond what
they now give as a return on the capital represented by
the soi\fl/us the growing stock (and the cost of production of
which exceeds 20 \ millions of pounds sterling), is surely
a matter of considerable national importance. It is by no
means advisable, or even justifiable, to pin one's faith to the
Laird o' Dumbiedyke's advice to his son, part of which has
been adopted as the motto of the Royal Scottish Arboricultural
Society : — l Jock, when ye hae naething else to do, ye may be aye
sticking in a tree; it will be growing, Jock, when ye 're sleeping^?
This is in itself fundamentally wrong, for the activity of the
chlorophyll of the foliage, and consequently the most active
assimilation, can take place only under the influence of sun-
light ; whilst all our trees have a long period of winter rest —
during which even the evergreen conifers merely transpire
through their foliage but do not grow.

1 Waverley Novels, A. & C. Black's edit. 1860, vol. xi. p. 294. If the
foot-note accompanying the Laird's advice be actual fact, and not also
included in the fiction, then it simply shows how ' enterprises of great pith
and moment ' are sometimes lightly embarked on in the crassest and most
unthinking ignorance. The judicious formation of plantations is no pastime
for an idle holiday; unless knowledge, circumspection, and thought are
brought to bear on the subject, it bodes an ill omen for the thriving and
ultimate development of the young woods.

1 6 Studies in Forestry [CHAP. i.

But even during the period of active vegetation the trees
may perhaps be growing in a way that is not at all economical ;
they may be dissipating their vital energy in an excessive
development of branches and crown instead of conserving and
utilizing it for the rapid formation of a longer, straighter, and
more full-wooded bole yielding the maximum of technically
useful, and at the same time financially profitable, timber.
Moreover, whilst that may be a very suitable motto for an
Arboricultural Society, concerned to a certain extent with the
planting of trees for their natural beauty, the full aesthetic
effect of which can only be attained by letting them hang as
they grow, it would be utterly out of place so far as Forestry
is concerned; for woodland trees require to be tended, and
educated, and carefully ministered to, during all the several
stages of their development, in order to produce the largest re-
turns during the various periodical thinnings, combined with the
largest and most valuable final yield, materially and financially,
when the crop attains its full maturity, and has to be cleared
for the reproduction of a younger generation of trees. And
can any one in his sound senses think that Forestry, any
more than Agriculture, may be conducted profitably and
economically merely by following old saws or unthinking rule
of thumb ? Does the old Horatian maxim, doctrina sed vim
promovet insitam, not equally hold good with regard to sylvi-
culture, as well as to other arts and sciences ? Is Forestry so
essentially different in its natural laws and fundamental prin-
ciples from Agriculture, that whilst University chairs have
been founded for the latter at Edinburgh, Belfast, Newcastle,
and in a manner also at Oxford1, and properly equipped
Schools of Agriculture are located at Edinburgh, Carlisle,
Cirencester, and Downton, absolutely next to nothing has yet
been done for the dissemination of sound and properly quali-
fied instruction in sylviculture ?

1 The Sibthorpian Professorship of Rural Economy at Oxford is at present
suspended, but has hitherto been held only by an Agriculturist.

CHAP, i.] Forestry in Britain 17

It may be urged against this, that at some Agricultural
Schools there are classes of Estate Management and Forestry.
This is quite correct, but it does not follow as a matter of
course that the teachers there have a really sound know-
ledge of the scientific principles and practice of Forestry.
Hence a question may very pertinently be asked similar to
the Quis custodiet ipsos custodes ? For where shall such men at
present get the scientific and practical training in Forestry,
without which they are in a certain degree like the blind
leading the blind ? In order that this picture may not seem
harsh, ungenerous, and overdrawn, permit me to quote from
the evidence given before the parliamentary Committee on
Forestry on June 15, 1887, by the lecturer on Estate Manage-
ment and Forestry at Cirencester (pp, 27-29 of Report dated
August 3, 1887).

468. You are Professor of Estate Management and Forestry at Ciren-
cester College ? — I am ; I am also a Fellow of the Royal Highland Agri-
cultural Society of Scotland, by examination,

470. Have you had practical instruction in forestry yourself? — No,
only on estates.

474. Would you give the Committee some idea of the course of instruc-
tion in practical forestry ? — There is a course of lectures forming a part of
the syllabus of estate management, consisting of about six or seven lectures,
as the case may be, and those are illustrated by field- classes in the woods,
timber measuring, and valuing standing timber, different processes of
planting, grafting, layering, and so on. This is done in the woods.

485. And are they (the students) shown specimens of good forestry
and bad forestry, and how to distinguish good from bad ? — We have not
that opportunity ; we have no bad forestry.

487. You show them what mistakes to avoid in wood management
I presume ? — Yes, but at present it is only on a very small scale in my
syllabus ; we have not an opportunity of going fully into the matter.

509. I gather, from what you have stated, that you do not consider
the course at Cirencester is sufficient for the education that land agents
should receive in forestry ?— No.

515. Is it your belief that instruction in forestry would be a national
gain ? — It is so.

521. Are you acquainted with the system of forest instruction pursued in
France and Germany ? — No, I am not.

C

1 8 Studies in Forestry [CHAP. i.

527. You were taught yourself at Cirencester College, were you not ? —
Yes. (Compare 509.)

528. And after then where did you go? — I went into King's College
in London for twelve months, and then up to Edinburgh, and took the
Highland Agricultural Society's Diploma ; that was about the year 1868.

529. So that you have had yourself as good an education in forestry as
t's possible in Great Britain ? — There was no teaching in forestry in my time.

530. But you have had a good insight into forestry ? — / have had an
insight into forestry.

541. Do you think it would have been an advantage to yourself if you
had had an opportunity of being trained in some regular school, or do you
think you have been able to acquire a practical knowledge? — I have
been fortunately situated with regard to that. I have had a very long
and happy experience with regard to forestry; but others who might
follow in my steps might not have the same opportunities of instruction,
and others ought to have the opportunity of hearing lectures upon the
matter.

Nothing that is said above is meant, malo grato^ to depre-
ciate the instruction given in Forestry at these Agricultural
Colleges. But the evidence tendered by one of the instruc-
tors himself is plain and to the point, as it shows most
conclusively that the instructors in Forestry have not them-
selves had good opportunities of qualifying for their special
task, so far as it relates to Forestry conducted on sound
scientific and economic principles, i. e. to Sylviculture as
contrasted with Arboriculture.

Perhaps the only place, with the exception of Cooper's
Hill, at which really properly qualified instruction in Forestry
is being given at the present moment is the Durham College
of Science at Newcastle. But as the lectures on Forestry
there only form a minor portion of the course of professorial
tuition dealing principally with Agriculture, they can hardly
be expected to be adequate to the proper qualification of
youths for the management of our existing woodlands in
full accordance with the principles and the practice of modern
scientific Sylviculture as fully expounded and demonstrated in
Germany, the home of Forestry in its highest technical and
practical perfection.

CHAP, i.] Forestry in Britain 19

The course of lectures which was organized in 1889 at Edin-
burgh University is, as at present constituted, merely a make-
shift ; and even as a temporary compromise it is only satis-
factory on the broad principle that ( half a loaf is better than
no bread.' At the present moment reference is made only
to a course of technical instruction fitting young men of
liberal education for the management of estates containing
a considerable area of woodlands. It does not take into
consideration the wants of that other very important class of
less highly educated men occupying the position of foresters,
wood-reeves, bailiffs, overseers, &c., for whose improved edu-
cation an experimental system of instruction has recently been
inaugurated by Professor Balfour at the Botanic Garden in
Edinburgh. For the ultimate success of both of these Schools
every lover of Forestry and of woodland growth must hope.

The only educational institution properly equipped with
duly qualified teachers for granting a sound Sylvicultural edu-
cation at the present moment is Cooper's Hill College, near
Staines in Surrey, originally built and fitted up as an Indian
Engineering College at a cost of £134,000. Without con-
sidering the causes which led to the necessity for terminating
the original course of study of the probationers for the Indian
Forest Service in Germany and France, and without discussing
whether the cessation of the continental training has proved
itself beneficial or not, it may be said that Cooper's Hill was
not primarily selected for any local or other advantages
it offered per se. Its selection was mainly due to other
reasons; because it was an expensive establishment already
in the hands of the India Office,, and needed financial support
after the reduction in the number of young officers annually
required in the Public Works or Civil Engineering Depart-
ment (in consequence of the fall in the rupee), for the
education of whom alone the maintenance of the College
had become unduly expensive. Previous to the education
of the probationers for the Indian Forest Service being

c 2

2o Studies in Forestry [CHAP. i.

begun there in 1885, an annual deficit had for some years
to be met ; but by arranging for the education of these,
and charging them the usual College fees of £183 a year,
this deficit was transformed into a surplus, — thereby proving
that the sum charged is in excess of what it actually costs
to feed and educate the lads. Had the large sums of money
which are being granted annually as salaries to the teaching
body there — which consists of three Professors, three Lec-
turers, and one Instructor on the Forest branch of the College
Staff, with the additional assistance of one Director of Practical
Study on the Continent, who superintends the course of
study and the tours of inspection made throughout different
parts of Germany in order to see practical work on a large
scale — been devoted to the foundation of two chairs, one of
Sylviculture and Management of Forests, the other of Pro-
tection of Forests and Utilization of Forest Produce, at each
of the three Universities, (i) Oxford or Cambridge, (2) Dublin
or Belfast, and (3) Edinburgh, or perhaps better still St.
Andrews or Aberdeen, from their proximity to extensive forests,
Great Britain might now have had a course of sound scientific
instruction at central points in England, Ireland, and Scotland,
fairly abreast of continental Forestry in so far as our own
particular requirements are concerned.

The present instruction in Forestry at Cooper's Hill can
never be regarded as capable of being converted, without
previous translation to some University or Agricultural College,
into a national place of education in Sylviculture. Because,
in the first place, the lectures on Forestry are not capable of
being listened to ex via along with any simultaneous course
of instruction in what may be more likely to prove better
bread-winning studies (although at a University this might
very easily be arranged for) ; whilst, in the second place, the
charge of £183 a year, and a three years' course, make such
a training absolutely prohibitive for the majority of those who
otherwise might profit by a shorter and less expensive course

CHAP, i.] Forestry in Britain 21

of instruction ; for, after reckoning all extras, clothing, tra-
velling, and various incidental expenses, it must cost a parent
or guardian at least £700 to £800 to provide his son or
ward with a three years' course at Cooper's Hill.

This is, however, not a matter that really concerns British
Forestry ; for Cooper's Hill is maintained by the India Office,
and if the Government of India choose to maintain an ex-
pensive institute for young men who might easily be educated
at one or other of the great Universities, it is no direct
concern of the British public, and is, at any rate in the
meantime, beyond the legitimate sphere of their control.

There are three distinct classes for which it has, face to
face with the existing decline in the agricultural and pastoral
value of many kinds of land, now become really of national
importance that some scientific instruction in Forestry should
be provided ; these classes are : —

I. The owners of woodlands, or of waste lands, or of
lands of poor quality now likely to be soon thrown out of
arable or pastoral occupation.

II. The higher educated class which supplies the land-agents,
estate factors, stewards, and the like.

III. The class of smaller stewards, bailiffs, foresters, wood-
reeves, overseers, &c.

There is no need to prove that each and all of these classes
really require instruction in Forestry. It has been often
admitted, and is apparent throughout both of the Forest
Reports previously quoted. Even should a man be born to
inherit broad acres of stately woods, it does not follow that
he is naturally endowed with an intuitive knowledge of the
laws of nature regulating the normal development and the best
technical methods of tending woodlands ; whilst estate agents
and managers may be satisfied with results, that would perhaps
not seem to them the best attainable if they were better
acquainted with the principles and practice of scientific
Forestry. The necessity for instructing landowners is nowhere

22 Studies in Forestry [CHAP. i.

more apparent than in Sir Herbert Maxwell's paper on
Woodlands in the Nineteenth Century for July 1891, in
which in less than a dozen lines he points out one great
blemish in our method of treatment of woodlands, and then
at the same time, in tendering advice on the subject, commits
himself to the expression of an opinion which distinctly shows
that his ideas on Forestry have no true scientific founda-
tion and are opposed to the very best and most thorough
natural knowledge on the subject 1. He boldly advocates the
formation of pure forest in preference to mixed woods. I am,
however, perfectly certain that, if once the formation and
retention of mixed woods be departed from on any extensive
scale, the woodland owners throughout Britain will begin to
form an intimate and unpleasant acquaintanceship with many
noxious insects, some of which, rejoicing in the euphonious
names of Gastropacha, Liparis, Tomicus, Pissodes, Hylesinus,
&c., will give ample reason for genuine regret at having
transformed mixed woods into pure forests. And there are
many other objections that can be named; but this is not
the proper time and opportunity for doing so.

The necessity for men of the second class receiving a better
instruction is also everywhere apparent throughout the Report
on Forestry. It may be summed up in the quotation of two
answers given to the Committee by Mr. Britton, the manager
and valuer of a large timber-firm in Wolverhampton : —

783. Do you find that many land-agents possess a capable knowledge
of forestry ? — Very few in all my experience ; / think I could pretty well
count them upon my fingers' ends.

829. What is the general result that you have come to ? — The general
result I have come to is, that very few land-agents know anything of forestry,
or very little.

And the same holds good with regard to Scotland, although
there are a few really good practical foresters holding charge
of important wooded estates. Thus the late Mr. Macgregor

1 See Chapter VI, On Mixed Woods and their Advantages over Pure
Forests.

CHAP, i.] Forestry in Britain 23

of Dunkeld, the Head Forester of the Athole woods, extending
to over 20,000 acres, gave the following evidence : —

877. Do you consider that the land-agents, or the factors, as they are
called in Scotland, are fairly well informed as to the management of woods
and timber ? — Very few of them, I think.

878. What, in your opinion, are the subjects on which factors and
woodmen are deficient ? — They are deficient in the knowledge of what trees
ought to be planted on suitable soils, and when thinning out ought to
commence ; and, in fact, the general management of the woods altogether.

And if the majority of the men concerned with the adminis-
tration of woodlands are thus ill-provided with knowledge
respecting the formation, the tending, and the management of
timber crops, it is certainly open to reasonable doubt if they
can possibly be in a position to have the soundest ideas with
regard to the utilization of the latter when they have- reached
their financial or their economic maturity.

It is, of course, by no means improbable that a shrewd,
observant, practical forester may often arrive at proper methods
of treating certain crops without at the same time having any
true scientific knowledge of the natural laws influencing either
tree-growth in general, or the various individual species of
trees in particular. Mr. Macgregor again spoke with no
uncertain voice on this point : —

1047. You have had no instruction (on forestry) ? — No.

1048. Do you think you would have done better if you had had a course
of scientific instruction ? — / have not the slightest doubt of it ; I have felt the
want of it all along. I had to read up, and there are very few books to read.

1049. That is your own experience, and you are prepared to recommend
that men beginning life as foresters should have some definite instructions ? —
Certainly.

The preparation of text-books on the various branches of
Forestry was to have been one of the functions of the Board
of Forestry recommended by the Committee in 1887. But
practically nothing has been done in this direction.

It would not be at all right if at the same time I did not
point out that evidence was given before the Committee on
Forestry tending to show that planting up in England could

24 Studies in Forestry [CHAP. i.

not promise remunerative returns, owing to the fact of the
timber marts being glutted with foreign timber, to the general
depression in trade which was then making itself felt, and to
the use of substitutes in many ways in which timber was
formerly employed. But it is important to note that among
Messrs. Thompson, Macgregor, and McQuorquodale, the able
practical head foresters then in charge of the Strathspey,
Athole, and Scone forests, there was a consensus of opinion
that properly managed woodland crops are undoubtedly profit-
able. On this point the late Mr. Macgregor's evidence may
be briefly quoted : —

1 122. Then you think the forest area in Scotland might be largely
increased? — Very largely ; it can be very much extended.

1123. With profit ?— With profit.

This practical advice becomes of all the greater importance
when collated with my previous statement relative to the
gradual appreciation which can be proved in the case of timber
up till now. Simply as a commercial speculation, timber can
and should be grown to a much larger extent than at present.
If any one studies the relative and steady appreciation of timber
in the past, it requires no subtle arguments to make out a fair
case for the judicious sylvicultural utilization of the soil in
many parts of our island.

I do not venture to make this indictment against the
Governments of late as well as of previous years, of being
utterly neglectful of really important national interests relative
to the already existing three million acres of woodlands, with-
out being in a position to offer some practical suggestion for
the removal of this blot on our system of technical education.

But though I cannot agree with the Committee on Forestry
in attempting to remedy the defect for so small a sum as £500
a year (reducible by fees for diplomas), yet it need cost a mere
nothing in comparison with the housing and maintenance of
our national Natural History Museums at Kensington and
elsewhere. Sir Herbert Maxwell, in his paper on Woodlands

CHAP, i.] Forestry in Britain 25

already referred to, stated that if the landowners of Britain
really wanted instruction to be provided at any educational
centre or centres, they could easily arrange for it among them-
selves without the necessity of appealing to aid from the State.
From one cause or another, though probably not that they are
already perfectly satisfied with the existing state of affairs, the
landowners have failed to subscribe sufficient for even half the
amount necessary for the endowment of one rather poorly-paid
Chair of Forestry at Edinburgh. Despite the efforts which
have continuously been made in this direction by the Highland
and Agricultural and the Arboricultural Societies of Scotland,
the Secretary of the former had to report to the Council at its
meeting on November 2, 1892 : —

' that he had sent out over 5.500 circulars requesting subscriptions for the
endowment of the Chair of Forestry in the University of Edinburgh.
He regretted that the result had been disappointing, but that the sum
now subscribed from all sources amounted to over ^"2,300.'

This apathy on the part of landowners does not, however,
justify any laissez faire policy on the part of Government ; on
the contrary, it should make the latter all the more anxious to
remedy the educational defect for the benefit of the rural
working-classes, and of our timber-consuming industries, both
of which would be very directly and materially benefited.

To commence with the lowest scale of requirements, those
affecting the forester or wood-reeve class, the experimental
tuition now being given under Professor Balfour's auspices at
the Botanic Garden and Arboretum in Edinburgh is a step in
the right direction. But whilst it affords the very best oppor-
tunities of providing lectures on elementary scientific subjects
affecting Forestry, it fails in one essential to practical success ;
for the work the men are engaged on, whilst going through the
course, is, and must continue to be, either Horticulture or at
best Arboriculture, but is certainly not Sylviculture or Forestry.
If we were to follow the excellent Bavarian example— and
I do not think we could do better — we should establish

26 Studies in Forestry [CHAP. r.

Sylvicultural Schools for young lads at Dunkeld in Athole, or
Grantown in Strathspey for Scotland, and at Coleford in the
Forest of Dean or Lyndhurst in the New Forest for England,
where it would be easy to provide a fair practical education for
a limited number. Of course in this event there would not be
the scientific teachers within easy reach to give short courses
of elementary instruction ; but a little extra payment for travel-
ling expenses might no doubt circumvent the difficulty, and
overcome that drawback.

For the first and second classes, those of landowners, land-
agents and factors, nothing short of the establishment of Chairs
of Forestry at Universities seems in any way to meet the neces-
sities of the case ; for, as I have already asserted, it is only at
such educational centres, and not at any special colleges, that
an opportunity can be given to students of hearing lectures on
this subject concurrently with other and more usual studies
fitting them for the ordinary vocations in life, And perhaps,
taking all things into consideration, the most suitable Univer-
sities for the dissemination of scientific instruction would be
Oxford for England, Edinburgh, and either St. Andrews or
Aberdeen for Scotland, and Dublin or Belfast for Ireland.
Even if Government were willing to establish Chairs of Forestry
at any or all of these places, it by no means follows that the
Universities applied to would accept the proposals, and permit
the incorporation of such Chairs into the existing teaching
body, unless they were granted a perfectly free hand with
respect to the selection and appointment of the Professors.

If any such Chairs be formed from national funds, then the
salaries attached to them should be sufficient to obtain the
services of really highly-trained men, and should not be less
than £700 a year at Oxford, Edinburgh, and Dublin, or £600
at St. Andrews, Aberdeen, or Belfast ; and the lectures should
be free to all who wish to hear them — whether matriculated
students of the year or not. The reason of this will be
apparent when it is stated that the attendance given to the

CHAP, i.] Forestry in Britain 27

lectures at Edinburgh was 7 in 1889-90, 6 in 1890-91, 40 in
1891-92, 10 in the winter of 1892-93, and 5 in the summer
of 1893, during the first, second, and fourth of which sessions
the fee for the course was £3 3^., whilst it was free (to matricu-
lated students only) for the merely incomplete course given
during the winter session of 1891-92.

If formed, none of the appointments should be filled except
by men thoroughly trained in Forest science, and fully quali-
fied to give lectures over the whole range of Forestry ; that is
to say, in —

1. Sylviculture, treating of the formation, tending, and repro-
duction of woodlands.

2. Protection of Woodlands ', showing how to safeguard them
from inimical inorganic agencies (winds, frost, &c.) or organic
enemies (fungoid diseases, insects, game, &c.).

3. Management of Woodland Estates, and Valuation of Timber
Crops, for the framing of Working Plans, and in order to
determine the most profitable methods and times of utilizing
the timber crops.

4. Utilization of Woodland Produce, showing how it can
most economically be prepared for, and brought to, market.

The matter is either one of true national importance, or it is
not. If not, then the owners of woodlands may well be left
to go on as indifferently and unintelligently as they have
hitherto been doing ; for they can help themselves out of the
difficulty whenever they choose to combine and open their
purse-strings to no very great extent. But if it really be of
national importance, then now, when large areas of land are
likely to be thrown out of arable and pastural occupation, is
the proper time for the Government to initiate a sound system
of instruction in Forestry. Even if my suggestions were carried
out to their very fullest extent ; if Chairs of Forestry could be
founded at Oxford, Edinburgh, Dublin (each at £700 a year),
and at St. Andrews, Aberdeen and Belfast (each at £600
a year), and if small schools of Practical Sylviculture for youths

28 Studies in Forestry [CHAP. i.

were arranged for at Dunkeld, Grantown, Coleford, and Lynd-
hurst (at about £150 a year each), the total annual expenditure
involved would only amount to £4,500. This is surely a very
slight insurance to pay for the probable better management of
woodlands already amounting in actual minimum cost to over
twenty-and-a-half millions of pounds sterling, and most likely
to be very considerably added to in the immediate future. It
amounts, in fact, to less than three farthings per acre per
annum for the land already actually under timber.

CHAPTER II

THE BRITISH SYLVA, AND THE GROWTH OF
WOODLAND CROPS IN GENERAL

AT the time of the Roman invasion of Britain a very con-
siderable portion of our island was still covered with forest,
as the gradually advancing requirements of increasing popula-
tion had not yet necessitated any very extensive clearance of
the primeval woodlands in order to permit of the expansion
of tillage and pasturage.

The species of forest trees of which the woods consisted
comprised Oak, Beech, Hornbeam, Scots Pine, Birch, Ash,
Willow, Alder, Scots Elm, Yew, Aspen, Mountain Ash, and
Hawthorn. The uplands of central and southern England,
and more especially those tracts having limy or chalky soils,
bore dense woods of Beech (which, however, was not indi-
genous to Scotland, where it was not introduced until the
beginning of the eighteenth century), whilst a stately growth of
Oak covered the richer alluvial stretches having deeper soil.
The sandy hills of southern England and all the mountainous
tracts extending from Yorkshire to the northern portion of the
island were probably mainly covered with Scots Pine (the only
species of the Abietineae indigenous to Britain), Birch, and
Mountain Ash, whilst Oak, Ash, Scots Elm, Aspen, Willow,
Alder, and Yew were for by far the most part restricted to
the dells, valleys, and lower-lying localities, where the soil was

30 Studies in Forestry [CHAP. n.

generally deeper and more productive, and the climate was less
rigorous.

During the Roman occupation of Britain (A. D. 44-410)
many species of trees were introduced from the continent of
Europe, including Sweet Chestnut, English Elm, Poplar, and
Lime, together with a good many other ornamental and
fruiting trees which failed more or less to establish themselves,
and never actually attained anything like true forest growth.
Even these four species named have only naturalized them-
selves to a certain degree ; for they cannot in our climate, and
more particularly in that of the northern portion of the island,
with its shorter and considerably cooler summer as compared
with the south of England, be relied on to produce seed of
normal germinative quality. To compensate for this, however,
they are richly endowed with the power of throwing out stoles
or suckers from the roots, and these are capable of being
transplanted like seedlings.

Of the various other species that are now entitled to rank
among our forest trees, Sycamore or Scots Plane, white and crack
Willows, and white and grey Poplars were introduced before
the end of the fifteenth century ; Spruce, and Cluster Pine
during the sixteenth century; Silver Fir, Maple, Horse Chestnut,
and Larch during the seventeenth century (although the Larch
was not introduced into Scotland till 1727); Weymouth, Mari-
time, Cembran, and Pitch Pines in the eighteenth century ; and
Austrian, Yellow, and Jeffrey Pines, Nordmann's and Douglas
Firs, Menzies Spruce, &c., during the present century.

The Forest Trees of any country may be considered, from
a sylvicultural point of view, as belonging to one or other of two
classes ; for they must be either Principal or Ruling Species,
forming, or capable of forming, pure forests without any assis-
tance from other kinds, or else Subordinate or Dependent
Species, which are practically found thriving best in admixture
with one or more of the ruling species.

The terms principal and subordinate are of course here used

CHAP, ii.] The British Sylva 31

in a purely sylvicultural, and not in any financial, sense ; for, as
a matter of fact, the most valuable species of timber are usually
to be found among the latter class. To the former belong,
among the conifers, Scots Pine, Spruce, Silver Fir, and occa-
sionally Larch, and among the broad-leaved trees, Beech, Oak,
Birch, and Alder principally ; whilst the latter include all the
other indigenous and exotic trees now of woodland growth in
Britain, of which the principal are the Douglas Fir, the Menzies
Spruce, the Black Pines (Austrian and Corsican), and the Wey-
mouth Pines among conifers, and the Ash, Maple, Sycamore,
Elm, Hornbeam, Aspen, and Willow among broad-leaved species.

For the sake of brevity the following details will be con-
fined to the above-named trees only.

Whilst in growth trees extract supplies of nutriment partly
from the atmosphere (in the shape of carbonic acid, the
carbon being assimilated, and the oxygen being set free) and
partly from the soil occupied by their root-systems (mineral
nutriment). If the trees were to be allowed to die off and
then rot, in place of being utilized as timber whilst still in healthy
growth, the supplies of mineral nutrients extracted from the
soil would be restored to it, by the formation of humus or
mould, on the ligneous tissue becoming decomposed under the
action of sunlight, moisture, and a moderate degree of warmth.
But, with the removal of the timber crops, the natural balance
is disturbed ; and, unless protection be afforded to the agencies
active in causing the chemical changes that result in the de-
composition of its mineral constituents, the soil runs a risk
of becoming gradually deteriorated and finally exhausted. In
agriculture, a similar danger is obviated by manuring the land,
the manure not only helping to replace the nutrients previously
withdrawn, but also stimulating to increased nitrification and
decomposition of the soil. In sylviculture, however, such
measures would be neither practicable nor remunerative ; and
the only recompense that can practically be given consists in
the fall of dead foliage, twigs, &c. Fortunately, however, in

32 Studies in Forestry [CHAP. n.

these debris is stored up a large portion of the mineral sub-
stances extracted from the soil. But the work of decomposing
and dissolving the mineral nutrients is indirectly aided by the
leafy canopy of the woodlands. This both prevents insolation
of the soil, and also safeguards the retention of a certain
amount of soil-moisture requisite for rendering the mineral
nutrients soluble ; because it is only in the form of soluble
salts that food can be- imbibed by the rootlets. By ramifying
throughout the soil, the root-systems help to cleave and fissure
the subsoil previous to other changes taking place; whilst
shrubs, grasses, and mosses, thriving under the shade of the
trees, also die off, decompose, and are transformed into forest
mould, which, from its strongly hygroscopic nature, absorbs
and retains the atmospheric moisture and precipitations, and
assists in regulating the flow of water within the soil.

When the leaf-canopy overhead is much interrupted or
broken, the soil is apt to be overrun with a rank growth of
noxious grasses and weeds, which consume the nutrients un-
profitably ; whilst at the same time it is exposed to the inimical
influences of sun and wind, whose action is apt to reduce the
quantity of moisture in the soil below that which is most
favourable for tree-growth.

For the retention of the soil-moisture, and the protection of
the soil generally, those species of trees are the most favourable
crops, which have a dense crown of foliage and maintain them-
selves in close canopy until their maturity — qualities with which
the different kinds of trees are very unequally endowed.
Among broad-leaved genera the Beech ranks highest in this
respect, its canopy being close and its foliage dense, whilst the
dead leaves are rich in potash and form mould of excellent
quality and strongly hygroscopic power. The leaves of Oak
do not form good humus, as a considerable amount of tannic
acid is evolved during decomposition. Hornbeam foliage
yields good mould, but the crop of leaves is lighter in every
way than in the case of the Beech ; Lime shades the soil

CHAP, ii.] The British Sylva 33

well and is thickly foliaged, though, as the leaves are thin in
texture, the amount of humus formed is only slight ; the Chest-
nut has a thick crown of foliage yielding good mould. None of
these last three genera occur, however, to any great extent form-
ing pure woods in Britain. Oak, Elm, Ash, Maple, Sycamore, and
the other valuable broad-leaved species are, owing to the com-
parative lightness of their crowns of foliage, not naturally well
endowed with capacity for protecting the productive power of the
soil, when they form crops by themselves, without the assistance
of other trees with denser crowns, — although they may be found
doing well on soils of so moist a character that insolation and
evaporation are rather beneficial than prejudicial in diminish-
ing the amount of soil-moisture. Among conifers the species
best endowed with soil-improving and soil-protecting qualities
are in particular Spruce, Menzies, Douglas, and Silver Firs, and
in a less degree the Weymouth and the Austrian and Corsican
Pines, the fine growth of mosses beneath which also acts like
humus in sponge-like absorption and retention of moisture.
Scots Pine and Larch are, owing to the sparseness of their foliage,
least endowed in this respect, although during the earlier stages
of their development a good layer of moss is usually to be
found covering the soil, and protecting it from the inimical
and exhausting effects of sun and wind. When once the canopy
begins, however, to get broken, this beneficial covering of moss
disappears ; and then the soil, with its new growth of rank
grasses, whortleberry, or heather, rapidly begins to deteriorate,
unless underplanting is taken in hand. Where marshy land is,
planted up with Alders, Birch, Willows, and Poplars, the action
of sun and wind is often beneficial, just because it tends to
reduce the quantity of moisture, which is apt to be excessive
on such low-lying situations.

One of the leading principles in the Management of Forests is
that in woods of normal composition, having crops of all ages and
classes properly represented from zero up to maturity on areas
of equal productive capacity, the annual fall of mature timber

34 Studies in Forestry [CHAP. n.

shall, under ordinary circumstances, be equal to the annual pro-
duction of the total area during one year; and this is repre-
sented, as the total growth throughout x years, by the mature
timber standing on the fall about to be harvested. To cut down
more than this, is to consume a portion of the capital represented
by the growing stock ; whilst to utilize less, is simply not to treat
the woodlands in an economic manner. In order, however,
that such normal average increment may take place annually,
it is necessary that the woods must be of normal density, that
is to say, neither too crowded on the one hand, nor too sparsely
stocked on the other, although of course the suitable and
proper degree of density that may be termed normal varies
with each species of crop. Crowding is disadvantageous. If
the individual trees forming the crop have not a sufficiency
of growing-space, then they cannot possibly obtain the supplies
of light, air, and warmth requisite for their most favourable
development, and therefore soon fall into a sickly condition of
growth, which predisposes them to dangers from wind, snow,
insects, and fungoid diseases. The constant struggle, too, which
is being waged for supremacy among the individual trees in
woods becomes thereby unduly prolonged ; and in this is dissi-
pated the energy which, with judicious tending and thinning,
can be advantageously utilized for the better and more vigorous
formation and development of the individual poles or trees of
more robust growth, from among which the trees finally form-
ing the mature crop must ultimately be selected. But if the
number of individuals per acre falls below the normal average
density for any particular species of tree and any given class
of soil and situation, or, in other words, if the growing-space
allotted to each individual be in excess of what is requisite to
maintain the pole or tree in vigorous growth, then its vital energy
becomes dissipated in branch-formation, instead of being con-
served so as to be concentrated and utilized in the formation of
a long, straight, full-wooded bole or stem, free from knots, and
consequently of higher technical utility and commercial value.

CHAP, ii.] The British Sylva 35

And, at the same time, from the leaf-canopy formed by the
crowns being much more apt to be interrupted here and there,
or sometimes quite broken in its continuity, the surface of
the soil must be exposed to the action of sun and wind and to
the consequent danger of rank growth of weeds, subsequent
deterioration, and perhaps final exhaustion.

This normal density, which should be maintained unbroken
or uninterrupted in order that the productive capacity of the
soil may be fully utilized, and yet at the same time protected
against deterioration, consists of a full or close leaf-canopy.
The different species of forest trees are very unequally endowed
with capacity to retain close canopy when once they have en-
tered on the later stages of development, for they make different
demands with regard to individual growing-space, and then the
density of the foliage forming the crown also varies with each
individual species. To estimate these differences it is only
necessary to compare the crown of a Beech or a Silver Fir with
that of a Birch or a Larch, although in these cases extremes are
purposely chosen in the two classes of broad-leaved trees and
conifers. This physical fact, that all trees of forest growth
are not alike endowed with the capacity of shading the soil
and protecting it against the exhausting influences of sun,
wind, and rank growth, is a matter of very great moment from
the sylvicultural point of view. Although all our forest trees
may be grown in pure woods, if worked with a low rotation,
owing to timber crops being naturally dense during the thicket
period (that is, till the crop begins to clear itself naturally of dead
branches), and during the pole-forest stage of growth (which
means till the leading stems have attained a girth of about two
feet measured at breast height), yet after that, when once they
have entered into the tree-forest or high-forest stage of develop-
ment, their natural individual differences with regard to demands
for light, i.e. growing-space, and with respect to density of foliage
in the interior of the leafy crown, begin to make themselves
unmistakably apparent. Thus whilst thickly foliaged kinds of

D 2

36 Studies in Forestry [CHAP. n.

trees, like Beech, Silver Fir, and Spruce, can be grown in pure
forests until they attain their full technical and mercantile
maturity, without the productive capacity of the soil being
endangered, it would be contrary to one of the leading prin-
ciples of sylviculture — viz. the conservation of the productive
capacity of the soil — to cultivate pure high forests of light-
demanding genera like Oak, Ash, Maple, Pine, or Larch,
except under special circumstances where the productive capa-
city of the soil is not endangered by insufficient cover, as, for
example, on some classes of marshy land where the evaporation
caused by insolation and by the free play of winds is directly
beneficial, or on low-lying tracts with fresh soil, whose depth
and porosity might perhaps be injuriously affected by any accu-
mulation of humus. It is solely with regard to the soil-protecting
capabilities of the different forest trees that the classification
above given of Ruling and Dependent Species is based; for it
may be briefly stated that the productive capacity of woodland
soil is only safeguarded to the necessary extent when the
timber crop consists either of thickly-foliaged species growing
in close canopy, and providing the soil with a good layer of
leaf-mould, or else of conifers having evergreen foliage, under
which a covering of mosses performs the functions of the humus
or mould elsewhere. The species of trees naturally fitted to
be grown in pure forests under the first of these conditions
are pre-eminently Beech, Spruce, Menzies, Douglas and Silver
Firs, and in a less degree Hornbeam, Lime, and Chestnut;
whilst those falling under the second condition comprise the
several varieties of the Pine genus, so long as they are not
worked with too long a period of rotation, i. e. so long as their
fall is not delayed too long after the time when they sink so far
below the normal density of canopy that the growth of mosses
gives place to weeds and berries, and the soil begins to
deteriorate through insufficient protection against insolation
and exhausting winds. Unfortunately the broad-leaved trees
best qualified by nature for the formation of pure forests are

CHAP, ii.] The British Sylva 37

not in Britain of sufficient technical and commercial value to
lead to their cultivation on any large scale ; but among them
the Beech and, on moister varieties of soil, the Hornbeam are
of great sylvicultural importance as the ruling species or matrix,
either in the shape of underwood or of tree-forest, along with
which the more valuable classes of timber trees, Oak, Ash,
Maple, Sycamore, Birch, &c., may be most profitably grown on
localities where the soil would be liable to deterioration if the
woods consisted of these thinly-foliaged and light-demanding
species only.

For the formation of woods of normal density or full leaf-
canopy the number of individuals per acre varies, as has already
been stated, according to the species of tree ; but wherever
reliable data have been collected, it appears that, on soils of
the best quality for the requirements of each genus of tree,
at the age of 120 years there are 37 % more Beech, 24^ %
more Silver Fir, and 60 % more Spruce than individual stems
of Scots Pine per acre. It also appears that at all ages
there is on soils of the best quality invariably a very much
smaller number of individual trees of any particular species than
on the poorer classes of soil. The difference may often be
enormous, for at eighty years of age Scots Pine woods on the
best class of Pine soil consist of only one-third of the number
of trees that are generally found on the poorest class of soil.
So far as these different results are concerned, with one and
the same species of tree, they are explainable through the
fact that the general development and the natural process of
selection of the fittest— the struggle for light and air, for domina-
tion, and for individual existence— is more energetic and
decisive on good soils than on those of inferior quality. The
differences exhibited by the various species of trees, however,
is dependent on their different sylvicultural characteristics
with regard to the natural development of their crowns, and
their special requirements as to growing-space. Through-
out the Spessart forest it has been found that the following

Studies in Forestry

[CHAP. II.

average density of crop is necessary for the formation of close
canopy : —

Age of Forest,
years.

Beech.

Oak.

Soil of best Quality.

Soil of best Quality.

60

120

5*7

2IO

1.234
326

Although at first glance this almost looks as if it might be
argued that the Oak is more capable of bearing shade than
the Beech, which would be contrary to experience, it actually
proves nothing more than that the Oak takes considerably
longer than the Beech to develop in that locality, and that the
Beech finds lateral expansion of its crown a sine qua non of
existence at an earlier period of age than the Oak.

Whilst the number of individual poles or trees forming
the crop is larger on poor than on good soils, yet the full
normal density of leaf-canopy is maintained longer on the
better classes of soil. But the actual extent to which the
ground is overshadowed varies also with the species of tree ;
for experiments and measurements have shown that in a Spruce
forest, of normal density for Spruce, the soil is overshadowed to
more than twice the extent that obtains in a Scots Pine forest,
of normal density for Pine.

If what has been stated above be correct — viz. that the pro-
ductive capacity of the soil can be best protected when close
canopy is maintained throughout woodland crops — then it must
naturally follow that the greatest production of timber per acre
must take place in woods having a leaf-canopy of normal density.
And practical experience shows that such is the case. In general,
other things being equal as to the productive capacity of
the soil, the increment per individual stem is greater in trees
revelling in the full enjoyment of light, air, and warmth, than

CHAP, ii.] The British Sylva 39

in those whose crowns are limited to a more or less restricted
growing-space; because they have larger root-systems, can draw
greater supplies of nutriment from the soil, and enjoy better
opportunities for carrying out assimilation and for utilizing
their nourishment in the formation of ligneous tissue. On soils
similar as to quality the total production per acre in close-
canopied forest is not only greater than in the more open
forest, but the technical quality of the timber produced is also
much higher owing to the better dimensions attainable by the
bole or stem, and to freedom from knots formed where the
branches emerge from the trunk of the tree. The larger the
growing-space allowed to each individual tree, the greater is the
tendency to branching growth taking place at the expense of
the bole; hence, for the production of long straight stems, it is
necessary to maintain as close canopy as is consistent with the
general health and vigour of the crop until it has passed through
the pole-forest stages, during which its growth in height is most
active, although this again varies according to species of tree
and other factors. When crops attain their chief growth in
height after being maintained in canopy of normal density,
experience has shown that the stems rapidly increase in girth
when the canopy is interrupted, artificially, for the purpose of
permitting the individual trees to obtain larger supplies of light,
air, and warmth. This sylvicultural operation, although pur-
posely diminishing the number of individual trees per acre,
often leads to a greater increment and a more valuable yield
than if the crop had been allowed to remain growing in normal
canopy, — but this is a subject that will receive full attention
subsequently (see Chapter X). As, in woods growing in close
canopy, the crown is circumscribed, and can for the most part
obtain only from above the light and warmth necessary for the
work of assimilation, the poles compete with each other for
a larger measure of exposure to these invigorating influences,
so that the growth in height becomes stimulated. And as,
owing to the crowns being limited to the upper portion of

4Q Studies in Forestry [CHAP. 11.

the stem, a larger proportion of the assimilated food is utilized
in the upper part of the tree than in the lower, the result is
that the boles are more full-wooded, i.e. they approach more
to the cylindrical in form, than is the case with poles growing in
crops below the normal density in leaf-canopy. Until the chief
growth in height has been completed, therefore, the mainten-
ance of close canopy affects not only the actual length of the
bole or clean stem and its shape, but also the proportion of
timber obtainable, as compared with branchwood ; and these
are matters of great technical and financial importance.

When seedling growth or young plantations, after having
passed through the thicket stage of growth, develop into pole-
forest, and finally into tree-forest or high-timber, the crop consists
of various classes of growth named, according to the position
they may occupy in the struggle for increased growing space :
(i) predominating, (2) dominant, (3) dominated, and (4) sup-
pressed, although of course there are no hard and fast lines
existent between these different classes. Until far on in the
life-history of the crop, the predominating class comprises
within it all the individuals that are likely to form any portion
of the mature fall of timber ; hence, in all clearings and thin-
nings undertaken with a view to the tending of woodlands —
a subject that will be considered later on (see Chap. IX) —
the removal of the suppressed and, to a greater or less extent
(according to the species), the dominated classes, is advisable.
Such cultural measures are not only for the purpose of assist-
ing nature in the work of eliminating the individuals no
longer required in the maintenance of a leaf-canopy of normal
density, and of helping the more vigorous stems towards their
more rapid development, but also for removing all poles and
young trees of enfeebled energy and perhaps sickly growth,
which might offer dangerous attractions to noxious insects.
Compared with the total number forming the crop, the per-
centage of individual stems necessary for the retention of a leaf-
canopy of normal density varies essentially according to (i) the

CHAP, ii.] The British Sylva 41

species of tree, (2) the nature of the soil and the situation, and
(3) the previous treatment that has been accorded to the crop.
In consequence of the competition for possession of the
soil, which takes place when different species of trees have
been intermixed either naturally or artificially, the law of
nature regarding the survival of the fittest has brought it to
pass that, wherever they have long had free scope to make
their special characteristics and influence felt, certain species
of trees usually predominate numerically over large tracts of
country. As has already been mentioned, the primeval woods
of Britain consisted mainly of Oak on the better soil, Beech
on limy and upland tracts, and Scots Pine on the higher hills
and on slopes having only inferior qualities of soil. If we
look at the continent of Europe, we find the Scots Pine the
chief tree over the bulk of the sandy stretches comprised
within the North German plain, and the Spruce asserting itself
throughout Scandinavia and north-western Russia and on the
humid mountainous tracts of central Europe, pre-eminently on
the Harz Mountains ; a covering of Beech clothes the lower
hills of central and north-western Germany, forming the Deister,
Soiling, and Thuringian forests ; the Silver Fir occupies similar
situations in south-western Germany and France, in the Black
Forest, and the Jura mountains ; whilst Austria has large tracts
wooded chiefly with Black Pine and Larch, and Russia can
show its well-defined areas on which Pines, Firs, Hornbeam,
Birch, Alder, and Aspen are the dominant species. Speaking
generally, the ruling species of trees throughout the forests
of central Europe, as they now exist, may be said to be Scots
Pine, Spruce, Silver Fir, and Beech in the first degree, followed
by other Pines, Larch, Oak, Alder, and Birch. These are
the species which form the bulk of the individuals in woodland
crops ; whilst Ash, Elm, Maple, Sycamore, Poplars, Willows,
and exotics like Weymouth Pine and Douglas Fir, are only to
be found in smaller numbers, or in situations specially suited
for their growth. It is, however, rarely that any of these species

43 Studies in Forestry [CHAP. n.

are now to be found forming pure forests in countries where
attention has been paid to the most recent developments of
scientific sylviculture ; for the tendency is now rather towards
the formation and maintenance of mixed woods as combining
important sylvicultural and financial advantages. But, if entirely
left to themselves, certain species of forest-trees will ultimately
suppress and eliminate most other kinds over tracts of soil
better suited to the former than to the latter. Evelyn was to
a certain extent aware of this more than two hundred years
ago, when he remarked, in one of his letters published in
Aubrey's Surrey, that : —

'Where goodly Oak grew, and were cut down by my grandfather
almost a hundred years since, is now altogether Beech ; and where my
brother has extirpated the Beech there rises Birch.'

What might just be expected happens. The shade-bearing
and densely-shading species — Beech, Spruce, Silver Fir, and in
a less degree Hornbeam and Black Pines — assert themselves
over large tracts; whilst other kinds of trees of woodland
growth are ousted, and occur merely as subordinate clumps,
or groups, or patches, or as individuals scattered here and
there over areas and situations unsuited for the predominating
species, either on account of the nature of the soil or situation,
or for some reason connected therewith (frost, want of moisture,
shallowness of soil, &c.). There can, of course, never be rigid
lines marking off the domain of the various species ; for there
must always, in consequence of the various factors connected
with the physical conditions of soil and situation, be belts of
land where the advantage lies sometimes with one species and
sometimes with the other. At the present time on the continent
one has many opportunities of seeing how, in consequence of
bad management and of servitudes, under wru'ch the peasants
were entitled to rob the woodlands of their soil-protecting
layer of dead foliage, the domain of the Oak and the Beech
is being encroached on by the Pine and the Spruce, which are
both more easily satisfied as to soil and situation ; whilst these

CHAP, ii.] The British Sylva 43

latter again have often to contend with the still more easily
satisfied Birch and Willow for the possession of their own
areas. It might be argued against what is here stated, that
the Scots Pine asserts itself to the exclusion of shade-bearing
species on the vast plains south of the Baltic ; but this is solely
due to the fact that, for the poor sandy soil there, the Pine has
proved itself better suited and more accommodating than any
other species of tree, and is in fact merely another example of
the survival of the fittest. Even on that sandy plain, near the
fertile lands along the riverine tracts, there is still to be found
a stately growth of Oaks, Ash, Elm, Maples, &c., able to hold
their own against any attempts at encroachment made by less
noble species of woodland trees ; whilst the Alder and Willow
coppices of those districts are famed.

From a study of the growth of trees in their natural habitats,
and of their development in varying situations into which they
may have been brought by artificial means, we are enabled to
classify and arrange them according to their sylvicultural
characteristics ; and a thorough knowledge of these is necessary
before we can hope to attain anything like the highest and
most successful results with regard to the formation, tending,
and reproduction or regeneration of woodland crops. To give
only one instance of error made in regard to a valuable species
of tree, owing to want of scientific knowledge regarding its habit
and conditions of growth, take the case of the Larch, which
was introduced into England in 1629, into the Lowlands of
Scotland in 1725, and into the Highlands in 1727. Of this tree,
27,000,000 plants are said to have been planted out in Scot-
land between 1738 and 1820; but it certainly has not fulfilled
all the anticipations that were then made as to its future value.
The Larch is essentially a tree of the mountains, where it
ascends higher than even the Spruce. It is found on the
Bavarian Alps at from 3,000 to 6,000 ft. above sea-level in
excellent development and often forming pure forests; lower
down it is naturally associated along with Spruce and Beech in

44 Studies in Forestry [CHAP. n.

the zones more congenial to these genera. The climate in
which it thrives best is the Alpine climate, that is to say, one
in which a long cold winter is succeeded by an exceedingly
short spring, and followed by an equable, warm summer, which
again, after a very short autumn, gives place to the long period
of winter rest and defoliation. Removed far from its true
Alpine home, and subjected to climatic conditions essentially
differing therefrom, can it be wondered at that its development
has been, on the whole, disappointing ? In place of having the
good straight bole, which is characteristic of its growth where
indigenous, it tends to curved, sabre-like form ; the stem and
branches are prone to favour the development of hanging
lichens ( Usnea barbata, &c.) ; the foliage is damaged by cater-
pillars of the mining-moth (Coleophora laricelld] and of another
Tortrix (Grapholitha pinicoland] ; whilst the boles are specially
liable, at from about ten to twenty-five years of age, and more
especially after bad attacks of these insects, to become infected
with the serious cankerous, fungoid disease due to Peziza
Willkommii. This has often necessitated a clearance at the
age of forty to fifty years, or long before the crops would, under
more favourable circumstances, have been anything like tech-
nically or financially mature. The investigations of Professor
R. Hartig of Munich have shown that the fungus which occa-
sions this disease is indigenous to the Alpine home of the
Larch, and sometimes occasions canker on stems there ; but it
has followed the tree to central and Northern Germany, and
to England and Scotland, where, owing to climatic condi-
tions and to its less vigorous growth, the stems are more
liable to become infected, whilst the ravages committed are
at the same time more serious. His own words are as
follows : —

' The enormous distribution which the Larch fungus, Peziza Willkommii
has obtained on the German plains, is almost solely explained by the
rich development of fully matured fruits and spores in the damp, and
more especially in the stagnating, atmosphere of close-canopied forests

CHAP, ii.] The British Sylva 45

in low-lying localities ; whilst with the free play of aerial currents in
Alpine tracts the fruits almost always dry up before they ripen V

The crookedness of the stem may be due either to want of
depth of soil interfering with the normal development of the
strong tap-root, or else to the growth of the tree being stimu-
lated beyond normal and healthy limits, owing to the much
longer period of activity necessitated by our climate, in which
spring and autumn are gradual and prolonged stages between
the periods of foliation and defoliation.

1 Lehrbuch der Baumkrankheiten, 2nd edit., 1889, p. 45.

CHAPTER III

THE CHIEF SYLVICULTURAL CHARACTERISTICS OF
OUR WOODLAND TREES

THE differences in sylvicultural characteristics exhibited by
the various species of our forest trees may be conveniently
classified with reference to the following matters : —

I. Climatic requirements.
II. Requirements as to soil and situation.

III. Capacity for bearing shade.

IV. Normal shape of the stem and crown.

V. Increment or rate of growth in height, girth, and cubic

contents.

VI. Reproductive capacity.

VII. Attainment of economic maturity and normal duration of healthy
growth.

When John Evelyn, as a Fellow of the Royal Society, read
his Sylva, on October 15, 1662, we were quite abreast of
continental knowledge relative to woodcraft; but since then
we have lagged behind nearly every other country, whilst
Germany has acquired by far the largest and richest stores
of natural knowledge with respect to the science of Forestry.
Yet, even in Germany, it is only within the last ten or twelve
years that Professor Karl Gayer's observations and classifi-
cations have found general acceptance as the fundamental
principles upon which the modern practice of Sylviculture — that
branch of Forestry which treats of the formation, tending,
and reproduction of woodland crops — has a firm, logical, and

CHAP. III.]

Characteristics of Trees

47

scientific basis. The first edition of his great work on Sylvi-
culture was issued in 1880, and the final expressions of his
matured conclusions, in the third edition of 1889, are the
source from which most of the following data have been
drawn *.

I. Differences of Forest Trees as to Climatic
Requirements.

The natural causes influencing the geographical distribution
of the forest trees of Europe are partly climatic, and partly de-
pendent on the physical conditions of soil and situation. The
energetic growth and development of any particular species
can only take place in localities that have such period of
vegetation, and such intensity of summer warmth, as to enable
the processes of assimilation and of the formation of ligneous
tissue to proceed satisfactorily. For the least exacting species
in this respect a three-monthly period of vital activity and
a mean summer temperature of 54° to 57° Fahr. are the
requisite minima2; whilst on the other hand the minima of
the cold during the winter months also fixes their limits, so
that large tracts of arctic Russia and Scandinavia are destitute
of forest growth. The polar or northern limits of some of
the more common forest trees are as follows : —

Species.

Western Europe
(Scandinavia & Germany).

Eastern Europe
(Russia).

Scots Pine . .
Spruce . . .
Oak (Q. pedunc.)
Beech. . . .
Silver Fir . .

68-70°
67-71°

60°
49-52°

6{i2°

And, in a similar manner, the reduction of the temperature

1 Waldbau, 3rd edit., 1889, pp. 18-49.

2 Weber, Die Aufgaben der Forstwirthschaft, in Lorey's Handbuch der
Forst-wissenschaft, 1886, vol. i. p. 13.

48 Studies in Forestry [CHAP. in.

in atmosphere and soil, with increasing height above sea-level,
also causes a more or less irregular and inconstant distribution
of species according to vertical zones in the mountains of
central Europe, although in this respect the variations due
to soil, situation and aspect are so great that it would perhaps
be misleading to attempt any classification. It must, however,
be remarked concerning the Scots Pine and the Spruce that
their limits towards the north, and towards Alpine heights, are
not so much due to the actual intensity of cold during winter,
as to the fact that transpiration by the leaves is stimulated
on bright sunny days in winter at a time when the frost-bound
soil can yield no supplies of moisture to replace what is
evaporated through the leaves J ; hence the natural consequence
is that the foliage grows yellow, the tree turns sickly, and death
ensues. These results can most frequently be observed after
long, dry, hard winters with frequent sunny days.

The southern limits of the forest trees of northern Europe
are mainly determined by the quantity and the regularity
of the rainfall during summer. As the results of careful
experiments conducted in Austria, von Honel2 found that,
computed by the unit of weight of their dry foliage, among
broad-leaved trees, Ash and Birch require the largest supplies
of water for transpiration, then Beech and Hornbeam, then
Elms, and finally Maples and Oaks. Among conifers, the
order was Spruce, Scots Pine, Silver Fir, Black Pine. He also
found that, taken as a whole class, the broad-leaved species
consumed on the average about ten times as much water as
the conifers, and that, owing to the light foliage of the Pine,
this species required very much less soil-moisture than Spruce
or Silver Fir. But although the actual total of average annual
rainfall may be considerably greater than what is required for
transpiration through the foliage during the active period of

. 1 R. Hartig, Lehrbuch der Battmkrankheiten, 2nd edit., 1889, pp. 104,
261.
2 Compare, however, the more recent data set forth in Chapter IV.

CHAP, in.] Characteristics of Trees 49

vegetation (and, even for Beech, a summer rainfall of twelve
inches would suffice according to Ramann 1), yet when rain does
not fall on the average once every 6 to 8 days throughout the
summer months, the woodland crops are, in the dry climate
of central Europe, exposed to more or less danger of being
killed off by being unable to obtain from the soil the constant
supplies of moisture requisite for the maintenance of healthy
and vigorous growth by means of normal transpiration ; or in
other words, they are liable to suffer from drought and to die off.

So far as the climate of Great Britain is concerned, it is,
both as regards temperature and atmospheric precipitations,
suited to all the species of woodland trees that occur in
central Europe ; but the Mountain Ash, the Wych Elm, the
Scots Pine and the Birch are more characteristic of, and
grow better in, Scotland than in England, where again the
Beech, the pedunculate Oak, the English Elm, and the Silver
Fir thrive better than in the northern half of the main island.
Pine, Spruce, Larch, Silver Fir, sessile Oak, and Sycamore, are
naturally the inhabitants of upland tracts and mountain ranges,
whilst Ash, Alder, pedunculate Oak, Aspen, Elm, and Willow
belong rather to low-lying localities ; Beech, Hornbeam,
Maple, and Birch seem capable of thriving equally well on
plains or on hilly country. But, on the whole, the nature of
the climate, soil, and situation mainly determines the quality
of any given species of tree in any particular locality.

Very little is as yet known regarding the absolute amount
of atmospheric warmth necessary for the most favourable
development of the different kinds of woodland trees. But
experience has shown that Elm and pedunculate Oak require
most warmth ; that Black Pines, Silver Fir, Beech, Weymouth
Pine, sessile Oak and Scots Pine can thrive with less than
Birch, Maple, Sycamore, Ash, Alder, and Spruce ; whilst Larch
does with least.

So far as their development is apt to be prejudicially
1 Forstliche Bodenkunde und Standortslehre, 1893, p. 311.
E

50 Studies in Forestry [CHAP. HI.

influenced by frost, Ash and Beech are most liable to injury ;
Oak; Silver Fir, Maple, Sycamore, Spruce, Douglas Fir, and
Alder are somewhat liable; whilst Hornbeam, Elm, Birch,
Larch, Aspen, and Pines are the most hardy species. It is not,
however, the winter's cold that is injurious to these species,
but the late frosts in spring, when the flush of young leaves and
shoots is still tender, and the early frosts in autumn before the
summer shoots have had time to harden sufficiently so as to
resist the effects of the cold.

The relative humidity of the atmosphere is also a climatic
factor exerting very considerable influence on the vigour and
general development of the various kinds of woodland crops.
Experience has shown that, so far as any difference can be
made in a generally damp climate like that of our islands, the
species thriving best in localities with great relative atmospheric
humidity are Willow, Poplar, Alder, Maple, Sycamore, and Ash ;
Silver Fir, Scots Pine, Beech, Aspen, Birch, and Douglas Fir do
best with a moderately damp climate ; whilst Oak, Elm, Black
Pines, and Larch naturally prefer a rather dry atmosphere. It
may be of interest to note that the Scots Pine, which thrives so
well in our moist insular climate, does not thrive in Denmark,
and is essentially a tree of dry localities in Germany ; whilst
Spruce, which thrives best in humid localities throughout
central Europe, does not appear to grow anything like so
well in Britain.

II. Requirements as to Soil and Situation.

The aspect or exposure of any particular locality tends to
exert an influence in the same direction as vertical elevation,
though on a much smaller scale ; for, as the mean annual tem-
perature of slopes facing from S.E. to S.W. is higher than that
of hill-sides with N.E. to N.W. aspect, this naturally affects
the thriving of woodland crops. Near their limits of vertical
distribution, however, all trees ascend the mountains to

CHAP, in.] Characteristics of Trees 51

a greater height on the southern than on the northern sides,
in consequence of their requirements as to warmth.

The root-systems of the various species of forest trees vary
greatly with regard to shape and to the depth to which they
reach ; but even shallow-rooting kinds derive advantage when
the soil over which they grow is deep, owing to the greater
supplies of nutriment within easy reach of their roots. Some
are characterized either by a strong tap-root, or else by a deep
heart-shaped root with stout ramifications, as in the Oak, Elm,
Pine, Silver Fir, Maple, Sycamore, Ash, and Larch ; others
have no pronounced tap-root, but develop strong side-roots
penetrating into the soil for a moderate depth, as in Beech,
Hornbeam, Aspen, and Birch ; others again, like the Alder,
throw out strong side-roots, whence strands are sent down into
the soil ; whilst some are unmistakably shallow-rooting, as in
the case of the Spruce. Spruce, Aspen, and Birch require
least depth of soil, and Oak and Larch greatest. Of the other
trees, Scots Pine, Silver Fir, and Douglas Fir need deeper soil
than Austrian and Weymouth Pines ; whilst Beech, Hornbeam,
and Alder, although by no means shallow-rooted, can do with
a less depth than Elm, Maple, Sycamore, and Ash.

In referring to von Honel's experiments regarding the tran-
spiratory power of the various species of trees per unit of
weight of foliage, it will be remarked (Chapter IV) that his
researches give us no reliable data for estimating the absolute
quantities of soil-moisture necessary for woodland crops so as
to supply their normal requirements throughout the annual
period of active vegetation.

Practical experience, however, shows that Alder, Ash, Willow,
Poplars, Maple, Sycamore, and Elm, then Larch, Weymouth Pine and
Spruce, prefer soils with a considerable degree of moisture ; whilst
pedunculate Oak, Hornbeam, Birch, and Aspen, and in a less degree
Silver and Douglas Firs, also make greater demands than Beech and
sessile Oak, or Scots, Corsican, and Austrian Pines, which are the three
species that can best accommodate themselves to dry soils (the former on
those of a sandy, the latter on those of a limy nature).

E 2

52 Studies in Forestry [CHAP. m.

On the whole, the conifers are more moderate in their
demands on soil-moisture than the broad-leaved genera of
trees. But the limits within which the different trees can thrive
vary greatly according to the species ; or in other words, the
various kinds of woodland trees exhibit great differences as to
their accommodative power with regard to the degree of
moisture contained in the soil.

Although trees derive the greater part of their nutriment
from the carbonic acid which they absorb from the atmosphere,
still they are also .dependent on the soil for supplies of mineral
nutrients; and these can only be taken up when held in solution
by the soil-moisture. Whether the soil be loose or binding is
also a matter of very considerable importance to the thriving of
the various woodland trees. As a rule the broad-leaved species
do better than conifers on the stiffer classes of land, although
soils of merely average tenacity are on the whole most suitable
for all kind of trees, owing to their better endowment as regards
physical properties. The chief constituents of soils are clay,
lime, and sand ; and as clay yields the most valued nutrients
for plants, the qualities of soils are often determinable to some
extent by the quantity of clay found in them. The effects of
the mineral constituency of soils are, however, very greatly
modified by the physical properties inherent in them, and
these become prejudiced whenever any one of those three
most important constituents occurs in undue excess. Clay
soils are tenacious and interfere with the movement of soil-
moisture ; sands are too porous, and limes are too easily heated ;
hence on the average, the mixed classes of loamy soils are in
general most fertile. The absolute demands of the various
species of trees on the mineral strength or fertility of soils is not
yet fully known, although they can to a certain extent be
estimated from the weight and analysis of the ash left after
reducing the different kinds of timber by combustion.

On this point, however, sylvicultural experience shows that Elm, Maple,
Sycamore, and Ash, make the greatest demands ; and that Oak, Beech,

CHAP, in.] Characteristics of Trees 53

Silver Fir, and Willow are more exacting than Larch, Hornbeam,
Alder, Spruce, and Aspen ; whilst Poplars, Pines, and Birch can thrive
fairly well on indifferent classes of soil.

Here again it may be noted that, on the whole, the broad-
leaved species of trees are more exacting than the conifers.
As a broad generalization it may be asserted that the power of
any species to accommodate itself to soils and situations not
naturally suited to its normal requirements varies in the in-
verse ratio of the demands it makes as to mineral strength ; for
it is greatest in Scots Pine and Birch, and least in Elms,
Maple, Sycamore, and Ash.

It would be wrong to state broadly that a clayey, limy,
sandy, or loamy soil is, or is not, suited for any given species
of tree; because so very much depends on other considerations,
and particularly on the amount of humus present in it, owing
to the very favourable influence which this exerts on the
physical properties of the soil. Gustav Heyer even went so far
as to maintain l that almost any soil was capable of producing
any given kind of timber, provided that it contained the
requisite amount of moisture.

Ney 2 thus summarizes the best practical opinions that have
yet been expressed on this subject : —

4 As regards the chemical composition of the soil, even slightly sour
marshy soils are unfavourable to all species of trees except Alder, Birch,
and Spruce ; whilst sour soils, liable to dry up at certain seasons, are
unsuited to all except Birch, Spruce, Scots and Weymouth Pines.
Only these last-named species thrive on pure peat, and not even the
Spruce when it is dry. Ash, Maple, Sycamore, and Elm require
a moderate quantity of lime in the soil, and Beech, Hornbeam, Oak, as
also Larch and Austrian Pine, thrive best on soils that have at least
some lime in their composition. The hardwoods — Oak, Ash, Maple,
Sycamore, Elm, Chestnut, Beech, and Hornbeam— also appear to de-
mand the presence of a considerable quantity of potash ; whilst, on the
other hand, Spruce, Silver Fir, and especially Scots Pine and Birch,
thrive on soils rich neither in lime nor potash.'

1 Forstliche Bodenkunde und Klimatologie, 1856, p. 488.

2 Lehre vom Waldbau, 1885, p. 64.

54 Studies in Forestry [CHAP. in.

The influence of the sum total of the factors dependent on
soil and situation find their expression in the amount of timber
produced per acre, and in the quality of the timber, since this
latter must determine its adaptability for technical purposes.
Practically speaking, the best and the most convenient general
standard for estimating the quality of timber is to be found in
the specific weight, as, for one and the same kind of wood, the
heavier specimen is the more durable1, owing to the thick
deposits of ligneous substance in the cells. This does not,
however, apply to any comparison of different species ; for the
light wood of conifers is more durable than heavy Beech
timber. High specific gravity, length, straightness, and full-
woodedness of bole, with freedom from knots and branches,
are the best indications that soil and situation are eminently
suitable to the woodland crops covering them.

III. Capacity for bearing Shade.

All trees require a certain amount of light in order to carry
out the work of assimilation of the carbonic acid which forms
so important a part of their nutriment. Hence the want of a due
intensity of light exerts an injurious influence ; otherwise there
is no reason why the density of the foliage in the interior of
the crowns of trees should not be as great as it is near the
circumference. It is true that excess of light may tend to
paralyse the action of chlorophyll ; but, so far as the forest trees
of Britain are concerned, they are exposed to no danger from this
cause in our climate; they will thrive all the more vigorously the
more light they receive the benefit of. But, with regard to the
measure of light necessary for the performance of the assimi-
lative functions by the foliage — or, in other words, to the
capacity for bearing shade — marked differences occur among
the various species of trees ; and though affected by soil

1 Gayer, Die Forstbenutzung, 7th edit., 1888, p. 66.

CHAP, in.] Characteristics of Trees 55

and situation, these differences are, especially in woodlands,
sufficiently distinct to admit of general classification into
shade-bearing trees, light-demanding trees, and trees that
occupy an intermediate position. The different species of our
forest trees may accordingly be classified as : —

Light-demanding trees:
Larch ; Birch.

Scots Pine ; Aspen, Poplar, Willow.
Oak, Ash, Elm ; Douglas Fir.

Trees less impatient of shade :

Alder, Maple, Sycamore ; Weymouth, Corsican, and Austrian Pines,
and Menzies Spruce.

Shade-bearing trees :
Spruce ; Hornbeam.
Beech ; Silver and Nordmann's Firs.

The capacity of the various species for bearing shade under
any given circumstances, or in other words, their demands for
light, may be gauged by the general density of the foliage of
the crown and the capacity of overshadowed twigs to retain
life. But, so far as regards the absolute quantity of light requisite
for the performance of the assimilative functions of any species,
we know as little as about the necessary amount of warmth.
For general sylvicultural purposes, Larch, Birch, Scots Pine,
Oak, Ash, Aspen, and Willow, may be considered the principal
light-demanding species of trees, and Silver Fir, Beech, Spruce
and Hornbeam the chief shade-bearers ; whilst the attitude of
the other woodland trees in this very important matter is
mainly dependent on the conditions of the soil as to depth,
moisture, and general quality.

The length of the annual period of vegetation also makes itself
'felt to a certain degree ; for in the far north, or at high eleva-
tions, where this is shorter than in lower latitudes or levels, the
demands for light become greater than obtain under the oppo-
site conditions. The same may also be said of cool northern

56 Studies in Forestry [CHAP. in.

exposures and misty regions, as compared with warmer southern
aspects and localities where the crowns can revel in the undis-
turbed possession of genial sunlight and warmth.

The relative powers of the various species of trees to bear
shade under any given conditions as to soil and situation are
of great, and indeed vital, importance in practical sylviculture.
For on these are mainly dependent the measures that may
seem prudent with regard to the selection of species of trees
for woodland crops, the extent to which admixture of species
may be advisable, the best method of treatment and tending
to be accorded to the woods, the most advantageous time for
harvesting the mature crops and reproducing them, &c. In fact,
without a due consideration of their individual characteristics
in this respect, it is impossible to accord rational scientific and
practical treatment to woodland crops.

IV. Normal Shape and Development of the Stem
and Crown.

The essential characteristic of a tree as compared with
a shrub is its habit of developing a bole or stem before be-
ginning to ramify and form a crown of foliage-bearing branches.
Some kinds of forest trees have a greater tendency to ramifi-
cation than others, as, for instance, the broad-leaved trees
generally in comparison with conifers ; but the individual
tendencies of each kind with regard to the length and straight-
ness of the bole are often to a very considerable extent de-
pendent on (i) the growing-space allotted to if, (2) the age of the
crop) (3) the nature and quality of the soil and situation.

Douglas Fir, Spruces, Silver Firs, Larch, and Weymouth Pine, then
Scots Pine, sessile Oak, and Alder have naturally a strong tendency
towards the formation of a good bole or stem ; whilst Hornbeam, pedun-
culate Oak, and Willow are prone to branching growth.

The other species of woodland trees occupy an intermediate
position between these two classes. But the natural tendency

CHAP, in.] Characteristics of Trees 57

to assume their normal shape has only free scope when the
individual trees are growing in full exposure to light and air.
Those in which the leading-shoot develops more vigorously than
the side-shoots then assume a conical form; whilst others,
whose side-shoots compete on anything like equal terms with
the axial shoot, remain short and stunted, and have low wide-
spreading crowns. The true characteristics of any tree are best
observable when it is grown in the open; but, when the growing-
space allotted to each tree is limited, these natural tendencies are
checked, and a struggle upwards for individual exposure to
light and air ensues, which transforms the whole vital energy
into activity of growth upwards. This impulse is greatest in light-
demanding trees, and, within reasonable limits, may be said to
vary inversely to the growing-space allowed. Even when grown
in the open, Spruces, Douglas Fir, and Silver Firs, Larch, and
Weymouth Pine retain a distinctly noticeable central axis, which
is yet traceable, though less clearly, in Scots, Corsican, and
Austrian Pines, Alder, Beech, and sessile Oak, and to a still less
degree also in Ash, Maple, Sycamore, and Elm ; whilst on the
other hand the pedunculate Oak and Hornbeam have a marked
tendency to ramification and to the formation of a diffuse crown
at no great height above the ground. In woodland crops of
normal density the leafy crowns of Larch, Pines, Oak, Birch
and Aspen reach only a little way down the stem; those of
Spruce, Douglas Fir, Beech and Hornbeam descend for about
one-third of the bole ; whilst in Silver Fir they often extend
almost half-way down. The effect of the concentration of the
crown of leafy foliage towards the summits of the stems ensures
the conservation of the assimilated nourishment for the forma-
tion of long, straight, full-wooded stems of the highest possible
technical and financial value, in place of this being dissipated
over a large branch-system and a stunted stem. That such timber
must be more full-wooded, i.e. that the relative proportion
between the upper girth or diameter and the lower should
show less difference, is easily intelligible, owing to the larger

58 Studies in Forestry [CHAP. nr.

supplies of assimilated nourishment offered under the above
circumstances to the upper portion of the bole than to the
under part.

In the earlier stages of development the age of the crop is
of little practical importance. All species of trees, when grown
in woods of normal density, assume a conical or spindle-shaped
crown till they outgrow the pole stage and become tree-forest ;
but, having passed through the most active period of their growth
in height, they then begin to exhibit their natural tendencies
more distinctly. Thus Larch, Spruces, Douglas Fir and Silver
Firs continue to develop more vigorously upwards than side-
wards • Pines, Elm, Beech, Maple, Sycamore, Birch, sessile Oak,
Ash, and Alder begin to assume an oval crown ; whilst English
Oak and Hornbeam get rounded off with a broad, obovate crown.
As they approach the limits of age of healthy vigorous growth,
all trees, except Larch, Spruce, and Douglas Fir, assume
a blunted or rounded off growth near the summit, due to the
growth in height declining sooner than the lateral expansion.

So far as soil and situation affect the shape and habit of
growth, fresh, fertile loams stimulate to full-foliaged coronal
development and large girth of bole, though somewhat at the
expense of its length. Deep, fresh, light sandy soils favour
length of stem ; but, as the crowns are thinner, and the branch-
development is sparser, the girth consequently remains less.
Shallow and rocky soils affect the stem-development very
prejudicially, and cause branching growth and excessive root-
systems spreading far around in search of moisture and nutri-
ment. Great elevation above sea-level, and raw, cold exposures,
militate against the formation of good stems. In Scotland,
at 2,500 ft., the Scots Pine is more like a shrub than a tree.

The conclusion deducible from the above facts is that wood-
land crops formed of shade-bearing genera able to thrive with
a small growing-space, i.e. Beech and Hornbeam, but more
particularly Spruces, Silver and Douglas Firs, are able to main-
tain close canopy better and longer than woods formed chiefly

CHAP, in.] Characteristics of Trees 59

of Larch, Pines, Ash, Maple, and Sycamore. And when, as
in the case of Oak, Birch, and Chestnut, a tendency to branch-
ing growth is combined with strong demands for light, the
leaf-canopy is apt to be interrupted early and to an injurious
extent; and the natural impulse in this respect is all the
greater, the less favourable the soil and situation may be for
the particular species of tree in question.

V. Increment, or Bate of Growth in Height,
Girth, and Cubic Contents.

Growth in height varies, both in energy and duration, accord-
ing to the species and the age of the tree, the soil and situation,
and the methods of formation and treatment of the woods. It
is most active in Douglas, Spruce, and Silver Firs, Larch, Scots
and Wey mouth Pines, which can attain an average height of from
110-140 ft. — the Douglas Fir grows to over 300 ft. in height,
and 1 8 ft. in girth, in its home in North America; Oak, Ash,
Beech, Maple, Sycamore, and less frequently Elm, Poplar, and
Birch reach a height of 100-130 ft. ; whilst Black Pines, Horn-
beam, Alder, and Willow are seldom over 80-100 ft. high when
mature. These data are only for crops of normal density.

But the maximum heights usually attained by the various
species of trees are reached in different periods of time. This
fact, combined with their varying demands as to light, is of
immense importance from the practical sylvicultural point of
view ; as these are two of the main points to be considered
(when once the protection of the productive capacity of the
soil has been duly safeguarded) with regard to the formation
and tending of mixed woods.

Birch and Larch, above all others, then Poplar, Alder, Ash,
Maple, Sycamore, Elm, Willow, Weymouth and Scots Pines,
and Douglas Fir, are the trees that shoot up most rapidly
during their youthful period of growth ; whilst Oak, Beech,
Hornbeam, and Black Pines may be classed as of moderately

6o

Studies in Forestry

[CHAP. III.

rapid growth, and Spruces and Silver Firs as relatively slow in
initial development.

These results show that, in a general way, the rate of growth
in height during the earlier stages of tree-life coincides with
the demands made by the species on light and growing-space.
Some species, like Douglas Fir, Larch, and on good soils
Pines and Birch, maintain the advantage gained ; but others,
like Ash, Maple, Sycamore, and Aspen, are caught up in
growth and overtopped by Spruce, Silver Fir, Beech, and Oak,
whose vigour increases on their attaining the pole-forest stage of
development. The duration of active growth in height in any
given species depends to a great extent on the quality of the
soil and situation; but, coeteris paribus, it is maintained longer
by Larch and Firs than by Pines among conifers, and longer
by the sessile Oak, Elm, and Beech than other species among
broad-leaved trees. The average heights (in feet, and ap-
proximate only) of some of our more common forest trees, on
soils of merely average quality for each different kind of tree, are
about the following in well-managed woods of normal density : —

Age of Crop.
Years.

Beech.

Silver Fir.

Spruce.

Scots Pine.

2O

10!

IO

II

17!

g

34 1

35 1

33

57

39

55

80

67

72

75!

65

TOO

76

M

88

75

I2O

83

85

95!

80

It is at once perceptible from these figures how careful the
tending will require to be in mixed crops between the fortieth
to sixtieth years, and even earlier on soils of inferior quality ;
for wherever light-demanding species are overtaken by shade-
bearing species they must be killed off in the struggle for
supremacy, unless favoured to a greater or less extent during
the special operations of tending.

CHAP, in.] Characteristics of Trees 61

Growth in girth is in all species of forest trees practically
proportional to the growth in height, as they are each the
expression of the vigour of the individual tree. In most of the
light-demanding species of trees this begins early, often attains
its maximum vigour between the twentieth to thirtieth year,
maintains itself till about the fiftieth to sixtieth year, and then
gradually declines. It begins later with Oaks and shade-bearing
species, but is often vigorously maintained till the seventieth
to ninetieth year before beginning to sink gradually. In
crowded woods the development in girth is more prejudiced
than the energy of growth in height ; but whenever the growing-
space allowed is more than sufficient for the normal require-
ments of any given species, growth in girth takes place at the
expense of growth in length. When trees still in vigorous growth
are heavily thinned after being accustomed to but a limited
growing-space, they rapidly thicken in the bole in consequence
of the greater exposure to light and air, and of the increase
in foliage and assimilative power due thereto. The largest
girths are attainable by Douglas and Silver Firs, Spruces, Wey-
mouth and Scots Pines among conifers, and by Oak, Elm,
Beech, and Black Poplar among broad-leaved species of trees.

Growth in cubic contents, or total increment, is the final
expression of the resultants of growth in height and growth
in girth, and is a convenient measure of the general energy of
growth. Owing to the reduction in the number of individual
stems per acre, consequent on increased demands for growing-
space, increment culminates earlier in light-demanding than in
shade-bearing species. So far as whole crops are concerned,
Gayer classifies their energy in total increment as follows : —

Spruce and Silver Fir woods.

Larch, Weymouth and Scots Pine woods.

Beech woods.

Oak, Ash, and Hornbeam woods.

Birch woods.

But he specially characterizes the energy of the Firs as nearly

62 Studies in Forestry [CHAP. in.

twice as great, and that of the Pines as about half as great
again as that of Beech, which is the most energetic of the
broad-leaved species. It will be seen, from what has previously
been said, that the productive energy of the individual tree
may be widely different from the productive energy per acre of
a pure forest of that species ; and it will therefore readily be
intelligible how advantageous — alike from the material, the
financial, and the sylvicultural points of view — the judicious
formation of mixed crops may be as compared with pure forests,
more especially if formed of the light-demanding species.

VI. Differences with regard to Reproductive
Capacity.

Trees may reproduce themselves either by means of seed,
or else by means of shoots from the stool, or through suckers
thrown up from the roots. Reproduction from seed is the
normal process of regeneration of all species that are indi-
genous, or that have thoroughly naturalized themselves in our
climate ; whilst the formation of stoles or root-suckers is princi-
pally confined to English Elm, and to exotic Poplars and Willows,
which cannot be relied on to form seed of anything like average
germinable capacity ; of indigenous trees, Aspen and Willow
are the only species endowed with this quality to any great
extent. The formation of shoots from the stool is not so much
a regenerative measure as rather an effort at recuperation and
replacement of the stem or bole when the ascending axis has
been removed. It is solely due to the vital activity of the
root-system, which, until late in life, remains active after the
stem and crown have been removed, and which endeavours,
by a new flush of shoots and foliage from the adventitious or
dormant buds at the neck of the stump, to obtain the means
of assimilating the food that it continues to absorb from the
soil. This same tendency is seen in pollarding as well as
in coppicing, but in another form and a more 'limited degree.

CHAP, in.] * Characteristics of Trees 63

The formation of seed depends on the supplies of starchy and
nitrogenous reserves stored up in the tree. These vary according
to its age, the soil and situation the amount of exposure to light,
and the warmth of the summer period of vegetation. In good
seed-years Beech, Oak, Spruce, Pine, Birch, Hornbeam, Elm,
Aspen, Alder, and Willow produce larger quantities of seed
than Ash, Maple, Sycamore, Silver Fir, and Larch. But,
classifying them as to the total quantities of seed produced
during long periods, it may be said that Birch, Aspen, and
Willow are most prolific ; next to them come the Pines,
Spruces and Douglas Firs, Elm, Hornbeam, and Alder ; behind
these again rank the Oak, Maple, Sycamore, Silver Fir, Larch,
and Ash • whilst last of all in this respect comes the Beech.

From this it cannot fail to be noted that in general the
species with small seeds are more prolific than those with
large and heavy fruits. As these light, and very often winged,
seeds are more easily wafted and borne far away by winds,
it must be admitted that species of trees like Birch, Aspen,
Pine, and Spruce have better natural reproductive power than
Oak, Beech, Silver Fir, and the like. It is worthy of note,
too, that the former are species which make less demands on
soil fertility than the latter, and are at the same time endowed
with greater accommodative powers as to soil and situation ;
for these are matters almost sure to be closely connected with
the power of accumulating reserves of starchy and nitrogenous
substances utilizable for the formation of flowering-buds.

The different kinds of seeds vary, however, greatly in their
germinative power. This is lowest in Birch, Alder, Elm, and
Larch. It amounts to about 50 % in Ash, Hornbeam, Maple,
Sycamore, Weymouth Pine and Silver Fir ; whilst it is some-
what greater in Oak, Beech, Spruce, and Scots, Corsican, and
Austrian Pines.

The seed of most species of trees germinates in the spring
after it has been shed ; but that of Birch, Elm, Aspen, and
Willow sprouts during the spring in which it falls, and that of

64 Studies in Forestry ' [CHAP. in.

Ash and Hornbeam germinates only in the second spring after
its fall, if the seed has been stored before being sown.

Seed-production is greatest when the main growth in height
is completed, and the natural tendency to coronal development
makes itself apparent in increased demand for light and grow-
ing-space, i.e. when the vital energy is at its maximum. Warmth
of situation, fertility of soil, and increase in growing-space, all
stimulate to production of seed, owing to the larger supplies
of nutrients, and the better assimilative opportunities then
available for each individual tree.

The formation of stool-shoots taking place in coppice-growth
is essentially an expression of recuperative power. It is inherent
in the broad-leaved species to a very much greater degree than
in conifers, among which, indeed, with the exception of the
Larch and the three-needled species of Pines, it is almost
practically non-existent. This power of replacing the stem
and crown is greatest during the younger stages of growth,
but is always to a great degree dependent on the quality of
the soil and the degree of exposure to light. Oak and Horn-
beam retain their recuperative power in this respect longest
(to about 85 years of age), whilst stools of Beech and Birch,
after being coppiced several times, lose their reproductive
vigour.

The formation of stoles or suckers appears to be the only
means of utilizing their surplus reserves of starchy materials with
which exotic species of trees (English Elm, Lime, Chestnut,
and most Poplars and Willows) are endowed, seeing that from
climatic causes they are unable to utilize them in the same
way as indigenous trees, or the other exotic species that are less
exacting with regard to warmth, that is to say, in the normal
production of seed of average germinative capacity.

Stool-shoots are more often produced than suckers by Oak,
Hornbeam, Beech, Elm, Alder, Ash, Maple, Sycamore,
Willow, and Birch; whilst stoles are more frequent than
stool-shoots from Aspen, non-indigenous Willows and Poplars,

CHAP, in.] Characteristics of Trees 65

and White Alder. But Willow, Chestnut and Elm at the same
time throw out a very fair proportion of stoles, which may
be cut away and transplanted like seedling growth.

VII. Differences as to Attainment of Maturity and
normal Duration of healthy Growth.

The ages to which the various kinds of forest trees may
be grown in a healthy condition without showing visible signs
of senile decay exhibit great differences. Thus we find Oak
and Scots Elm attaining 500 years and more, English Elm,
Silver Fir and Beech 300-400 years, Ash, Maple, Sycamore,
Spruce, Larch, Scots Pine and Hornbeam about 200 years,
whilst Aspen, Birch, Alder and Willow seldom attain over
100 years. Indeed, many historical trees are known to be
very much older than any of these limits ; but even the above
ages are far in excess of any rotations that could possibly be
maintained in woodlands worked on sound economic sylvi-
cultural and financial principles.

For the attainment of healthy old age the essential con-
ditions are (i) that the opportunities of growth must be such
as to permit of the normal development of all the organs of
nourishment, and (2) that the soil and situation must continue
to supply all demands as to warmth, moisture, &c., made by
the individual species. But very frequently the economic re-
quirements of sylviculture are incompatible with the demands
as to growing-space, &c., that are involved in the above. And
the capacity of different genera for regaining normal vigour,
after being first grown for a long time in close canopy and
later on allowed a larger measure of light and air, varies con-
siderably ; it is greatest in Oak, Lime, Willow, Elm and Silver
Fir, and least in Alder, Aspen, Maple, Sycamore, Beech, Horn-
beam, and Spruce.

From the practical sylvicultural point of view, the following
may be regarded as the ordinary average limits of age which

F

66

Studies in Forestry

[CHAP. III.

it is advisable to allot to timber crops grown in high forest ;
but so much depends in each case on the concrete conditions
as to climate, soil, and situation, that the figures must be
regarded as rough generalizations only : —

Kind of Tree.

On soils of good
quality.

On soils of inferior
quality.

I. Silver and Douglas Firs
2 Spruce . .

Years.
IOO-I2O
8o—IOO

Years.
60-80

60- vo

3. Scots Pine and Larch

8O-IOO

50-70

i. Oak

120-150 ; 180—200

GO- I 2O

2. Beech. . .

oo 1 20

8o—IOO

3. Hornbeam, Elm. Maple,
Sycamore, Ash . .
4. Willow, Birch, Aspen .

60-80
50-60

40-50
40-50

From these approximate data it will be at once apparent
that when mixed crops are formed of several genera, these may
attain their technical and financial maturity at different ages ;
hence it is the duty of the forester to utilize those which mature
soonest, by extracting them at the time of their highest
economic value. This is done not only with a view to obtain-
ing the maximum monetary returns, but also for the purpose
of protecting, to the greatest possible extent, the productive
capacity of the soil. For the realization of both of these
objects abundant opportunities are given during the process
of tending the timber-crops throughout all stages of their
development, to the consideration of which matter one of
the succeeding chapters will be devoted (see Chap. IX).

CHAPTER IV

THE NUTRITION AND FOOD-SUPPLIES OF
WOODLAND CROPS

'Concerning the growth of plants a large amount of informa-
tion has been amassed, but we are far from possessing even an
approach to a knowledge of the laws which regulate this
important subject.'— RoscOE's Elementary Chemistry^ 1888,
page 413.

ALL plant life is governed by what is known in agricultural
chemistry as the Law of the Minimum. According to this
law the essential factor occurring in minima regulates the total
extent of production ; whilst any given species of plant attains
its finest growth and development in localities where all the
essential factors are most favourably combined. These essential
factors are partly of a physical, and partly of a chemical
nature. To the former belong the action of warmth and
of light, and to the latter carbonic acid, oxygen, and the
water requisite for dissolving and holding in solution the
mineral nutrients that can only be absorbed by the plant in
the shape of soluble salts.

Temperature makes itself felt, throughout both the soil and
the atmosphere, in calling into activity the process of vegetation
in spring, and in continuing it during the summer and the
autumn. Most of the trees indigenous throughout central and
northern Europe begin their period of active vegetation in
spring when the temperature rises to 6° or 8° C, although with
exotics from the warmer south a higher temperature is requisite
in order to stimulate them to activity.

F 2

68 Studies in Forestry [CHAP. iv.

This is a subject which has hitherto been little studied, as
the following extract from Willkomm 1 may show : —

'Despite a mean winter temperature of + 17-5° R. (71-4° Fahr.) the
Beech in Madeira has a period of rest for 149 days, during which it
remains leafless ! This strange phenomenon is to be noted also in the
Elm, Silver Poplar, Willow, and other broad-leaved trees distributed
through the whole of Europe, as well as in the Apple, the Pear, and
other fruit-trees over all the most southern parts of Europe. They also
lose their foliage in autumn, and only flush anew in spring, although
during the whole of winter the temperature does not sink below + 5 to
7° R. (43^° to 47!° Fahr.). And whilst in central and northern Europe
the buds of the above-named trees open early in spring after warm
winters, this is not the case in the south. This phenomenon must be
due to some law of nature which remains as yet unknown.'

And in another place2 he remarks with regard to woodland
trees that —

' The absolute minima during the period of vegetation are of far
greater importance, with regard to the thriving of trees, than the minima
of winter, and the average temperatures of the months and seasons.'

Indeed he goes so far as to say that 3 —

' It may be stated as a general law that the polar or northern limit of
any particular species of tree is determined by a certain definite isotherm of
July, whilst its equatorial or southern limit is determined by a certain definite
isotherm of January.'

Seebohm's observations in Siberia agree with the first part of
that statement. For he observed that 4 —

* The limit of forest growth does not coincide with the isotherms of
mean annual temperature, nor with the mean temperature for January
nearly so closely as it does with the mean temperature for July.'

When once active vegetation has been stimulated by increasing

1 Die Forstliche Flora von Deutschland und Oesterreich, 2nd edit., 1887,

P- 452-

3 Op. «/., p. 364.

3 Op. cit., p. 39.

4 Presidential Address to Geographical Section of the British Association,
1893, in Royal Scot. Geog. Society's Magazine, October, 1893, p. 511.

CHAP, iv.] The Food of Trees 69

warmth in spring, the energy of the vital process is enhanced
as the temperature rises, until it may reach a point at which
the plant is unable to carry out the vital operations in a normal
manner. In Britain, hot southern slopes with light sandy soil
may often prove too warm for woodland trees like Spruce and
Silver Fir, whilst cold land with a northern exposure may not
supply the amount of warmth requisite for the best develop-
ment of Oak. In forestry, no measures can be taken to regulate
the atmospheric temperature. But by maintaining a close
canopy of foliage, or by the underplanting of standards, much
can be done to regulate the soil-temperature, and to retard the
commencement of active vegetation. This may even be delayed
for about a fortnight or more, and may thus be made to com-
mence only at a time when, the atmospheric temperature and
the intensity of the light being greater, the process of assimila-
tion may be more thorough as well as more energetic.

Light, which is closely allied to heat, is essential in order that,
with the aid of the chlorophyll contained in the leaves, the
decomposition of water and of carbonic acid may take place in
the elaboration of substances to be used for structural purposes;
whilst at the same time various other processes, such as
transpiration, the deposition of matter on the cell-walls, and,
in fact, the whole nutrition, are all likewise more or less
dependent on the action of light. The intensity of light
necessary for the different species of trees, before they can carry
out the process of assimilation, varies considerably, as may be
seen from the different densities of their foliage; whilst the
amount and intensity of light required by one and the same
species of tree also varies according to the other factors of the
soil and situation. Thus, for example, under unfavourable
circumstances of soil the foliage is less dense, and the leaves
are in every way smaller, than if the same species of tree be
growing on more favourable localities. Leaves growing in full
exposure to light are thicker, contain more chlorophyll in their
parenchym, and have a much larger number of stomata than

70 Studies in Forestry [CHAP. iv.

those growing in shade. The latter are sometimes only about
one-third of the thickness of the former, and great differences in
size may even be noticed in the buds throughout the winter. If
young growth, that has hitherto stood in shade, be suddenly
exposed to the full action of light, these thinner leaves are not
always capable of carrying out the new and more energetic work
thrust upon them ; hence they often fall into a sickly condition,
which predisposes them to disease, and may even induce the
death of the plant. Thus, in areas regenerated naturally, the
clearance of the parent standards should be made gradually,
although the period over which it must be extended varies
considerably according to the kind of tree, and, for one and
the same species, according to the concrete conditions of the soil
and of the plants concerned. Broad-leaved deciduous trees can
in general accommodate themselves comparatively easily to rapid
transition from shade to light, owing to their leaves only lasting
for one season • but in conifers this accommodative power is
necessarily more gradual, and is least in those genera that retain
their foliage for a long period, like Spruces and Silver Firs. The
poorer the soil of any locality, and more particularly the nearer
it approaches the minimum with respect to the water-supply
requisite for the normal transpiration of any species of woodland
tree, the greater is the necessity for a free supply of light in order
to carry out in as thorough a manner as possible the assimila-
tive process with the limited amount of sap and of nutriment
yielded by the soil. But the quantity of foliage decreases along
with these latter supplies. Hence it becomes of all the more
importance that the limited amount of nutriment should be
elaborated in a most thorough manner ; and this is only
possible with the comparatively free exposure of each individual
leaf to light and air. Or, in other words, this naturally leads to
the formation of a loose crown of foliage, instead of a dense
leafy canopy being maintained.

Carbonic Acid or Carbon Dioxide (CO2) becomes de-
composed under the action of light by the chlorophyll con-

CHAP, iv.] The Food of Trees 71

tained in the parenchym of the leaves, and is assimilated, or
prepared for being made of use for structural purposes, in
different combinations of carbon 1. As on the average 0-03 %
by volume, and 0-05 % by weight, of the atmosphere consists of
carbonic acid, there is never any want of this essential factor
to the due thriving of any kind of woodland tree in any
given locality.

Whilst there is no reason to deny to ordinary plants, with
foliage containing chlorophyll, a certain capacity for absorbing
nutriment directly from humus or organic matter in the soil, as
is done by those which are not provided with chlorophyll, yet
the thriving of woodland growth on soils poor in humus is of
itself a proof that any direct absorption of carbon compounds
by the root-system cannot be of essential importance to their
existence. The discovery, by Sadebeck and Frank about nine
or ten years ago, of the mantle of fungoid tissue around the
extreme points of the rootlets of cupuliferous trees (Oak, Beech,
and Chestnut), and since also proved in the case of other
woodland trees, coniferous as well as deciduous, has given rise
to a theory that the introduction of organic matter is often
carried on by means of the symbiosis of a fungus or Mycorhiza at
the points of the suction-roots. This Mycorhiza is supposed by
Frank to act as a go-between, absorbing water, and nitrogenous
and non-nitrogenous organic matter from the soil, and giving
these to the rootlets, from which again the fungus receives other
nourishment in exchange. According to Ramann 2, however,
the appearance of the Mycorhiza must be considered as already
the indication of an abnormal or diseased condition, rather than

1 The chemical process is probably as follows (see R. Hartig's Anatomic
d Physiologic der Pftanzen, 1891, pp. 172 and 229): C2O + H2O =
CH2O + 2O set free ; 6(CH2O) = C6Hi2O6 dextrin, glucose, or grape

und Physiologic der Pftanzen, 1891, pp. 172 and 229): C2O + H2O =
CH2O + 2O set free ; 6(CH2O) = C6Hi2O6 dextrin, glucose, or grape
sugar, in which form the assimilated product is capable of being translated

from the leaves to other parts of the organism. When formed quicker
than it can be transported, this loses one molecule of H2O, and becomes
C6H10O5 or starch, which is secreted temporarily in the solid form and
transformed again into grape sugar, when required, by resuming the molecule
of H2O.

2 Ramann, Forstliche Bodenkunde und Standortslehre, 1893, p. 302.

72 Studies in Forestry [CHAP. iv.

a genuine symbiosis bringing mutual advantages both to the
fungus and the tree.

Oxygen (O), requisite for the process of respiration, is,
like carbonic acid, always present in sufficient quantity in the
atmosphere, which is composed of 20-93 % oxygen and 79-04 %
hydrogen by volume, or 23-28 % oxygen and 76-67 % hydrogen
by weight. Unless, however, the aeration of the soil is also
favourable, it may happen that the root-system has difficulty in
finding a sufficiency of oxygen for the supply of its requirements.

Ebermayer found that under Beech the soil was always much
poorer in carbonic acid than under crops of Spruce and on fallow
land, a fact which he ascribed to the better aeration of the soil
by the numerous and deep-going roots of the Beech. Ramann
agrees with this view and adds * : —

'The "soil-improving" action of the Beech is probably mainly ascrib-
able to its thorough aeration of the soil. As a large percentage of
carbonic acid in soils rich in humus indicates a considerable reduction in
the amount of oxygen in the air circulating throughout the soil, there is
no reason why the former should be advantageous to plant life — on the
contrary, the greater amount of carbonic acid may rather be taken to be
a sign of deficient aeration and of deterioration in the soil/

Prof. Ebermayer's own most recent utterance with regard to
the soil-improving qualities of the Beech — an opinion that
must be accepted as of the highest authority — is by no means
so direct and unconditional as the above. It is as follows 2 : —

' The shallow surface-roots of the Beech mostly ramify throughout
the loose upper layers of soil that are rich in humus. Under normal
circumstances the suction-roots are not here provided with hairs, but
are covered with a fungus (Mycorhiza^, which acts in the capacity of
a go-between with respect to water and food-supplies, and by means of
which the trees derive much better nutriment from the layers of soil
rich in humus, than is obtainable through the root-hairs from the
mineral soil (B. Frank). A very valuable attribute of the Beech is that,
judging from my numerous investigations as to the influence of woodland
growth on the percolation of soil-moisture and on the chemical compo-

1 Op. cit., p. 266.
. 2 Forstlich-naturwissenschaftliche Zeitschrift, 1893, p. 237.

CHAP, iv.] The Food of Trees 73

sition of the air contained within the soil, in consequence of the
ramification of its roots it keeps the soil more open or porous than the
Spruce does. To this property, combined with the circumstance that it is
a shade-bearing species of tree, which yields a more nutritious and more
easily decomposible humus than the conifers, it owes its soil -improving
capacity and its great importance for mixed forests.'

Where aeration is insufficient, the same practical effects take
place as in the case of inundations. The plants consume the
available supplies of oxygen within reach of their root-systems,
and then sicken and die off ultimately, although of course
different kinds of plants show great specific differences with
regard to their accommodative power in this respect.

Nitrogen (N) is essential to the formation of the albuminoid
substances which play so important a part in relation to the
growth of plants. When organic matter decomposes, the
nitrogen becomes sooner or later transformed into ammonia
(NH3), which again in turn becomes transformed with the aid
of a fungus (as Winogradski has proved) into nitric acid or
hydrogen nitrate (HNO3). For the development of this fungus
(Bacillus), or main intermediate agency, a certain amount of
oxygen is requisite ; but when there is a deficiency of oxygen
in the air contained within the soil, nitrous oxide or nitrogen
monoxide (N2O) and free nitrogen are produced. This nitrifica-
tion is confined to soil within about 18 inches of the surface.
Other sources open to plants for obtaining the requisite supplies
of nitrogen are the ammonia contained in the atmospheric
precipitations, and also, but under special circumstances only,
the free nitrogen of the air. Observations have shown that
the summer showers contain a higher proportion of nitro-
genous combinations than those that fall in autumn or winter.
Although the older agricultural chemists, led by Boussingault,
and strongly supported in 1861 by the Rothamstead experiments
of Lawes and Gilbert, denied that plants could directly utilize the
free nitrogen contained in the air1, yet this was strenuously com-

1 Compare Prince Kropotkin's article On Recent Science in the Nineteenth
Century for August 1893, pp. 205 et seq.

74 Studies in Forestry [CHAP. iv.

bated by Ville all along, and since 1888 it has been abundantly
proved by Hellriegel, B. Frank, Wilfarth, and others, that this
can and does take place indirectly, more particularly in the case
of Leguminosae (e.g. in the Acacia among our common trees). So
long, however, as a supply of nitrogenous food is available in
the soil, this capacity, for which the symbiotic aid of a Bacillus
(Bacillus Radicicola or Rhizobium leguminosarum} is requisite, is
not called into play *. The researches of these last-named scien-
tists during the last decade have shown that all leguminous
plants possess, by means of their root-nodules or tubercules,
which contain these bacteria, the power of withdrawing from the
air a sufficient supply of nitrogen for the requisite formation
of essential albuminoid substances when these are not other-
wise easily obtainable. According to Frank's researches also 2,
the Alder is endowed with similar capacity to the Leguminosae
for the formation of nitrogenous and albuminoid substances ;
for the tubercules on its roots are found to contain an albu-
minoid protoplasma filled with the germs of a bacteroid fungus.
Through a symbiotic process quantities of albumen are pro-
duced within these root-nodules, which become gradually
absorbed into the tree and utilized for general requirements.
Alders therefore thus appear, like the Acacia, able to derive
supplies of nitrogen from the air, when requisite, through this
symbiotic aid. So far, however, as woodland crops are con-
cerned, though any abnormal increase in the ordinary supply
of nitrogen obtained from the soil might probably exert great
influence on the extent of seed-production and the frequency
of mast-years, it certainly would not stimulate the increment
in timber3. The precise manner in which woodland trees
obtain the supplies of nitrogen requisite for their development
has not yet been satisfactorily determined. But as woodland
soils contain at best very small amounts of nitric acid, and are

1 Ramann, op. cit., p. 306.

2 Report of the Deutsche Botanische Geselhchaft for 1891, p. 250.

3 R. Hartig, op cit., p. 221.

CHAP, iv.] The Food of Trees 75

often totally deficient in it, their wants must be met by the
nitrogenous compounds set free on the decomposition of
organic matter within the soil ; and, even from this alone, one
important function of the invaluable humus or leaf-mould can
easily be seen. The warmer a soil, the more thorough its aeration,
and the more its supply of moisture is removed from either of
the extremes of dryness or wetness, so much the more rapidly
and successfully will the nitric acid (so essential for agricultural
crops especially) be evolved from decomposing organic remains.
But as nitric acid is apt to be easily washed out of porous
soils, this partially explains why loose sandy soil is less fertile
than loams and other soils of a more retentive nature.

Water (H2O) is also one of the essentials to the support of
plant life. It not only forms a very direct source of nutriment,
but it is also requisite for the solution of inorganic substances
(nutrient salts\ which can only be absorbed by the root-hairs
when held in solution. By far the greatest portion of the water
that is imbibed is transpired through the foliage. A certain
quantity, however, is utilized in the formation of the organic
tissue, the requisite hydrogen being exclusively obtained from
this source; whilst, during the process of assimilation, the
organic substances are formed from water and carbonic acid
by the elimination or setting free of oxygen (when CO2 + H2O
becomes CH2O + O2 &c. : see note i to page 71).

The requirements of woodland crops as to water vary greatly
according to the species of tree, and for one and the same
species according to the nature of the soil, the climate, and
the exposure of any given locality. The finer the particles of
soil, and the richer the admixture of humus, the more moisture
can a soil contain. In situations with humid atmosphere the
spiracles of the leaves open much wider than in dry air ; for
the leaves have a certain power of accommodating themselves
to the temporary conditions of the atmosphere so as to stimu-
late transpiration during a humid, and to retard it during a dry,
state of the air. They are thus endowed with a certain

Studies in Forestry

[CHAP. IV.

capacity for regulating and maintaining as steady a rate of
transpiration as possible. For all kinds of woodland crops,
however, there is on the one hand a minimum supply of
water requisite for thriving and for healthy development, and
on the other a maximum normal limit beyond which any
surplus of soil-moisture is prejudicial to their well-being.
Although, with decreased transpiration, the process of assimi-
lation may not be essentially interfered with, yet the imbi-
bition of soluble salts is considerably decreased, and the
amount of ashes or mineral constituents contained in the wood
is less than in timber produced in a drier atmosphere.

Observations relative to the amount of "water transpired by woodland
crops were made by von Honel in experiments made in 1879-1881. He
found that, with the exception of the deciduous Larch, conifers transpire
on the average only about one-sixth to one-tenth of the quantity of
water that is evaporated by broad-leaved trees l.

Taking the average of these three years, his experiments led to the
result that the average transpiration of water per 100 grammes (0-22 Ibs.)
of dry leaf-substance amounted during the active period of vegetation
annually to the following number of Kilogrammes (2-204 Ibs.) : —

Broad-leaved Trees.

Conifers.

Aspen

Kilogrammes.
- QtvQ7O

Kilogrammes.
Larch 120-234

Alder

Q3.3OO

Spruce ... . 13-501

Lime .

88-3.4.0

Scots Pine 9-426

Ash . . .

. . . 85-615

Silver Fir 7>J79

Birch

81.4.33

Black Pines 6-735

"Rpprh

Hornbeam
Elm

74 °59
73-107
66-170

Mean average for all
trees . .... 69-800

Sycamore

. e;8-<;o6

Mean average for broad-
leaved trees . . . 82-520
Mean average for conifers 1 1-307

Oak . . .

Maple

c 3.-o6^

He also found that, whilst in conifers transpiration is greatest from
foliage fully exposed to insolation, in broad-leaved trees it was greatest
from foliage growing in shade, as the following table shows : —

1 See Ramann, op. cit., pp. 309-312.

CHAP. VI.]

The Food of Trees

77

•

Kilogrammes per 100 grammes of
dry leaves.

In the sun.

In the shade.

Beech

76-180
81-300
61-690
19.150
13.910
8760

107-800
98.900
76-190

5-020

4-850
5-250

Hornbeam

Sycamore .

Scots Pine ....

Silver Fir

Black Pines ....

As, however, the normal density of foliage, natural to the different
kinds of woodland trees, varies greatly with each species, and also for
one and the same species of tree according to the nature of the soil, the
age and the method of treatment of the crop, and various other factors
of sylvicultural importance, these data, which are by no means complete
or intended to be advanced as finally authoritative, are rather of theo-
retical interest than of practical sylvicultural value. When investigating
the actual quantity of water required by the Beech for normal transpira-
tion annually, von HOnel estimated that —
A Beech tree 35 years of age

consumed per diem i kilo.= 2-204 Ibs. = 0-220 gals, of water.

A Beech tree 50-60 years of

age consumed per diem ... 10 kilos. = 22-040 Ibs. = 2-204 gals, of water.
A Beech tree 115 years of age

consumed per diem 50 kilos. = i 10-200 Ibs. = n.O2Ogals. of water.

Computing the average number of trees per acre, he arrived at the
following results : —

Age of
pure crops
of Beech.

No. of trees
per acre.

Amount of Water consumed Annually.

Years.

35

50-60
"5

1, 600
520
160-240

Kilogrammes.
280,000
920,000
1,400,000 to 2,l6o,000

Gallons.
61,712
202,768
308,560 to 476,064

Hence a summer rainfall of 1 2 inches suffices to meet these requirements.

But it should be remembered that the quantity of soil-moisture
requisite for transpiration through the foliage must be very considerably

78 Studies in Forestry [CHAP. iv.

less in our damp insular climate than in the inland tracts of the continent
of Europe with their much drier climate and consequently enhanced
activity of transpiration. There are many places along the east coast of
England where even the total average annual rainfall is less than 12 inches,
and where timber crops are still capable of thriving perfectly well.

Of much more practical interest than von Honel's experi-
ments must be considered the investigations that have more
recently been made by Ebermayer with a view to determine
the relative transpiration of the different kinds of forest trees,
and the results of which correspond better than von Honel's
with the facts of actual sylvicultural experience. Ebermayer
analyzed foliage for the purpose of determining this by means
of the percentage of water contained in the fresh leaves, and of
*pure mineral ash obtained afterwards from the combustion
of the dry leaf-tissue. The former table is now given, whilst
that relating to the mineral ash will be referred to later on. It
need only be remarked that, as the nutrient salts are imbibed
in a weak solution, and as the water is mostly transpired
through the foliage in the form of aqueous vapour, whilst the
salts eliminated are to a great extent deposited within the leaf-
tissue, a steady and normal degree of transpiration is essential
for the due conduct of the nutritive processes and the well-being
of the trees ; but during sunlight, and also in warm dry situa-
tions, the rate of transpiration is of course greater than in
shadow, or in cool, damp exposures, and at high localities
where the relative humidity of the air is great. Hence, coeteris
paribus, it seems justifiable to conclude that leaves, which
show large accumulations of pure mineral ash within them,
not only make larger demands for mineral nutrients per unit
of weight of foliage, but also at the same time transpire more
water through their leaves in order to concentrate these de-
posits. For the solutions taken up by the rootlets of various
kinds of trees do not appear to vary much as regards strength
(except in localities like Alder swamps where the solutions are
abnormally weak), although of course in fertile soils (or on

CHAP. IV.]

The Food of Trees

79

manured land) the solutions are richer than in land of inferior
quality. Proceeding from this point of view, Ebermayer made
the following classification of trees with regard to their relative
power of transpiration or relative requirements as to soil-
moisture, by tabulating them according to the percentage of
water the fresh leaves contained as compared with their total
weight.

Broad-leaved Species of Trees.

I.

*7O

II.

Oak

61

Horse Chestnut . . .
Ash . .

• k

, 6*

White Alder

. 6*

Elm

. . ^5

. 61

. 64

. . 6*

Acacia (Robinia) ,

. 6\

III.
Birch

. 61

IV.
Beech

. 57

Mountain Ash

61

Hornbeam ....

cy

Sycamore .

. 61

Willows (in general) .
Maple

. 60

CQ

Aspen .

CQ

Coniferous Species of Trees.

I.
Cembran Pine .
Black Pines . .
Larch ....
Weymouth Pine

II.
64 Scots Pine - f
63 Spruce. . . .
62 Mountain Pine .
61

III.
59 Silver Fir . . . 55
59

57

Taken on the whole, these scientific conclusions correspond
fairly accurately with the knowledge acquired by sylvicultural
experience, although at the same time certain kinds of trees,
like Acacia, Birch, and Pines, are better fitted than other trees
to accommodate themselves to conditions not exactly satisfying
their normal requirements with regard to moisture. It cannot

8o Studies in Forestry [CHAP. iv.

fail to be noted from the above that long-needled Pines
transpire more freely than the true Firs having short foliage.
But in the conifers (which, as has been previously remarked,
require only about J- to y1^ as much water as broad-leaved
trees) the rate of transpiration is limited very considerably by
their thick, strongly-cuticularized epidermis impregnated with
resin and wax. Hence, not only the rate of transpiration, but
also the movement of the sap upwards within conifers is much
more sluggish than in deciduous trees like the Oak, Ash, Elm,
&c. And whilst the needles, with their weaker transpiratory
capacity, contain as much water as the leaves of many kinds of
deciduous trees, the woody tissue of conifers contains more
water than that of the latter.

The Indispensable Mineral Ingredients in the food-
supplies of plants comprise Potash, Lime, Magnesia, Iron,
Sulphur, and Phosphorus as well as Nitrogen. And at the
same time Silica (often in large quantities), Chlorine, Soda,
Manganese, and occasionally Alumina, are also to be found in
the ashes of timber, after Carbon, Hydrogen, Oxygen, and
Nitrogen have been eliminated by combustion ; but the former
can hardly be considered indispensable constituents. The
different uses to which these mineral substances are put in the
vegetable economy have not yet been quite satisfactorily
determined. Potash (K2O) is found chiefly in the foliage
and the parts of more recent growth, which are concerned
with the active processes of assimilation and of vital ac-
tivity. Lime (CaO) is supposed to play a very important
part in connexion with the formation and distribution of
the carbo-hydrates, and in the formation of insoluble com-
pounds with oxalic and similar injurious acids which are
thus rendered harmless to the tender tissues of the plant.
Whilst Beech and Black Pines show a decided preference for
soils rich in lime, it has been proved by Fliche that even
a slight percentage of carbonate of lime seems to act as
a poison in the case of the Sweet Chestnut and the Maritime

CHAP, iv.] The Food of Trees 81

Pine1. Magnesia (MgO) is utilized in the formation of
albuminoid substances, and is supposed to have an important
influence with regard to the production of seed. Iron (FeO
and Fe2O3) is requisite, though only in small quantities, for
the formation of the chlorophyll in the foliage, by means
of which the work of assimilation is carried on with the aid
of sunlight. Sulphur, taken up in the form of sulphates, i. e.
salts containing sulphuric acid2, is, like magnesia, employed
in the formation of albuminoid substances, for which also
Phosphorus, in the active form of phosphoric acid (P2O5), is
most essentially requisite. The presence of Chlorine (Cl) and
of Soda (Na) is most pronounced in plants growing near the
sea-coast and on brackish soil. The specific action of these
minerals is not very clearly understood ; but they are supposed
to assist in the movement of carbo-hydrates within the plant*.
For the practical purposes of Forestry the most important soil-
nutrients are water, then lime, potash, and phosphoric acid;
and the chief nitrogenous compounds are nitrates and am-
moniacal salts or certain nitrogenous organic constituents in
humus.

On soils which offer to woodland crops richer supplies of
food than can be thoroughly assimilated by them, deposits
of mineral substances take place within the plants in excess
of their physiological requirements. Wherever this occurs in
any excessive degree, it leads to a condition at once pre-
disposing to disease and, at the same time, capable of offering
least resistance to any attacks that may be made by fungoid
parasites or by insect enemies.

1 Annales de la Station Agronomique de I'Est, 1878, pp. 3 et seq.

2 A common impurity to a slight extent in the atmosphere is sulphurous
acid, which is carried by rainfall into the soil, and oxidizes into sulphuric
acid (SO2fH2O becomes H2SO4). When present in the air in anything
like excess, as in large towns and at all populous and manufacturing centres,
where sulphurous acid is evolved on the combustion of mineral coal, it
affects the thriving of trees. The sulphurous acid is imbibed by the foliage,
and, on rain falling, becomes transformed into sulphuric acid ; this rapidly
acts as an irritant poison with regard to the internal, soft, cellular tissue of
foliage.

G

82 Studies in Forestry [CHAP. iv.

The demands of the different species of woodland trees
vary greatly with regard to mineral nutriment, as can be proved
easily by an analysis of the amount of mineral matter found
in the ash yielded on combustion and elimination of the
non-mineral portions of their tissue (formed by Carbon, Hy-
drogen, Oxygen, and Nitrogen). The younger parts of the
organism, and especially those actively engaged in the work
of circulation, assimilation, and secretion (the foliage and the
cambium), yield more ash because they are richer in salts
of potash, phosphates, and nitrogenous compounds, than
the older portions (the alburnum), and the lifeless tissue
in the interior of the stem forming the hard heartwood (the
duramen).

The leaves are much richer in mineral matter than any
other part of the plant ; whilst the bark contains more than
the wood, and the younger portions of the tree contain more
than the older portions. When parts of the tree are about
to die off (as, for example, in the case of the foliage of
deciduous trees in autumn), the more important classes of
mineral nutrients — Potash, Phosphoric Acid, Magnesia, Lime
— are transferred into the still active portions of the organism,
to which they wander back together with albuminoid substances
and soluble carbo-hydrates.

The total proportion of mineral matter in the timber of
broad-leaved genera of trees is seldom under J% or exceeding
\% of the dry substance of the wood. It usually ranges
between 0-3 and 0-45%; but, in the case of Birch and of
conifers, it varies from about \ to \% (0-17 to 0-27). The
heartwood of old sterns contains less ash than the sapwood.
It is also comparatively devoid of albuminoid substances, and
is therefore more durable, i.e. it is less exposed to the disinte-
grating and decomposing influences of alternating damp and
heat, or to the organic attacks of saprophytic fungoid growth
and insects.

According to the demands of the different kinds of trees for food-

CHAP. IV.]

The Food of Trees

supplies, their wood shows the following- percentages of mineral matter
per TOO parts of dry tissue, according to Ebermayer1 : —

Class of Trees.

Wood of the

Percentage
of Ash.

Potash.

Lime.

Phosphoric
Acid.

Deciduous

Stem
Twigs
and small!
branches)

033-0.94
0-75-2.00

c-o6-o-i6

0-16-0.46

0-10-0-65
0-21-1.39

003-0-06
0-12-0-30

Coniferous

Stem .
Twigs j
and small >
branches J

0-31-0.45
LOI-2.30

0.04-0-15
0.11-0-40

0.06-0.14
0.25-0-44

0-OII-0-027
O-IO-O-22

In the majority of plants cultivated by the farmer the quantity of
pure ash left after the combustion of the dry tissue varies from 6 to
8% of the total weight.

And, according to the same high authority, the annual demands made by
pure crops of forest trees, for the formation of wood only, are per hectare
in kilogrammes, or approximately per acre in Ibs. avoirdupois, as under : —

Species of Tree.

Age of Crop.

Total
Quantity of
Ash.

Potash.

Lime.

Phosphoric
Acid.

years

Ibs.

Ibs.

Ibs.

Ibs.

Scots Pine

So-IOO

12-16

2—3

^_H i

t2

Spruce . .

IOO-I2O

23-24

4-5?

9-11

2|

Silver Fir .

9°

39

IO

4^

3

Beech . .
Hornbeam

4°

30-49
3°

6|-8J

15-20
20

a^4l

Common

Alder . .

70

18

2

13

i|

Birch . -.

5°

•*i

2i

4

4

And in investigations in which all previous thinnings were left out of

calculation.

Beech . .

50

23i

5

nf

•I

Oak (Q. ses-

silt/lora) .

•

27i

3

20|

i

1 Forstlich-naturwissenschaftliche Zeitschrift, 1893, pp. 225, 226.
G 2

84 Studies in Forestry [CHAP. iv.

In trees on which the bark long remains thick and fleshy,
larger quantities of mineral deposits are stored up in the rind
than in those which tend to the early formation of a rough
and rugged cortex.

As the great bulk of the mineral matter is to be found
in the foliage of trees, it therefore follows that woodland crops
must make the greatest demands on mineral nutrients just at the
time when they develop the greatest density of leaf-canopy —
that is to say, about the twentieth to thirtieth year for Scots
Pine, the thirtieth to fortieth year for Spruce, and the fortieth
to fiftieth year for Oak and Beech, on the better classes of
soil, or perhaps about a decade later on soils of poorer quality.
On the inferior classes of land it is therefore just about these
ages that crops of those particular kinds of trees will be most
likely to show signs of the soil not being able to supply easily
the normal demands made for fully adequate supplies of
nutrient salts.

But, at the same time, the absolute demands in this respect
vary enormously in the different genera and species of trees.
For the production of any given volume of wood, Weymouth
Pine, Scots Pine, and Birch make relatively the smallest demands
on mineral nutriment ; after these follow Alder, Spruce, Silver
Fir, Hornbeam, Beech, and Oak ; whilst Ash and Acacia
make the greatest demands.

The quantities of the different kinds of mineral nutrients,
required annually by the various species of woodland trees
for their normal production of wood, range between wide
limits for the different individual kinds of trees, as the
above table shows. But mere analyses of the timber alone
will give no useful key to the total annual requirements;
for, as has already been stated, the most of the mineral salts
absorbed from the soil are finally stored up or deposited in
the foliage during the process of assimilation, and are returned
again to the soil after the fall of the leaf. It may, however,
in passing, be again briefly remarked that, for the production

CHAP. IV.]

The Food of Trees

of wood only, the demands vary as follows in high-forest
crops of various sorts : —

With regard to Lime from 4 to 20 Ibs. per acre per annum.

Potash „ 2 to 10 „ „ „

„ Phosphoric Acid „ | to 4^ „ „ „

In order to arrive at more definite estimates than these
investigations alone could yield, Ebermayer made analyses for
the purpose of determining the amount of mineral ash con-
tained in the dried foliage of the more important kinds of
forest trees, and obtained the following results as to the
percentage of pure ash deposited in the dry leaf-tissue.

A. DECIDUOUS, BROAD-LEAVED TREES.

Ash

7.61

I.

Exacting.

Italian Poplar .

7-04

Elm

6-Q2

Lime . ...

\j yt

6-Kc;

II.

Making considerable
demands.

Mountain Ash . . .
Acacia (Robinia) . .
Horse Chestnut . .

6-2O

6.16
6-03

Ill

Making moderate de-

Sycamore ....
Maple
Aspen . .

5-33
5.21

e.ic

mands.

Willow
Oak

5-II
5-10

IV.

Making slight demands.

Silver Poplar . . .
Hornbeam ....

4.69

4-20
4-02

White Alder . . .

3-92

3-9°

Common Alder . . .

3.69

86

Studies in Forestry

B. CONIFEROUS TREES.

[CHAP. IV.

I.

Making greatest de-
mands.

Silver Fir . . t .
Cembran Pine . . .
Larch . . ~. .

2-93

2.78

2-K.A

Spruce

2. 3Q

II.

Making moderate de-
mands.

Weymouth Pine . .
Scots Pine . . v. .

• oy
2.35
2-28

III.

Making least demands.

Black Pines ....
Mountain Pine .

I. 2
I-36

From these tables it appears that none of the conifers
make anything like such large demands as the broad-leaved
genera of trees per unit of foliage; for the most exacting
of the former makes considerably less demand than the least
exacting of the latter. But the amount of nutrients annually
withdrawn depends on the total quantity of foliage and of
timber formed annually; and, as yet, no exact data of this
description have been collected and tabulated. As a matter
of actual experience, however, we know that soil improves
greatly under coniferous crops, so long as a good canopy of
foliage is maintained ; hence there is good reason for believing
that, in making very moderate annual demands, they enable
the capital in nutrients to be increased within the soil year
by year. But the very favourable physical influences exerted
simultaneously on the soil by means of the canopy of ever-
green foliage overhead must not be left out of the reckoning
when this matter is being considered.

It will be noted, by a comparison of the above table with
that previously given for requirements as to water, that,
in a general way, the trees transpiring most freely, also with-
draw the largest mineral food-supplies from the soil. And
these results correspond very fairly with actual sylvicultural
experience. Where discrepancies seem apparent, a study of
all the circumstances connected with the growth of the tree

CHAP, iv.] The Food of Trees 87

in question will soon explain the paradox. Take the case
of the Acacia (Robinia) for example. The analysis of its
foliage distinctly shows it to belong to the exacting class of
trees ; and yet it is to be seen in vigorous growth on soils
of inferior quality. It must, however, be borne in mind that
the total leaf-production of the Acacia is not heavy ; hence,
even on poor classes of soil, it has less difficulty in supplying
its higher requirements per unit of weight of dry leaf-sub-
stance than other genera having more moderate requirements
in this latter respect but endowed with a heavier total crop
of foliage. And that, in the case of this particular tree, the
symbiotic aid of the Bacteria — which are to be found in the
nodules of all Leguminosae^ and which are capable of assimi-
lating nitrogen from the free nitrogen of the air — may possibly
be of assistance in supplying nitrogenous food, to be used
for the easier assimilation of other mineral food, is not at all
difficult of comprehension.

In the case of the Ash, again, which makes the greatest
demands of all the woodland trees as to mineral food-supplies
per unit of weight of dry leaf-substance, this really withdraws
only a moderate actual quantity of nutrient salts from the soil,
as its total amount of dry leafy substance is slight compared
with that of many other genera of trees, which require smaller
quantities of nutrients per unit of dry leaf-tissue, but yet with-
draw far larger total quantities from the soil annually. Subject,
however, to the Law of the Minimum, referred to at the open-
ing of this chapter, the productive capacity or fertility of any
soil is dependent on the quantity of nutrients available within
it in a form that can be absorbed by the rootlets, and on the
extent to which their absorption is favoured by the combination
of the various physical factors determining its tenacity, moisture,
warmth, and depth. But every soil is not,, as one of the earlier
sylvicultural chemists, Gustav Heyer, asserted \ adapted to the

1 Forstliche Bodenkunde tmd Klimatologie, 1856, p. 3. He assumed
that almost any soil could produce any given kind of timber, if it only had
the requisite amount of moisture.

88 Studies in Forestry [CHAP. iv.

growth of every kind of forest tree ; for the supply of nutrients
available in a soluble form varies with the chemical and the
physical composition of the different classes of rocks, the
degree to which disintegration and decomposition have ad-
vanced, the depth of the soil permeable by the root-systems, the
amount of organic matter contained in the soil, and the physical
properties with which this is endowed. And the want of any
one food-material, or perhaps even an unfavourable condition
of one physical factor (more especially one of those relating to
moisture or depth), may render a soil unsuitable for the normal
development of any given kind of tree. But, undoubtedly, the
inferiority of many woodland soils may also be due to poverty
in one or other of the essential soluble nutrients, though this
is generally combined at the same time with unfavourable
physical conditions. The object of scientific sylviculture is,
therefore, to plant only such trees as are most likely to attain
normal development, and to yield the best monetary returns,
without exhausting the soil or allowing its physical properties
to become prejudiced or impaired by want of protection from
sun and wind.

From this it follows, theoretically, that the cultivation of
coppice- woods, in which the crop is formed entirely of small
branches containing relatively larger quantities of mineral sub-
stances than are to be found in mature wood, must tend to
exhaust the easily available supplies of lime, potash, and phos-
phoric acid sooner than crops grown under high-forest. And
this theoretical deduction coincides exactly with the results of
practical experience; for it is well known that Oak-coppice
for tanning-bark, or Osier-holts for withes, should only be
made on good land, and that if inferior soil be cleared of Oak-
coppice every twelve to sixteen years, it runs great risk of
deteriorating. The treatment of timber-crops in high-forest
is, as long sylvicultural experience has clearly shown, the most
conservative manner of utilizing the soil; whilst copse or
coppice tinder standards stands about midway between the

CHAP, iv.] The Food of Trees 89

two other systems, as being less exhausting than coppice,
though more exacting than high-forest.

High-forests of timber can never lead to exhaustion or
deterioration of the soil, so long as this remains protected by
a sufficient leaf-canopy, and is not robbed by wind, or other-
wise, of the natural manure obtainable through the decom-
position of the dead foliage. On the contrary, and more
especially in the case of trees like Scots Pine and Spruce,
which make lower demands for potash and lime than other
species, it is almost always the case that the nutrient salts
contained in an available form within the soil at the end of
the period of rotation, i. e. on the fall of the mature timber,
are considerably in excess of the quantity that was present at
the time of such crop being formed — provided always that
the fertility or productive capacity of the soil has been duly
safeguarded by the maintenance of a good, unbroken canopy
of foliage throughout all the life-periods of the crop. For this
reason, woods formed of trees like Pines, Spruces, and Firs,
recommend themselves for the recuperation of the productive
energy of soils that have been allowed to deteriorate by being
kept long under lightly-foliaged kinds of trees, like Oak, Ash,
Elm, or Larch ; because the broken canopy formed by these
light-demanding species is unable, without the aid of under-
growth, to protect the surface-soil from the exhausting influ-
ences of sun and wind, and from having the accumulated
supplies of humus consumed unprofitably by a more or less
rank and unremunerative growth of weeds.

CHAPTER V

iV

\ I SOIL AND SITUATION IN RELATION TO

WOODLAND GROWTH

7

I. Soil in Relation to Woodland Growth.

,/ BY Soil is understood the product of the decomposition of
the rocks forming the crust of the earth. Soil is formed
mechanically and physically by rains, frosts, rivers, volcanoes,
&c., or chemically and organically by oxidation, deokidation,
and changes effected by carbonic acid. Through its permea-
bility and its other physical factors, the soil enables trees
to develop the root-systems necessary alike for their support
mechanically and physiologically. By far the greatest portion
\J of the food of all plants possessing chlorophyll is obtained
from the carbonic acid of the atmosphere ; but certain neces-
sary substances (nutrient salts) are only obtainable from the
soil when held there in solution, so that they may be imbibed
by the rootlets. A distinction is made between the soil or
surface-soil and the subsoil. The former consists of the
usually more thoroughly decomposed earth forming the upper
layer permeated by the root-system ; whilst the latter may, or
may not, be of similar composition to the superposed layer.
Even when such patent signs of shallowness of soil as stony
outcrops are not visible, the want of depth may easily be
noted by the stunted appearance of the timber-crops, in which,
owing to the deficiency in soil-moisture and food-supplies, an

CHAP. V.]

Soil and Situation

91

abnormal development of the root-system takes place relatively
to the ascending axis, and to the crown of foliage charged
with the duties of transpiration and assimilation. The chief
signs of depth of soil are length of bole, fuller coronal develop-
ment, and richer soil-covering of underwood, brushwood, and
weeds. A tolerably correct estimate may, in fact, be obtained
concerning the depth and the general quality of the soil from
the mean average height of the timber crops on such soils as
are usually to be found under woods. Thus Grebe gives the
following averages for the Thiiringer Wald in the middle Saxon
states J :—

AGE OF FOREST IN YEARS, AND AVERAGE HEIGHT IN FEET.

Kind of Forest.

Quality
of Soil.

Yrs.
40

Yrs.
So.

Yrs.
60

Yrs.

70

Yrs.
80

Yrs.

90

Yrs.

100

Yrs.
no

Yrs.

120

ft.

ft.

ft.

ft.

tt.

ft.

ft.

ft.

ft.

I.

43

55

69

81

90

97

103

107

I09

II.

37

48

60

69

84

88

91

93

Spruce . .

III.

30

40

49

58

64

69

72

75

76

IV.

23

30

39

45

5°

54

57

58

V.

16

21

27

32

36

39

40

—

—

I.

39

52

65

75

84

90

95

98

96

II.

36

47

58

67

73

79

83

85

98

Scots Pine

III.

41

49

57

62

66

68

70

IV

25

33

40

45

48

51

53

54

—

V.

25

29

33

36

37

38

—

I.

34

48

59

69

78 84

89

92

94

II.

29

41

5°

59

67 73

76

79

81

Beech

III.

24

33

42

49

57 j 61

64

66

67

IV.

19

27

33

40

44

48

50

8*

52

V.

(Not grown on such inferior soil.)

How the general quality of the soil affects the outturn in
timber from the different kinds of woodland crops may be seen

1 Die Betriebs- und Ertragsregelung der Forste, 2nd edit. 1879. These
heights are of course only rough approximations so far as growth of these
trees in Britain is concerned. But there is no climatic reason why they
should not be equalled, or even excelled, in properly managed woods.

92 Studies in Forestry [CHAP. v.

from a reference to the tables on pp. 43-45 of the author's
British Forest Trees (1893).

The Chemical Composition of any soil is in so far of im-
portance to tree-growth that each of the necessary mineral
constituents, always found forming part of the ash to which
timber may be reduced by combustion, must be present in it
in sufficient quantity in a soluble form. The adaptability of
any given soil for the growth of any particular species of
woodland crop is determinable by the Law of the Minimum,
according to which the minimum amount of any one essential
constituent of the necessary food-supply in the soil limits its
total productive capacity for a given kind of timber. Thus,
for example, Oak and Beech extract very much more potash
and phosphoric acid from the soil for the production of their
timber than Scots Pine or Spruce ; hence the latter may thrive
well on soils where (according to the law of the minimum) the
former are of exceedingly indifferent growth owing to the com-
parative scarcity of these ingredients.

As a matter of fact most soils contain the essential con-
stituents of tree-food in sufficient quantities to maintain tree-
growth of any kind. But as they are not always held in
solution, they are not continuously available for imbibation by
i/ the root-system ; for it is only when occurring in the form of
soluble salts, that the nutrients can be absorbed by the
suction-rootlets. It was from this point of view that Gustav
Heyer asserted that almost any soil could produce any given
kind of timber, provided that it contained the requisite degree
of moisture — an assertion which, as has previously been shown,
is only approximately, but not scientifically correct.

Sylviculture varies essentially from Agriculture in being less
J directly dependent on the fertility or inorganic richness of the
soil. Though it is quite certain that rich soils, yielding toa
copious supplies of food-material to be assimilated thoroughly,
would produce large quantities of timber, yet it would be of
a soft spongy nature, little able to withstand either the attacks

CHAP. V.]

Soil and Situation

93

of fungoid diseases whilst growing, or of red and white rot after
conversion. According to Weber1, the analyses of different
woods show that the composition of timber consists, on a rough
average, of 50 % Carbon, 42 % Oxygen, 6 % Hydrogen, i %
Nitrogen, and i % Ash only, for a great many of the mineral
constituents abstracted from the soil are deposited in the
foliage during the process of preparing the food- supplies
for assimilation, and are returned again to the soil when
defoliation occurs, and the dead foliage decomposes into
humus or mould. But the whole demand for mineral food
made by woodland growth is, roughly speaking, only about
one-half of what it amounts to in the case of agricultural
crops, according to the investigations made by Ebermayer2,
which may thus be tabulated : —

Average of

1-s

jo

|q

|d

4 •

lf°

•H.I

"a^O

ther
ituents.

3°

wm

£

3o

^

«•«*

>2^:c«

0|

£

u

Mixed agricultural

crops ....

235

37

78

43

17

28

II

21

Woodland growth

— timber & leaves

126

29

II

62

10

8

3

3

Woodland growth

— timber only .

19

1.6

4

9

2

1.4

0-4

0-6

Approximate ratio

of sylvicultural

demands to agri-

cultural needs . .

*

3

*

1

if

f

*

7

As, in sylviculture, the greatest demands are for lime and
silica, constituents abundant in every soil, and, as by the fall
of the leaf, most of the mineral food is returned to the soil again,
it will be at once apparent that woodland growth does not

1 DieAufgaben der Forstwirthschaft (Lorey's HandbucK}, p. 62.

2 Physiologische Chemie der Pflanzen, 1882, vol. i. p. 761.

94 Studies in Forestry [CHAP. v.

exhaust the land to anything like the same extent as agricultural
crops, which require manuring in order to supply deficiencies,
and to stimulate the upper soil to increased decomposition. And
when the dead foliage is retained on the ground and decomposes
to form humus, this in turn exerts a very beneficial hygroscopic
influence, stimulates the soil to more rapid decomposition,
renders the mineral food-materials more easily soluble, and, in
short, improves the productive capacity of the land, instead of
exhausting it. This shows the importance of maintaining a close
leaf-canopy, and of adopting all practical measures in order to
obviate insolation of the soil, and prevent the free play of winds
that may remove the foliage and exhaust the surface-moisture.

But the mineral constitution of the soil is not the only factor
determining its productive capacity sylviculturally ; for various
physical factors are of equal, and often greater, importance —
e.g. depth, porosity (aeration), consistency, &c. So far, however,
we may be guided by practical experience as to assert that
Elm, Maple, Sycamore, and Ash can only be grown satisfac-
torily on fertile soils ; whilst Birch and Pines are least exacting
as to mineral richness. Between these extremes, Oak, Beech,
Lime, and Silver Fir make somewhat greater demands than
Sweet Chestnut, Larch, Hornbeam, Spruce, Alder, Aspen, and
Willow. When planted out on soils not naturally favourable
to their growth and development, Scots Pine and Birch show
a decidedly greater capability of accommodating themselves
to any given conditions than Oak, Beech, Spruce, and Silver
Fir; whilst Ash, Oak, Elm, Maple, and Sycamore — those
genera whose demands on fertility are greatest — possess the
least power of accommodation.

Soils are largely made up of Salts, with Oxides and some-
times Chlorides. The Salts are mostly Silicates (often com-
bined with water), Carbonates, and Sulphates; whilst the
Phosphates, so important for plant-life, only occur occasion-
ally. In the formation of these Salts, the most important of
the Acids are Silica (Si O2), Carbonic acid (CO2), Sulphuric

CHAP, v.] Soil and Situation 95

Anhydride or Sulphur Trioxide(SO3) and Phosphoric Anhydride
or Phosphorus Pentoxide (P.2 O5) ; whilst the chief Bases
are Potash (K2O), Soda (Na2O), Lime or Calcium Oxide
(CaO), Magnesia or Magnesium Oxide (MgO), Ferrous
Oxide (Fe O), Sesquioxide of Iron or Ferric Oxide (Fe2 O8),
Alumina (A12 O3), and Manganese Dioxide (Mn O2). The
Silicates comprise quartz, serpentine, talc, felspars, mica,
hornblende, augite, and chlorite; the Carbonates include
carbonate of lime, chalk, and dolomite ; to the Sulphates
belong anhydrite and gypsum or calcium sulphate. When
the water of crystallization in many salts composing rocks
becomes heated and driven off, the salt crumbles into powder ;
and, at the same time, all rocks, being porous, are pervious to
water, which not only dissolves certain salts, and holds them in
solution ready for absorption by the roots of plants, but also
effects transformations in many chemical compounds. Thus
water impregnated with carbonic acid dissolves silicates con-
taining alkaline earths and ferrous oxide, as also carbonate of
lime (Ca CO3) and ferrous carbonate (Fe CO3) which are easily
soluble in it, whilst magnesium carbonate (Mg CO3) is much
less so. The products of the decomposition of rocks are mostly
alkalies in combination with silica and carbonic acid, together
with carbonate of lime, magnesia, and ferrous oxide, whilst
soluble sulphate of lime is also found in most soils ; but as
these salts act and re-act on each other, many various com-
pounds are formed.

Rocks of complicated structure decompose most rapidly, as,
for instance, those rich in felspars, or in compounds of iron, in
contrast with silicious slate or quartz-rock ; pure limestone de-
composes slowly, but this difficulty diminishes with any increase
of alumina and iron. Sandstones and conglomerates decompose
in proportion to the cementing matter they contain, and to the
degree in which this is affected by moisture. Fine-grained
and massive rocks are less apt to fissure and crumble than
coarse-grained stones or slaty beds, as they afford fewer points

9 6 Studies in Forestry [CHAP. v.

of attack to water, mosses, herbage, and other disintegrating
influences.

Vegetation plays no unimportant part in the formation of
earth, not only by helping to fissure and cleave the soil and
subsoil, so as to enable water to effect an entrance, but also by
reason of the decomposition of the organic debris of foliage,
dead wood, &c., and the formation of humus or mould, which
takes place under the combined action of oxygen, moisture,
and a minimum warmth of 52° Fahr. When the humifica-
tion takes place only under partial exposure to the atmosphere,
humic and similar acids are formed, and saprophytic fungi
aid in the work of decomposition, by attacking the albuminoid
substances first of all. These acids (humic, ulmic, geic, &c.)
have a strong affinity for ammonia (NH3), which is itself
essential to the nourishment of trees, and which cannot be
assimilated by the foliage from the free nitrogen of the air,
although, as Hellriegel, Frank and others have shown, it can be
obtained by the Leguminosae from the air circulating within
the soil by means of symbiosis with a fungus (Bacillus radicicola)
found in the nodules on the roots (see page 74).

Humus condenses gases and atmospheric moisture, and
possesses a certain amount of warmth, partly owing to reten-
tion of atmospheric warmth received from sunshine, and partly
to the generation of heat by the chemical process of decomposi-
tion. Thus, whilst mechanically making clayey soils less stiff,
and sandy soils more binding, it also warms the former, and
makes the latter less liable to be affected by the changes in the
atmospheric temperature.

II. The Classification of Soils.

Any classification of soils according to their geognostic or
geological origin would be very misleading, for (i) the same
kmd of rock does not always yield 'similar soil, (2) the quali-
ties of the soil depend on the extent to which decomposition

CHAP, v.] Soil and Situation 97

has taken place, and (3) some of the lighter products of
decomposition (clay) are more easily washed away than others
that are heavier (sand). Hence, for practical sylvicultural
purposes, no better classification of soils can be adopted than
that made by Grebe, which is now generally adopted at the
experimental stations on the continent : —

Sandy Soils, containing 75 % or more of disintegrated sand. They
occur as sand-drifts, or are the product of the decomposition of sand-
stones.

Sand consists of abput 90 % of sand, and not more than 10 % of

clay and other constituents.
Loamy sand consists of about 75 to 85 % of sand, and from 15 to

25 % of clay and other constituents.

Loamy Soils, always tinged with iron, containing 60 to 70 % of fine
sand and silicious dust, the rest being chiefly made up of clay with less
than 5 % of lime, and an almost constant quantity (5 %) of hydrated
ferric oxide.

Loam consists of about 60 % of sand and 40 % of clay.
Sandy loam consists of about 70 % of sand and 30 % of clay.
Clayey Soils, containing 50 % or more of clay. They are mostly
formed from rocks rich in feldspars, augite, and hornblende, of sand-
stones and conglomerates cemented with clayey cohesive substance, and
of the clayey layers and bands throughout sandstones and lime forma-
tions.

Clay consists of about 60 to 70 % of clay, the rest being chiefly

sand, and also other constituents.

Loamy clay consists of about 50 % of clay, and 50 % of sand.
Limy Soils, containing not less than 10% of carbonate of lime.
They are produced chiefly by limestones, but also by other rocks
containing lime felspar (labradorite). It often happens that limestone
rocks produce a loamy rather than a limy soil on decomposition.

Lime consists of at least 50 % of carbonate of lime, the rest being

chiefly clay.

Clayey lime consists of about 40 % of lime and 60 % of clay.
Loamy lime consists of about 30 % of lime and 70 % of loam . When
rich in carbonate of magnesia it is called dolomitic lime or
dolomite.

Marl consists of 10 to 20 % of carbonate of lime, with 80 to 90 %
of clayey and sandy ingredients.

Sandy soils have a coarse gritty feeling when slightly mois-
tened. When there is any considerable admixture of loam,

H

98 Studies in Forestry [CHAP. v.

marl, iron, or humus, sandy soils are said to be loamy, marly,
ferrugineous, or humose. Sands become easily heated or
cooled, and have a poor capacity for retaining moisture and
nutrient salts in solution j hence they form the inferior quali-
ties of soil, on which trees require a considerable growing-space
in order to obtain the requisite supply of food, fail to maintain
good leaf-canopy, become deficient in increment, produce little
seed, and are otherwise deficient in reproductive capacity.
Owing to their becoming easily warmed by day, they stimulate
to the early germination of seed, and movement of sap, and flush-
ing of foliage in spring ; but, as they cool rapidly at night, this
exposes the young vegetation to danger from late frosts. Earthy
ingredients, and humus in particular, improve the quality of
sandy soils. When forests approaching maturity show good
development on such soils, their natural regeneration is safe
and simple ; but where the tree-growth is indifferent, it is advis-
able to resort to planting, as the young growth of seedlings is
often too intolerant of shade to make natural regeneration under
parent standards a success. In the planting up of such soils for
the first time, Scots Pine is the best crop, mixed with whatever
other species of trees may seem likely to thrive at all well,
as, for example, Douglas Fir, Black Pines, Spruce, Menzies
Spruce, &c.

Clayey soils stick if brought in contact with the tongue, and
smell of ammonia if breathed upon ; rubbed between thumb
and forefinger they feel fatty to the touch, and take a polish
or burnish if rubbed with the thumb-nail. They may be grey,
yellow, or brownish-red in colour, and are usually tinged
with iron. Their leading characteristics are tenacity, weak
hygroscopic power, and impermeability to moisture ; but they
are strongly retentive of moisture when once saturated. Such
soils are cold, and are apt to become water-logged. Any con-
siderable admixture of sand, iron, lime, or marl — forming sandy,
ferrugineous, limy or marly clays — tends to modify these char-
acteristics. As the soluble nutrient salts are not apt to be

CHAP, v.] Soil and Situation 99

washed out of the soil, clays offer comparatively large supplies of ^
tree-food within a small space ; hence the crops have a greater
density of leaf-canopy at all stages of their development than
similar woods growing on sandy soils. Unless the subsoil be
permeable, however, there is a danger of such tracts becoming
marshy. Owing to their low conductivity of heat, woodland
growth on clayey soils seems backward in spring. In the
natural regeneration of mature crops a good deal of soil-pre-
paration is usually required on clays in order to assist in the
decomposition of the dead foliage, which often forms a thick
layer on the soil in consequence of the density of the canopy
overhead. Not only is more foliage thrown down, but this
also retards the formation of humus by keeping the soil at
a low temperature. On such soils natural regeneration is very
easy; for the preliminary clearances stimulate to increased
production of seed, and the young seedling growth bears shade
better than on poorer sandy soils. The reproductive capacity
of copse and coppice is also greater on clays than on sands.

Limy soils effervesce when tested with drops of nitric acid.
Marls and true limes are both comprised within this group;
but in the former the limy constituent is equally admixed
throughout each particle of the soil, whilst in the latter it is
not. These also become by admixture sandy, loamy, clayey,
or stony limes or marls. Limy soils are apt to be wanting in .
depth ; but with careful treatment they often show fine growth
of timber. Their consistency favours the equable distribution
of soil-moisture, even on steep hill-sides ; hence the root-system
easily attains normal development, and has few difficulties to
overcome in satisfying its requirements in the way of food-
supplies. But, when such soils have deteriorated through in-
solation following on bad management, the soil-moisture is not f :'
retained ; the finer particles of earth get washed away rapidly ;
the soil rapidly becomes shallow, dry, and hot ; and timber
production diminishes considerably. The re-wooding of dry,
limy hill-sides is one of the most difficult of sylvicultural tasks.

H 2

ioo Studies in Forestry [CHAP. v.

Some very good results have occasionally been attained by
sowing out lucerne (Medicago sativd] and beech-nuts at the
time of planting out Austrian Pine (Pinus Laricio var. austriaca
Endl.), the lucerne being left to form humus in place of being
utilized as fodder. A soil-covering of dead foliage and humus
on limy tracts is essential for the maintenance of a productive
capacity anything like commensurate with their mineral
strength ; hence natural regeneration is advisable when removing
the mature crop. As the dead foliage rapidly decomposes,
and seed-production is usually good on limy soils, little or
no preparatory clearance is necessary previous to the seed-
felling ; whilst, as the seed is generally of good quality and high
germinative power, and the seedlings are not apt to wilt or
droop under the shade of the parent standards, the regenera-
tive process is comparatively easy. But, when limy soils are
sandy or stony, greater care must be taken not only in making
the regenerative fellings, but also in all the operations of
tending throughout the whole life-period of the crop. Limy
soils that are properly protected against insolation -are in every
way well endowed with reproductive capacity as coppice.

Loamy soils have greater resemblance to clay than to sand,
but neither feel fatty when rubbed between finger and thumb,
nor take any definite polish when rubbed with the finger-nail.
A general mildness is their leading characteristic; but they
approach more to the one or other of the three main groups
according to the amount of sandy, clayey, or limy admixture

; contained in them. Though their capacity for absorbing and
*.jT retaining soil-moisture is determined to a great extent by the
nature of the subsoil upon which they rest, yet they are in
general favourable to sylvicultural crops ; and the species of trees
selected for growth are usually chosen for financial reasons, or
for reasons connected rather with the physical properties than
with the mineral composition of the soil. At high elevations with
humid atmosphere the Spruce or the Douglas Fir is recom-
mendable as the ruling species on loamy soils ; whilst at lower

CHAP, v.] Soil and Situation ' ,', ; ;

levels the Oak is one of the species thriving best in mixed
forests of broad-leaved trees. Natural regeneration is easy on
loamy soils when a good seed year comes round ; but, as good
seeding or mast-years can not be depended on in crops on
loam, it is best to sow seed procured from elsewhere rather* .XT
than to risk deterioration of the soil from insolation after *
once the preliminary fellings have been made.

As the fertility or productive capacity of soils is neither
dependent on, nor mainly proportional to, the mineral richness I ,r
of the rocks from whose decomposition they are formed, no \^f
hard and fast classification as to their mineral strength is
possible. It can only be said that, in general, clayey soils are
slow in forming humus and giving nutrients to tree-life, whereas .
limy soils decompose organic matter rapidly and stimulate
tree-growth, and that intermediate positions between these two
groups are occupied by sandy and loamy soils, except when
the sands are deficient in soil-moisture.

All soils are improved by an admixture of humus to a mode-
rate extent. It not only adds depth to the land, but, being .^f"
of a strongly hygroscopic nature, also condenses and retains
atmospheric moisture ; whilst, owing to its low conductivity, it
protects the soil against evaporation. It is also directly active
in aiding the continuous decomposition of the soil by means
of the carbonic acid set free during the process of decomposi-
tion. It modifies all extremes of physical properties in soils ; '
and though not an absolute necessity for the production of
woodland crops, yet it is of inestimable value in stimulating
the action of soils, no matter of what geognostic origin.
Indeed, as Gayer remarks1, there can be little doubt that
' hu mus forms the most important factor relative to tree-growth, and -^ < E?
is a priceless treasure as regards the production of woodland crops'
And the beneficial influence it exerts on the aeration of soils
is by no means its least important quality. When soils contain
20 % or more of humus they are termed humose ; fertile silt left
1 Waldbau, 1889, p. 27.

Studies in Forestry [CHAP. v.

after inundations is often of this character. Sometimes, as in
the case of marshes, moors, and peat bogs, the accumulations
of humose soil is so great that the roots of trees are unable to
reach the mineral soil below it ; such formations usually take
place on sandy soil resting upon clay.

Ferruginous soils are coloured brownish-red, and contain at
least 10 to 15% of ferric oxide or hydrated ferric oxide. But
even by 2 to 5% of ferric oxide the general character of sandy
soils may become affected, although considerably larger quan-
tities may fail to effect any noticeable alterations in clayey or
loamy soils. Thus moorpan, sometimes containing only about
2% of ferric oxide, is just as impenetrable to the roots of trees
as iron-band or limonite with its 60 to 70%. In both cases tree
growth is hindered until the impenetrable layer has been
broken through, so as to allow of the roots reaching the sub-
soil, and of the moisture circulating normally.

III. The Physical Properties of Soils.

To these, in a far greater degree than to the mineral com-
position of any soil, is due its capacity to sustain timber crops,
and to yield to them in due proportion the various forms
of nutriment requisite for their growth, development, and
reproduction. All the physical properties act and react on
each other in determining the quality of any given land.

Cohesiveness or Tenacity is the resistance offered by a soil
to instruments used in separating its particles, or to force
employed in disintegrating them. This property is not alone
of importance in relation to air, moisture, and warmth, but
also indicates the resistance to be overcome by the root-
systems in penetrating into, and ramifying throughout, the soil.

Clay soils have the greatest cohesiveness, sand the least ;
lime approaches more to the clay, while loam resembles rather
the sand. An admixture of humus tends to level all classes,
making clays and limes less tenacious, and loams and sands

CHAP, v.] Soil and Situation 103

more binding. The tendency of soils to expand with mois-
ture, and to shrink on parting with it again, is practically
proportional to its tenacity. Soils may be classified in this
respect as —

Heavy, stiff, or tenacious soils, which fissure and crack deeply when
dried up. Clays and clayey loams, limes and marls belong to this
class.

Mild soils, exhibiting superficial cracks when suddenly dried up, but
which when nearly dry have the power of retaining the form of
clods. They are usually composed of favourable admixtures of
clay, sand, and lime, as in loams, sandy loams, and loamy limes.

Light soils, capable of forming clods when moist, but when dry show-
ing a strong tendency to disintegrate, as in the case of loamy sands
and sandy marls.

Loose soils, which even when moist have little tendency to form clods.
To this class belong the poorer sandy soils.

Shifting soil, liable in a dry condition to be carried away by the wind,
as in the case of sand-drifts and dunes.

In a light soil, which is not deficient in moisture, humus, and ^ /
mineral nutrients, a maximum of rootlets can be developed,
and through these the maximum of timber. Hence one finds
the greatest increase in cubic contents, and in particular the
greatest average annual increment in height, on alluvial
deposits having finely pulverized particles. But when loose
soils are wanting in soil-moisture, planting operations are ,.-
apt to be unsuccessful; for the plants have great difficulty
in establishing themselves so as to send down their roots
to lower levels and thus obtain an assured supply of the
water requisite for transpiration through the foliage. Thus,
on the sandy soils in some parts of Sussex, for example,
seedling Oaks are only found to thrive when planted out
among weeds, such as brambles, which keep patches of soil
here and there cool and moist.

The degree of moisture contained in any soil is one of the
most important factors concerning woodland growth. No
plant can grow without imbibing supplies of water; it is
requisite for germination ; without it, the nutrient salts could

IO4

Studies in Forestry

[CHAP. V.

not be made soluble for imbibition by the suction-roots, nor
could transpiration through the foliage and assimilation possibly - ^
take place; it assists likewise in regulating the ^temperature-^' ''
of the soil, by making stiff soils milder and loose soils more
binding. But excess of soil-moisture interferes with the
normal processes of decomposition, both of the soil and of
the humus ; it leads to the development of injurious acids and
acid solutions, and tends to the formation of marshes ; seed
and roots also suffer from want of oxygen or insufficient
aeration of the soil, and hence become easily infected with
fungoid diseases; whilst, in consequence of its poor con-
ductivity, and of the amount of heat necessary for raising the
temperature of water, it both retards the natural activity of the
soil, and increases danger from frost. Fineness of the soil-
particles favours hygroscopicity, or absorption and retention
of moisture ; whilst permeability, or diffusive capacity relative
to moisture, is proportional to their coarseness. Soils are in
these respects classifiable as follows : —

Absorptive Power as to

Power of retaining
Moisture.

Power of diffusing Moisture.
(Permeability.)

Rain

Aqueous
Vapour.

I

2

Lime
Clay
Loam

Clay
Lime
Loam

Clay
Lime
Loam

Sand
Loam
Lime

4

Sand

Sand

Sand

Clay

The addition of humus tends, however, to modify the
various characteristic differences exhibited in these respects.

With regard to the degree of moisture they contain, the
following classification of soils has been adopted at all the
sylvicultural experimental stations in Germany : —

Wet, when water flows out, without pressure being applied, on a clod
being lifted up.

CHAP, v.] Soil and Situation 105

Moist, when water falls in drops from a clod on pressure being

applied.
Fresh, when only traces of moisture are left on the hand, after pressure

being applied to a handful of soil.
Dry, when the soil does not resolve itself into dust on being rubbed.

Such soils lose their moisture within a few days after rainfall, and

their colour is not much deepened by the moisture retained.
Arid, when, on being rubbed, the soil resolves itself into dust that is

carried away by the wind. Traces of rainfall rapidly disappear

from such soil, and the slight quantity of moisture it is able to

retain does not much affect its colour.

Most of our forest trees — Oak, Beech, Maple, Spruce, Scots
Pine, Larch, Silver Fir — thrive best on a fresh soil ; Willows,
Poplars, Ash, Elm, and Hornbeam prefer a moist soil, and
the Alder even a wet one ; but stagnating moisture is favour-
able to no kind of tree-growth. Dryness of soil is not an
essential for any of our forest trees ; but Birch, Rowan, Aspen,
Black Pine, and Scots Pine in general, and Beech on a limy
soil, appear to be able to accommodate themselves to less
soil-moisture than other species.

The sylvicultural qualities of a soil are frequently, to a very great
extent, indicated by the nature of the forest weeds that grow upon it.
Thus the following characteristic species of plants may be recognized :

i. On wet or boggy soil: — Bog moss (Sphagnum^, hair moss (Polytri-
chum), cranberry (Vaccinium Oxycoccos\ bog bilberry ( Vaccinium uligi-
nosum\ heath or bell-heather (Erica Tetralix), marsh cistus or marsh
rosemary (Ledum palustre), cotton grass (Eriophorum), sedges (Carex\
bulrushes (Sdrpus), rushes (Juncus), — the last three genera in many
different species.

a. On fresh fertile land, or soil rich in hu mus:— Raspberry (Rubus
idceus}, bramble (Rubus fruticosus*) , red foxglove (Digitalis purpured),
willow herb (Epilobium angustifolium) , deadly nightshade (Atropa
Belladonna), balsam (Impatiens Noli-we-tangere], stinging nettle (Urtica
dioicd), hemp nettle (Galeopsis Tetrahif), vetches (Viad), and species of
clover (Trifolium), as well as ferns and broad-leaved grasses of different
sorts.

3. On drier and more sandy soils :— HeatheY or ling (Calluna vulgaris),
bilberry or whortleberry (Vaccinium Myrtillus\ red whortleberry or
cowberry (Vaccinium Vitis idea), whin, gorse, or furze (Ulex}, broom
(Cytisus scoparius), greenweed (Genista), groundsel and ragwort (Senecio],

io6 Studies in Forestry [CHAP. v.

mullein (Verbascum), hawkweed (Hieracium), spurge (Euphorbia] , — these
last-named genera occurring in various species, — and the narrow-leaved
meadow grasses.

The shrubs which occur most frequently on hills and valleys, especially
when the soil is fresh, include the following : alder buckthorn (Rhamnus
Frangula), blackthorn or sloe (Prunus sptnosa), hawthorn (Cratcegus
oxyacantha), spindlewood (Euonymus europ&us), dogwood (Comus
sanguined), barberry (Berberis vulgaris), holly (Ilex Aquifolium), honey-
suckle (Lonicera Periclymenuwi), elderberry (Sambucus) ; on drier soil,
juniper (Juniperus vulgaris}, and on sandy soil, sea-buckthorn (Hippophae
rhamnoides).

Relation to warmth is exhibited in changes of soil-tempera-
ture in accordance with changes in the atmospheric tempera-
ture. It is determined to a far greater extent by the quantity
of moisture in the soil, and by its colour, than by its specific
warmth. Retentive soils, like clay, are cold and inactive ;
but, when once heated, they only cool down again gradually.
Sandy and gravelly soils become easily warmed and stimulated ;
but they cool down again rapidly, and hence, in damp localities,
increase the danger from frost. In Britain diurnal variations
of temperature are obliterated at a depth of about 20 inches
from the surface, weekly differences at about 40 inches, and
monthly variations at about 6J feet.

Depth expresses the extent to which decomposition of the
soil has taken place below the surface. The finest earth is
to be found near the top-level, where the soil has been most
exposed to the disintegrating effects of 'weathering'; the
deeper one digs below the surface the larger will the stones
and breccia be found, until at last a layer of subsoil is struck
which is practically beyond the reach of the decomposing
agents, and which may, or may not, be of different geological
origin from the soil resting upon it. When decomposition
has proceeded so far that the ground is easily penetrable by
the root-system for a considerable distance below the surface,
a soil is termed deep ; but when the decomposed and aerated
layer of earth is only slight it is said to be shallow.

CHAP. V.]

Soil and Situation

For trees forming a decided tap-root — like the Oak, Scots
Pine, and Larch — depth of soil is of very great importance ;
for, unless the root-systems can develop normally, the growth
in height of the trees becomes prejudicially affected. But trees
with only moderately deep root-systems, like Beech, Horn-
beam, Silver and Douglas Firs, or even rather shallow-rooting
kinds like Birch, Aspen, and Spruce, also thrive better on deep
than on shallow soils, as these latter generally contain more
equable supplies of soil-moisture, and larger stores of food-
material in an easily available, soluble form. Deep soils are
much less apt to dry up or to become too moist than shallow
soils ; and the disadvantages of the latter are intensified when
the subsoil happens to consist of horizontal layers of stiff clay
or other impermeable strata, or of ferruginous deposits like
moorpan or limonite. The following is the classification of
soils as to depth adopted at the sylvicultural experimental
stations throughout Germany : —

Description of
Soil.

Depth.

Nature of Wocdland Crops for which
such Depth suffices.

Very shallow .

up to 6 in. only .

Not really sufficient for any
species ; but often found under

mixed coppice.

Shallow . .

from 6 in. to I ft.

Spruce, Aspen, Rowan, Birch,

Mountain Pine.

Medium . .

„ i to 2 ft. .

Austrian, Corsican, and Wey-

mouth Pines, Beech, Horn-

beam, Alder.

Deep . . .

„ 2 to 4 ft. .

Elm, Maple, Sycamore, Ash,

Lime, Sweet Chestnut, Silver

and Douglas Firs, Scots Pine.

Very deep . .

over 4 ft. ...

Oak and Larch.

But in Britain, as a matter of fact, woodland soils will
seldom be found of great depth : for, when deep, they can
generally be used to better economic and financial advantage
as arable or pasture land.

io8 Studies in Forestry [CHAP. v.

IV. Situation in Relation to Woodland Growth.

The growth and the regeneration of the different kinds of
forest trees are dependent on combinations of various con-
ditions regarding temperature and moisture, which are united
under the term climate. Some demand for their normal
development an amount of warmth which is absolutely fatal
to others ; an4 these again can bear, and often even prefer,
a low temperature during winter, which causes the vital energy
of the former to cease, never to re-awaken. Some transpire
so freely through the foliage (e.g. Spruce) as to need rather
a damp soil and atmosphere, whilst others (e. g. Scots Pine)
prefer a drier condition. Without light and warmth the action
of chlorophyll in absorbing carbonic acid from the air, and
consequently assimilation, would be impossible.

Warmth is in general dependent on, and inversely propor-
tional to, the distance of any locality from the equatorial line,
although practically the nature of modifying circumstances
connected with the distribution of land and water, high moun-
tain-chains, &c., is always of more or less influence. Thus, in
Britain, owing to our insular climate, and to the humid and
essentially equalizing tendency of the Gulf-stream, we have no
such extremes of summer heat and wintry cold as annually
occur in the continental areas lying along the same degrees of
latitude in Europe, Asia, or America. Owing to these local
modifying influences, there are nowhere hard and fast zones of
woodland crops. With ascent above the sea-level, and conse-
quently above the densest and heaviest layers of atmosphere
capable of acquiring most warmth in summer, temperature
falls at about the rate of i° Fahr. for every 300 ft., and Angot
has estimated that for every 333 ft. in vertical ascent woodland
growth is retarded for about fourteen days in the awakening of
vegetative activity during the spring.

Recent investigations made in the Bavarian Alps (Brenner Pass,
4,500 to 5,000 feet above sea- level) have led to the following conclusions

CHAP, v.] Soil and Situation 109

with regard to the effect of vertical elevation on the increment and the
shape of forest trees * : —

A. For individual Trees.

1. Growth in height diminishes regularly and noticeably.

2. Growth in basal area, or sectional area of the stem at breast-

height, does not diminish so rapidly as growth in height.

3. Total increment diminishes gradually.

4. The period of development is prolonged in all of the above three

directions (i. e. the attainment of maturity is slower).

5. The bole or stem deviates more and more from the shape of the

cylinder and approximates towards that of the neiloid.

6. The distribution of the increment over the various portions of

the tree increases relatively from above downwards.

7. The form-factor at breast-height (i. e. the proportion which the

actual volume of the stem bears to a cylinder having the same
base) becomes smaller.

8. The coronal development gradually comes lower down, nearer to

the ground (i. e. the stems become short and stunted).

9. The proportion of branches and brushwood increases (i. e. as the

stems grow stunted, the coronal development increases rela-
tively).

B. For whole Crops.

1. The number of stems per acre increases, but the proportion of

those which form the larger girth-classes diminishes.

2. The mean average height of the crops diminishes.

3. The total basal area at breast-height does not diminish so

perceptibly as the average height of the crops, but it is made
up mostly by units belonging to the smaller classes of stems.

4. The total quantity of wood available as timber or fuel decreases

perceptibly ; hence the total average annual increment of the
mature crop becomes considerably less.

5. The quantity of small branches and brushwood increases.

6. There is a decided tendency towards growth of the trees in

groups instead of being equally distributed over the whole
area.

Near the polar regions, or at very high elevations, there is
no woodland growth. This may not be solely due to the actual

1 S. Honda, Ueber den Einfluss der Hbhenlage der Gebirge auf die
Verdnderung des Zuivachses der Waldbaume, 1892, p. 27.

no Studies in Forestry [CHAP. v.

amount of cold in winter. It may, as Hartig has shown \ be
caused by transpiration being excited through the leaves of the
evergreen conifers (which reach to the highest latitudes and
elevations) on bright, sunny days, whilst the soil still remains
frost-bound and unable to allow of imbibition of fresh supplies
of moisture by the root-system in order to replace what is being
evaporated. Wilting and death are then the inevitable results if
the winters are long and dry, and if the sunny days have been
frequent.

But, although woody plants suffer comparatively little from
the effects of winter cold, yet late frosts in spring are apt to
injure the young leaves and shoots, and also early frosts in
autumn before the shoots have hardened. These dangers are
greater in low-lying and confined localities than where aerial
currents have free play. Ash, Acacia, sweet Chestnut, and
Beech are most sensitive to frost ; Lime, Hornbeam, Elm,
Birch, Larch, Aspen, Austrian, Corsican, and Scots Pines are
decidedly hardy ; whilst Oak, Silver and Douglas Firs, Maple,
Sycamore, Spruce and Alder occupy an intermediate position,
in which the influence of other factors than atmospheric tem-
perature merely (e.g. humidity of soil and air) determine whether
they are likely to incur danger or not.

The absolute equivalent of heat necessary for the normal
development of any given species of tree is as yet unknown.
But experience shows 2 that Elm, sweet Chestnut, pedunculate
Oak, and Black Pines require the greatest amount of warmth,
and that Larch, Cembran, and Mountain Pines can do with
least ; whilst, between these extremes, Silver and Douglas Firs,
Beech, sessile Oak, Scots and Weymouth Pines require de-
cidedly more than Maple, Sycamore, Ash, Alder, Birch, and
Spruce. Although their general requirements as to warmth
limit the different species to more or less normal zones of

1 Lehrbuch der Baumkrankheiten, 2nd edit. 1889, pp. 104, 261. But
compare the remarks already made on p. 68.
a Gayer, op. cit., p. 20.

CHAP, v.] Soil and Situation 1 1 1

elevation, yet quality of the soil, aspect, and local climatic
conditions modify these demands in the most marked degree. It
is more particularly the amount of warmth during the period of
active vegetation which determines whether or not the different
species of trees can thrive and regenerate themselves naturally
in any given locality. If, between the time of their flowering
and the natural term of their ripening the fruit, there has not
been a sufficient development of warmth, accompanied by an
absence of destructive frost, to enable the seed to attain
maturity and germinative capacity, then the natural conditions
for thriving and regeneration are not offered to any given kind
of tree. The further northwards deciduous broad-leaved trees
occur, the later is usually the time at which they break into
leaf, as the amount of warmth requisite for stimulating active
vegetation is only obtainable later in spring than at similar
elevations situated further southwards.

Light is also a factor which is undoubtedly of immense
importance with regard to the thriving of woodland crops. A
careful study of their demands with respect to light, and their
capacity for enduring shade, will quite logically explain many of
the concrete conditions in which woodland growth exhibits
itself, as was first pointed out by Gustav Heyer1 (see also

P- 54)-

The Relative Humidity of the atmosphere is governed by
the atmospheric temperature ; for, as regards any given quantity
of moisture, the saturation-point will be much sooner reached
when the air has only a low temperature, than when its
temperature is high2. But, whilst the absolute humidity of
the air varies inversely to the latitude above the equator, no
such rule obtains regarding its relative humidity, as local
circumstances determine the supplies of moisture available for
evaporation. Thus, in Britain, the soft, mild, westerly winds
which reach this island only after sweeping over the Atlantic

1 Das Verhalten der Waldbaume gegen Licht und Schatten, 1852.

2 See Roscoe's Elementary Text-book of Chemistry, 1888, pp. 55, 56.

ii2 Studies in Forestry [CHAP. v.

in the track of the Gulf-stream, have a high relative humidity ;
whilst those from the east, which come from about the central
area of Asia and Europe, are comparatively dry, although (in
consequence of the moisture acquired in passing over the
North Sea) not so dry as on the continent, where the relative
humidity of the air decreases with longitudinal progress east-
wards.

As aqueous precipitations must occur whenever the air is
reduced so far in temperature that the corresponding saturation-
point renders it impossible for all the moisture to be retained,
rainfall is more frequent at higher elevations than at lower
levels, whilst at the same time aerial disturbances of various
kinds are also more frequent and violent.

For the maintenance of normal transpiration through the
foliage of woodland crops enormous supplies of moisture are
requisite in the soil. When a period of drought occasionally sets
in during summer for about a fortnight to three weeks, this often
forces vegetation to close its activity for the year in the case
of broad-leaved trees, or can even be fatal to species like the
Spruce, which transpire freely1. Though the actual amounts
of soil-moisture requisite for the various species of trees of
woodland growth are -not accurately known, yet observation
and experience show that Spruce, Black Pines, Alder, Maple,
Sycamore, and Ash thrive best in a humid atmosphere, whilst
Beech, Birch, and Silver Fir grow better in damp than in dry
localities. If, therefore, the former species be planted out in
situations where the air is usually dry, they make considerably
greater demands as to soil-moisture than when growing in
localities where, owing to a higher relative humidity of the
atmosphere, the transpiration of water through the foliage is
not so much stimulated 2.

The Aspect, or Exposure towards one or other of the
cardinal points of the compass, exerts great influence on the

1 Compare Chapter VIII, Section i.

2 See British Forest Trees > 1893, pp. 27, 28.

CHAP, v.] Soil and Situation 113

temperature of soils, and on the amount of moisture retained
in them. Southern and south-western aspects, owing to their
greater warmth and to the stimulation of evaporation, both "
through the foliage and direct from the surface-soil, are usually
much drier and more apt to get heated than northern and
north-eastern exposures, which are cooler and damper, and
whose soil is usually less active both in awakening vegetation
in spring, in stimulating to assimilative processes, and in
decomposing the dead foliage on the ground so as to form
humus. On high ranges of mountains, however, trees will still
be found on the warmer aspects at levels above those limiting
their growth on the northern slopes. Eastern exposures are
most liable to danger from late frosts; whilst western and
south-western aspects are most exposed to damage from wind-
fall and breakage, as the heavy storms coming from these
directions are usually accompanied by rain, and often occur
at times when the soil is still sodden from recent downpours.

The Slope or Gradient of any soil is necessarily of influ-
ence; for the opportunities which rainwater has of percolating /
down to the lower layers decreases as the angle formed with
the horizontal by the surface of the soil increases. According
to Grebe, soils with a slope of from 5 to 30° form the true
home of woodland growth; hence much land which is too
steep for agricultural cultivation is well adapted for sylvi-
cultural occupation. Grebe's classification of gradients, now
adopted at the experimental stations throughout Germany, is
as follows: —

gentle 5-10° steep 21-30°

medium 11-20° very steep 3I~450

precipitous over 45° ; this is, however, incapable of sustaining tree-
growth.

The Configuration of the Soil and of the surrounding
Country exerts a considerable amount of influence on the
woodlands. The soil near the base of hills is generally deeper, /
richer, and more productive than on the slopes or ridges ; but

i

1 14 Studies in Forestry [CHAP. v.

the danger from frosts is greater in hollows and throughout
low-lying tracts than where currents of air have free play.

Mountain masses have greater uniformity of soil and situation
than ranges of hills. On these the well-being of the woodland
growth depends to a great extent on the amount of protection
that can be given to it from winds ; for the bad effects of want
of protection may only too clearly be seen in exposed planta-
tions or woods near the sea-coast or on bleak hill-sides.

In the assessment of the quality of soil the best standard is
that which makes five distinctions, thus : —

I. Very good ; II. good; III. average or moderate; IV. inferior;
V. poor.

In Germany the decimal system is often adopted. But
practical men will have less difficulty in making up their minds
as to whether any given soil is average or inferior in quality,
than they will find in estimating it at 0*3, or 0*4, or 0*5 of the
first-class soil classed as equivalent to i 'o. Such assessments
are very useful, but are in each case only relative ; for a soil
that might only be regarded as inferior so far as the cultivation
of mixed crops of Oak, Maple, Sycamore, Larch, Douglas Fir,
and Beech are concerned, might perhaps be considered a
moderately good, or even a good soil if considered with regard
to woods in which Pines, Spruces, and Firs were to be the
ruling kinds of trees.

CHAPTER VI

ON THE ADVANTAGES OF MIXED TIMBER-CROPS
OVER PURE WOODS

AT p. 33 of the Nineteenth Century for July, 1 891, Sir Herbert
Maxwell, Bart., in his article on Woodlands, in endeavouring to
assist landowners towards a better system of Forestry than at
present exists throughout Britain, makes a statement that the
general bad growth of our forest trees as timber trees is attribut-
able to the fact that —

'Mixed planting is generally practised, in sharp contrast to what
Continental foresters call " pure forest " — that is, a woodland composed
of one species of tree. This is in itself a hindrance to profitable manage-
ment, because pure forest is much more easily tended than mixed planta-
tion, and the timber is more readily marketable.'

In England we are not accustomed to look upon the French
as a particularly practical nation ; but, in regard to the treatment
of their great forests, with which 17-7 % of the total area of
France is clothed, it must be admitted that, although the
methods adopted are not quite so scientific as in Germany, they
are generally of a very high standard and thoroughly practical.
Now in France, where sylviculture is well understood and
practised, mixed forests form the great bulk of the woodlands,
as, according to the last statistics available (Mathieu's, for

I 2

n6 Studies in Forestry [CHAP. vi.

1876) these formed more than 70 % of the total wooded area,
as exhibited in the following data ] : —

Mixed forests of —

Broad-leaved trees 50-3 % of total wooded area.

Broad-leaved trees and Conifers 17-6 % ,, ,,

Conifers 2-5% „ „

Pure forests of —

Various species of Trees 26-7 % „ „

Data for Germany are not available. The imperial statistics
for 1884 only showed 65 % of the total forest area (which aggre-
gates 26 % of the empire) as covered by coniferous crops,
whilst 34'5 % were clothed with broad-leaved species ; but the
area of mixed forests was not computed.

In sharp contrast to Sir Herbert Maxwell's dictum, is the
following matured opinion of the most celebrated of living
sylviculturists, Prof. Gayer of Munich 2 : —

* We may say, in general, that the leading principle in the rational and
economic treatment of woods must be less in the direction of pure than
of mixed crops, and that the degree to which, and manner in which, mixed
Woods occur throughout any system of management must be considered
as the best test and standard by which one can estimate the knowledge and
the capacity of those to whom are entrusted the duties of obtaining the
best possible results from any given conditions as to soil and situation.'

And, to prove that this is no mere new nostrum of these
latest days, it may be permitted to quote the late Prof.
Grebe of Eisenach, formerly Director of the Saxon forests in
Thuringia, who wrote as follows in 1867 3 : —

'The more recent tendency of forestry is — and with full justification —
towards the formation of high timber forests containing a suitable mixture
of different species of trees, thereby duly acknowledging the manifold
advantages to be gained with respect to increased outturn, more valuable
assortments of timber, greater general security, and greater power of
resisting inimical influences.'

1 Gayer, Der gemischte Wald, 1886, p. 9.

2 Der Waldbau, 3rd edit., 1889, p. 178.

3 Die Betriebs- und Ertragsregelung der Forste, 1867, p. 151 (2nd edit.,
1879). See also Preface to the author's British Forest Trees, 1893.

CHAP, vi.] Advantages of Mixed Woods 1 1 7

As arboriculturists we have nothing to learn from con-
tinental nations ; but as sylviculturists we may learn a very great
deal indeed. There is a need for the dissemination of sound
knowledge, in the first instance regarding the proper density at
which sowings and plantations should be made, and in the
second instance as to that which should be maintained afterwards
at all the various stages of their development. Sir Herbert
Maxwell attributes the formation of mixed woods in great
measure to neglect in cutting out the nurses originally planted
for the purpose of stimulating the crops to quicker growth
and of keeping down weeds. He says — and the statement
is undoubtedly a true indictment of neglect and incapacity in
those charged with the supervision of woodlands : —

' Want of system leads to irregularity in thinning out the nurses,
which often remain to compete with what was intended to be the per-
manent wood, and the result is a mixed plantation.'

As will be pointed out in another chapter (see p. 183), such
nurses should be removed during the weedings and clearings of
the young woods ; whilst, if for any reason they have been
allowed to stand till thinnings commence, an opportunity is
then still given to remove them gradually.

It would, however, hardly be rational to set up these mis-
managed woods — admittedly the outcome of neglected tending
operations, and not at all in conformity with the intentions or
wishes of the proprietor — on anything like the same platform as
mixed woods formed after deliberate consideration as to the
best kinds of trees suited for each portion of the soil to be
utilized under woodland crops. But, where mixed woods, are
formed by capable foresters, they have, in comparison with pure
forests, the great advantages of denser growth, larger and finer
production of timber both as regards quantity and technical
quality, comparative immunity from throwing or breakage by
wind, snow, or ice, as well as from dangers arising from insects,
fungoid diseases, and fire ; whilst against all these very solid
advantages only one drawback can be named, — that the

u8 Studies in Forestry [CHAP. vi.

tending of such mixed woods is much more difficult, and that
their proper formation and management require considerably
greater knowledge of sylviculture than is requisite for the
treatment of pure forests.

In comparing the advantages and disadvantages of mixed
woods, relative to pure crops, the following matters are worthy
of consideration : —

Advantages —

1. A greater density of crop is obtainable.

2. The soil is maintained in better condition as to pro-
ductive capacity than under many pure crops.

3. A larger percentage of the outturn is available as timber
for the higher technical purposes, at any rate in mixed crops of
broad-leaved species of trees.

4. Demands of varying nature for timber can more easily
be supplied.

5. It is easier to modify or transform the crop at any one
time so as to meet the present or the probable future require-
ments of the market.

6. Experience has shown that mixed crops are much less
exposed than pure forests to dangers from external causes
whether of organic or inorganic origin.

7. Natural regeneration of mixed woods is on the whole
easier than with pure crops.

8. By concentration of various species in one series of crops
the operations of tending, harvesting, &c., can be carried out
most economically.

Disadvantages are summed up by Gayer in the following
words * : —

'It is easy to understand that mixed crops make higher demands on
the capacity of the sylviculturist, as it is much more troublesome and
difficult to give proper care and attention to each of several species in

1 Waldbau, p. 216.

CHAP, vi.] Advantages of Mixed Woods 119

a mixed crop than to look after one species only; but when weighed
against the many solid advantages offered by mixed crops, this drawback
can surely seldom be seriously taken into account.'

Mixed woods are such as are formed by two or more species,
of which the matrix or ruling species should be one that is
capable of safeguarding and retaining the productive capacity
of the soil against insolation and the exhausting action of
winds. The subordinate or dependent species of trees may
be admixed with the ruling species either in clumps or hursts \
in groups or clusters, in patches or knots, in rows or fines, or
merely scattered about singly as individuals. In mixed woods,
wherever natural regeneration is permitted to the fullest extent,
there will be a tendency for genera of trees with heavy seeds
(Oak, Beech, and among Conifers the Silver Fir) to reproduce
themselves in clumps on the patches of soil best suited to
them ; whilst trees with lighter and often winged seeds (like
Birch, Aspen, and Willow) will have a much greater repro-
ductive power of asserting themselves individually and in
small knots at some distance from the parent trees.

i. A greater Density of Crop is obtainable. — Wherever the
area under woodlands is of any considerable extent there are
almost certain to be many variations of soil and situation with
regard to the nature and the depth of the earth, its degree of
moisture, its aspect, &c. ; and the best, most complete, and
most economical utilization of the soil can only be expected
when each such varying portion is stocked with the species of
tree best suited for growing there. For, when thus growing in
admixture on the patches of soil most suitable to their natural
requirements, it will be found that the various species of trees
do not thin themselves so soon as they otherwise must on soils
less favourable to their natural development and requirements.
And, by thus maintaining close canopy for the longest possible
period, they not only avail themselves more fully of the pro-

1 The older term Bosc, often referred to by Manwood (History of the
Forest Laws), is now obsolete.

I2o Studies in Forestry [CHAP. vi.

ductive capacity of the soil, but also conserve this in a higher
degree than could otherwise be the case ; whilst, at the same
time, they are able to utilize to the utmost possible extent the
chemical power of the light requisite for the due performance
of the assimilative functions by the foliage. This closer canopy
and greater density of crop generally become of all the more
importance as the crops advance in age, and begin to approach
maturity ; hence in this prolonged maintenance of canopy lies
the principal value of many kinds of mixed crops.

2. The Soil is maintained in better Condition and Productive
Capacity than is the case under many kinds of Pure Crops. Pure
woods of thinly-foliaged and light-demanding genera of trees,
like Oak, Ash, Maple, Larch, and Pine, when once they have
completed their chief growth in height and have begun to
exhibit their natural specific tendencies with regard to increase
of growing-space, are unable to conserve for themselves the
general quality and productive capacity of the soil in conse-
quence of the interruption of canopy, the decrease in the
number of stems forming the crop, and the subsequent bad
effects to the surface-soil wrought by insolation and exhausting
winds. Hence the expenses of underplanting are usually un-
avoidable. But as, during the earlier periods of development,
these light-demanding genera are at the same time of more
rapid growth than the shade-bearing kinds, Beech, Spruces,
Silver Firs, and Hornbeam, in mixed crops they can, with now
and again a little assistance in the way of tending wherever
necessary, usually assert themselves as the predominating poles
and trees, thereby acquiring just the position naturally best
suited for their present growth and good future development. At
the same time the shade-bearing genera, forming the dominant
and more or less dominated classes of the crop, mechanically
protect the soil against the exhausting and deteriorating in-
fluences of sun and wind ; whilst, by their richer fall of leaves,
they contribute valuable material for the formation of humus
or mould, that natural manure of woodlands, which exerts very

CHAP, vi.] Advantages of Mixed Woods 121

beneficial influence in enhancing the productive capacity of
most classes of woodland soil.

Pure forests make constant demands of one unvarying sort ^
on the land, so that on soils of merely average quality there is
far greater risk of one particular class of nutrients being rapidly
diminished and being less readily available than when a variety
of species of trees induces a more general demand for the
various different kinds of mineral food-substances. Thus,
whilst in general the chemical composition of dry woody-
substance of the different kinds of timber is, in round figures,
approximately constant as follows l : —

50 % Carbon, 42 % Oxygen, 6 % Hydrogen, i % Nitrogen, and i %
Ash (or mineral residuum),

yet the nature of the substances found in the ash varies
greatly in the different species of trees. Thus, with regard to
lime, the principal constituent in the ash, there are 3-5 times
as much found in Oak, and 2-3 times as much in Beech, as
in the Scots Pine, which, however, exhibits more than Birch.
Taking the quantity contained in Scots Pine as unity, then
the amount of potash requisite is about 5 times greater in
Beech, 3! times greater in Oak, 2\ times greater in Silver Fir,
twice as much in Larch and Birch, and about if times as
much in Spruce. And again, with regard to Phosphoric Acid,
the wood of Beech contains in its ash about 2j times as much
as Scots Pine, Oak 3 times as much, Birch twice as much,
Larch and Silver Fir i^ times as much, whilst Spruce contains
considerably less.

There can be little doubt that the theory enunciated by
Georg Ludwig Hartig, the father of Dr. Theodor Hartig, and
grandfather of Prof. Robert Hartig (of Munich), that the soil
can be most thoroughly utilized by an admixture of shallow- \/
rooting species with deep-rooting, in order that each may draw

1 Weber, Die Aufgaben der Forstwirthschaft (Lorey's Handbuch, &c.),
1886, vol. i. pp. 72 and 62. More accurate details have already been
given in Chapter IV. pp. 82-85.

12,2 Studies in Forestry [CHAP. vi.

its main supplies of nutriment from a different layer of soil —
although long scoffed at by a certain class of sylviculturists
(headed by Hundeshagen), who saw the advisability of admix-
ture explained solely by the relation of the various species
towards light and shade — is based on a principle equally sound
from the theoretical and the practical points of view ; for it is
a fact that, in the majority of mixtures acknowledged to be good,
the root-systems of the different species vary considerably in
depth.

That, in addition to greater density of growth, which has
already been referred to in the previous section, the productive
capacity of the soil is at the same time more thoroughly utilized
can be proved, if requisite, by actual crop measurements made
in Silesia in 1880. These showed that, on soil similar as
to conditions and quality, the average annual increment in
eighty-year-old crops was : —

Cubic ft. per acre.

Pure forest of Scots Pine 18-3

Pure forest of Spruce 19-9

Mixed forest of Scots Pine, Spruce, and Silver Fir . 23-5

But, beneficial though the influence of the overshadowing of
the soil by the leaf-canopy undoubtedly be, there are occasions
on which even it may perhaps be carried farther than is de-
sirable or advantageous ; as, for example, in dense woods of
pure Spruce or Silver Fir, where the close, thickly-foliaged
canopy overhead, and the deep sponge-like growth of moss
covering the soil, intercept and retain a very much larger pro-
portion of the atmospheric precipitations, both in winter and
in summer, than deciduous trees or other coniferous species
(Pines) with somewhat thinner growth. For whilst, of all the
precipitations in the course of the year, on the average about
25 % are intercepted by the foliage and branches, and 75 %
reach the soil in woodlands, these data vary considerably
according to the kind of tree forming the crop. The averages

CHAP, vi.] ^Advantages of Mixed Woods

123

of long-continued observations in Switzerland, Prussia and
Bavaria gave the following results l : —

Species of Tree.

Percentage of total Atmospheric Precipitations

reaching the soil.

intercepted by, and evaporated
from, the foliage and branches.

Deciduous

Larch . .
Beech . .

85
81

'5
19

Evergreen

Spruce . .
Scots Pine

76

70

24

3°

And of the moisture reaching the soil, Weber calculated that —
leaving out of account the transpiration of the foliage for which
the supplies of moisture are withdrawn by the roots from deeper
layers of soil — its disposal was as follows : —

Woods.

Amount evaporated.

Remained in the soil.

Beech ....
Spruce ....
Scots Pine . . .

per cent.
40-4

45-3
41.8

per cent.

59-6

54-7
58.2

Owing to the smaller percentage of precipitations reaching
the ground, to the larger evaporation from the soil-covering, and
to the strongly hygroscopic nature of the moss, we can easily
understand the dried-up appearance that soils under pure
Spruce woods sometimes assume in early summer, just at the
time when transpiration is becoming most active, and when the
greatest necessity exists for a free supply of moisture from the
soil so as to permit of the assimilative and productive processes
going on to their fullest possible extent.

In former times, when the work of nature was comparatively
uninterfered with, mixed woods almost everywhere formed the

1 Compiled from data given by Weber, op. cit., pp. 47-49-

124 Studies in Forestry [CHAP. vi.

covering of the uplands, and the hilly tracts, and stretches not
yet required for arable land or pasturage. Rain and snow were
then more equably precipitated over the soil itself, and were
not so apt to be sucked up and retained by a strongly hygro-
scopic surface-growth of weeds and mosses, which likewise is
exceedingly active in afterwards utilizing and exhausting the
supplies of moisture contained in the upper layer of the soil.
The aqueous precipitations were, on the other hand, preserved
by a good layer of dead foliage and of the humus or mould
resulting from their decomposition, and could thus percolate
normally into the soil downwards towards the subsoil, so as
to maintain a tolerably equable distribution throughout the
whole, owing to the effects of gravity being counterbalanced
by capillarity.

Whilst Boussingault has shown in France that, with increase
in the area stocked with conifers, a gradual local sinking of
the water-level below the soil has taken place, practical sylvi-
cultural experience in Germany has also shown that— except
at high elevations with humid climate — extensive plantations
of pure Spruce rapidly lead to a marked decrease in the
quantity of soil-moisture. And Runnebaum's comparative
investigations in 1885 showed that in mixed woods of Scots
Pine with Beech the conditions relative to soil-moisture were
more favourable for tree-growth than in pure forests of Pine.
It is, however, only right to point out that this must to
a certain degree be ascribed to the influence exerted on the
soil by the good humus or mould formed by the dead foliage
of the Beech.

3. A larger percentage of Timber is available for the higher
technical purposes^ at any rate in mixed crops of broad-leaved
genera of trees. Many of our more valuable kinds of timber
trees are, when once they have passed through the initial stage
of pole-forest, so light-demanding, and so dependent on increase
of growing-space for the continuation of vigorous growth and
further normal development, that they are unable to maintain

CHAP, vi.] Advantages of Mixed Woods 1 25

for themselves such degree of density of canopy as is requisite
for the due conservation of the productive capacity of the
soil, and for the prevention of its gradual, but inevitable,
deterioration.

Even on the better classes of soil, pure crops or mixed woods
of valuable light-demanding species only — Oak, Ash, Maple,
Larch, Pine, &c. — grown without admixture of any shade-
bearing species, are apt to thin themselves out naturally at so
rapid a rate as to favour branch and coronal development to
an extent inconsistent with a studiously economical utilization
of the woodland soil. This, too, is a drawback not in any way
obviated by underplanting. But an admixture of one or other
of the shade-bearing species (Beech, Hornbeam, Spruces, Silver
Firs), according to the nature of the soil and situation, not only
protects and stimulates the productive capacity of the soil, but
at the same time acts mechanically in stimulating to growth in
height, and in preventing the formation of short boles and of
stout branches that would prejudice the technical utility and
the market value of the timber produced.

It is a matter of practical experience, needing no discussion,
that Larch and Scots Pine form more valuable boles, and
contain a larger percentage of heart-wood, when grown in
admixture with Spruce or Silver Fir than as pure crops.
And all the more valuable species of deciduous trees gain
in shape, increment, and age up to which they may be advan-
tageously grown from technical and financial points of view,
when the Beech, or on moister descriptions of soil, the
Horn-beam, forms a part of the crop. But these beneficial
effects are even more distinctly noticeable when mixed crops
are formed, on suitable soils, of conifers and broad-leaved
trees — even when all are shade-bearing, as in the case of
Spruce and Silver Fir forming crops along with Beech.

In consequence of the greater increase in the total quantity of
timber produced in mixed crops as compared with pure woods,
and of the more favourable circumstances affecting the forma-

126 Studies in Forestry [CHAP. vi.

tion of long, full-wooded, clean stems with comparative freedom
from knots and branches, the timber produced attains its
highest possible technical and financial value. And owing to
the tendency towards confinement of the crown to the upper
part of the tree only, to which these favourable results are
practically due, a considerable portion of the upper wood is
comprised within the bole that must otherwise have been
dissipated in the formation of branches of comparatively little
technical or monetary value. By concentrating the energy
of growth in good bole-formation, the actual cubic content
of the stem is not only increased, but also its value per
cubic foot, as this rises with the length, straightness, and
freedom from flaws occasioned by knots and branches.

4. Demands of varying nature for Timber can more easily be
satisfied. This statement may almost be said to be of an
axiomatic nature. It plainly stands to reason that, where several
species of trees are grown together on the same area, the classes
of material periodically yielded during the necessary operations
of tending, thinning, and removal of diseased or already mature
individual stems, must offer a considerably greater variety to
the different classes of local consumers than is possible in the
case of pure forests. And the same holds good when the period
comes for the harvesting of the mature crop. At the same time
that variations in the local demands can be more easily satisfied,
the wider, more general, and more important requirements of
timber marts at some distance can also be better met by
mixed than by pure forests ; whilst there is less danger of the
over-production of any one kind or assortment of timber to
any such extent as might possibly glut the market and cause
a sudden fall in the prices obtainable.

5. // is easier to modify or transform the Crop at any. time so
as to meet the present or the probable future requirements of the
market. Of the necessity for such considerations no better
example can be given than is shown in the Crown Oak woods
of the New Forest, Alice Holt, Parkhurst, and the Forest of

CHAP, vi.] Advantages of Mixed Woods 1 27

Dean, which were planted up for the purpose of supplying Oak
timber for the use of our navy. But now all our ships of war,
and the best classes of liners, are constructed almost entirely
of iron or steel and of Teak timber from Burma. Teak — in
place of corroding iron with which it comes in contact, as Oak
does owing to its tannic acid — is, through an essential oil
contained in it, preservative of the steel screws, bolts, &c.
But notwithstanding the present extensive and ever-increasing
use of substitutes like iron in place of timber, and the vast
improvements in communication — by means of which the
forest produce of far-distant countries can be brought to
build the navies of Europe, and even to pave the streets of
London — timber is, along with gold, almost the only com-
modity which has not during the past half century depreciated
in relative exchangeable value with most other articles of com-
merce. All classes of timber do not, however, command equally
favourable market quotations. But the sagacious sylviculturist
will easily know from a study of selling prices, of the stocks
of timber held at the chief marts, and of the reports as to
the probable quantity and the quality of imports from abroad,
what kinds and classes of timber are most likely to be re-
munerative in the immediate future. And it is self-apparent
that he will be in a far better position to tend and foster
those species which hold out the fairest financial promise,
when several kinds of trees are growing together in mixed
woods, than when each species forms a pure forest worked
quite independently of the other crops.

Mention has above been made of the Oak woods planted by
the Crown for the future supply of navy timber, which is not
now required. As crooks were formerly an essential before
the framework of hulls was made of iron or steel, the most
economical method of producing them was to grow the Oaks
as standards enjoying as full supplies of light and air as possible.
But, under ordinary circumstances, the most economical manner
of growing Oak timber for general technical purposes (requiring

128 Studies in Forestry [CHAP. vi.

length and full-woodedness of bole, straightness, and freedom
from knots or twists), and for the highest possible financial
returns, is undoubtedly to confine the individual stems within
the least growing-space sufficing for their actual requirements
as to light, warmth, and the normal activity of their assimilative
organs, until the main growth in height has been completed, and
until natural demands for freer exposure to light and air, and
greater lateral expansion of the crown of foliage, can no longer
profitably remain unheeded. Crops, however, which have been
originally formed and treated with the express view of yielding
crooked stems, cannot be forced later on to form fine, straight,
clean boles showing a minimum of tendency to tapering growth
near the top-end. Such existing crops must first be cleared and
regenerated before others can be formed and produced with
the express intention of utilizing the productive capacity of
the soil in the fullest and most economical manner.

And, on the other hand, whenever present market rates offer
inducements for the speedy clearance and sale of certain
classes of timber, advantage can much more easily and con-
veniently be taken of the favourable opportunities of disposal
without at the same time threatening the well-being of the
woodlands by departing to a greater or less extent from the
normal methods of treatment that may have been forecast by
the provisions of the Working Plan. And a Working Plan
must be the basis of all operations in any well-managed
forests.

In short, when the growing-stock consists of one series of falls
of mixed woods, varying in age from zero to maturity, in place
of having a similar series for each of the species of trees grown
by themselves in pure crops, the Working Plan is capable of
much greater elasticity of treatment. It affords larger scope
for the somewhat premature utilization of portions of crops,
whenever the market may be exceptionally favourable for that
particular kind or assortment of timber, without necessarily
exposing the soil to deteriorating influences likely to weaken

CHAP, vi.] Advantages of Mixed Woods 129

its productive capacity. By removing or diminishing the
number of individuals of other species during the ordinary
operations of thinning and tending, or, if necessary, even in
special revisions for this purpose, the probable immediate
future requirements of the timber marts within reach can be
more economically, conveniently, and speedily arranged for
than when one has to deal with pure forests only.

As an example of this the safety-match industry throughout
Norway, Sweden, and Germany, may be instanced. The
woods best suited for the requirements of this industry are
Willows, Aspen, and Poplars ; and it very frequently occurs
that the match-factories have to be removed from one district
to another solely on account of the supplies of suitable timber
falling off. The heavy expenses thus involved mean that if
steps were taken to provide better supplies of these softwoods,
the factory proprietors could well afford to pay higher rates to
secure them. The full advantage of such favourable markets
can only be derived when patches of moist soil have been
utilized for the growth of these softwoods in mixed deciduous
forests.

6. Experience has shown that Mixed Woods are much less
exposed than Pure Forests to dangers from external causes,
whether of organic or inorganic origin. Shallow-rooting species,
like the Spruce in particular, when mixed with deeper-rooting
kinds of trees, like Pine, Larch, and Silver Fir, are much less
exposed to be damaged or thrown by storms than when grown
in pure crops ; whilst conifers of all kinds suffer less damage
from wind, fire, snow, ice, insects, or fungoid diseases, when
grown in admixture with broad-leaved trees than if forming
pure woods, or even mixed woods consisting of conifers only.

If associated along with broad-leaved trees, conifers usually
attain a better development than under any other circum-
stances. This alone would partly account for the decreased
liability to attacks from insect enemies ; whilst, at the same
time, a much better check is kept on any tendency to increase

K

130 Studies in Forestry [CHAP. vi.

in the number of insects, as insectivorous birds are much
more frequent where broad-leaved trees exist than in purely
coniferous woods. But even where attacks of noxious insects
take place in such mixed woods, they seldom become wide-
spread over all species, and never necessitate the clearance of
whole crops, as unfortunately sometimes happens in the case
of Spruce and Scots Pine.

Trees like the Oak, which are somewhat sensitive to late
frosts in spring during the early period of their growth, are
apt to suffer less damage whilst growing under the protection
of hardier kinds of quicker development, like Birch and Scots
Pine. And again, in mature mixed woods of conifers and
broad-leaved species, the technical value of the boles is less
likely to be diminished by frost-shakes than when these latter
are grown by themselves.

The woodland proprietors, of Scotland especially, know
what ravages can be committed in pure Larch forests by the
fungoid disease, due to Peziza Willkommii^ which causes
a cankerous outbreak on the stems, and induces crooked
growth. And in pure woods of Spruce, Silver Fir, and Scots
Pine, red-rot and other fungoid diseases of the stem and the
root-system, occasioned by Trametes radiriperda, T. pini,
Aetidium elatinum, Peridermium pini, Agaricus melleus, &c.,
are often productive of very serious sylvicultural and financial
results. Speaking of ' leaf-shedding] a disorder to which Scots
Pine is liable at an early age — an infant ailment, due some-
times to frost, or to the drying-up of the needles when
stimulated to transpiration by bright sunshine in winter or
early spring, whilst the soil is still frost-bound and unable to
yield fresh supplies of moisture to replace that evaporated,
but in many other cases undoubtedly occasioned by a fungus,
Hysterium pinastri, — Gayer says * : —

' About thirty years ago the sporadic occurrence of " leaf-shedding " in
Scots Pine was merely " an interesting observation" whereas now it is

1 Der gemischte Wald, 1885, p. 24.

CHAP, vi.] Advantages of Mixed Woods 131

nothing short of a wide-spread calamity all over Germany. At first, two
to four-year-old seedling growth was chiefly attacked, but nowadays
sowings and plantations are both liable to be affected, and it is even be-
ginning to attack young thickets. And wherewith shall we replace the
Scots Pine, if even it refuse to serve our purposes ? R. Hartig says, at
page 40 of his book on the Diseases of Trees l : — " the best prophylactic
measure against the occurrence and spread of epidemics is the cultivation
of mixed forest crops.1' '

A direct and fuller quotation may, however, also be per-
mitted from Professor R. Hartig's celebrated work, in which
the opening words of the Introduction are : —

' The transformation in the natural woods of Germany, the formation
of pure, equal-aged crops of the same species of trees, instead of the
composite mixed forests and copses made up of all sorts of trees of all
ages, and especially the restriction of the broad-leaved species by the
formation of pure crops of conifers, have during the present century,
and most particularly in the last few decades, threatened the well-being
of our woods to an extent which was formerly unknown. And it is
chiefly the enemies belonging to the animal and vegetable kingdoms
which find in the recent developments of our woodland economy the
conditions favourable to their increase in enormous strength, so that the
complaints made concerning larger and ever larger devastations, appear
in no wise unfounded.'

But it is perhaps more with regard to damage caused by
injurious insects, than in any other way, that the beneficial
effects of the formation of mixed crops may be judged of, so
far as Spruce and Scots Pine are concerned. Simultaneously
with the disappearance of the natural mixed crops, which can
be proved to have formed the chief portion of the wooded
areas throughout Germany during the first quarter of the
present century, and with the formation of extensive pure
forests of coniferous species, the damage done by insect
enemies has increased enormously, and has on several occa-
sions during the past half-century attained the dimensions of
actual calamities, sometimes of national importance.

Thus, referring to the ravages of the Black Arches, * Nun/

1 Lehrbuch der Baumkrankheiten, 1882 (2nd edit. 1889, p. 55).
K 2

132 Studies in Forestry [CHAP. vr.

or Spruce moth (Liparis monacha) which — together with the
bark-beetles (Bostrychini and ffylesinini) that followed it and
attacked the stems left in a sickly condition of growth — between
1853-1862 devastated the coniferous forests of eastern Prussia
and western Russia over about 7,000 geographical square
miles, and necessitated the felling of over 420,000,000 cubic
feet of timber, Hess recommends *, as the first measure of
prevention, ' avoidance of the formation of pure forests of Spruce
or Scots Pine ; formation of mixed crops of suitable species.1
This same insect has quite recently, in southern Bavaria and
western Austria (1889-1891), necessitated the clearance of
40,000 acres, mostly of pure Spruce; and during 1892 an
outlay of £75,000 was incurred solely in order to combat its
further attacks in the State Forests of Bavaria alone 2.

That the calamitous extent to which attacks by moths
(Bombycidae\ bark-beetles (Scolytidae), and weevils (Curcu-
lionidae] occur every now and again in Germany, arises from
the want of natural admixture of different species is a fact
which receives practical recognition in the endeavours now
everywhere being made in order to effect a re-transformation
to the former mixed state of the woodlands. As Gayer
says 3 : —

* Endeavours are in general being made to prepare the way for
a return to mixed forests in all suitable localities. And that, face to face
with the late fearful devastations (by insects) in the Spruce forests of
southern Bavaria, these principles should be even more strongly insisted
on, can easily be understood.'

It is a well-known matter of experience that forests of broad-
leaved species are not exposed in anything like the same degree
to serious damage from insects. Even after crops may have
been stripped of their spring flush of leaves — as sometimes

1 Der Forstschutz, vol. i., 1887, p. 355.

a A detailed account of this moth and its ravages will be found in the
Transactions of the Highland and Agricultural Society of Scotland, 1893,
pp. 176-207.

3 Zeitschrift fur Forst- und Jagdwesen, 1892, p. 386.

CHAP, vi.] Advantages of Mixed Woods 133

happens when swarms of caterpillars of the Processionary Moth
( Gastropacha processionea) defoliate the Oak, for instance — the
injury is not of a permanent nature, owing to the much larger
reserves of starchy matter accumulated by the broad-leaved
kinds of trees, and the stronger reproductive and recuperative
capacity with which they are consequently endowed.

By admixture of broad-leaved genera, therefore, and parti-
cularly of Beech or Hornbeam, along with conifers, the danger
of attacks from insects can be greatly diminished without
prejudicing the other advantages derivable from the formation
of mixed crops. Thus Danckelmann states 1 that woods
which consisted of four-fifths Scots Pine and one-fifth Beech
or Hornbeam practically did not suffer at all in Prussia from
any of the insect calamities caused by moths between 1860-
1880, whilst the pure woods of Pine suffered severely.

The beneficial effect of mixed crops in obviating extensive
injuries from insect enemies is perhaps almost the only point
concerning which German sylviculturists are absolutely unani-
mous. That such calamities as have from time to time
occurred in different parts of Germany have not taken place
similarly, though on a smaller scale, in any part of Britain is,
most probably, solely due to the happy chance or the prudent
sagacity of woodland proprietors imitating nature by the forma-
tion of mixed woods rather than pure forest over areas of
considerable extent. Experience on a large scale in Germany
has shown that the number of dangerous insects is not only
less in mixed than in pure crops, but also that at the same
time the number of insectivorous birds is greater. Should
Sir Herbert Maxwell's advice be extensively adopted, however,
the days of such comparative immunity will almost to a cer-
tainty be numbered.

What is true about dangers from injurious insects, may also
be repeated as to windfall and breakage from storms, and to
damage wrought by accumulations of snow or ice on the
1 Zeitschrift fur Forst- und Jagdwesen, 1881, p. I.

J

134 Studies in Forestry [CHAP. vi.

crowns of trees. In these respects again, conifers suffer to
a far greater extent than broad-leaved genera, among which
Beech suffers more than Oak, Ash, Maples, or Elms. Of all
forest trees Spruce is, owing to the shallowness of its root-
system, most apt to become windfall ; whilst Scots Pine is, owing
to the brittleness or low degree of elasticity of its branches,
more apt to have its crown injured by violent winds or heavy
accumulations of snow or ice. A year seldom goes past
without the necessity of registering damage from one or other
of these causes ; though, fortunately, destructive storms like
the N.E. gale of November 17, 1893, in Scotland are rare.

To prevent, so far as possible, damage from storms, Hess1
recommends the admixture of. deep-rooting species along
with those which have shallow root-systems, and adds that —

' The injuries caused by storms during the last decades should be
a warning to those sylviculturists who are over-eager to transform
forests of broad-leaved trees into coniferous woods ; such transforma-
tions should only take place when justified by extreme necessity,'

as, for instance, when soils have become greatly deteriorated by
faulty treatment.

Accumulations of snow on the crowns of trees become
diminished in mixed crops, especially when the conifers are inter-
spersed with broad-leaved trees. Besides allowing the snow
to reach the ground, the bare crowns of the latter afford some
slight support to the snow-laden crowns of the former. Even
when breakage results, it is then more of an individual nature,
and does not extend throughout large patches, or over the
whole of the crop as sometimes happens in Spruce and Pine
woods. Here again Hess lays down 2, as the first sylvicultural
measure to be taken for the prevention of damage from snow
and ice : —

1 The avoidance of the formation of pure forests of species liable to
suffer. Scots Pine is entirely out of place in such localities. So far as

1 Op. cit.t vol. ii., 1890, p. 287.

2 Op. cit., vol. ii. p. 315.

CHAP, vi.] Advantages of Mixed Woods 135

possible, broad-leaved species of trees should be scattered, in sufficient
quantity and at convenient distances, throughout Spruce woods.'

That similar drawbacks are also incidental to the formation of
too extensive pure crops of either cereals or roots in agricultural
utilization of the soil, may be seen by a reference to Fream's
Agriculture \ from which the following short extract may here
be given : —

' In other words, side by side with the excessive, or exclusive, cultiva-
tion of one kind of plant, the pests — whether insects or fungi — which
prey upon that plant may be expected to become more abundant, for
they find their victims literally crowded together, and therefore ex-
tremely accessible.'

7. Natural Regeneration of Mixed Woods is on the whole
easier than in the case of Pure Crops. This is but of minor
importance compared with many of the other more substantial
advantages offered by mixed crops. It is due to the special
treatment and tending which must be bestowed on the crops
in order that, so far as possible, each species may be placed in
the natural conditions most favourable to its growth and further
development. With some attention given towards securing for
each kind of tree the soil and situation best adapted for it,
a healthier growth, and a richer production of seed are natural
results, owing to larger secretions of starchy reserves of surplus
nourishment. Hence regeneration from seed in small groups
and patches is comparatively easy, and is more likely to be
successful than when one single species predominates over
the whole woodland area notwithstanding the usually frequent
changes with regard to the depth of soil and the quantity of soil-
moisture. The species of tree which gains most in this way is
again the Spruce, which cannot usually be regenerated under
parent standards owing to danger of windfall ; but, when treated
thus in mixed crops, it can be reproduced without the danger
otherwise threatened to young seedling crops by weevils (Cur-
culionidae\ The natural regeneration of the other great shade-

1 Elements of Agriculture, 4th edit. 1892, p. 333.

136 Studies in Forestry [CHAP. vr.

bearing species, Beech, Hornbeam, and Silver Fir, offer in
general but slight difficulty. In mixed crops these trees
would usually be reproduced naturally and cleared away as
soon as possible, thus leaving the young seedling crop to
grow up as underwood under the light-demanding standards
of other kinds of trees left to thicken into stems of fine
marketable dimensions.

In the regeneration of mixed woods it will be almost in-
variably found advisable to plant out large transplants of the
more valuable species of timber trees ; for their disposal through-
out the soil-protecting, ruling species, and the advantage in age
and development which it is desired to give them over it, are
much better ensured by this than by any other means. But,
at the same time, wherever special conditions of soil render
the natural regeneration of the light-demanding species desir-
able, this can also be effected : and any blanks that remain
afterwards can easily be filled up with one or other of the
shade-bearing and soil-protecting kinds of trees.

8. By Admixture of Various Kinds of trees in one series of
Crops, the operations of tending, harvesting, &°<r., can be conducted
most economically. This is another advantage of an almost
axiomatic nature. Suppose, for example, that any landowner has
800 acres of woods, which he wishes to have stocked with the
four kinds of trees, Larch, Scots Pine, Spruce, and Silver Fir,
worked with a rotation of say 80 years each. If formed into
pure forests, when once the crops were in full working order so
as to yield annual falls of timber, there would need to be four
distinct series of annual crops from 0-80 years old, in place
of one series of mixed crops of the same ages ; and all opera-
tions of thinning, tending, felling, extracting, and reproducing
would have annually to be carried out in four different direc-
tions and over small areas of 2\ acres each, instead of being
concentrated on one compartment or compact area of 10 acres
in extent for each annual crop. This latter method represents
a very great saving both in time and money; hence when

CHAP, vi.] Advantages of Mixed Woods 137

woodland estates are small, the formation of mixed crops is
practically the only way of obtaining an annual outturn con-
sisting of more than one kind of timber.

Such are the advantages which Mixed Woods possess over
Pure Forests. And what can be urged against them ? Nothing,
except that their management needs a better knowledge of
Forestry, and greater care and attention on the part of the
forester.

In the above, Sir Herbert Maxwell's assertion that the forma-
tion of mixed woods is ' in itself a hindrance to profitable
management ' has been disproved ; and it has been shown that,
on the contrary, they have many advantages over pure forests.
By no means the least of these is the greater security with
which the crops may be expected to attain their normal
maturity. But, in sylviculture, there are no hard and fast rules
applicable to all soils and situations; and circumstances can
often occur not only to justify, but even to recommend, the
formation of pure forests. The case has been very well put
by Heyer in the following words * : —

* Notwithstanding the manifold and decided advantages which mixed
forests offer in general, the formation of pure crops, to be permanently
worked as such, is by no means precluded ; for they in many cases offer
such peculiar advantages as render it advisable or even necessary to
retain or form them. Where, for instance, the local market or the
nature of the soil and situation (e. g. when the soil is either very wet or
very dry) is favourable to one particular species of tree only, that
individual kind should be cultivated. But, at the same time, such cases
are rather exceptional ; hence, as a rule, the formation of mixed woods
is certainly to be recommended'

1 Der Waldbau* 4th edit. 1891, p. 39.

CHAPTER VII

CONCERNING THE FORMATION AND GENERAL
TREATMENT OF MIXED WOODS

IN the preceding chapter it was shown that although in pure
forests, where only one species of tree has mainly to be taken
into account, each block of woodland may have the advantage
of being easier to work as regards its tending, the harvesting of
its mature crop, and its regeneration (though not necessarily,
so far as the latter is concerned), yet such woods are much more
exposed to climatic dangers like extensive windfall over areas
covered with Spruce, or damage from snow and ice in Pine
tracts, or devastation from noxious insects, as in the case of
both Spruce and Pine, or fungoid diseases, as in Larch, Silver
Fir, Spruce, and Pine. Pure forests cripple and confine the
management to one kind of timber practically in any one
locality ; and if the market for that particular kind of wood
falls so as to become unremunerative, it is not easy all at once
to transform the woods into more profitable crops.

It will in general, therefore, be considerably to the advan-
tage of landowners to avoid the formation of pure forests over
extensive areas, though it may sometimes happen that there
is very little free choice about the matter. Thus, when the
soil is too poor for mixed crops of Oak, Ash, Maple, Sycamore,
Elm, Larch, &c., to be grown along with Beech, Hornbeam,
Spruce, and Silver or Douglas Firs, the choice is often confined
to conifers alone, or on the poorest classes of soil to the Scots

CHAP, vii.] Formation of Mixed Woods 139

and Black Pines alone, if timber crops are to be grown at all ;
or undrained tracts may be better suited for Alders, Willows,
or Poplars than for any other genera; or again, the circum-
stances of local marts may be such as to ensure a constant
demand for one particular class of timber, which thus becomes
the most remunerative crop under these special conditions.

In most mixed woods of about equal age certain species,
either through greater energy of growth in height, or in conse-
quence of soil and situation specially favouring their develop-
ment, or from some combination of both these factors, attain
such advantages in rate and extent of development as to induce
or necessitate a corresponding decrease below the normal de-
velopment in the other species. Hence sooner or later these
latter trees, unless specially tended, have to be removed from
the crop even although they may not have attained their
physical and technical maturity. It thus happens that, in many
cases, towards the end of the period fixed by the Working Plan
for mixed woods, the mature crop consists mainly of one
species ; and this is usually that which has shown itself most
capable of bearing shade. And when this species is being
reproduced and harvested, advantageous opportunities are once
more given for the formation of mixed crops by the planting
out of stout transplants of the more valuable kinds of trees
on, whatever patches of soil seem most suitable to their healthy
growth and vigorous development.

With their denser crops, their better conservation of the
productive capacity of the soil, their higher percentage of stems
of large dimensions, clean growth, and good technical pro-
perties, their power of satisfying demands for various kinds
and qualities of timber, and their comparative security from
calamities and devastations arising from either organic or in-
organic causes, it can hardly be denied that mixed woods are
more profitable, and rest on a much more secure financial basis
than pure forests,— provided always that they are formed of the
species for which the soil and situation are best suited, and

14° Studies in Forestry [CHAP. vn.

that the timber grown is such as suits the requirements of the
ordinary markets. One of the highest authorities on the sub-
ject gives the following practical advice l :—

1 Considering the circumstances of the timber market in general now-
adays, and of local demands (i.e. in Germany), and considering also
their incontestibly thriving growth, no argument is required to show
that conifers, and in particular Spruce, must nearly everywhere claim
the lion's share in the composition of the mixed forests of the future.'

For Britain, however, the Douglas Fir and the Menzies
or Sitka Spruce hold out very much better financial promise
than the common or Norway Spruce.

In the primeval forests of Britain mixed woods of Oak and
Beech covered most of the low-lying tracts and the better
qualities of soil on the uplands ; Beech was the principal
tree on the limy hills of central and southern England ;
whilst Scots Pine probably asserted itself over the poorer hill-
sides, with patches of Birch here and there. On the richer,
deeper soil Oak was of quicker growth than Beech, and, grow-
ing in localities eminently suited to its requirements, could well
regenerate itself naturally under the shade of the parent trees,
as may even now be seen in the case of pure woods formed
on rich alluvial tracts. The great forests of the Highlands of
Scotland were composed for the most part of Scots Pine,
because it was content with indifferent classes of soil where
few other trees were able to dispute its foothold. A thick
growth of moss helped to maintain the productive capacity
of the soil when the Pine began to thin itself about the
twentieth to thirtieth year, and then became somewhat broken
in canopy. In our damp insular climate this not only dimin-
ished the danger of soil-deterioration through sun and wind,
but it also favoured good natural reproduction and the forma-
tion of a closer canopy. Scots Elm, Ash, Alder, Aspen,
Willows, and Mountain Ash were all practically confined either
by their demands for moisture, or for soil-fertility, or for both,

1 Gayer, Zeitschrift fur Forst- und Jagdiuesen, 1892, p. 386.

CHAP. VIL] Formation of Mixed Woods 141

to the ravines on the hillsides and the lower-lying tracts where
the deeper and richer soil lay, and where the abundance of
soil-moisture rendered a loose, broken canopy and a light
annual fall of leaves matters of no particular moment — where
often, in fact, superabundance of soil-moisture made the
evaporating action of sun and wind beneficial rather than
prejudicial. The wet soil, the severe winters, and the frequent
late and early frosts in such humid localities safeguarded
their domain from being encroached on by the Oak or the
Beech. That most light-demanding, but hardiest, and most
graceful, of all our indigenous trees, the Birch, was forced to
seek its permanent home wherever no other genera of trees
could assert a foothold and maintain themselves in growth.

Rules for the Formation of Pure Forests.

Whenever %it is deemed advisable to form pure forests
artificially, the following rules laid down by Heyer l should be
noted as having proved themselves sound both in principle
and in practice : —

I. As a rule, only those species should be grown in pure forests,
which retain or increase the quality or productive capacity of the
soil. Such are : —

1. Those which are thickly foliaged, and grow in close
canopy. — These qualities are pre-eminently exhibited by the
Beech, Spruces, Douglas Fir, and Silver Firs, and in a less
degree by the Hornbeam, Lime, and Chestnut. Whether or
not the Sycamore and the Maple may also be included in this
class for Britain, depends to a great extent on the mineral
strength and freshness of the soil in each concrete case.

2. Those lightly-foliaged conifers which are evergreen. — The
thick, spongy growth of Hypnum mosses that springs up when
such woods begin the natural process of thinning themselves,

1 Der Waldbau, 4th edit. 1891, pp. 30-32-

142 Studies in Forestry [CHAP. vn.

and which acts like humus or mould in protecting the soil-
moisture against the effects of sun and wind, gradually dis-
appears when the canopy commences to become very much
interrupted and broken. The utilization and reproduction of
such pure forests should therefore not be delayed too long.
The species coming under this description are the various
members of the Pine genus, although Black (Austrian and
Corsican), Weymouth, and Maritime Pines are all more
densely foliaged, and maintain better canopy, than our indi-
genous Scots Pine.

II. Such species as do not retain the productive capacity of the
soil may \ however ; be grown in pure forests : —

1. When worked with low rotation. — All species of forest
trees protect the soil during the earlier stages of their develop-
ment, because the crop is denser and the crowns of foliage are
nearer the ground. This applies, along with qther crops, to
osier-holts and coppice-woods, for example.

2. When the productive capacity of the soil is not endangered
by imperfect cover. — Under this head are classifiable such cases
as marshy soil, where evaporation of the moisture by insolation
and by the free play of winds is directly beneficial; or as
valleys or low-lying tracts whose soil always remains fresh or
damp, and whose depth and porosity would only be injuriously
interfered with by an accumulation of humus. Alder and
Birch are not infrequently to be found on soils of such
description, and Ash, Elm, and Oak on those of a better class
formed by rich alluvial deposits.

It may be noted that in the above no provision seems made
for such trees as Larch and Oak in general. Pure forests of
these species may of course be formed under II. i ; but, if they
are to be maintained as pure forest to be worked at the
ordinary periods of rotation for such classes of timber, they
should certainly be underplanted with a shade-bearing species
to protect the soil. Many of the Larch forests of Scotland

CHAP, vii.] Formation of Mixed Woods 143

would (from a sylvicultural point of view— but pasturage would
then be out of the question) be much healthier and more
vigorous in growth if they had been well thinned and under-
planted with Spruces or Silver Firs about their twenty-fifth to
thirtieth year. This is apparently anomalous, for Larch forests
occur pure in its Alpine home, though only at high elevations,
where the atmosphere is humid, where there is a strong tendency
to the growth of moss even in such open forests, where the
general growth of Larch is much more vigorous, where there is
nearer approach to the maintenance of good canopy, and
where, finally, the soil is protected by a deep covering of snow
for most of the six to seven months of the year during which
the tree is bereft of its foliage.

Rules for the Formation of Mixed Forests.

In the same way,, general rules for the formation of mixed
crops can also be framed in accordance with the laws of nature
and the principles of sylviculture. Those tabulated briefly by
Gayer * are as follows : —

1. The concrete conditions of soil and situation must be such as
are favourable to the normal development of all species of trees
intended to be grown in admixture. — It would be erroneous to
suppose that mixed crops are advisable only on the better
classes of soil, although of course the quality of the latter is
an important factor in determining the choice of species to be
admixed. In fact, it is on some of the poorer kinds of land
that the greatest general advantages of mixed woods make
themselves most apparent, particularly when the soils are of
a sandy nature.

2. The admixture of species must not be such as ultimately to
endanger the productive capacity of the soil. — This is practically
a repetition of the first principle laid down with regard to the

1 Der Waldbau, 3rd edit. 1889, pp. 216, 217.

144 Studies in Forestry [CHAP. vn.

formation of pure forests, and amounts, in other words, to the
statement that the capital value of the woodland soil, i. e. its
capacity for yielding interest or returns in timber under proper
treatment, must not be tampered with, risked, or diminished by
injudicious management.

3. Throughout the whole period of rotation each species must
find the due amount of growing-space and of exposure to light, air,
and warmth suited to its requirements. — This condition is not
at all confined to the development of the crown, but applies
equally to the extension of the root-system ; and it becomes of
all the more importance the nearer the individual species of
trees approach to their physical maturity.

Proceeding from the general considerations that the possi-
bility of forming mixed crops of various species is de-
pendent—

i. On their individual capability of protecting or improving
the productive capacity of the soil,

ii. On their relative demands with regard to light, and

iii. On their relative rate of growth in height, —
the following rules for the formation of mixed forests were
formulated by Heyer * : —

1 . The principal or ruling species must be capable of improving
the soil. — That is to say, the matrix should consist of genera
and species like Beech, Hornbeam, Spruces, Silver Firs,
Douglas Fir, and Scots or Black Pines.

2. Shade-bearing species may be grown in admixture with each
other when their rate of growth is about equal, or when the
slower-growing species is protected against the quicker-growing.
— The protective measure adoptable in the latter case consists
of giving some start at first to the slower-growing species, of
allowing it to form the great majority of the crop, or of favour-
ing it at the time of natural reproduction, and later on by

1 Op. cit., pp. 45-57.

CHAP, vii.] Formation of Mixed Woods 145

lopping, topping, or even cutting out the other species of trees
threatening to suppress it.

3. Shade-bearing (thickly-foliaged) species can be intermixed
with light- demanding (thinly-foliaged) species^ when the latter
are of more rapid grmuth in height, or when they are afforded
some advantage as to age or height, — If, however, the shade-
bearing species is to be expected to develop vigorously, instead
of being suppressed during the youthful period of growth, it
must form the principal or ruling species numerically.

4. Light-demanding species should not be permanently associated
together as timber crops. — When the slower-growing species is
at the same time relatively the more capable of bearing shade
(e. g. Austrian Pine and Larch, Austrian Pine and Scots Pine),
exception to this rule can be made : —

(a) On very good soil not exposed to deterioration under
the light canopy of the thinly-foliaged species. Under such
conditions mixed growth of Alders and Ash, Oak and Elm, Oak
and Maples, &c., are not at all injudicious.

(b) On very poor (sandy) soil, principally given up to
conifers, where of broad-leaved trees the Birch alone is
content to grow.

Except on soils and situations where the Scots Pine shows
a decided tendency towards a fuller degree of shade-bearing
capacity than usual, a mixture of this species and Larch is not
at all advisable, although very often made in Britain (see
P- 155)-

5. The subordinate species should be introduced individually
and not in patches or groups. — Here, again, however, exceptions
may be made : —

(a) When the quality of the soil is variable, so that patches
here and there are specially suited for any one particular
class of tree (e. g. Spruce on shallow, stony soil ; Ash and
Alder on damp, wet spots ; Pines on dry patches).

L

146 Studies in Forestry [CHAP. vn.

(£) When a light-demanding species is to be grown along
with a shade-bearing species of quicker growth (e. g. Oaks grown
in admixture with Beech on soils specially favourable to the
latter).

(c] When standards (e. g. of Oak) are retained for a second
period of rotation. Here some protection is afforded to the
soil until the young seedling crop forms canopy, and at the
same time the formation of shoots from dormant buds along
the stem, leading too often to ' stag-headednessj is prevented.

A. — Concerning Mixed Crops of Shade-bearing
Species.

Spruce and Silver Fir. — Where Spruce forms the ruling
species, the introduction of Silver Fir as part of the crop is of
great advantage in diminishing the danger of windfall and of
destructive attacks from injurious insects ; but where the soil is
good enough for the Silver Fir to form the bulk of the mature
crop, any admixture of Spruce has just the opposite effects. As
in early youth Spruce is the more rapid in growth, the Silver
Fir should be introduced in considerably larger numbers than is
ultimately desired. Thus, if originally planted in the proportion
of two of Silver Fir to one of Spruce, the mature crop would
ultimately consist of about equal numbers of each kind of tree.

Beech and Spruce. — Although Beech is of somewhat quicker
growth at first, it soon gets caught up by the Spruce, which
then usually remains predominant. Unless the Beech is to
be ultimately suppressed, the Spruce must only be scattered
singly throughout the crop ; and even then some lopping of the
branches will have to take place. Where stony outcrops occur
in Beech woods, it is best to form pure clumps of Spruce.

Beech and Silver Fir. — At first the Beech develops more
rapidly, and interferes with the growth of the Silver Fir ; but
later on this overtakes and threatens to suppress the former.

CHAP, vii.] Treatment of Mixed Woods 147

B. — Concerning Mixed Crops of Shade-bearing and
Light-demanding Species.

Common Spruce as ruling Species or Matrix.

During the youthful period of development all light-demand-
ing kinds of trees are of quicker growth than the Spruce,
and damage the latter by injuring the tender leading-shoots
when it begins to catch them up in growth. Later on, most
of the light-demanding species are overtaken by the Spruce ;
and unless it is intended to utilize them by removal during
the periodical thinnings, the former require special tending
and protection against the latter.

Spruce with Oak, Ash, Maple, Sycamore, or Elm as sub-
ordinate Species. — All these species are overtaken in growth
by Spruce between the fifteenth to twenty-fifth year as a rule,
although on very good soils they retain their advantage some-
what longer, especially when they also predominate numerically.
For the most part, however, these valuable species should be
grown in admixture with the Beech. Even when Oak has an
advantage in growth up to about twenty years, it is still usually
liable to be caught up when the Spruce gets to about fifty years
of age ; and then it is either suppressed, or else hindered in
afterwards attaining its normal girth as mature timber. Expe-
rience shows that a mixture of Oak with Spruce should only
take place when once the former has advanced considerably
towards maturity. This can best be effected by cultivating
the Oak in pure forest first of all, and then, about the sixtieth
to seventieth year, making a strong thinning or partial clear-
ance, with simultaneous sowing or planting of the Spruce.
The whole crop is then harvested as one mature crop about
eighty to a hundred years later on.

Spruce and Birch.— Of all the subordinate species of trees
which are at first of quicker growth than the Spruce, the Birch
does most damage, owing to the extent to which the whip-like
twigs scour and injure the leading-shoots. Thus, although

L 2

148 Studies in Forestry [CHAP. vu.

useful as a nurse in localities exposed to frosts, an admixture
of Birch is not much favoured. The reason is more especially
owing to its strong reproductive capacity from the stool ; for it
is extremely difficult to get rid of the latter tree when it is no
longer desired as part of the crop.

Aspen and Willow are also prejudicial to the development
of the Spruce, but not to the same extent as the Birch.

Spruce with Scots Pine. — During the earliest period of
development the quicker-growing Pine affords the Spruce
beneficial protection against frost and heat; but the Pine
cannot exceed one-fifth to one-seventh of the crop without
threatening to interfere for a long time with the normal growth
of the Spruce. Later on the Pine, owing to its tendency towards
a spreading crown, does more or less damage by rubbing and
scouring the shoots of the Spruce. On some situations the
Pine lags behind the Spruce in growth between the thirty-fifth
to fiftieth year ; but on good soil it regains the lost advantage,
and continues till maturity among the dominating or pre-
dominating classes. In other localities observations have
shown that on somewhat dry sandy soils the Pine is of quicker
growth throughout its whole period of development ; whilst
on fresh soils the Spruce shoots continuously ahead when
once it has caught the other up. A permanent mixture of
these trees is as a rule only recommendable on medium
classes of soil ; but by this means the Pine can be made to
hold out longer periods of rotation than otherwise, and can
develop into large-girthed stems of considerable marketable
value.

Spruce with Larch — This mixture is at first very similar to
that of Spruce and Pine, except that, on soils suited to it, the
Larch remains permanently predominant. Where, however,
the soil is wanting in depth or in mineral strength, and very
frequently in low-lying localities, the Larch is apt to be over-
taken in growth in height by the Spruce, and then it is hardly
profitable to endeavour to retain the former so as ultimately

CHAP, vii.] Treatment of Mixed Woods 149

to form part of the mature crop ; it is better to cut it out at
once.

Silver Fir as a ruling species closely resembles Spruce.
But it is less active in suppressing the subordinate species when
once it catches them up in growth, as its shade is somewhat
less dense. The same will also most probably prove correct
with regard to the Douglas Fir.

Black Pines, i.e. Austrian and Corsican, can bear a con-
siderable amount of shade, and certainly improve the soil in
no slight degree through their rich fall of needles ; hence they
are naturally adapted as ruling species, more especially when
grown along with very lightly-foliaged trees like Larch.

Beech as ruling Species.

Writing in 1791, Gilpin spoke thus slightingly of the
Beech :—

'The Oak, the Ash, and the Elm, are commonly dignified in our
English woods, as a distinct class, by the title of timber trees . . .
After timber trees, the Beech deserves our notice. Some indeed rank
the Beech among timber trees ; but, I believe, in general it does not
find that respect, as its wood is of a soft spongy nature ; sappy and
alluring to the worm.'

But in what different estimation is this noble woodland tree
held by the continental sylviculturists who have studied the
subject most thoroughly, and have the best right to speak
authoritatively concerning it !

Thus Prof. Gayer of Munich says l : —

< There are many localities in which Beech will continue to be a valu-
able wood from a financial point of view (i. e. for fuel in Germany). But
where such may not be the case, it will still retain its insurpassable
sylvicultural value ; for without the Beech there can no more be properly
tended forests of broad-leaved genera, as along with it would have to be
given up many other valuable timber trees, whose production is only
possible with the aid of Beech.'

1 Op. cit. 1889, p. 448.

150 Studies in Forestry [CHAP. vn.

And Ney's opinion is as follows l : —

'The Beech, which in pure crops belongs to the more valuable species
of trees only on account of its protective influence on the productive
capacity of the woodlands, is of extraordinary value in mixed crops
owing to its capacity for casting a dense shade over the ground and
for improving the soil by its strong fall of leaves. When an admixture
of Beech is judiciously formed, all species of timber trees show a much
greater energy of growth than in pure crops. It safeguards the pro-
ductive capacity of the soil better than any other species of tree, and
therefore well deserves the name of " the Mother of the Forest " which
has been given to it.'

Beech with Oak. — In exposed localities, or on shallow, and
especially on limy soils, Oak is slower in growth than Beech,
although on most other soils and situations it is decidedly of
more rapid development. But, even in this latter case, the
advantage won is seldom so great as to obviate the necessity
for adopting measures to protect it against the Beech. This
is in some cases effected by forming pure crops of Oak first
of all, and then underplanting them with Beech either during
the pole-forest stage of growth, or about the seventieth to
ninetieth year, when the main growth in height has been
completed. A heavy thinning or partial clearance previously
takes place in each case. Again, in mature mixed crops, the
Oak can be favoured by either being reproduced first in groups
of 20 to 30 feet in diameter, or else by planting up the blank
patches in Beech seedling-growth with strong Oak transplants.
And, by favouring the Oak during all operations of thinning,
or by stimulating it to increased growth in height through
removal of the lower branches of the crown periodically, before
they attain a diameter of over four inches, much can be done
to assist its development.

On very good soil, not apt to deteriorate under the loose
canopy of the Oak, this genus can be introduced to such an
extent as to far outnumber the Beech ; but, on the less fertile

1 Lehre vom Waldbau, 1885, p. 93.

CHAP, vii.] Treatment of Mixed Woods 151

and the merely average classes of forest soil, considerations
regarding the conservation of the productive capacity of the land
necessitate each- Oak being surrounded with Beech. Where
this is fully acted up to; there will be seldom more than eight
to ten Oaks per acre attaining maturity at 100 to 120 years
of age, though on the best classes of soil the number of Oaks
in the crop may perhaps amount to as many as thirty to forty
per acre. When the Oaks have been introduced in too large
numbers at first, an early commencement should be made to
reduce them gradually to the proper proportion they are
intended ultimately to form in the mature crop. This can
best be done by the removal of all stems of indifferent growth.
If, in order to obtain very large-girthed timber, it seems desir-
able to allow the Oaks to remain on good soil for a second
period of rotation of the Beech, they can be left in the numbers
above given ; but, before the end of that time, they will, in the
latter case, have formed canopy, under which the Beech may
still grow up as a tree, though not so as to attain normal dimen-
sions. On average classes of soil eight to ten Oaks per acre
will, at the end of the second period of rotation, overshadow
about one-fourth of the soil, and sixteen to twenty about one-
half of the area.

Beech with Ash, Maple, Sycamore, and Elm. — Despite
a very considerable density of foliage in the Sycamore under
certain circumstances, all these species strongly resemble the
Oak in its attitude towards the Beech ; for all are light-demand-
ing and of quicker growth at first than the latter. This advantage
they usually retain on deep, fresh soils; but otherwise they
are, as a rule, caught up in growth by the Beech during the
pole-forest stage of development. In many situations they are
apt to sow themselves so freely as materially to interfere with
the natural reproduction of the ruling, soil-protecting species ;
hence it is advisable to utilize them at the time of preparing
the soil for the reception of the Beech-mast, and merely to intro-
duce them here and there singly or in small patches throughout

152 Studies in Forestry [CHAP. vn.

the new seedling crop. By the use of healthy transplants, and
by selection of the most suitable patches for the growth of
these various species, better results can be attained than by
endeavouring to reproduce the whole crop as mixed forest. In
addition to some advantage in age and height at first, careful
tending of these more valuable species is requisite during all
the operations of thinning. It is only on the soils most favour-
able to their growth that these kinds of trees can hold out the
usual period of rotation (90 to 120 years) best suited to the
Beech ; hence, by the time fixed for the fall of the mature
crop, they will in many cases have disappeared from the
woods, having been removed for disposal when they had
reached their full physical and economic maturity. The more
the soil is suited for the Beech, the earlier will the fall of these
subordinate species be necessitated; but, in any case, the
quantity and quality of the timber harvested will yield better
returns than if attempts be made to grow these kinds of trees
in pure forest without the beneficial assistance of the Beech.

For moister classes of soil the Hornbeam can often yield
better service than the Beech; and, as its growth is not so
energetic, there is less likelihood of its catching up the nobler
species and threatening to suppress them. Although it gives
much smaller returns in timber, the latter is, owing to its
extreme toughness, valuable for machinery work. Again, as it
attains its physical and economic maturity much earlier than
the Beech, it is in some respects even a more favourable ruling
species than the latter, — for example, when it is desirable to
allow the soil to remain as short a time as possible in the sole
possession of the ruling species : for, practically, the natural
reproduction of the Hornbeam could take place immediately
after the fall of the subordinate species.

Beech with Birch, Aspen, and Willow. — As a rule no arti-
ficial efforts are necessary to attain an admixture of the soft-
woods in seedling crops of Beech. In fact they sometimes
occur self-sown to such an extent as to come under the

CHAP, vii.] Treatment of Mixed Woods 153

heading of ' forest weeds] for the removal of which a considerable
expenditure of time, trouble, and outlay is often necessitated.
Where they occur singly and individually here and there, not
only is no damage done by them, but they may prove beneficial
in protecting the slow-growing Beech against late and early
frosts ; and, with favourable opportunity of disposing of small
material, they can often be made to yield fair returns when cut
out during the cultural operations of weeding and clearing.
Wherever they occur in considerable numbers, however, they
interfere considerably with the development of the Beech, and
must be cut out as soon as possible in order to avoid the forma-
tion of blanks. On account of their strong reproductive capacity,
and of the rapidity in growth of their coppice-shoots and stoles,
it is better merely to lop them, and to leave snags of two or three
feet standing, than to cut them flush with the ground. With
the timely removal of such softwood nurses, a good opportunity
is offered for the introduction of sturdy transplants of the
nobler species of our forest trees. But when once the proper
time for their clearance has been allowed to slip by, it is difficult
to adopt any other measure than their very gradual removal
during the subsequent operations of tending, without at the
same time exposing the principal crop to the danger of being
bent down or laid • for the young Beech poles are apt to be
drawn up so fast as to become top-heavy without the partial
support of the softwoods.

Beech with Scots Pine. — Each of these trees accommo-
dates itself well to the peculiar requirements of the other, for
the light-demanding Pine is throughout all the stages of its
development of more rapid growth than the Beech. If intro-
duced to a moderate extent only, Pine does little damage to
the latter by overshadowing ; whilst, at the same time, it acts
beneficially as a nurse in protecting the Beech from extremes
of heat and cold. In such mixed crops the Scots Pine attains
more valuable dimensions, and is of better quality, than when
grown either pure or in admixture with other conifers. And

154 Studies in Forestry [CHAP. vu.

it can also be then worked with a higher period of rotation,
without incurring any financial loss.

It is a curious fact that, under the light shade of the Pine,
the natural reproduction of the Beech can be more easily and
successfully carried out than under the shelter of parent
standards themselves.

As the natural habit of the Scots Pine tends towards an
early lateral development of the crown, it should not be given
any advantage in age or height to begin with • its introduction
can therefore easily take place either by sowing or by planting
here and there throughout the young seedling crops of the
ruling species.

The Larch, as a subordinate species in admixture with
Beech, on the whole closely resembles the Scots Pine, except
that it then often reaches its physical and economic maturity
at about fifty to sixty years of age, and that it makes higher
demands on the quality of the soil.

C. — Concerning Mixed Crops of Light-demanding
Species.

Considerations relative to the conservation of the productive
capacity of the soil demand that under ordinary circumstances
some shade-bearing species should form a portion of the
crop ; for the true scientific principle is, as has already been
stated above, that it should, in fact, form the major part of
the crop, i.e. it should be the ruling species. But, under
certain special conditions as to soil and situation, it may
seem desirable to the proprietor to depart from this prin-
ciple, and to form mixed forests consisting entirely of light-
demanding trees. Such crops must ultimately, however, from
their natural habits of growth, fail to maintain close canopy;
hence, unless the soil is possessed of such physical properties as
render it little likely to deteriorate through insolation and the
action of winds, the practical formation of a mixed crop, by

CHAP, vii.] Treatment of Mixed Woods 155

means of underplanting with the shade-bearing species for
which the soil is best suited, is rendered advisable. Where fresh
or moist, low-lying tracts with good soil are still under forest
growth, mixed woods of Oak with Ash and Elm, or with Alder
and Birch, — Alder with Ash, Birch, and Aspen, — Pines with
Aspen and Alder, — and the like, are often to be seen in
luxuriant growth and yielding good returns to the proprietors.
In Britain, the light-demanding species which is most fre-
quently to be found forming the ruling species or matrix is
undoubtedly the Scots Pine. But, even in our damp insular
climate, the admixture with it of some species capable of bearing
shade has a very beneficial effect on the soil, and through that
on the quantity of timber obtained at the fall of the crop. For
the better classes of Pine soil the Beech or Silver Fir, or on
moist localities exposed to frosts, the Hornbeam and Douglas
Fir, and for average and inferior localities the Spruce, Black
(Austrian and Corsican) and Weymouth Pines are recommend-
able as subordinate species ; but as, on the inferior tracts classifi-
able as Pine soil, these trees are less tolerant of shade than
elsewhere, they must receive a fair amount of consideration
during all operations of tending and thinning. The admixture
of Larch with Scots Pine on such localities indicates want of
knowledge of the natural requirements of the Larch with respect
to fertility and depth of soil ; whilst at the same time, owing to
the more rapid growth of the Larch, the Pine suffers even from
the light shade cast over it by the former.

Kecapitulation.

As this subject is of great practical importance it may be well
to summarize briefly what has been said at length in this and
the preceding chapter in exposing the fallacy contained in Sir
Herbert Maxwell's statement quoted on page 115. Where only
one species of tree has mainly to be taken into account, each
block of forest may have the advantage of being easier to work
with regard to tending, to the fall of the mature timber, and

156 Studies in Forestry [CHAP. vn.

to the reproduction of the crop (though not necessarily, so far
as the latter is concerned), but it is much more exposed to
climatic dangers like extensive windfall over areas covered with
Spruce, or to damage from snow and ice in Pine tracts, or to
attacks of insect enemies as with both Spruce and Pine, or
to cankerous fungoid diseases as in the case of Larch or Silver
Fir, &c.

Pure forests cripple and confine the management to one kind
of timber practically in any one locality; and if the market for
that particular kind goes down and becomes unremunerative,
it is not easy all at once to pave the way for the production of
other and more profitable woodland crops.

It will in general, therefore, be to the advantage of the land-
owner to avoid the formation of pure forests over extensive
areas. But occasionally it happens that there is little practical
choice about the matter. The land may be too poor for Oak,
Ash, Maple, Sycamore, Elm, Larch, &c. to grow in mixture
along with Beech, Hornbeam, Spruces, and Silver or Douglas
Firs, and then Pine forests are the best crops that can be formed
if the land is to be put under timber at all ; or undrainable
tracts may be better suited for Alders or Willows and Poplars
than for other genera ; or local requirements may be such that
a fairly well-assured and constant future market for one parti-
cular class of timber seems to point to its cultivation as most
advisable and attractive.

In most mixed crops of about equal age certain species,
either through greater energy of growth in height, or in conse-
quence of soil and situation specially favouring their develop-
ment, or from a combination of both these factors, attain
advantages in rate and extent of development which induce
or necessitate a corresponding fall below the par of normal
development in the other species ; hence sooner or later these
latter species, unless specially tended, have to be removed
from the crop, even although they may not have attained their
physical and technical maturity. It thus happens that in many

CHAP, vii.] Treatment of Mixed Woods 157

cases mixed woods must, towards the end of the period fixed
by the Working-Plan for the fall of the mature crop, consist
principally of one species, which is usually that most capable of
bearing shade. But when this species has been either naturally
or artificially reproduced, the most advantageous opportunities
are again offered for the re-formation of mixed crops by the
introduction of stout transplants of the more valuable timber-
producing trees of other genera or species.

With their denser crops, their better conservation of the
productive capacity of the soil, their higher percentage of
stems of large dimensions, clean growth, and good technical
properties, their power of satisfying demands for various kinds
and qualities of timber, and their comparative security against
calamities and devastations arising from organic or inorganic
causes, it can hardly be denied that mixed forests are more
profitable, and rest on a much more secure financial basis, than
pure forests, — provided always that they are formed of the
species of trees for which the soil and situation are best suited,
and that the timber grown is such as meets the requirements of
the ordinary markets. In fact, as compared with pure forests,
mixed woods exhibit the economic paradox of holding out fair
promises of a higher rate of annual interest, combined at the
same time with better security for that very considerable por-
tion of the capital which is represented by the growing stock
of timber throughout the woodland area.

CHAPTER VIII

CONCERNING THE FORMATION AND REGENERATION
OF WOODLAND CROPS

' Where any system of management satisfies all reasonable expecta-
tions, there can be no object in changing it Not infrequently,

however, in one and the same forest, certain operations are carried out
in a masterly manner, whilst others might be better performed ; and
observations and experiences made in one locality often remain unknown
for a long time in another.' — Burckhardt's Sden und Pflanzen, 1854
(ist edition), Preface.

Choice of Species of Trees to form the Crop.

WHETHER viewed from a purely sylvicultural standpoint
relative to the production of the largest quantity of timber of
the best quality, or from the financial standpoint relative to
the obtaining of the largest annual returns from the capital
represented by soil and growing stock, the choice of the kinds
of forest trees to form the crop is of the first importance under
all circumstances. Not every given soil and situation will pro-
duce any particular kind or assortment of timber ; hence the
relegation of the various genera of woodland trees to the tracts
most likely to afford them a suitable permanent home is one
of the first duties of the sylviculturist. When dealing with
indigenous trees, or with such as have become naturalized by
long association with our native sylva, nature never makes
mistakes ; and where any self-sown genera show good growth,

CHAP, viii.] Formation of Woodland Crops 159

it may in general be accepted that soil and situation are
favourable for their cultivation there. But this general rule
is of course capable of being followed only in certain cases,
and need not be always acted on — as, for example, when
a spontaneous growth of Birch or Aspen asserts itself on soil
from which the owner is entitled to expect better returns, and
a more valuable yield of timber, than in the ordinary nature
of things these kinds of crops can possibly promise.

The selection of trees is, however, by no means a free one ;
for there are many soils and situations where it is decidedly
limited, or on which it is practically a case of 'Hobson's
choice.' Thus, on dry sandy soils, no forest tree can compete
with the Scots Pine, whilst on wet, sour, marshy land the
common Alder holds equal sway; on peat bogs, that have
been drained, a mixture of Scots and Weymouth Pines and
Birch often offers the most advantageous crop; on low-lying
tracts, liable to inundation annually, Willows and Poplars are
best endowed by nature for growing under these special cir-
cumstances ; whilst Spruce and Larch thrive in elevated
localities with cool, humid atmosphere, above the zone where
deciduous broad-leaved trees could find their natural and
congenial habitat.

On many soils and situations a considerable number of
genera of forest trees find conditions fairly well suited to their
general growth ; but, in general, one or other of the physical
properties determines the elimination of certain kinds when
crops are to be formed for profitable timber-production in
contradistinction to ornamental growth and aesthetic effect.
Thus, deficiency of soil-moisture may frequently preclude the
idea of forming crops of Alder, Ash, Maple, Sycamore, and
Elm, whilst want of atmospheric humidity may militate against
the full normal development of Beech, Hornbeam, Spruce,
and even Silver Fir; or, where the soil is wanting in depth
and penetrability, Oak, Ash, Maples, Elm, Lime, Larch, Pines,
Silver and Douglas Firs cannot extend their root-systems so as

160 Studies in Forestry [CHAP. vin.

fully to utilize its nutrient soluble salts. It also happens that
the favourable admixture of a certain mineral element in the
soil affords special advantages to particular classes of trees —
as, for instance, the better growth of Beech, Maples, Ash, and
Black Pines on soils that are of a limy composition. And,
in a certain degree connected with the conditions as to atmo-
spheric humidity and soil-moisture, danger from late frosts in
spring, or from early frosts in the autumn, can be so great as
to preclude the planting out of Oak, Beech, Ash, Silver Fir,
and even Spruce without a certain admixture of quick-growing
softwoods as protective growth and nurses. Again, where
heavy falls of snow are apt to occur, the brittle Scots Pine
is less able to support the masses of snow and ice accumu-
lating on its loose crown than other more elastic evergreen
conifers.

And when one comes to the practical question, not only as
regards the suitability of soil and situation for any given
genus, but also with respect to their suitability for one particular
species above all others, or with a view to the selection of the
best genera for the formation of mixed crops, which have
invaluable advantages over pure crops (see Chapter VI), the
difficulties connected with the choice become increased. Thus
the cultivation of the pedunculate Oak, Larch, Spruce, and
Silver Fir will only prove satisfactory on soils and situations in
every respect suited to their normal requirements. But over
every large woodland tract there are variations, in quality of soil
and degree of soil-moisture, which must be carefully observed
and taken advantage of in the formation of mixed crops, instead
of attempting to carry out the mixture in anything like a rigid
or stencilled manner. No better example of want of prudent
consideration, or want of knowledge, of the natural requirements
of any species of forest tree can be given than to point to the
mistakes made in the latter half' of last century and the begin-
ning of the present with respect to the extensive introduction
of the Larch into Scotland. These errors have only had

CHAP, viii.] Formation of Timber Crops 161

their natural results in diseased growth of the trees and dis-
appointed hopes as to the financial returns anticipated.

When soil and situation seem about equally favourable to
more than one kind of tree, prudential reasons will point to the
formation of mixed woods of those genera. And considerations
relative to the conservation of the productive capacity of the
soil will naturally lead to a shade-bearing, soil-protecting kind
forming the ruling species or matrix ; whilst the admixture
of subordinate genera may be formed either individually or
in small groups or patches, to such an extent as promises to
be most remunerative until the final clearance of the. crop
takes place on its ultimately attaining maturity. Of course,
when certain woods and assortments of timber have a good
local market, the ease and readiness with which the timber of
particular kinds, or classes, or qualities may be disposed of,
will naturally lead the proprietor to their cultivation, even in
preference to other genera for which the physical qualities of
the soil and the local peculiarities of the situation are perhaps
in reality better adapted.

Owing to its comparatively low value as timber, the Beech
finds its place as the ruling tree solely with a view to the
conservation of the productive energy of the soil, and need not
be cultivated to any greater extent than this consideration
demands. But the indirect benefits thus conferred on the
lightly-foliaged trees grown in admixture with it enhance con-
siderably the returns obtainable in quantity, quality, and
monetary value from crops of Oak, Ash, Maple and Sycamore,
Elm, Pines, and Larch formed together with Beech.

Where financial considerations have more weight given to
them than those concerning the outturn of timber of special
value for certain technical purposes (e. g. Oak for ship-building
before the days of Teak-lined iron steamships) there can be
no doubt that, for high-forest crops, the conifers, and, in par-
ticular, mixed woods of Spruce, Douglas Fir (a species very
strongly to be recommended), Menzies Spruce, Silver Fir,

M

1 62 Studies in Forestry [CHAP. vin.

Noble Fir and Pines, yield a much larger outturn in timber,
and, despite less value per unit of bulk, a higher percentage
on the capital involved than can generally be obtained by
the growth of mixed crops of deciduous forest trees.

At the same time, on suitable soil, coppices of Alder, Oak,
and Willow may show financial results far exceeding those
obtainable from conifers ; but, in such cases, the quality of
the soil and its location are usually very different from those
of the areas which have naturally been set apart for sylvi-
culture, owing to their unsuitability for arable or pastural
utilization.

Where all genera seem to have about equal chances of
thriving, pure forests of Douglas Fir, Silver Firs, and Spruces
offer the greatest financial advantages, owing to the large
quantities of timber produced and the large percentage of
it utilizable for the higher technical purposes ; Oak, Ash, Elm,
and Maples come next ; then Pines, softwoods, and last of all
the Beech. These, however, are merely rough generalizations ;
for in each concrete case local climatic conditions exert their
influence. Hence, in warm southern districts, Oak and other
light-demanding genera yield more favourable results than
the densely-foliaged Spruce, which thrives best in the cool,
humid atmosphere prevalent within mountain ranges and at
high elevations.

In technical value and financial returns obtainable per unit
of volume, none of our indigenous timbers equals the Oak ;
whilst, for furniture and ornamental purposes, Ash, Maples,
and Red Elm approach nearest to it. For the manufacture of
agricultural implements, and for similar purposes requiring
toughness combined with lightness, Ash timber has a value
specially its own. Among conifers, good, sound, large-hearted
Larch is of highest value, whilst Pine, Spruce, and Silver Fir
vary locally in price. But as Spruce and Silver Fir are so
much more productive per acre than other conifers, the large
supplies of their timber annually thrown into the continental

CHAP, vin.] Formation of Timber Crops 163

market may account for the comparatively low prices. The
monetary returns available in general from the softwoods
depend to a very great extent on local conditions of the
timber market ; whilst the Beech usually yields comparatively
poor returns, despite its being the best, and the most heat-
producing kind of fuel obtainable from woodlands. Its timber
is, however, now coming largely into demand again.

Whilst the advantages derivable from mixed forests — in-
cluding conservation of the productive capacity of the soil by
the shade-bearing, ruling species ; better utilization of the soil
through differences in root-system, and of the light, air, and
warmth by the crowns being generally at slightly different
levels ; protection against insect enemies, fungoid diseases, and
damage from inorganic causes, &c. — are only attainable to the
fullest degree when the admixture of genera occurs in indi-
vidual stems, yet the casual differences in the physical properties
of the soil can only be fully availed of when admixture takes
place in patches or groups varying in extent with the variations
in the'soil. The general principles guiding the choice of species
in mixed crops, apart from the fundamental rule regarding
conservation of the soil applicable alike in the formation of
pure and of mixed woods, are, broadly stated, that the conditions
of soil and situation must suit all the kinds of trees to be inter-
mixed, and that the more or less normal development of each
species should be interfered with as little as possible by the
others. Hence mixtures of trees with similar requirements as
to light, or nearly equal capacity for bearing shade, usually re-
commend themselves only when one kind can be utilized so
much earlier than the other as to permit of underplanting (e. g.
Oak, with Ash, Maples, and Elm on good soil), or when, besides
producing a greater quantity of timber with a higher percentage
of technical and consequently of monetary value, other advan-
tages are gained in protection against violent storms or the
ravages of insects (e. g. when Spruce is mixed with Beech and
Silver Fir). Thus, on soils and situations suitable for the Silver

M 2

164 Studies in Forestry [CHAP. vm.

and Douglas Firs, an admixture of Spruce could only endanger
the stability *of the crop and increase the risk from injurious
insects ; whilst, on soils naturally best suited for Spruce, the
introduction of these other genera can be of considerable advan-
tage in the protection afforded against windfall and insects.
The formation of mixed forests of Scots Pine and Larch, so
often hitherto favoured in Scotland, is not one that can be
recommended -; for it is not in conformity with the principles
of sylviculture. And practical experience has shown that the
theoretical point of view in this matter is correct.

The most advantageous results are obtainable when a happy
choice has been made combining light-demanding and shade-
bearing genera, and when the former retain for a long time
the early advantage they gain owing to their more rapid growth
during the. earliest stages of development. Where it is suited
to the soil, Beech, owing to the very superior .quality of leaf-
mould formed by its dead foliage, or Hornbeam, yields the
best results as matrix from a purely sylvicultural point of view.
But, in Britain, financial considerations undoubtedly deserve
greater attention from the land-owning classes than the scientific
sylvicultural principles that ought to underlie .the treatment
of the State lands and Crown forests if they were properly
administered ; hence Spruces, -Silver Firs, Douglas Fir, and in
certain cases Austrian and Corsican Pines, are the forest trees
most deserving of cultivation. Even though these species may
be to a certain, and often to a considerable, extent influenced
in their development by the other species of more rapid growth,
yet even then they are still capable of yielding timber of good
marketable quality and dimensions. Where, however, the
interference with their normal .development is only compara-
tively slight, the quality of the .timber of the above kinds of
forest trees decidedly gains by admixture.

And when once the choice of species has been made, the
proportion which they shall each bear to the total number of
plants per acre requires equally careful consideration. The

CHAP. VIIL] Formation of Timber Crops 165

shade-bearing, soil-improving kinds of trees must of course at
first form the ruling species numerically ; but in course of time
they may become so reduced in number as, towards the end
of the period fixed for harvesting the ultimate crop, to be in
a minority. For example, in crops formed by Oak, Ash, and
Maples, with perhaps a few softwoods here and there, through-
out a matrix of Beech, the processes of clearing, thinning,
and tending throughout the various stages of growth of the
crop will in most cases have led to the elimination of the
softwoods between the thirtieth to fiftieth years, and of the
Ash,, Maples, and other similar woods between the sixtieth to-,
eightieth years ; whilst, from that time onwards, the main crop
will consist of Oaks, with just a sufficient proportion of Beech
to maintain the soil against deterioration. And if the health and '
the vital energy of the Oak- trees seem to justify their retention j
as a remunerative crop for a prolonged period of rotation, the
Beech can be naturally reproduced below them as an under-
wood, or artificial sowing or underplanting can be resorted to,,
in order to prevent the soil from deteriorating or diminishing
in its productive capacity.

Choice of Form and Density of the Crop.

The choice of the most advantageous form of crop to be-
grown on any woodland soil is determined partly by the genera
selected for cultivation, partly by the nature of the soil and
situation, and partly by the requirements of the land-owner.
Should the proprietor have only a limited area under wood
and yet desire to obtain, if possible, an annual outturn, he will
naturally favour such methods as yield quick returns and only
involve the locking-up of least capital in the way of soil plus
growing stock. And where bark for tanning, or withes for
basket-making, are at all well paid, on soils that are favourable
to the growth of Oak and Willows these forms of crop are
amongst the most remunerative that can be grown. On low
wet tracts, too, Alder-coppice worked with a rotation of twenty-

1 66 Studies in Forestry [CHAP. vm.

five to thirty years gives very excellent results, as the demand
for this light wood for cigar-boxes and similar requirements is
constant, and is not likely to be replaced in the immediate
future by any other kind of wood, or by any substitute of
a different nature.

High-forest of trees grown from seed produces absolutely
higher monetary returns than ordinary methods of coppice ; but,
owing to the greatly increased capital locked up in the soil and
the timber stock ranging from the yearling growth to the mature
crop, the financial result is often not in favour of the former.
Again, in consequence of the bulky nature of forest crops, and
the heavy costs of transport, local market conditions have such
immense influence in determining the remunerativeness of any
particular crop, that no general dictum can be laid down on
the matter. This much, however, can be asserted, that, where
woodlands are of considerable extent, mixed coniferous crops,
worked with a rotation varying from 70 to 100 years, are in
general most remunerative where the soil is of the average, or
below the average, in quality; whilst, on soils of the better
class, where conifers have a predisposition to suffer from
fungoid diseases in the roots and stem, mixed crops of Beech,
with a suitable large admixture of the nobler species of
deciduous trees, really offer the safest and the best investments
in the long run.

With the endless combinations of the various factors deter-
mining the rate of growth of, and the quality of timber
produced by, woodland crops, the formulation of anything like
hard and fast rules must be out of the question. The system
of total clearance and artificial reproduction is simplest and
easiest to carry out. The young growth is not endangered by
the gradual removal of any parent standard trees ; a freer hand
is allowed for the intermixture of subordinate species ; and,
where it pays to undertake it, the grubbing up of the large
quantities of fuel represented by the root-systems is a very
simple matter. But, on the other hand, there is much greater

CHAP, viii.] Formation of Timber Crops 167

danger to the young crop from rank growth of weeds, and from
insect enemies (Melolontha and Curculionidae especially) ; whilst
it is also more difficult to recognize and to deal with the variations
in the quality of the soil with a view to making the best choice
of genera for mixed crops. Except on good land and with kinds
of trees hardy against frost, this method of treatment of the
crop should only be adopted, on soils below the average in
quality, when special considerations regarding either the land
or the kind of trees to be reproduced render inadvisable the
process of gradual clearance of the crop with simultaneous
regeneration under parent standards. Where the soil is shallow
or is apt to be easily heated, and to become deteriorated, as is
often the case when the percentage of lime contained is great,
the first point must be to maintain the land against the risk of
deterioration; hence the form of gradual clearance will be
advisable only to so small an extent as to consist merely in the
selection and utilization of mature trees, individually or in small
patches, without materially interrupting the density of the canopy.
Similar treatment will also be necessary in all localities exposed
to violent winds, or wherever the woodland covering is essential
for the maintenance of a good permanent supply of moisture
in the soil. Wherever sylviculture is practised on a consider-
able scale, coppice-woods are practically confined to mild
situations, and to shallow soils unsuited for the normal
development of the larger root-systems of trees when growing
in high forest.

For the production of the more valuable assortments of timber,
growth in high forest is a necessity in the case of conifers. It
is also generally advisable with regard to broad-leaved genera,
although the composite form or copse, in which light-demanding
trees of various age-classes form the standards over a coppice-
growth of shade-bearing genera, is often highly remunerative
where any favourable market exists for the produce yielded by
the latter.

The density of the crops is a factor which exerts no little

Studies in Forestry [CHAP. viu.

influence on their development and ultimate remunerativeness.
Crowded woods have practically no greater total enjoyment of
light, warmth, atmospheric food, and soil-nutriment than less
densely packed crops growing in closed canopy ; and as the
production of timber is distributed over a smaller number of
individual stems, the share which each is capable of receiving
is greater than when the total of the available food-supplies has
to be divided by the larger number. At the same time, in close-
canopied, but not crowded, woods, the natural selection of the
predominating stems to form the future mature crop proceeds
more rapidly, as the individuals of forward growth utilize some-
what above their average share of light, &c., and consequently
have a -larger annual increment, than if the struggle for life and
domination were more prolonged by having to be waged against
a larger number of individuals of equal vigour. Where, owing
to wide planting, the canopy is not of full normal density, the
productive capacity of the soil and of the atmosphere is not
utilized economically; hence a loss in timber takes place, which
might easily be avoided. The earlier the young growth forms
close canopy, the thinner are the branches formed, and the
sooner do they die and drop off. A normal density of canopy
therefore increases the technical value of timber by the pro-
duction of clean boles having a high form-factor and approxi-
mating, more than otherwise would be the case, to the
cylindrical shape represented by i-o. All crops intended for
timber production should, therefore, be maintained in close
canopy till they have entered the pole-forest stage of growth.
This is more particularly important with coniferous trees, whose
technical, and consequently monetary, value is dependent, to
a considerable extent, on freedom from hard horny branches
and knots. And it is of course all the more necessary in the
case of shade-bearing genera, whose lower branches are longer
retentive of life. Where, therefore, the early attainment of full
normal canopy can be achieved without special outlay at the
time of the young crop being formed, it is undoubtedly of great

CHAP, viii.] Formation of Timber Crops 169

financial advantage to see that due steps are taken to secure
this end. Now, with this object in view it is by no means
necessary to crowd plantations; for it is quite sufficient if
the twigs and branchlets die off before becoming strong
enough to leave snags or rotten ends in the timber, and if they
can be displaced by the new annual zones of wood. This
period varies with the different kinds of forest trees. The
branchlets of the ring-pored, broad-leaved species of trees rot
much sooner than those of conifers ; small twigs of Oak or
Beech snap off through their own weight when they have been
dry for two or three years; whilst similar twigs of Spruce
remain often as snags for ten or fifteen years, and get partially
embodied in the stem if not removed. For the production of
clean boles, therefore, conifers, and in particular the shade-
bearing kinds, should be maintained in close canopy consider-
ably longer than broad-leaved trees.

When the normal density of canopy is exceeded — that is,
when young woods are crowded— the development of the
individual stem is injuriously affected ; for the crowns are
liable to be drawn up so rapidly as to exceed the normal
proportion which in well-developed trees should exist between
height and girth. Crowded thickets should consequently be
weeded and thinned as diligently as possible, even though this
may involve considerable outlay. Otherwise the maintenance
and prolongation of the individual struggle for supremacy on
the one hand, and existence on the other, may have a very
prejudicial effect on the ultimate remunerativeness of the crop
throughout all the later stages of its development.

Where available, normal yield-tables in so far furnish hints
regarding the most advantageous density or initial number of
plants per acre in pure woods, that they show what the
minimum number should be at the various ages for the
particular genus of tree forming the crop on a soil of similar
average quality. Supposing, for example, it were found that
in Spruce forests, growing on soils of medium quality, the

170

Studies in Forestry

normal and most advantageous degree of density of canopy
is attained by about 3,000 stems per acre, then it stands to
reason that the formation of young crops, by planting at a
distance of 4 ft. by 4 ft. (2,722 per acre), would entail loss by
delaying the formation of canopy; whilst planting at 3 ft. by 3 ft.
(4,840 per acre) might, even after 'allowing for casualties, go to
the other disadvantageous extreme of crowding the plantation.
Many of the older plantations in Scotland that I have seen
were undoubtedly carried out without due consideration being
given to the desirability of having canopy formed within
fifteen to twenty-five years after the formation of the crop ;
hence the productive capacity of the soil cannot possibly
have been utilized to its fullest extent.

A little consideration will show that even in the case of
plantations which have been slow in attaining full canopy,
i. e. which have not been formed of the most advantageous
density, the crop may still form overcrowded woods between
twenty to forty years of age, owing to the tendency to rami-
fication induced by the individual plants having had larger
growing-space than was requisite, or would have been dictated
by sound economical considerations. Want of knowledge of
the most advantageous density for young crops is undoubtedly
one of the great faults of British sylviculture.

For planting, subject of course to variations according to
the nature of the soil and the situation, Gayer 1 recommends
the following distances : —

For shade-bearing genera and the Oak.

Class of Plants.

from

to

ft.
I XI

2

ft.

X 2

Small transplants, from i to 2 ft. high . . .
Stout transplants, from 3 to 4 ft. high ....
Very large transplants, from 6 to 8 ft. high . .

2 X 2

af x af
4x4

2|

4
10

X2|

x 4
x 10

Waldbau, 3rd edit. 1889, p. 355.

CHAP, viii.] Formation of Timber Crops

For light-demanding genera.

171

Class of Plants.

from

to

ft.

ft

Seedlings (Scots Pine, Larch) under 8 in. high .
Medium transplants, from 2 to 4 ft. high . . .

If Xlf

3i x 3$

5x5

Stout transplants, 6 ft. high and above . . .

5x5

as desired

Of course, when close planting is carried out, the young
plantations and thickets require very frequent and careful
tending in the way of clearings, before the regular thinnings
can be begun.

With reference to sowing, the amount of clean seed of
average quality recommended by Ney as sufficient for the
production of a moderate density of crop on soils of fair
average quality, may be seen on reference to the author's
British Forest Trees , 1893, page 50.

Choice of Method of Formation or of Reproduction
of the Crop.

The great advantage derivable from artificial reproduction
of forest crops consists in not being in any way dependent on
the occurrence of favourable seed-years, as nowadays seed
of all sorts can easily be obtained of good quality from
nurserymen in whatever quantity may be desired for sowing
out direct or for rearing seedlings and transplants in nurseries.
That greater uniformity and regularity of the crop can be
obtained artificially than when regeneration takes place natur-
ally, either under parent standards or from seed shed from
mature trees flanking the area to be re-wooded, hardly requires
demonstration. As the methods of sowing or planting are
usually simple, and as the operations are confined to a smaller
area than when several annual falls are grouped together for
gradual clearance, supervision and control are undoubtedly
at the same time easier.

172 Studies in Forestry [CHAP. VIIT.

This seems a not unsuitable opportunity of noting one
great difference between human beings and trees of the forest,
and of pointing out that there is no such thing as hereditary
disease in tree-growth. Thus Professor Hartig says l : —

* The hereditary transference of diseases to sup ceeding generations is
unknown in the vegetable world. The seed of plants inflicted with all
possible sorts of diseases may be utilized, without the slightest concern,
for the formation of new crops.'

Where woodland crops are to be formed for the first time,
a choice exists only between sowing and planting, in connex-
ion with which — leaving out of sight the special requirements
of the various genera and individual species of forest trees —
certain general considerations require to be weighed.

With regard to the soil, experience has shown that, on
places unfavourable to the early development of young crops,
planting is preferable to sowing, owing to the greater sensitive-
ness and need of protection of young seedlings during the
first stages of their existence. And better results are usually
obtainable from planting than from sowing, both on very
damp, wet, cold, or stiff soils with a tendency to being lifted
by frost, and on very loose soils apt to dry up easily, or such
as may have become deteriorated superficially through insola-
tion and exposure to exhausting winds, or which are liable to
inundation, &c. Where, owing to rank herbage of grass and
weeds, young growth has to struggle for its very existence,
sowing is the exception, and planting the rule, more especially
when the genera of trees forming the young crop are of slow
initial development. Unfavourable situation with regard to
climate, by retarding the growth during the first few years,
also weights the balance in favour of planting, especially in
raw, damp localities exposed to frost. Where planting up is
to take place on tracts that have been drained, but which
are still damp enough to show a strong growth of rank weeds,
sturdy transplants of hardy species, little sensitive to frost
1 Lehrbuch der Baumkrankheiten, 2nd edit. 1889, p. 16.

CHAP, viii.] Formation of Timber Crops 173

(Pines, Birch, Aspen, Alder), should be planted out during
autumn with balls of earth attached to their roots, or even
tumped on mounds if the soil is actually moist. For, as Hartig
well remarks l : —

' When trees or shrubs are planted out in any year and their natural
process of development has been so much interfered with that the new
shoots are not thoroughly developed by the time frost sets in, i. e. that
the process of forming woody tissue has not been properly completed,
such plants possess an abnormal disposition towards damage from frost.
They may hold out mild winters ; but, if severe cold occurs, the plants
may be killed outright.'

On all soils that are merely fresh and of a light, mild con-
sistency— the happy mean between loose and stiff, neither
apt to become too heated nor too rapidly cooled, and having
no immoderate tendency towards rank growth of weeds —
sowing is principally adopted, as also on rocky, stony outcrops
where there is hardly sufficient soil for the proper carrying out
of planting operations.

On the continent, sowing was formerly most generally
practised, and it was not until the introduction, on an extensive
scale, of the method of total clearance with artificial reproduc-
tion, that the present preference for planting became general
abroad. In Scotland, the total destruction of the Pine woods,
originally clothing vast extents of mountain sides now barren,
naturally led to the artificial formation of forests wherever the
proprietors desired to grow timber. And, in the vast majority
of cases, the conditions of soil and situation — raw northern
climate, rank growth of heather, heath, and other weeds, and
deterioration of the surface-soil by long exposure to the effects
of sun and wind — naturally pointed to planting as the best,
and often the only, means of attaining the object in view.
Good nursery seedlings, and especially sturdy transplants, must
have fewer difficulties in establishing themselves than tender
seedlings are exposed to in germinating on the area and over-

1 op. «'/., p. 15.

T74 Studies in Forestry [CHAP. vin.

coming the disadvantages with which they have to struggle
during the first two or three years of their existence.

Where sowing can take place under the shelter of standards,
or in the lee of crops nearly mature, it is much more likely
to be satisfactory than in the open. But, under nearly all
circumstances, there is usually a good deal of work and outlay
required for the filling up of blanks ; hence the final cost
of the formation of such young crops is not always less than
if planting had been carried out over the whole area at the
very outset.

Until nursery seedlings or transplants have established
themselves in their new abode, there is always a disturbance
and a diminution of the activity of the root-system ; and this
is accentuated by the trimming often requisite even in young
plants, and always necessary in older transplants. In this
respect sowing certainly has the indisputable advantage over
planting of permitting a more natural and uninterrupted
development of the root-system, and of effecting a better
accommodation of the latter to the nutrient characteristics
of the soil. The disturbances occasioned in transplants vary
according to the species of tree, the method of planting, and
the nature of the soil. Shallow-rooting species with good
reproductive capacity establish themselves much more rapidly
than deep-rooting species; while, on fertile soils, the efforts
made towards accommodating themselves to the new con-
ditions are more quickly responded to than on soils of merely
average or indifferent quality.

By the use of transplants, too, many of the dangers from
insect enemies during the first years of growth are avoided,
although experience in many different localities has shown
that sowings suffer on the whole less from Curculionidae than
where plantations are formed with small seedlings.

Comparisons between crops formed by sowing and by
planting during the last half-century have shown1 that in
1 Gayer's Waldbau, 3rd edit. 1889, pp. 383, 384.

CHAP, viii.] Formation of Timber Crops 1 75

very many cases plantations yield the better results both with
regard to height and to girth ; whilst, as regards total produc-
tion of timber (inclusive of thinnings), there is no particular
difference, although the proportion of branches is larger in
plantations owing to the greater initial growing-space enjoyed
by each individual stem. Whether or not the advantages as
regards dimensions will be maintained by plantations up to
the time of their fall as mature crops, is a question for the
answering of which no data are yet available for a trustworthy
comparison.

On the following point, however, it is well to note the
words of so eminent an authority on sylviculture as Professor
Gayer of Munich : —

' That the rapid initial development of many plantations considerably
affects the quality of the timber produced in comparison with what
is yielded by crops formed by means of sowing, and that consequently
the timber of the former is less able to withstand the attacks of fungi
later on, is no longer a matter of doubt or question.

' It must, however, be expressly stated that the youthful development
of timber crops can afford no reliable indication for the future quality of
the mature fall. Expectations, anticipations, and suppositions in this
respect have no justification ; as the whole matter depends most essen-
tially on the later treatment of the crops (whether formed by sowing or
by planting) during the operations of thinning out?

In estimating the financial advantages likely to accrue from
one or other of these methods of formation of crops, the
initial costs, of course, form an important factor. And, as
planting is, on the whole, more expensive, often very con-
siderably so, than sowing, a choice in favour of the latter
method can generally be advised wherever special conditions
of soil and climate do not indicate any necessity for planting.
Where, however, the inexpensive method of notching can be
carried out with very young seedlings without any special
preparation of the soil, planting operations can frequently be
undertaken just as cheaply as, or even cheaper than, sowing ;
and in all such exceptional cases planting deserves the prefer-

176 Studies in Forestry [CHAP. vni.

ence. But the initial costs of sowing are apt to be mis-
calculated ; and the subsequent filling in of blanks with
transplants often brings up the actual cost to more than
would have been the initial expense had planting been chosen
as the original method of forming the crop.

Plantations have, in general, notwithstanding the inter-
ference and disturbance that takes place before the plants
have thoroughly established themselves, a more rapid develop-
ment in youth, and especially a more energetic growth in
height, than young crops resulting from natural regeneration ;
whilst those formed artificially by sowing occupy a position
between these two. These results are explainable by the
greater amount of soil-preparation connected with both forms
of artificial production and reproduction, and, in the case
of plantations, with the larger amount of individual exposure
to light, air, and warmth, together with a less prolonged
struggle with weeds and rank growth of grass.

Natural reproduction is, on the whole, much cheaper than
either of the artificial methods. And, when properly conducted,
it affords greater protection against frost, drought, and injurious
insects ; whilst, at the same time, it maintains the surface-soil
subject to the least possible variations in its quality, its cover-
ing, and its productive capacity. As greater density of the
young crop is usually attained, the thickets grow up remark-
ably free from branches; but the superior quality of the
straight-grained timber is apt to be counterbalanced by the
danger to which the young crop is exposed if the poles are
allowed to be drawn up too quickly in their mutual struggle
for light and air. This struggle for existence is more severe
and of longer duration than in the case of crops formed
artificially, and especially of plantations; hence careful, oft-
repeated clearing and weeding in thickets, and thinnings in
pole-forest, are absolutely essential for the avoidance of over-
crowding.

For the successful accomplishment of natural regeneration

CHAP, viii.] Formation of Woods 177

higher demands are made as regards sylvicultural knowledge
than when total clearance with artificial reproduction is the
method followed ; and, when seed years are apt to be irregular,
it often taxes the ingenuity of the manager of large woodlands
to maintain the annual fall of timber without over-stepping
the limits dictated by prudence with regard to the gradual
clearance preliminary to the seed-felling.

It has frequently been objected to natural reproduction that
the growth of the young crop is at first much slower than in
plantations; but such objectors evidently do not attach suffi-
cient weight to the quantitative, the qualitative, and especially
the financial, increment which takes place simultaneously on
the parent standard trees before the final clearance of the
mature crop.

There is one great drawback of plantations, as compared
with crops formed either naturally or by sowing, which seems
inherent from the larger amount of growing-space enjoyed by
each individual plant — that is, an undeniable tendency to
forked or branching growth. This was conclusively proved
by the experimental section of the Forestry Department at
Munich University in 1885 to 1887 ; and it has been also con-
firmed for the tropics by my own observations in the extensive
Teak plantations of Burma. The reason is obvious. As the
individual struggle is not at first so great in plantations as
in sowings or in natural regenerations, it more frequently
happens that one or other of the side-buds throws out a shoot
almost equal in size to the axial, true leading-shoot ; and as
years advance the fork becomes more developed, thereby
reducing the value of the timber through spoiling the bole
for technical purposes. This tendency may best be observed in
coniferous forests, especially of Spruce, where three, four, and
even five definite and more or less successful efforts at forked
growth are often distinctly recognizable. The same influences
are also at work in other kinds of trees. They tend to dissipate
in ramification the energy in growth which it is the great aim

N

1 7$ f Studies in Forestry [CHAP. vin.

of the sylviculturist to confine to the main object of the pro-
duction of a large, clean bole as nearly cylindrical as possible.
The necessity for artificial formation of forests in Scotland
during the past century has already been recognized. But as, in
very many cases, mature crops are now awaiting utilization and
reproduction, the attention of those concerned in the manage-
ment of wooded estates may well be called to the later
advantages offered by natural reproduction, even although at
first the rapid increment in plantations seems to point to that
method of regeneration as being the most profitable. Yet
there is no reason why a compromise should not be effected,
natural reproduction being carried out at first to whatever
extent it shows itself easy of success, and artificial assistance
being then availed of without waiting for the further production
of seed by the parent standards. The means thus offered
for the formation of mixed crops should in reality add to,
rather than detract from, the advantages offered from both
a sylvicultural and a financial point of view.

CHAPTER IX

THE TENDING OF WOODS

IN one respect there is a strong analogy between human
beings and woodland growth ; for education or tending is just
as necessary in the one case as the other in order to achieve
the best results ultimately attainable. With regard to wood-
land crops this is most particularly requisite in mixed woods.
The ultimate shape and value of the boles of the light-
demanding species of timber-trees depend to a very great
extent on the treatment accorded to the woods during the
earlier stages of their development.

Whether the crops be formed naturally by regeneration
under parent standards, or artificially by means of sowing
or planting, many young woods require a certain amount of
protection against dangers arising from inorganic causes like
frost, snow, raw winds, and drought, and from organic causes
like weeds, insects, and fungoid diseases.

When mature falls of timber are reproduced naturally, or
by means of sowing before removing the whole of the mature
trees, the requisite degree of shelter can be to a certain extent
attained by leaving a sufficient number of parent or other
standards per acre. Fortunately, the great majority of trees
grown in Britain are of rapid growth during their earliest years,
and soon outgrow danger from frost and drought, to which
the light-demanding genera, Larch, Pine, and Birch especially,
and in a less degree also Oak, Ash, and Maples, are naturally

N 2

1 80 Studies in Forestry [CHAP. ix.

less exposed than the shade-bearing species, Beech, Silver
Fir, and Spruce. But, when sowings or plantations are formed
in the open, it is often necessary to plant out quick-growing
and hardy species as nurses, in order to minimize any dangers
existing from late and early frosts ; and for this purpose Birch,
Scots Pine, and Larch are best suited, as they naturally suffer
little from cold, are rapid in growth, make least demands on
the soil, and cast but a light shade around them. In damper
localities Willow and Alder are often to be found spontane-
ously performing similar duties for the benefit of Oak, Ash,
and Spruce.

A protection against raw winds may be obtained by carry-
ing out the annual falls of mature timber, and consequently
the re-formation of young crops, in the direction contrary
to that of the prevailing winds. Although this measure is
adopted chiefly on account of the older and more valuable
crops of timber, to protect them from being thrown, yet the
youngest falls at the same time receive the benefit of lying
to the lee of the high tree-forest.

That rank growth of weeds, whether consisting of grasses or
berries, or of woody-fibrous plants like heather, gorse, whortle-
berries, and the like, must be cleared away so far as they
interfere with the development of the young crop, is of course
self-evident, unless the future financial value of the mature
crop is to be allowed to run the risk of being considerably
prejudiced.

It may be remarked here that, as fully explained previously on page
132, coniferous trees are much more liable to such dangers altogether, and
to serious damage from insects and disease especially, than broad-leaved
genera, and also that mixed woods suffer less in this respect than pure
crops of only one kind of tree practically.

And, in the same way, any outlay for combating the attacks
of injurious insects, or for annihilating fungoid diseases that
may have gained a foothold, is just as essential for the
present and the future well-being of the crop as if it had

CHAP. ix.] Tending of Woods 181

actually formed a necessary portion of the initial cost of
formation ; for no matter whether raised naturally, or artificially
by sowing or planting, the development of the young growth
is essentially dependent on the time when, and the extent
to which, a full and compact leaf-canopy is attained.

Sometimes, in natural regenerations and in sowings, the
young seedling growth is so crowded that the crop becomes
half choked, and the individual plants, in their resulting
struggle for light and air, become drawn up so attenuatedly
as not to be able to bear their own weight. In the case of
the shade-bearing genera, they then remain to all appearance
almost stationary ; but the natural process of selection is very
much more rapidly effected by the light-demanding kinds of
trees. Yet in both classes of trees some artificial aid in the
struggle is of untold benefit to the survivors from among which
the future mature crop is to be formed. The earlier such
operations of tending are begun the better ; and when young
plants are not required for transplanting, the best and cheapest
way is to use the shears as much as possible in cutting off
weaklings close to the ground. Should this measure, from one
cause or another, have been delayed till the young crops are
from ten to twenty years of age, then the general reduction in
the number of plants must be undertaken very cautiously, else
the remaining saplings, bereft of support, are apt to lean over
and even to get quite laid after heavy snowfall. It is therefore
best to cut narrow lines through the thicket, thus allowing
the plants along the edges a good chance of developing more
rapidly and vigorously than those between the lines. These
dangers are not so great in plantations, where the greater cost of
close planting secure comparative immunity from such a risk.

In practice it much more frequently happens that in young
crops, whether formed naturally or artificially, the density is
below the normal degree most favourable for their develop-
ment. Wherever blanks may thus occur, they should be planted
up at once with the species of tree best suited for soil and

1 82 Studies in Forestry [CHAP. ix.

situation, and most likely to be in accordance with the wishes
of the proprietor in regard to the ultimate form of the crop.

It also, however, not uncommonly occurs that the general
development of the young crop is somewhat backward, in
which case it may be necessary to stimulate its energy by the
introduction, temporarily, of quick-growing and lightly-foliaged
species, not apt to cast any heavy shade around them. In
general the special trees chosen for performing this duty are
again Scots Pine, Larch, and Birch, on ordinary classes of soil,
or Aspen, Willow, and White Alder, on land of a moister
description. By planting single rows of these trees at good
distances apart, very stimulating effects can be attained in
backward growth of young crops of Oak, Beech, Spruce, and
Silver Fir. As, however, this measure is temporary only, and
not permanent, these rows of supplementary nurses should
be gradually removed wherever, and whenever, the growth
of the principal genera forming the crop permits of this
being done.

When once the normal density of canopy has been attained,
the manner in which the different operations of tending are
carried out in thickets of sapling growth, in young pole-forests,
or in tree-forests, has unmistakable influence on the imme-
diately subsequent development, as well as on the quantity, the
quality, and the financial value, of the future mature timber-crop.
These operations are of three distinct kinds, viz. : —

1. Weedings and clearings, including all operations involv-
ing an outlay which is not covered by the amount realizable
for the disposal of the material cut out.

2. Thinnings, when the costs of the removal of the super-
fluous or undesirable poles or trees are covered, or more than
covered, by their sale.

3. Partial clearances, carried out in tree-forest, after the
chief growth in height has been completed, with a view to
the more rapid development of large-girthed, full-wooded

CHAP, ix.] Tending of Woods 183

boles — that is to say, for the production of stems with good
top-diameter relatively to the base or butt-end.

1. Weeding and Clearing.

Practically, weeding and clearing, and thinning, are identi-
cally similar measures. But in the former case the outlay is
properly debitable to the cost of formation of the young crop.
The operations are cultural charges which must be met in almost
every case, as well as the cost of soil-preparation, sowing,
planting, filling up of blanks, &c. As the outlays for weeding
and clearing are, as a rule, greater in thickets formed by natural
reproduction, or by thick sowing, than in plantations, this
tends to equalize the costs of formation, although lower initial
outlay is often claimed as an advantage of the former methods
over planting. Comparatively few crops are raised from seed
without softwoods (Birch, Aspen, Willow) at the same time
managing to effect a foothold on the soil, which they often
retain with extreme tenacity by throwing up stool-shoots and
suckers whenever they are cut back. They thus often interfere
with the normal development of the young crop only in just
a less degree than if they had been allowed to remain where
they took root uninvited. The removal of all such intruders
is the special aim of weeding ; whilst clearing is undertaken
for the removal of all such individuals, of whatever species,
forming part of the original crop as may, if allowed to stand
longer, so as to compete with them for light and air, detri-
mentally affect the further development of other kinds of trees
which it is desired to encourage or to stimulate in energy of
growth.

So long as the material to be thus removed is gaining in
value, the object is not to remove as much as one safely can,
but rather to confine operations solely to the removal of what
is necessary for the well-being of the rest of the crop. The
process of clearing must be repeated as often as necessary ;
but under ordinary circumstances, in fairly populous tracts,

184 Studies in Forestry [CHAP. ix.

or where small poles are required for pea-sticks, hop-growing,
and the like, they should cease to be requisite before the crop
enters on the period of its most active growth in height as
pole-forest. Under such circumstances thinnings should begin
early, and may often prove highly remunerative.

From the purely financial point of view the results attainable
by weeding and clearing are commensurate with the ultimate
disadvantages that may probably, and, as continental experience
has shown, will almost invariably, accrue, if such cultural
measures be neglected. Of these the principal include danger
from accumulations of snow and ice, ravages by insects finding
a suitable breeding-place in sickly, suppressed, or dominated
saplings, and diseases of roots and stems occasioned by fungi
like Trametes, Agaricus^ &c. Neglect of these early measures
of tending leads in a very short time to dissipation of the
vital energy of the crop, to the overstocking of the area with
an excessive number of individual stems of small technical or
financial value, to the crowding out and suppression of the more
valuable trees by kinds of less value, and ultimately to the
necessity of clearance and utilization of the crop at a date
much earlier than its technical and commercial maturity would
otherwise have been indicated financially.

Wherever reliable data may exist for a comparison of the
ultimate returns obtained from two different crops grown on
similar soils and situations, and both formed by similar
methods, though subjected to essentially different treatment
during the early stages of growth, it will invariably be found
that, when a less valuable species or individual has been
allowed to interfere with the development of a more valuable,
on comparison of the net ultimate returns from the mature
crop plus all the intermediate returns from thinnings, capital-
ized up to the time of utilization of the two mature falls of
timber, then the capitalized outlay on weedings and clearings
can be proved to have been money very well laid out
simply as a further investment of capital.

CHAP, ix.] Tending of Woods 185

2, Thinnings in Pole-forest and Young Tree-forest.

Under thinnings are understood all operations for the
removal of unnecessary species or individuals in timber crops,
dating from the time that the outlay thus occasioned is
covered by the returns obtained for the material removed, and
thence onwards throughout the pole-forest and the tree-forest
stages of growth, till a commencement is made of the clear-
ances for reproduction or utilization, or until partial clearances
are made, after the chief growth in height has been completed,
for the more rapid development of large-girthed boles with
good top-diameter.

The ultimate quantitative and qualitative outturn from
woodland crops depends much more on the proper conduct
of the thinnings than on the preliminary operations of weeding
and clearing. Practically, there is generally a period, of shorter
or longer duration, in which the thickets formed from natural
reproduction or from sowing are almost impenetrable ; and in
mixed forests, in which the more valuable subordinate species
occur individually, and not in patches, this is often the most
critical period for these latter kinds of trees.

The object of thinning any crop is to stimulate and to assist its
development so that the aim of the proprietor may be attained
as completely and as soon as possible, without necessitating any
such interruption of the canopy as may prejudice either the
growth in height of the crop or the productive capacity of the
soil. The crops which stand most in need of thinning, and of
a frequent repetition of the operation, are those in which the
individual stems are all of about the same age ; as the natural
struggle for individual existence is then more keen and pro-
longed than where some plants of advance-growth have from
the very outset won an advantage. In this process of natural
selection four classes of stems become distinguishable, viz.

1 86 Studies in Forestry [CHAP. ix.

(i) predominating, (2) dominant, (3) dominated, and (4) sup-
pressed.

As, during the gradual process of death and decay that
takes place when stems become suppressed, certain physio-
logical conditions obtain, which are extremely favourable to the
breeding of insect enemies and the propagation of fungoid
diseases, this class of individual stems should invariably be
removed during thinning operations. By this means a freer
circulation of air and a better utilization of the soil-nutrients
are also at the same time effected.

To what extent a simultaneous removal of the dominated
class should proceed, depends in each case on the ccncrete
factors of soil, situation, species of tree, age of crop, mode of
treatment, &c. If the struggle were left to nature unassisted
it would be carried out most rapidly on fertile soils ; but, on
soils of merely average or inferior quality, it would be so much
prolonged in the case of shade-bearing species of trees as to
result in overcrowding of the crop throughout the pole-forest
and the young tree-forest stages of growth.

From the sylvicultural point of view, however, the main
objects of care are the timber-trees which it is desired to
utilize on their attaining full financial maturity ; and any
measures that will aid in stimulating them to the speedy attain-
ment of large remunerative dimensions must deserve favour-
able consideration. Year by year the number of individual
stems, from which it is possible that the future mature crop
may be formed, becomes diminished ; and the removal and
the utilization of all unnecessary stems are not only a means
of improving the growth of the predominating and dominant
portions of the crop, but are likewise a source of revenue,
which should be realized as soon as available, in order to
reduce the capital cost of the crop both at present and up to
its final clearance. And these preliminary or intermediate
returns are often of no mean value where any good market exists
for small timber like poles and pit-props. Thus Grebe, a dis-

CHAP, ix.] Tending of Woods 187

tinguished sylviculturist of Thuringia, who was for many years
the Principal of the Forest School at Eisenach, wrote as
follows * : —

' Granted that the thinnings begin at the proper time — in the case of
the Beech about the twenty-fifth to thirty-fifth year, the Spruce about the
twentieth to thirtieth year, and the Scots Pine about the fifteenth to
twenty-fifth year — that they are regularly conducted, that the yield
therefrom is not reduced by any peculiar local circumstances (such as
right of collection of windfall, or interruption of density in canopy due to
snow accumulations, &c.), it may be expected that on the average the
proportion which the intermediate yield from thinnings bears to the final
yield of the mature crop will be : —

In Beech Woods, with a rotation of —

80 years, from 12-20 per cent.

100 » » i4-25 »
120 „ „ 16-30 „

The lower percentage is obtainable from poor soils, the higher from
the better classes of soil.

In Spruce Woods, with a rotation of —

60 years, from 15-17 per cent.

80 „ „ 20-22 „

ioo „ „ 23-26 „
The higher percentages are obtainable from the inferior classes of soil.

In Scots Pine Woods, with a rotation of —

60 years, from 1 8-24 per cent.
80 „ „ 22-28 „
ioo „ „ about 25 „
The higher percentages are obtainable from the inferior classes of soil.'

For pure Spruce forests on the Harz Mountains, Theodor

Hartig found the following total number of stems per acre 2 : —

At 20 years of age, 9,2653 of which 49

„ 40 „ 1,249 „ 42

» 60 „ 603 „ 32

» 80 „ 388 „ 21

>, ioo „ 282 „ ii

» I2° » 238 „ 4

1 Die Bctriebs- und Ertragsregelung der Forste, 1879, p. 300.

2 Gayer, Waldbau, 3rd edit. 1889, p. 15.

3 This only refers to natural reproduction and sowing ; it would of course
be much less in the case of plantations. But compare with the above the
remarks made on page 57.

might be advantage-
ously removed by
thinning.

i88

Studies in Forestry

[CHAP. IX.

In mixed forests the practice of thinning must, of course,
be conducted on quite a different principle from that obtaining
with regard to pure woods. Thus in order to save a valuable
species of tree, it may very often be found necessary to cut out
other kinds of more energetic growth, which may threaten to
prejudice its development, or even to endanger its existence.

As regards the influence which the species of tree has on the
extent to which thinnings are necessary, Schuberg3 found in
the Black Forest that in forty to eighty-year-old crops, which
had been regularly thinned, the following were the results on
soils of average quality : —

Kind of Crop.

Scots Pine.

Spruce.

Beech.

Silver Fir.

Average number of
stems per acre

545

619

686

864

Absolute individual
growing - space in
square feet

80

70

63

5°

Relative individual
growing-space

100

87

' 79

63

If the chief light-demanding genera (Pine, Larch, Oak, Ash,
Maple, Birch, &c.) be grouped together, and be compared with
the various shade-bearing kinds of trees, it will be found that
on the whole these, latter only require on the average from
50 to 75 %, or one-half to three-quarters, of the growing-space
demanded by the former for their proper development as
a woodland crop.

The quality of the soil is also a very important factor in deter-
mining the number of stems per acre. Owing to the more

1 Gayer, op. tit., p. 550.

CHAP, ix.] Tending of Woods 189

equal strength with which the individual struggle for supremacy
is waged on soils of indifferent quality, the growing-space per
stem is, up to the sixtieth to eightieth year, often considerably
less than on better soils, although in the case of the Scots Pine
this difference is less marked than in any other species. The
practical lesson thereby conveyed is that, on soils just of or
below the average in quality, both financial and purely sylvi-
cultural considerations point to the advisability of stimulating,
by means of early, oft-repeated, and moderate thinnings, the
development of all individuals which it is desired to retain.
Thin early, often, and moderately is the golden rule of tending
woodlands. Anything approaching interruption of the canopy
during the period of most active growth in height must of
necessity lead to a further development of the crown at the
expense of the length and cleanness of the bole ; and this will
consequently tend towards a diminished technical and monetary
value of the timber produced.

Between the two extremes of overcrowding and of free
individual growing-space there must be in every kind of
crop a happy medial point or a normal density of canopy, at
which the quantity and the quality of the crop attain their com-
bined maximum. To show the practical effect which thinning
has on the increment of the basal area of the individual stems left
forming the crop, the following example may be given. In two
different parts of an extensive forest three areas were selected
on soil of similar nature and quality, and thinnings were carried
out on equal areas in the following degrees : —

I. Slight, only dead and dying poles being removed.
II. Moderate, all suppressed poles being removed.

III. Heavy, all dominated poles being removed.

The conditions as to soil and situation were in each locality
as similar as possible, the soil being a fresh, loamy sand
throughout. The results of the experiment were tested five
years after the thinnings took place.

190

Studies in Forestry

[CHAP. IX,

I. — In the first instance, that of a thirty-seven-year-old crop
of Spruce, raised by planting, the data 1 were : —

Previous to thinning:

Area No.

Nature of thinning.

No. of stems
per acre.

Total Basal area,
sq. ft.

I.

Slight ....

2,126

242

II.

Moderate . . .

2,IOO

25J

III.

Heavy ....

2,044

234

During the thinning there were removed —

Area No.

Stems per acre.

Basal area removed,
sq. ft.

Percentage of Basal
area removed.

I.

502

9

About 3f

II.

822

28

„ XI

III.

971

37

„ 16

In consequence of the thinning, the arithmetical mean
diameter at breast-height (4^ ft.) of the stems that were left
was found to be —

On area I, 5-12 inches ;

On area II, 5-68 inches;

On area III, 5-84 inches;

whilst five years later , just before another thinning was to take
place, it was found to have increased —

On area I to 5-48 inches, or an average diametral increment
of 0-36 inches per stem.

1 These and the following data are, by permission, excerpted from
Dr. M. Behringer's prize thesis Ueber den Einfluss wirthschafflicher
Massregeln auf Zuwachsverhaltnisse ^lnd Rentabilitdt der Waldwirthschaft,
1891, pp. 19 et seq.

CHAP. IX.]

Tending of Woods

191

On area II to 6-16 inches, or an average diametral increment
of 0-48 inches per stem.

On area III to 6-40 inches, or an average diametral increment
of 0-56 inches per stem.

II. — In the other locality, a thirty-six-year-old Spruce wood,
raised by sowing, the data were : —

Previous to thinning:

Area No.

Nature of thinning.

No of steins
per acre.

Total Basal area,
sq. ft.

I.

Slight ....

7,707

2I9

II.

Moderate . . .

7,725

235

III.

Heavy ....

7,497

22O

The operation of thinning removed —

Area No.

Stems per acre.

Basal area removed,
sq. ft.

Percentage of Basal
area removed.

I.

4736

29

About 1 3

II.

5,6l9

53

„ 22

III.

5,9*5

71

32

when the arithmetical mean diameter at breast-height of the
remaining stems was found to be —

On area I, 3-44 inches ;

On area II, 4-00 inches ;

On area III, 4-20 inches ;

and, just previous to another thinning five years later ^ it had
risen —

On area I to 3-88 inches, or an average diametral increment
of 0-44 inches.

192

Studies in Forestry

[CHAP. IX.

On area II to 4-48 inches, or an average diametral increment
of 0-48 inches.

On area III to 4-72 inches, or an average diametral increment
of 0-52 inches.

The actual average increment in basal area was found to be
per annum per acre —

I. In the Plantation.

II. In the Sowing.

Area

I.

sq. ft.

6-6

Area.

I.

sq. ft.
8-9

»

II.

7-7

>»

II.

8-7

»

III.

8-2

>?

III.

8-2

Comparing the average annual increment with the total basal
area at the middle of the period of five years, the percentage
of annual basal increment was found to be —

In the Plantation.

In the Sowing.

Area.

I.

per cent.
2-68

Area.

I.

per cent.

4-27

r»

II.

3-22

>»

II.

4-39

5>

III.

3-85

>>

III.

5.02

The obvious conclusions from these data seem to be that
in plantations, in which from the very outset each individual
plant has a fixed amount of growing-space, the natural process
of selection proceeds so much more rapidly than otherwise
that—

I. There is less risk of any overcrowding of the leaf-canopy.

II. Despite the smaller number of stems per acre, the total

CHAP, ix.] Tending of Woods 193

basal area (i. e. the sum-total of all the stem-superficies at breast-
height) is certainly not less than in dense crops raised from
seed or by natural regeneration.

III. A far less percentage of the total number of stems
belongs to the dominated and suppressed classes.

IV. The stimulation of the increment in basal area takes
place in accordance with (though it is not necessarily propor-
tional to) the degree to which the thinning takes place.

So long, therefore, as thinning is not carried to such an
extent as to prejudice the energy of growth in young crops that
have not yet nearly completed their activity, i. e. which have not
yet culminated in average annual increment, a free thinning
stimulates to the earlier maturity of the crop, and is there-
fore decidedly advantageous from a financial point of view.
Thinnings are, generally speaking, said to be slight when only
dead or dying poles are removed, moderate when all suppressed
poles, and also a portion of the dominated poles, are cut out,
and heavy when at the same time all the dominated poles are
eliminated l.

It may be noted here that, in tree-forest, a slight thinning
removes about 5 % of the basal area of the stems at breast-
height in crops of normal density of leaf-canopy, a moderate
thinning about 10 %, and a heavy thinning about 15 %. Where
it goes beyond this last degree, it becomes in reality a partial
clearance, and must be regarded as such.

The average percentage of basal increment has been given
above ; but it must be observed that these figures are subject to
modification. For the actual percentage of basal increment is

1 In the special case referred to on p. 64 the moderate thinning was
particularly stated not to include any of the dominated stems, as these
were all included in the heavy thinning. But it must be borne carefully in
mind that the thinnings were carried out in dense crops of Spruce, which is
one of the most shade-bearing kinds of trees. For crops of light- demanding
trees, like Oak, Larch, Pines, Ash, Maple, Sycamore, Elm, Birch, Willow,
and Poplar, even a moderate thinning would certainly remove a portion of
the dominated individuals ; but the extent to which these should be cut
out would, in each concrete case, depend on the kind of trees forming the
crop, the general vigour of the latter, and the nature of the soil and situation.

O

194 Studies in Forestry [CHAP. ix.

greatest just immediately after the thinning takes place ; and it
gradually decreases as the crowns close up again towards the
termination of the period at which another thinning becomes
necessary. The physiological explanation of this decrease is to
be found in the fact that the assimilative functions of the lower
foliage again become weakened through the gradual exclusion
of the light, air, and warmth requisite for assimilation.

Experience has shown that the height of timber crops, as
well as being practically proportional to the quality of the soil
for the species of tree in question, is, in all regular crops grow-
ing on soils and situations of similar quality, and under similar
conditions as to their development, as a rule proportional to
their basal area until they have completed their chief growth
in height. But when the conditions of development vary, as
must be the case when, ceteris paribus, certain woods are only
slightly thinned, and others moderately, or perhaps even heavily
thinned, then the natural proportions between height and girth
become to a greater or less extent interfered with. The fuller
the leaf-canopy remains, the more, does the form of the bole
approximate to the cylindrical (i. e. the higher does the form-
factor become) ; and the freer the growing-space, the greater is
the tendency to conical growth of bole (i. e. the lower does the
form-factor become) with simultaneous increase of branch de-
velopment. Experiments carried out in Beech and Scots Pine
woods by Dr. Behringer, under the direction of the experi-
mental section of the Forest Branch of Munich University,
went to prove l that —

' When thinnings were carried out freely, the development in height was
relatively much greater than the diametral increment : and that at any
rate during a certain period in the growth of crops, the heaviest degree
of thinning produced the loftiest and the cleanest boles.'

Of course, the correctness of this statement, or of any other
dictum with regard to most of the operations of practical
sylviculture, depends in each case on the nature and condition
1 Op. cit., p. 28.

CHAP, ix.] Tending of Woods 195

of the crop in question as to species of tree, age and mode of
formation of crop, condition previous to, and at time of, thin-
ning, nature of soil and situation, &c. But Weise1 seems
perfectly correct in making the broad generalization that—

' When a crop is too thick, increment in height and in girth both suffer
to an extent not compensated by the outturn jnelded from the greater
number of stems ; when it is too thin, however, the crop remains back-
ward in growth in height.'

Experiments made in order to endeavour to formulate a
natural law regarding the effect of slight, of moderate, and
of heavy thinnings on increment in height, girth, form-factor,
and total yield of timber per unit of area, have hitherto failed
to yield any practical result. On the whole they simply lead one
in a general way back to appreciate the wisdom and the prac-
tical value of the rule, founded on experience, that * thinnings
should be begun early^ carried out moderately, and repeated
frequently' This does not militate against the correctness of
the theory and the practice of partial clearance, after once the
chief growth in height is completed, for the purpose of stimu-
lating the trees to rapid increment in girth and to improvement
in the shape of the bole.

And, practically, the same conclusion must be come to when
the matter is viewed from the financial standpoint. Although
increased returns from material thinned out and profitably
disposed of — regarding them not only as items reducing the
capital represented by the growing stock, but also as sums
which, for correct reckoning, must be taken as growing in value
at compound interest till the whole mature crop is harvested —
would point to the desirability of heavy thinnings, and would
perhaps yield fair results where the market for small timber is
favourable, yet the future well-being of the ultimate crop is
undoubtedly the main object to be kept in view. And here,
again, experience has shown that considerations affecting both
the productive capacity of the soil, and the normal development

1 See Chronik, 1881, p. 25.
O 2

196 Studies in Forestry [CHAP. ix.

of the crop, are most favourably kept in view when the degree
to which thinning is carried out, at each time of repeating the
operation, is only moderate — although on soils of better than
a merely average quality it may well be somewhat freer than on
those of a poorer nature.

3. Partial Clearances in Tree-forest.

Partial clearances are made in tree-forest when over 15 %
of the basal area is removed for the express purpose of affording
freer supplies of light and air, so as to stimulate the rate of
increment, and thus enhance the technical and the financial
value of the timber.

This sylvicultural operation, which is merely a more vigorous
and emphasized expression of the theory of thinning, may be
carried out after once the timber crop has passed through the
most active period of growth in height ; for then the advantages,
offered by increment in girth and in full-woodedness towards
the top-end of the bole, are not, to anything like the same
degree as during any earlier stage of development, prejudiced
by such increment being perhaps stimulated at the expense
of the rate of growth in height. The removal of up to 15 %
of the total basal area, when the crop stands in full canopy,
is still a thinning; whereas the removal of 18 or 20 % is
already a partial clearance. But the latter operation is practi-
cally merely a continuation of the former ; only it is carried out
with a freer hand.

Whilst, in thinnings, the conservation of the productive
capacity of the soil is one of the most important objects to
receive consideration, in a partial clearance its maintenance, by
means of the tree-crop alone, is seldom attainable except on
soils of the very best quality ; hence underplanting is usually
necessary, simultaneously with the partial clearance being
made \ Throughout the whole of the operations of tending —

1 A fuller consideration will be given to this subject in Chapter XI,
On Underplanting.

CHAP, ix.] Tending of Woods 197

the weedings and clearings, the thinnings, and the partial clear-
ances— the same object is definitely kept in view, viz. the
best possible ultimate development of the individual stems
forming the chief financial factors in the mature crop. During
all these tending operations the more valuable kinds of trees
are not only protected against other species threatening their
existence, but efforts are also consistently made to procure for
them, at all the various stages of their development, such
conditions relative to growing-space, &c., as may produce the
greatest outturn of long-stemmed, large-girthed, and full- wooded
timber in the shortest space of time — or, in other words, as may
produce the most valuable timber, technically and financially,
at the least cost of production.

In practical forestry this method of partial clearance is
to a great extent naturally confined to Oak, Scots Pine, and
Larch ; for the other light-demanding species of trees, Maples,
Elm, Ash, Birch, &c., which are in request for ornamental work
chiefly, are generally utilized during the later thinnings. When
forests, in which the ruling species is Silver Fir or Beech, are to
be naturally reproduced, the same stimulation to increment in
girth, and to improvement in the shape of the bole, is prac-
tically obtained during the clearances made preparatory to, and
following after, the seed- felling. In sheltered localities the effects
of partial clearance are also very profitable in the case of Spruce
crops, which, owing to the great danger to which this shallow-
rooting species is exposed from windfall, are not generally
regenerated naturally, except under very favourable circum-
stances as regards protection from winds.

When the first partial clearance is made — in Oak woods
about the fiftieth to sixtieth year, in Scots Pine between the
thirtieth to fiftieth year, and in Larch about the thirtieth to
thirty-fifth year — the fall is confined to all stems of inferior
development, or to such as do not give promise of ultimately
producing timber of the better class. Later on, in about five,
or ten, or fifteen years, when the standard trees gradually begin

198 Studies in Forestry [CHAP. ix.

to approach each other in an endeavour to form canopy, the
clearance has of course to be repeated, in order that the
foliage on the lower branches, and within the interior of the
crowns, may not be hindered in its assimilative functions,
owing to the decreased measure of exposure to light and air to
which they must be reduced in anything like close canopy.
As in regard to thinnings, there can be no hard and fast rules
for the conduct of partial clearances ; for so much depends on
the quality of the soil and situation. But, practically, they
should be repeated at intervals of about five to ten years at
first, and about ten to fifteen years later on. Oak woods
treated in this manner about the fiftieth to sixtieth year should,
according to Gayer1, yield a quantitative annual increment of
from 3 to 3^ % up to their looth year, and 2 to z\ % after that,
without taking into consideration the qualitative, technical,
and financial increment simultaneously rising more rapidly. At
120 years of age the Oak woods treated thus should show about
thirty-six to forty-eight stems per acre. Larch crops partially
cleared from the thirtieth to thirty-fifth year onwards should,
on situations naturally adapted for their growth, at sixty to
seventy years of age show about sixty to seventy trees per acre
with an annual increment of from 3 to 4 %. In Scots Pine
woods a repetition of the process is only advisable on the
better classes of soil, as, otherwise, experience has shown that
better results can generally be achieved by letting the whole of
the standard trees come together to form the light canopy
which is their characteristic on inferior soils and situations,
and beneath which a crop of underwood can usually thrive fairly
well. In mixed woods of Spruce, Silver Fir, and Beech
excellent results have been attained by beginning to thin rather
heavily about the thirtieth year, repeating the thinnings every
tenth year, and then making a partial clearance between the
sixtieth to seventieth year, so as to leave per acre about 120
to 1 60 trees of sound, promising growth. In crops thus
1 Op. cit., pp. 574, 575.

CHAP, ix.] Tending of Woods 199

treated, after the lapse of twenty years natural regeneration
will generally be found to have been effected spontaneously,
the standard trees will be of good marketable dimensions and
excellent quality, and the seedling growth will vary from
about 3 to 15 feet in height. Blanks left by the removal of
the standards can easily be most advantageously filled up by
planting with Pine, Oak. Larch, Ash, Maple, &c.

Of course, an essential condition for the success of this
measure is that the crops are still in active vitality and capable
of being stimulated to quantitative and qualitative increments.
The operation would be useless in the case of trees already
entering, even prematurely from injudicious treatment or any
other cause, into the stage of senile decay. With reference to
the relative and the absolute increment on individual stems
after partial clearance, Behringer l gives some interesting and
instructive data, which are exhibited in tabular form on the
two following pages.

Measurements made at the same time showed that the rate
of growth in height had been sensibly diminished in con-
sequence of the greater amount of growing-space afforded after
the partial clearance. But as the operation was not performed
until after the most active period of growth in height had been
completed, this diminution was of comparatively little technical
or financial importance.

So far as these experiments go they prove not only that,
owing to the larger growing-space, each of the standards was
stimulated to produce more than double the increment in
cubic contents which it had before the partial clearance took
place, but also that, whilst in regard to the Spruce the enhanced
increment culminated within the first decade after this opera-
tion, the culmination was delayed in the cases of the Scots
Pine and the Silver Fir until the second decade had been
entered on. This had also previously been found by Konig to
be the case in Beech woods.

1 Op. tit., pp. 59, 60.

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2O2 Studies in Forestry [CHAP. ix.

That, at the same time, a qualitative enhancement takes
place along with the quantitative increment of the timber is
clear from the researches of R. Hartig, who asserts1 that in
general, without variations according to the species of tree,
the quality of the timber grown in the comparatively full
exposure to light and air is better than that formed under
other conditions. This is due to the fact that the extent to
which transpiratiofi is carried on through the foliage does not
increase pan passu with the enhanced rate of increment, as
the conductive capacity of the vessels in the new zones of
wood is relatively smaller, in consequence of the ligneous
deposits within the cellular tissue being thicker and denser.
And, further, when underplanting is simultaneously carried
out, the undergrowth keeps the soil and the root-system cool,
and thus retards, for at least a fortnight, the awakening of active
vegetation in sprirlg; hence the latter is only entered upon
when the weather has become somewhat warmer, and when
the assimilative and constructive processes can consequently
be performed more thoroughly and energetically, owing to their
taking place under more favourable conditions as to warmth
and sunshine.

To determine whether or not a partial clearance is likely to
be financially remunerative, practical figures, based on past
average results for crops of similar kinds on soils of similar
quality, are requisite. Where these are available, the reckon-
ing is very simple by means of the following equation : —

When C = the cubic contents that may be expected from the mature

crops with ordinary treatment only,
V = the value of same per load, or per cubic foot, at time of

harvesting the mature crop,
ta • • • • tq — outturn in cubic contents from ordinary thinnings from

now till harvesting of the mature crop,
va - • . . v q = the sale-price of same per load, or per cubic foot,

capitalized until the clearance of the mature crop.

1 Centralblatt fiir das gesammte Forstwesen, 1888, pp. 8, 363.

CHAP, ix.] Tending of Woods 203

And Q = the cubic contents expected from mature crop after treatment

by partial clearances,
Vx = the value of same per load, or per cubic foot, at time of final

clearance,
to. ---- t£ = outturn in cubic contents from partial clearances up till

the harvesting of the crop,

va . . . . v$ = the sale-price of same per load, or per cubic foot, capi-

talized until clearance of the mature crop takes place.

When x is a minus quantity, then the method of partial clearance is

remunerative, and therefore advisable.
„ x = o, then there is no financial advantage to be gained by partial

clearances.

„ x = a plus quantity, then the ordinary method of treatment by
thinnings merely is the more advantageous.

But when underwood, which should almost always be
formed — even on the better classes of soil — can only be pro-
duced after a certain amount of outlay, then the complete
and correct formula for estimating the financial prospects of the
operations must be : —

CV + fava+
or, in another form similar to that originally given, —

Where /* = the outlay for producing underwood, capitalized until final

clearance of the mature crop,

and r — the market value of the underwood at the time of clearance
of the mature crop.

Practical experience in Germany has shown that this method
of partial clearance should, under ordinary circumstances, only
be adopted on the better classes of soil, and when undergrowth
can be formed either naturally or without any considerable
outlay.

Pruning or Removal of Branches.

High-forest crops, which have been properly tended and
thinned throughout the various stages of their growth, require,

204 Studies in Forestry [CHAP. ix.

as a rule, no clearance of branches in order to improve the
shape of the bole. The cutting and the lopping of branches
are both merely measures adopted, often at considerable outlay,
to cover the effects of faulty treatment of the crop during the
past, and are, in general, not requisite where trees have gradually
been accustomed to a fuller measure of individual growing-
space. In the case of copse or standards over coppice some
diminution in the amount of shade cast may be necessary for
the well-being of the underwood; and, within certain limits,
this can be effected by thinning the crowns of the standard
trees forming the overwood.

Under ordinary circumstances, the removal of living branches
can only take place to a limited degree, and must in any case
(for financial reasons) be confined to the more valuable species
of trees. The manner in which the crown is set on the tree is
of well-known influence in determining the shape of the bole,
as stems with lofty crowns are more full-wooded at the top-end,
and approximate more to the cylinder in shape, than such as
have deep-seated crowns of foliage. In order that any benefit
may be derived from the operation, it is necessary that pruning
should be carried out when the trees are in their full energy
of growth, and as early as possible before the period fixed for
their mature fall.

In many cases, too, where the crowns of the trees are very
dense, a fillip may be given to their general energy in growth
by thinning out some of the branches, so that the foliage re-
maining may have a larger share of the nutrients extracted
by the root-system from the soil. The stimulation thus given
to the energy of assimilation is perhaps nowhere more notice-
able than with regard to young Larch trees, the lower portions
of whose foliage may have already been attacked by the Larch
mining-moth (Coleophora laricelld).

The removal of dead branches, when carefully conducted,
so as to leave no ragged surface likely to offer a favourable
germinating-bed to fungoid spores, interferes in no way with

CHAP, ix.] Tending of Woods 205

the performance of the vital functions of the rest of the tree.
On the contrary, when the operation is carried out smoothly
and close to the stem, it prevents the formation of hard, horny
knots in the wood ; and this consequently enhances the value
of the timber, considerably diminishes the danger from fun-
goid diseases, and favours an early and complete cicatrization
of the wound-surface. It is therefore particularly to be recom-
mended in the case of Oak, Pine, Larch, Spruce, and Silver
Fir, whose dead branches are much more apt than in other
genera to form hard, tough snags, which, becoming gradually
embedded in the stem by the new growth of annual zones of
wood, diminish the value of the timber for technical purposes,
and thereby affect its market price.

The removal of living branches is, however, a direct inter-
ference with the vital condition of the growing tree, and can
therefore only be ventured on to a limited extent. Under no
circumstances should more than one-third of the total quantity
of foliage be removed at one time ; practically, only about one-
fifth of the foliage is generally the extent removed during such
operations. Experience has shown l that, even in the case of
quick-growing kinds of trees, the removal of living branches
should ordinarily be confined to those that are not over
2\ inches in diameter for conifers, or not over 4 inches for
broad-leaved species of trees, as, otherwise, the process of cica-
trization cannot take place quickly enough to ensure hindrance
of the germination of fungoid spores producing disease.

As the broad-leaved species of trees are not so liable as
conifers to fungous infection, they usually stand trimming
better. With reference to this matter Professor R. Hartig
remarks that 2 : —

• When branches are removed from a tree, it thereby acquires a pre-
disposition for a number of wound-diseases, of an infectious or non-

1 See Ney, Die Lehre vom Waldbau, 1885, p. 300; also Gayer, op. cit.,
p. 584.

a Lehrbuch der Baumkrankheiten, 1889, p. 15.

206 Studies in Forestry [CHAP. ix.

infectious nature, which may be obviated by timely and effective closure,
i. e. by antiseptic treatment.'

And at another place he adds * : —

' In broad-leaved trees, especially the Oak, to which my investigations
have hitherto been confined, wounds over 4 to 4-8 inches in diameter,
should not be made.'

The species of trees which best stand the removal of green
branches are the Oak, Silver Fir, Larch, and Pines, when they
are in energetic growth on favourable soil and situation and
have normally developed crowns. Ash, too, can well bear the
operation ; but, as Ash and Alder both grow with naturally clean
stems, pruning is hardly requisite in their case. Whenever the
removal of branches takes place to any great extent from Oak,
Maple, Sycamore, or Elm, the result is that the bole has a ten-
dency to become covered with shoots from the dormant buds.
This, of course, interferes very considerably with the technical
and financial value of the stem, besides, particularly in the case
of the Oak, exposing the tree to the danger of becoming ' stag-
headed' or dead in the upper portion of the crown. The soft-
woods— Birch, Willows, and Poplars — are not naturally adapted
for this kind of treatment, owing to the comparatively slight
resistance which their soft, porous wood is able to offer to the
development of fungoid disease ; hence any wound-surfaces
formed afford only too favourable a germinating-bed for the
disease-producing spores.

In order to diminish the danger from fungoid diseases, it is
highly recommendable that the wounds should be coated over
with some antiseptic substance impervious to moisture. In
conifers this takes place naturally by the oozing out of resin ;
but some coating must be provided artificially in the case of
the broad-leaved genera. The tree-wax, formerly in general
demand for the purpose, consisted of a mixture of 1-20 parts
(by weight) of bees-wax, 2-70 parts of pure resin, 0-60 of tur-
pentine, 0-15 of wood-oil, and 0-15 of suet, all dissolved in

1 Ibid. p. 228.

CHAP, ix.] Tending of Woods 207

warm methylated spirits. Nowadays, however, the simpler
method of coating over the surfaces with coal-tar, slightly
thinned with oil of turpentine, finds general adoption owing
to its cheapness. The coating of tar will only bite into the
surface satisfactorily whilst the wood is relatively free from
sap ; hence it should be administered either towards the end
of October, immediately after the vital functions of the foliage
have been completed, or at any rate some time during the
first half of winter. Unless the removal of the branches takes
place in autumn or early in winter, the experiments made by
Professor R. Hartig of Munich tend to show that, in addition
to the tar not obtaining a good hold on the wound-surface, the
condition of the woody tissue is such as to make it less able
to resist the penetration of fungoid, disease-producing spores.
Practically, the same principle holds good here as in regard to,
the thinning of young tree-forest ; for it is much better to thin
out branches to a moderate extent only, and then repeat the
operation subsequently if necessary, than to endeavour to effect
the object in view by one coup de main.

The cost involved by the operation varies, in each particular
case, according to the local rate of wages and the handiness of
the workmen, the species of trees, the height at, and the extent
to, which the branches are to be removed, &c. ; but in Germany
it has been found to vary generally in amount from about \d.
to 2d. per stem for sawing off the branches and tarring the
wound-surfaces. In Britain, it will, for various reasons, prob-
ably cost quite the double of this amount ; but, even then, it
may, under certain circumstances, prove a highly remunerative
operation if judiciously conducted.

With regard to the remunerativeness of the removal of
branches, Alers, who invented the patent long-handled saws
now usually employed in the operation, estimated that if begun
in the thirtieth year of age of the crop (coniferous ?), and re-
peated every five years till the fiftieth year, at a cost of about
i\d. per stem, the net results at eighty years of age, after

208 Studies in Forestry [CHAP. ix.

deducting the various outlays capitalized at compound interest
up to that date, would show a profit of 12 %. It is impossible
to criticize such a vague estimate without examining all the
data closely, and ascertaining what the results would be for
a fall of timber fixed at 100, 120, or 150 years; but, at any
rate, it is worth remarking that the practical effect of Alers'
agitation has been to induce the Prussian Government to
undertake regularly the removal of all dead branches in forests
grown for the production of valuable timber stems, and not
intended merely to be utilized as fuel. From the national-
economic point of view this may be advisable in State forests,
though for private landowners it is a purely financial question,
concerning which local experience will best guide the sylvicul-
turist to a sound judgement about the matter. In accordance
with the natural laws of tree-growth, as increment begins at the
top and is gradually continued towards the base, the removal
of a portion of the foliage diminishes the amount of elaborated
nourishment available for structural purposes towards the
butt-end of the trunk, and thus leads to improvement in the
form-factor of the bole ; whilst at the same time, as R. Hartig
has also shown, the quality of the timber produced improves
the more, the less difference there is in the quantitative incre-
ment proportionately to the surface of the foliage through
which the process of transpiration is carried on. That, in
consequence of this artificial thinning of the crown, the growth
in height is stimulated, is a point about which experts have
hitherto differed, and which has not yet been determined by
any series of authoritative experiments.

Thus, while special circumstances have most influence in-
each particular case relative to the remunerativeness of such
measures in private woodlands, the general statement can at
any rate be made, that the removal of sickly, rotting branches —
or of all those infected with parasitic growth of Loranthus or
Mistletoe, or of such as exhibit deformities like twig-clusters
(e. g. those caused by Aeddium elatinum on Silver Fir, and

CHAP, ix.] Tending of Woods 209

called ' witches' brooms ' in Germany), or show any other forms of
fungoid diseases — is certainly advisable, even at some consider-
able outlay, in order to prevent the propagation of the disorders,
and the penetration of diseases into the stem. But, at the
same time, in coniferous forests it also diminishes the liability
of the crops to be damaged by storms or by heavy accumula-
tions of snow and ice. And, finally, not its least utility is to
be found in the fact that, in mixed forests, the judicious removal
of lower branches often enables a greater density of crop to be
maintained for some years longer than can possibly be the
case if tending is confined solely to the operations of thinning.
For species like Ash, Maple, and Sycamore, which attain
maturity at a comparatively early age, this last consideration
is a matter of no little sylvicultural importance.

CHAPTER X

METHODS OF STIMULATING THE INCREMENT IN
TIMBER-CROPS WHEN APPROACHING MATURITY

IT is a well-known fact that, when trees growing in close
canopy are thinned out, or when in the case of old crops
approaching maturity a partial clearance is made, the annual
increment on each individual stem naturally rises in con-
sequence of the decrease in the number of stems drawing
food-supplies and moisture from the soil, and engaging in the
unavoidable struggle for light and air.

In the system of selecting only the largest trees for ex-
traction, in standards over coppice, and in standard trees
retained in high forest for a second period of rotation, such
increment in growth is certainly attained. In the following
cases, however, the question to be considered is mainly con-
nected with heavy thinnings, or a partial clearance made shortly
before a crop falls to the axe, in order to stimulate the remain-
ing trees to more energetic growth in girth before the date at
which the fall should take place according to the Working-Plan.
It is, in fact, but the continuation of the thinnings that have
been made as measures of tending throughout the whole life-
time of the crop, only it is carried out more freely on account
of this being the last thinning that is to be made before the
trees attain their full maturity. If less than one-fifth of the
total amount of timber on the area be removed the operation
may still be considered as a heavy thinning, whilst if one-fifth

CHAP, x.] Stimulation of Increment 211

or more of the crop be thus prematurely utilized it must
certainly be considered a partial clearance.

That such measures undoubtedly do lead to a stimulation of
the annual increment is a fact not only abundantly shown by
practical experience, but also proved more than half a century
ago by the more eminent sylviculturists of Germany, C. Heyer,
Th. Hartig, Nordlinger, and others. These authors showed
conclusively that a stimulation of the increment on individual
stems took place, as the natural result of all such thinnings as
exceeded in degree the natural process of that unavoidable
struggle for existence in which the stronger first overtops and
finally suppresses the weaker individual stems, whenever such
free thinnings were made in forests growing in dose canopy, and
at an age not exceeding to any considerable extent the normal
periods of rotation under which the species of tree in question
was usually grown as a timber crop. Every now and again,
however, some champion steps forward to dispute what have
long been accepted as facts; but the plausible deductions
drawn from his observations are always, on closer investigation,
found to have some flaw. Thus, for example, he may have
confined his attention to the bole only, or have neglected to
discriminate between the direct effects of the freer exposure
to light and air, and the adventitious circumstances under
which the latter may have taken place, although these concrete
conditions are at times of such influence as to diminish, or even
to counteract, the intended results of the thinning or partial
clearance.

There is generally some very easily determinable reason when
this latter measure fails to produce more energetic increment.
The thinning or partial clearance may, for example, have been
carried so far as actually to have interfered with the normal
functions of the root-systems and the crowns of foliage of the
individual trees left forming the crop. These nouveaux riches
may often require some little time to settle down and accustom
themselves to their altered circumstances ; and the first form

P 2

212 Studies in Forestry [CHAP. x.

in which this makes itself apparent is very frequently rather
in the energetic formation of new roots and of thicker foliage,
which ultimately exert their due influence on the increment of
the stem, than in the immediate thickening of the annual rings,
or the immediate formation of woody-fibrous tissue. And,
wherever the other main factors exerting influence on the pro-
ductive capacity of the soil are not at the same time tended
and well provided for, stimulated increment cannot always be
expected as the natural result of diminishing the number of
trees forming the crop. Thus, for example, care must be taken
to prevent deterioration of the soil (where necessary, even by
underplanting) in consequence of insolation, and of the drying
and exhausting effects of winds, or with regard to the soil-
moisture and to the soil-covering of dead foliage requisite for
the formation of humus or vegetable mould.

In one case, however, the current increment of the trees
may be directly decreased at first in place of stimulated.
This is, when the fuller exposure to light and air leads in
the first instance to abnormal increase in the production of
seed, in consequence of a tendency to the formation of albu-
minoid substances in place of carbo-hydrates ', as is especially
liable to take place in the case of trees that were already pre-
dominating throughout the canopy at the time of the partial
clearance being made. And, of course, if the partial clearance
be carried too far, the increment on the remaining crop will
probably be injuriously affected by the natural consequences
resulting from over-exposure of the soil to insolation and the
action of winds, and from exposure of the stems themselves
to sunburn or scorching of the bole in smooth-barked species,
to increased danger from windfall and insects, as well as to
the greater damage apt to be done during the felling of the
stems that are being removed, and the grubbing up of their
stumps.

1 Rinicker, Der Zuivachsgang in Fichten- und B^uhenbestdnden, 1886,
p. 30.

CHAP, x.] Stimulation of Increment 213

Theodor Hartig was the first to assert l that, as the direct
and immediate consequence of the freer exposure to light and
air, without reference to the species of tree, stimulated incre-
ment on each individual tree invariably took place, though
subject to the influence of the other factors determining the
rate of growth. When any apparent exceptions to this rule
are met with, they are neither ascribable to differences in the
species of trees, nor to differences in respect of soil and situa-
tion, but are solely due to one or more of the above-indicated
causes. Species of timber, soil, and situation certainly exert
their influence as regards the extent to which increment may
take place ; but they are not of themselves the direct or primary
cause. There is, however, good reason for believing that deci-
duous trees are enabled by nature to avail themselves of
the direct and immediate increment to a somewhat greater
extent than those coniferous trees which retain their foliage
throughout the whole year.

The enhanced increment need not assume the form of
broader annual zones of woody-fibrous tissue along the bole.
It may, and very often does, at first take the shape of con-
siderable changes throughout the root-system and the crown
of foliage, primarily and undoubtedly due to the freer ex-
posure to light, air, and warmth. This paves the way for the
succeeding form of enhanced increment, due to these changes
in, and increment of, the assimilative organs, which makes
itself more readily distinguishable throughout the stem and
branches.

The extent to which the annual increment thus becomes
enhanced varies in any particular species of tree according to
the individual stem, its age and reproductive capacity, the soil,
situation, and exposure on which the crop grows, the density
of the canopy throughout the crop, and the development of
the crown of foliage borne by the individual stem. The
younger and sturdier the tree, the better developed its crown,
1 LehrbuchfiirForsier% 1861, vol. i. p. 105.

214 Studies in Forestry [CHAP. x.

the more favourable the soil and situation may be to the
thriving of the particular species of tree, and the denser or more
crowded the wood, so much the more likely is the influence
of the thinning or partial clearance to be readily observable.
That the extent to which it is perceptible varies in the different
genera of our forest trees has been above indicated and really
requires no explanation. Thus, for example, Oak, Pine, and
Larch, that have been grown in pure forests, in which there is
a strong tendency for the trees to thin themselves naturally to
such an extent as to make the canopy loose, if not broken,
and to allow of each individual stem forming a larger crown
than is usual in the case of shade-bearing genera like Beech,
Spruce, and Silver Fir, can hardly be expected to derive so
much benefit as these latter from any artificial diminution of the
number of stems per acre. In many such cases, indeed, this
natural thinning, especially when the Oak, Larch, and Pine are
approaching the time of maturity of the crop, may have pro-
ceeded so far that any further artificial clearance might lead to
diminution instead of enhancement of the increment of the
remaining stems in consequence of deterioration of the soil,
unless underplanting take place at the same time in order to
improve, or at any rate protect, its productive capacity. As it
is well expressed by Gayer l, the founder of the modern school
of scientific sylviculture —

' Whenever the partial clearance is likely to lead to interruption of the
canopy of the crop, it should only be carrried out when the productive
capacity of the soil is such as promises, in all its essential factors, to
supply continuously the increased demands made in consequence of
greater energy in the crown of foliage (transpiration and assimilation),
i. e. that the soil in question is fertile, or that care may be taken to
stimulate the productive capacity of the soil in some suitable way at the
proper time. This can only take place through the maintenance of
a good layer of humus and the careful retention of soil-moisture, and
consequently in many cases only by means of underplanting in order to
protect the soil against sun and wind.'

1 Waldbau, 3rd edit. 1889, p. 571.

CHAP, x.] Stimulation of Increment 215

But in the case of the shade-bearing genera, Beech, Spruce,
and Silver Fir, which (except in cases of accident) remain in
dense canopy throughout their whole period of growth, right
up to their normal maturity, the effects of the freer exposure
to light, air, and warmth procured for the individual stems by
heavy thinning, or by partial clearance when they approach
the prescribed time of fall, are often during the first year
marked by a two-fold to ten-fold increase in the breadth of the
annual zone of woody-fibrous tissue1. This stimulation of
increment can also in the case of these trees be attained with
a far less degree of clearance ; hence, with proper care, there
need be small danger of the soil being in any way injuriously
affected owing to the partial and temporary interruption of the
canopy to a slight degree. This fact is easily explained by the
smaller absolute measure of light and air available for these
shade-bearing species when grown in canopy of normal density.

Thus, whilst the laws regulating the increment in all species
of forest trees are substantially constant, the extent to which
the enhancement of increment may take place after partial
clearance has, so far as observations have yet been recorded,
been found to be practically in the inverse ratio to the require-
ments of any particular species with regard to light and
freedom of crown.

The Causes of the Enhanced Increment explained.

Various causes have been assigned to the effects produced
in enhanced increment after partial clearance2. Th. Hartig
considered it to be due rather to the utilization of reserves of
productive matter collected and stored up in the stem whilst it
stood in close canopy, than to any increased assimilation in
direct consequence of the increase in foliage that takes place
when the individual tree obtains a larger growing-space;

1 Grasmann, Beitrag zur Lthre vom Licktungszuwachs, 1890, p. 9.
3 Idem p. 4.

216 Studies in Forestry [CHAP. x.

whilst Nordlinger, on the other hand, ascribed the enhance-
ment in increment to the increase in the foliage, but laid
particular stress upon what he considered the fact, that the
enhancement was not so much the direct result of the increase
in the mass of foliage as of the stimulated assimilative activity
of the leaves and needles, with simultaneous temporary increase
in the productive capacity of the soil.

The correct explanation as to the enhanced increment is
probably to be found in a combination of these views. It seems
much more than probable that the utilization of the reserves
of productive matter (principally starch in various forms) is
most likely greatly favoured by the more active assimilation of
nutrients whenever the increase in the foliage takes place;
and there is no reason why this should not be directly con-
nected with the formation of the fuller crown of foliage
immediately after the partial clearance has been made. It is
still an open question how such reserves of nutrients are
formed, how they circulate throughout the tree, and how they
are finally utilized, although their existence in the parenchym-
cells of woody-fibrous plants is just as well known as that of
similar reserves in orchids, perennial tuberous plants, &c. The
recent destruction of forests in Bavaria by the Nun moth has
given Professor R. Hartig of Munich special opportunities for
studying a part of this subject, particularly with regard to the
Spruce l ; and he has conclusively proved that this species of
tree has much fewer reserve supplies of nutrients than the Scots
Pine. In general, as is well known, such reserve supplies are
far more plentiful in the broad-leaved deciduous species of
trees than in conifers, and larger in the deciduous Larch than
in the evergreen conifers. All the changes that take place in
trees prior to the commencement of the assimilative activity in
spring are ascribable to these nutrient reserves — the flowering

1 See Forstlich-naturwissenschaftliche Zeitschrift for January, February,
and March 1892.

CHAP, x.] Stimulation of Increment 217

of Hazel, Alder, and Willow, the swelling of the buds and the
flushing of the young leaves, the formation of rootlets, &c. In
fact, all the similar phenomena previous to the development of
independent cambial activity must be ascribed to these reserve
supplies of starchy and nitrogenous nutrients. The supply of
reserves is usually sufficient to maintain vegetation for one
complete year, and often for longer; indeed, in many cases
it amounts to 7 or 8 % of the total weight of thirty-year-old
timber crops. Diminution of light and foliage, consequent on
limitation of growing-space, must interfere with the utilization
of these reserve nutrients ; hence it is quite logical and reason-
able to expect that with more growing-space, and a consequent
increase of foliage, these reserves should be largely drawn upon
and utilized.

That any stimulation of the productive capacity of the soil
takes place in consequence of the freer penetration of the
atmosphere, and the stimulus given to the formation of humus
or vegetable mould, is doubtful, or even more than doubtful ;
for, unless the canopy still remains comparatively dense, the
soil soon becomes covered with forest weeds, which often
really consume the mould, and tend to exhaust the soil, in
place of allowing the timber crop to have the full benefit of
the humus.

The true physiological cause of the enhancement in incre-
ment, after heavy thinnings, or partial clearance of crops of
trees approaching maturity, is to be found in the stimulus to
the formation of starchy matter afforded by insolation ; for the
degree of activity of the assimilative organs is dependent
on the purity or brilliancy of the rays of light, as the decom-
position of the carbonic acid in the atmosphere can only take
place when the waves of light attain a certain length. Whilst
a crop is growing in full canopy, the assimilative activity of the
foliage forming the lower portion of the crown is extremely
small, owing to the low quality of the diffused light which is
alone available ; but, when the canopy is opened up to a suffi-

2i 8 Studies in Forestry [CHAP. x.

cient extent, these portions of the lower foliage, which have
been practically inactive, or may perhaps even have been
existing on the work done by the upper leaves or needles,
reassume their normal assimilative functions and help to
enhance the general increment of the tree. And, besides this
increased assimilative power of the foliage, the consequent
increased formation of new leaves and needles is undoubtedly
of enormous influence in maintaining and increasing the
general enhancement of increment throughout the stem. As
remarked by Konig1, the direct result of the freer exposure
to light and warmth leads to the better and more energetic
development of the leading-shoots, the strengthening of twigs,
and the formation of twigs from buds that would otherwise
most probably have remained dormant.

The enhanced increment continues until the crop once
more forms close canopy. But, if it be again stimulated by
a repetition of the thinning out or partial clearance, this may —
if not accompanied by underplanting — be carried so far as to
involve deterioration of the soil to such an extent that the
beneficial influence of light and warmth on the crown is
cancelled by the diminished activity of the root-system, con-
sequently involving decreased supplies of moisture and of
mineral nutrients for conveyance to the assimilative organs.

The simultaneous underplanting of crops subjected to this
system of partial clearance, and especially of those of light-
demanding kinds of trees — Oak, Ash, Maple, Larch, and Scots
Pine — has an undoubtedly stimulating result in effecting and
maintaining the enhancement of increment after partial
clearance, and is of particular interest from the financial point
of view. The influences exerted by the soil, the situation, and
the age of the crop, exhibit themselves rather with regard to
the extent of the enhancement in increment than to its
production and continuance. Unless the individual trees are

1 Ueber Lichtungszuwachs, insbesondere der Buche, 1886, p. 7.

CHAP, x.] Stimulation of Increment 2 1 9

already far past their normal maturity, and have begun to show
signs of the loss of energy in growth due to a foreshadowing
of the approach of senile decay, they must receive a fillip from
admission to larger growing-space and freer exposure to light
and warmth. When, however, the vital energies of the trees
are weakened by age or disease, normal enhancement of
increment need not be looked for. The circulation of the sap
throughout the stem must already be to a greater or less extent
interfered with; whilst the root-system is also unfitted to
discharge the extra duties it is called upon to perform. Trees,
that are not very far past the period at which their current
annual increment has culminated, as well as such as have not
yet attained the culminating point, are, however, unquestion-
ably stimulated to livelier energy, which manifests itself in
enhanced increment. But, in practice, this system of partial
clearance, for the speedy formation of the more valuable
assortments of timber, is seldom applicable to very young
woods, or to crops that are already much older than the usual
periods of rotation. It generally finds proper scope only in
mature crops of high forest and in those approaching maturity.
And in these cases the age of the crop has little influence on
the length of time throughout which the enhancement of
increment is maintained ; for this is determined rather by the
length of time which it takes the crop to form close canopy
once more. The nature of the development of the crown is,
however, of greater importance than the age of the crop. If
the previous thinnings have been neglected, and if the canopy
has been allowed to remain so dense that the woods are
crowded, it often happens that, on receiving increased growing-
space, the trees with their weakly crowns are unable to avail
themselves of the advantages thereby offered, and exhibit,
as may so often be seen in the case of Oaks, a tendency
to the development of dormant buds, which leads to * stag-
headedness* or death of the crown, and malformation of
the bole.

220 Studies in Forestry [CHAP. x.

Practical Advantages of the Method of Partial
Clearance.

From the practical sylvicultural and the financial points of
view such heavy thinnings or partial clearances should not be
made until after the crop in question has completed its chief
growth in height.

Along with the other advantages of natural reproduction
under parent standards, the rapid increment in timber, as well
as in the technical and financial value of the latter, which
takes place after partial clearances made for the purpose of
regeneration, has drawn considerable attention to this method
as a system of treatment of woods, even when their artificial
reproduction — as in the case of Oak, Maple, Larch — may
generally be considered more advisable than natural regenera-
tion. The favourable returns received from the gradual
clearance of parent standards in the case of natural repro-
duction of Beech, and of Silver Fir in particular, as well as
the financial advantages that accrue ultimately from the partial
clearance and underplanting of indifferent crops of Oak, Larch,
and Scots Pine when they approach maturity, have to a great
extent dispelled the prejudices that existed against the system
in the minds of some as being entirely inconsistent with the
natural course of things, and have won for it recognition as
a method of treatment worthy of adoption wherever circum-
stances admit of its practice. There seems little doubt that in
the near future it will be carried out to a much greater extent
than at present, as it combines most of the advantages of
standards over coppice with decided sylvicultural and financial
advantages of its own. Thus, for example, by means of this
method of partial clearance, the larger and more valuable
assortment of stems can be produced in a shorter time, i. e. at
a less cost ; whilst, instead of a high forest of normal density
composed of nearly mature trees, with an average annual
increment long past their point of culmination and gradually

CHAP, x.] Stimulation of Increment 221

sinking, an equal and often a greater annual increment per
acre is attainable after the partial clearance. This pays as
well, and often better, than if the full crop had been allowed
to attain maturity, besides yielding substantial returns from the
timber prematurely utilized. When the gradual clearance of
the parent standards is effected during natural reproduction, it
is in no way inconsistent with what has been above said, if,
before the formation of the young crop, the average annual
increment of the standards is below that of normal high
forest reproduced by total clearance and sowing or planting ;
because, counting from the time the young crop may be
considered formed, the enhanced increment on the more or
less isolated standards is undoubtedly more favourable finan-
cially than when a total clearance is immediately followed
by artificial reproduction.

That portion of the fixed capital which is represented by
the growing crop is considerably reduced by means of the
partial clearance ; and the money thus derived as intermediate
returns can be otherwise utilized in order to yield interest for
itself, whilst the material left standing increases in the per-
centage it affords. Thus, if the partial clearance amounts
to one-fifth, or one-third, or one-half of the total crop in close
canopy, it has been satisfactorily proved by several authorities *
that the enhanced increment on the area partially cleared at
least equals, and often exceeds, the total previous current
annual increment, notwithstanding the diminution in the
number of trees thereafter forming the crop.

The financial advantages derivable are thus summarized by
Grasmann 2 : —

i. The larger and more valuable assortments of timber can
be produced in shorter time, and therefore more cheaply, by
this method.

1 Wagener, Der Waldbau und seine Fortbildung, 1884, p. 208; Kraft,
Beitrdge zurforstlichen Zuwachsrechnung, 1885, pp. 99 et seq.; and others.

2 Op. «'/., p. ii.

222 Studies in Forestry [CHAP. x.

2. Instead of the full crop, with small annual increment on
a larger number of individual stems, three factors are favourably
introduced and combined, viz. : —

i. Good intermediate returns are available, capable of

producing interest for themselves.

ii. The enhanced annual increment on the remaining crop
equals, and often exceeds, that produced by the full
crop previous to its partial clearance.

iii. The young crop produced naturally or artificially under
the parent standards often practically equals in incre-
ment a young crop formed artificially by sowing or
planting.

What Loudon says l of the Oak may be applied to all our
forest trees grown as crops with a view to remunerative returns
from the capital invested : —

' The age at which Oak timber ought to be felled, with a view to profit,
must depend on the soil and climate in which the tree is grown, as
well as on other circumstances. Whenever the tree has arrived at that
period of its growth, that the annual increase does not amount in value
to the marketable interest of the money which, at the time, the tree
would produce if cut down, then it would appear more profitable to cut
it down than to let it stand.'

Whilst this is perfectly correct for each individual tree
grown in the comparatively isolated positions that timber
trees usually occupied in Britain at the time the above was
written, it in no way precludes the possibility, which in fact
we know from actual experience to be the case, that when the
current annual increment per acre has sunk below the point
up to which it is not unprofitable to allow a crop to remain in
the full normal canopy of its species, it can be stimulated and
rendered more profitable, often very considerably so, by the
above-indicated method of partial clearance with a view to the
earlier production of valuable stems of large girth. In regular
high forest, with natural reproduction, the time of regeneration
1 Arboretum et Fruticetum Britannicum^ 1838, vol. iii. p. 1809.

CHAP, x.] Stimulation of Increment 223

is often, in order to attain good boles of valuable dimensions,
prolonged till after the period when energy for the formation
of seed, or the natural reproductive capacity is already some-
what weakened. By means of partial clearances, however, the
regeneration can be favoured during the chief natural seed-
producing period of growth ; whilst, at the same time, as good
dimensions of timber may be obtainable as in the regular
high forest, and in a more profitable manner. Thus, for
example, in the reproduction of Spruce in sheltered localities —
where windfall is not likely to occur, and where the period of
reproduction may be taken to be usually about a hundred
years — if partial clearance be made about the seventieth year,
during the time of the most active production of seed, the
financial position of soil plus crop during the succeeding thirty
years will almost, beyond question or doubt, be much more
favourable than if the crop had been allowed to stand as
regular high forest till the full period of rotation originally
fixed in the Working Plan had been attained ; for it is almost
certain that the partially cleared crop will contain a relatively
higher number of boles of valuable assortments than would
have developed themselves under the system of regular high
forest. And what is said here with regard to Spruce is still
more applicable in respect to the other two great shade-bearing
genera, the Silver Fir and the Beech. The whole system
is, in fact, merely a modification of, and improvement on, the
older system of natural reproduction under parent standards.
But, whilst in the latter case the seed fellings (partial clearances)
before and during the time of seeding, and the gradual clear-
ances after the formation of , the young crop, took place mainly
with the object of effecting natural regeneration, the partial
clearances under the new method are made with the distinctly
avowed intention of stimulating the standard crop to enhance-
ment of the annual increment, and to the yield of more
favourable returns from the capital represented by soil and
growing crop. In the former case formation of a young crop

224 Studies in Forestry [CHAP. x.

was the motive, and enhanced increment on the parent
standards the effect; in the latter, enhancement of annual
increment is the object, and simultaneous natural reproduc-
tion of shade-bearing kinds of trees is the result of this
sylvicultural operation.

Rules for the Conduct of Partial Clearances.

With the light-demanding species of trees, when they are
not grown in mixed forests along with shade-bearing species,
underplanting is almost a necessity after heavy thinnings or
partial clearances, in order to maintain the productive capacity
of the soil. The manner in which this method of treatment is
applied to the various chief genera of our light-demanding
forest trees — Oak, Pine, and Larch — is as follows : —

Oak. — When pure forests of Oak have passed through the
regular processes of thinning, and approach the time for a partial
clearance taking place, their canopy is in general somewhat
light and thin, although perhaps not broken ; and the under-
growth is usually already beginning to form canopy for itself
below the older crop. To avoid the formation of twigs and
shoots from the dormant buds along the stem, often leading
to ' stag-headedness V the partial clearance should not be made
by one fall, but is better attained by one or two heavy thinnings
conducted to the extent deemed advisable for each individual
crop. The time at which it should take place is also dependent
on the special circumstances of each crop, special regard being
given to the time of underplanting and the development
of the undergrowth, the energy of growth of the trees, and
the nature of the soil and situation. As, however, the efficacy
of this method of treatment is all the more apparent the earlier

1 In his Lehrbuch der Baumkrankheiten, 1889, p. 14, R. Hartig remarks
that : — ' Oaks, which have grown up in close canopy along with Beech and
have only a slightly-developed crown of foliage, acquire a predisposition
towards a drying-up of the top of the crown (stag-headedness) when they
become fully exposed to light and air ; whilst, under similar conditions, trees
with well-developed crowns do not suffer from this disease.'

CHAP, x.] Stimulation of Increment 225

it can be begun, the thinnings should, if possible, be com-
menced about the fortieth to sixtieth year. They should at first
be confined to the young stems of backward growth, and to
such as are never likely to attain good marketable shape. The
oftener the thinnings can be repeated at short intervals the
better, as any sudden exposure of the boles should be carefully
avoided.

About ten or fifteen years after these preliminary operations
have been begun, the main partial clearance will in most cases
seem advisable ; for by that time the crop should be in a state
of active increment, due to the favourable influences of the
undergrowth and the previous thinnings. Here, again, as also
whenever further partial clearances are considered necessary
later on, the fall is in the first instance confined to trees that
have been damaged by organic or inorganic agencies, or that
do not continue to yield satisfactory increment ; and not until
all such unremunerative material has been removed should
any sound trees in energetic growth be cut out.

When the main partial clearance has taken place about the
seventieth year, and has been followed by minor gradual
clearances at intervals of five years at first, then of ten, and
later on of fifteen, the preliminary yield or intermediate returns
thus obtained should amount, according to Kraft *, respectively
to about 288 to 628 cubic feet, then to 720 to 1,080 cubic feet,
and ultimately to 1,800 cubic ft. per acre, inclusive of branch-
wood. Past experience seems, according to Gayer 2, to justify
the hope that by this method of treatment the same dimen-
sions of bole can be attained in about 120 years as are
obtainable in pure forests worked with a rotation of 200 to
240 years, provided that up till about the hundredth year the
rate of increment has been maintained at 3 to 3! %, and after
that at 2 to 2\ %, conditions which are quite conformable with
the actual results obtained on suitable soils. The crop of Oak

1 Aus dent Walde, vol ix., p. 80.

2 Op. fit., p. 574-

226 Studies in Forestry [CHAP. x.

then ultimately harvested numbers about thirty-six to forty-
eight stems per acre, which on good soil yield valuable and
remunerative assortments of timber \ Where soil and situation
are good enough to fulfil the demands made on them, there
can be little doubt that this system of underplanting with
a shade-bearing species, and partially clearing the main crop
from time to time, is the method best calculated to produce
timber of the highest value for technical purposes, and to yield
the most favourable returns financially from the capital repre-
sented by the soil, together with the growing crop.

Scots Pine. — For the practice of this method a good deep
soil is necessary, as it differs essentially from the custom,
common on poorer qualities of soil, of thinning out crops
during their twentieth to fiftieth year of age and underplanting
them with Spruce or other suitable shade-bearing species. In
the latter case they are often allowed to grow on to maturity
without any further thinning or interruption of the canopy to
speak of; but, though they continue to improve in growth and
form, this is due to the beneficial influence of the undergrowth
both on the soil and the standards. As a good formation of
the crown is requisite for Scots Pine, in order to enable it to
continue for a long time in active energetic increment,
thinnings should be made towards the end of the pole-forest
stage of growth, and afterwards repeated whenever there seems
any danger of the crowns interfering with each other. Under-
planting should also be here carried out as soon as the
thinnings have taken place with a view to the formation of

1 The following passage from London's work already quoted (p. 1809) is
interesting, although not quite intelligible as regards the largest scantlings
being produced at 130 years of age — though if larger be read in place of
the largest the statement readily becomes intelligible : —

' A writer in the Gardener s Magazine states that Mr. Larkin, an eminent
purveyor of timber for ship-building, stated, when examined before the
East India Shipping Committee, that, in situations the most favourable for
ship timber (the Weald of Kent, for example^, the most profitable time to
cut Oak was at ninety years old ; as, though the largest scantlings were
produced at 130 years' growth, the increase in the forty additional years
did not pay 2 per cent. (Card. Mag. vol. xi. p. 690.)'

CHAP, x.] Stimulation of Increment 227

good individual crowns. By this means, in place of having
a pure forest formed, according to Weise's Yield-Tables \ on
soil of average quality at eighty years of age by 317 stems
per acre (having a mean average girth of 29 inches at breast-
height, which would only be attained by about 40% or 127
stems, with a form factor of 0-45 and a current annual
increment of only 44 cubic ft. per acre), it can hardly be
doubted that a smaller number of trees with enhanced incre-
ment and the finer dimensions of stem effected by the com-
paratively rapid thickening of the bole at the top end must
yield more favourable financial returns on the capital invested
in timber production. Reliable comparative data are, how-
ever, unfortunately not yet available to illustrate this point.

Larch. — In regard to general treatment by partial clearance
with a view to the speedy production of large-girthed timber,
the Larch has much in common with the Oak ; but the under-
planting may sometimes take place more advantageously with
the Silver Fir than the Beech. So far as experience goes, this
method of treatment is well adapted to the cultivation of the
Larch on good, deep soil ; and it is most satisfactory when the
partial clearance and underplanting takes place as early as the
twenty-fifth to thirtieth year. When the previous tending of
the plantations has been good, and the thinnings have been
regularly made, the main partial clearance can be heavier than
in the case of the Oak, so that subsequent clearances are often
almost unnecessary. On good soil from sixty to seventy trees
per acre may remain to form the final yield of the standard
crop ; and wherever soil and situation are at all suitable for the
growth of Larch, sixty- or seventy-year-old crops can often yield
an increment of 3 to 4 % up to that age, when they should
already show very good marketable dimensions.

As the Beech is not in favour or demand as a timber-tree of
large dimensions, this method is only apt to find any practical

1 Yield-Tables for the Scotch Pine, translated by W. Schlich, Ph.D.,
1888, pp. 18, 19. -

Q 2

228 Studies in Forestry [CHAP. x.

application with the Spruce and the Silver Fir among shade-
bearing genera ; and as they show many points of similarity,
these two trees may be considered together. Where, however,
there is any likelihood of windfall or damage from storms, this
method is totally unsuited for the Spruce.

Spruce and Silver Fir. — The way towards partial clearance
should be paved by preliminary operations carried out about
the twenty-fifth to thirtieth year in such a manner as to let the
predominating poles have a clear space of 2 or z\ ft. around
the crowns. These favoured individuals should stand about
15 to 17 ft. apart, all the rest of the crop being thinned out in
the ordinary manner customary in pure forests without inter-
ruption of canopy. During the thirtieth to fiftieth year, when
the influence of this measure has made itself apparent in the
re-formation of close canopy, the main partial clearance takes
place in a somewhat similar manner. The stems between the
favoured individuals should be freely thinned so as to permit
of the formation of an undergrowth either naturally, or where
necessary artificially, wherever the minor portion of the crop
is of itself insufficient to protect the productive capacity of the
soil. When the favoured stems have at breast-height a girth
of about 36 to 40 inches, which they should attain between
the sixtieth to eightieth year, the marketable trees can then be
gradually cleared away on the same principle.

Another method, practised in the neighbourhood of Salzburg
in Western Austria throughout mixed forests consisting of
Spruce, Silver Fir, and Beech, consists in carrying out the
thinnings once every ten years after the crop has attained thirty
years of age, and in making them heavier each time the opera-
tion is repeated, until the main partial clearance is made about
the sixtieth or seventieth year, leaving 120 to 160 stems per
acre, all of them conifers and in energetic growth. Under
such a crop natural reproduction can easily be effected, so that
about twenty years later the standard trees are of large market-
able dimensions, whilst the young growth may vary from

CHAP, x.] Stimulation of Increment 229

5 to 15 ft. in height. On the removal of the standards the
blanks thus formed in the new crop can easily be filled up
artificially, and may be advantageously utilized for the forma-
tion of mixed forests by the introduction of other species.

Actual measurements of crops thus treated are not yet
available for comparison with the yield-tables published for
pure forests ; but the approximate data already given may be
contrasted favourably with the more accurate information con-
tained in these latter. According to v. Baur, pure forests of
Spruce of 120 years in age and growing on good soil have
288 stems per acre, the mean girth of which at breast-height is
39 inches, but this is only attained or exceeded by about 40 %
or 1 1 5 stems ; the mean average stems have also been found
to have a form-factor of 0-48, which is undoubtedly lower than
that of stems treated by the method of partial clearance.
Again, according to Lorey, the Silver Fir, when grown in pure
forest on good soil, yields 200 stems per acre with a mean
girth of about 52 inches at breast-height, which also is only
attained by about 40 % or eighty stems per acre.

As has already above been pointed out, this method of
partial clearance with the distinct object of stimulating the
remaining crop to the speedy development of the larger and
more valuable assortments of timber cannot be successfully
attempted with 'regard to any species of tree when once its
natural energy of growth has practically abated to any con-
siderable extent, or on the poorer classes of soil ; but wherever
the trees are still capable of stimulation in respect to incre-
ment, and the productive capacity of the soil can be easily
safeguarded against deterioration, the method has decided
practical advantages which should strongly recommend them-
selves to the woodland proprietors of Britain, where sylvi-
cultural operations on any extensive scale should only be
conducted on strictly financial principles.

CHAPTER XI

THE PRACTICAL EFFECTS OF UNDERPLANTING

THE conservation of the productive capacity of the soil is
one of the first fundamental principles of Sylviculture ; for the
sustained yield of the best classes of timber can only reasonably
be expected when measures are taken to safeguard all factors
determining the quantity or quality of the food-supplies avail-
able for the root-systems. One of the first practical steps in
this direction consists in the protection of the soil against
insolation, and against loss of soil-moisture, by means of the
maintenance of a good, close leaf- canopy and the consequent
thicker layer of dead leaves. This both forms humus or mould
for the benefit of the soil, and also acts mechanically to prevent
evaporation from drying winds. Beech, Spruce, Douglas and
Silver Firs, and Black Pines — species of trees that are densely
foliaged and therefore naturally capable of bearing shade well —
are endowed with good soil-protective qualities throughout the
whole period of their development until they attain their
technical and financial maturity ; but most of our other valu-
able forest trees, Oak, Ash, Maple, Birch, Larch, and Scots
Pine, lose their power of conserving the productive capacity
of the soil long before they attain their maturity, owing to the
natural demands they exhibit for increased growing-space and
relatively greater coronal development when once they have
nearly completed their main growth in height. These latter
species, in fact, prove themselves light-demanding in place of

CHAP, xi.] Effects of Underplanting 231

shade-bearing ; and, if measures are not taken to counteract
the consequences of the gradual interruption which takes
place in the leaf-canopy, the effects of insolation and of
exposure to the freer action of wind and rain on the soil,
tend to diminish its productive power, and must ultimately
lead to its deterioration.

To obviate the consequences of this natural tendency on
the part of the lightly-foliaged species, which is not reconcil-
able with the conservation of the productive energy of the
soil, the best plan capable of adoption is to underplant them
with shade-bearing species for the purpose of maintaining the
soil cool and moist, and of improving it through the larger
quantities of mould formed by their dead foliage.

In most of the open forests of Oak, Larch, or Pine, for
example, there will usually be some sort of natural undergrowth
found under the comparatively light shade of these forest trees ;
but the practical influence exerted by an underwood of brush-
wood, scrub, or berries, is by no means so beneficial as that of
undergrowth formed either naturally or artificially by Beech,
Hornbeam, Sweet Chestnut, or Sycamore — or by evergreens
like Spruce, and Silver, Douglas, or Nordmann's Firs l.

The first occasion on which underplanting is known to
have been carried out under Oak, with the express intention of

'giving a covering of dead foliage to a soil already overgrown with
whortleberry, and thus strengthening its productive capacity, and stimu-
lating the diminished increment of the Oaks,'

took place in the Spessart forest in central Germany about

1 Under Firs are included only the genera Picea, Abies, Tsuga, and
Pseudotsuga, including Spruce, Silver Fir, Hemlock, Nordmann's, Menzies,
and Douglas Firs, but not the Pines (Pinus) incorrectly though perhaps
more commonly called Firs, e. g. Scots Fir for Scots Pine. Etymologically,
Fir is properly the name of the Scots Pine, from the old Anglo-Saxon/~z<M ;
but if we retain it, then we must coin distinctive names for Spruce and Silver
Fir, which are distinctly different genera not indigenous to Britain, and only
introduced during the seventeenth century. For these trees we have never
adopted any generic names such as are current in France and Germany,
whence they were brought over.

232 Studies in Forestry [CHAP. xi.

1 840 *, since which time the practical and financial advantages
of the measure have been duly observed and recognized.

Copse or coppice under standards has, of course, for cen-
turies been cultivated both in Britain and on the Continent ;
but in 1840 the first case of under planting took place solely
for the benefit of the standard trees, and not for financial
considerations mainly dealing with quick and frequent returns
from the coppice underwood.

There are, however, two methods of effecting the end in
view; for the underwood may be formed either for soil-
protection only, or else with the intention of allowing it to
grow up into tree-forest to be ultimately felled along with the
present stock of standard trees, in which latter case the crop
really attains maturity as a mixed wood, and therefore parti-
cipates in the advantages offered by such over pure forests 2.

As on most matters, whether practical or scientific, concerned
with Forestry in Germany, a paper war has been waged on this
subject. Whereas the benefits of underplanting should have
been patent to all, there were not wanting some (headed by
Professor Borggreve) who contended that, in place of stimu-
lating the standards to greater increment, the practical effect of
the underwood was to consume a large portion of the food-
supplies available in the upper portion of the soil, whilst its
formation often necessitated a considerable outlay3. Owing
to these differences in opinion, the matter was taken up for
careful investigation by the experimental section of the Forest
branch of the Faculty of National Economy in Munich
University.

The opponents of underplanting based their objections on
three different classes of experiments : —

i. Experiments made with standards in copse (i.e. over
coppice).

1 See Monatschrift fur Forst- und Jagdivesen, 1874, P- I-

2 See Chapter VI. On the Advantages of Mixed Woods over Pure Forests.

3 Forstliche Blatter, 1877, p. 20; 1883, p. 41.

CHAP, xi.] Effects of Under planting 233

2. Observations as to the rate of growth in crops that had
been underplanted for some time, and a comparison of that
with the rate of growth in other portions not underplanted.

3. Clearance of underwood in crops underplanted, and
comparison of the next year's increment with that on those
under which the underwood had been left untouched.

So far as the first class of experiments was concerned,
Borggreve found that the stems exhibited increment in the
breadth of the annual rings only for five years, whilst a decrease
set in whenever the underwood began to close up and form
canopy, and that the decrease became greater as the canopy
grew more dense. He therefore concluded that the initial
enhancement was solely due to the more complete insolation
of the trees and the diminution in the number of plants
drawing their food-supplies from the soil, and denied that
it could be due to any better and more rapid formation of
mould by the dead foliage covering the soil. But he over-
looked two points — -firstly, that the degree of insolation of the
crowns of the standards could in no way be affected by the
removal of the coppice ; and secondly, that the demands on
food-supplies from the soil made by the coppice during the
first few years of its rapid growth would certainly be at least
equal to (and most probably higher than) were made later
on when it was growing in close canopy. When these points
are duly considered, it seems evident that the cause of incre-
ment must certainly be assigned to the advantageous formation
of humus or mould when the dead foliage was exposed to the
decomposing influences of sun, rain, warmth, and fungoid
growth. He maintained — with a show of reason, but incor-
rectly— that these processes were retarded rather than favoured
by the clearance of the coppice. Full, clear consideration of the
actual facts warrant the opinion that the increment took place
on the standards owing to the larger formation of humus from
the dead foliage which could not decompose normally under
the dense shade of the coppice, and that the subsequent

234 Studies in Forestry [CHAP. xi.

decrease, five years later, was due to the fact that the richer
supplies of nutrient salts, rendered soluble and available as
food in the soil owing to the larger quantities of humus
formed after the fall of the coppice, began to get exhausted
after about four to five years' time.

The argument is also, however, open to another grave
objection; for the observations were confined to the lower
end of the stem, and were not continued all the way up the
bole. Now, Weise has shown that on Oak standards increment
becomes stimulated near the base of the stem, but that, when
undergrowth gets over twenty years in age, the basal incre-
ment decreases, whilst that near the top of the bole becomes
enhanced — or, in other words, the top-girth becomes relatively
larger, so that the stem tapers less and has a higher technical
and financial value.

The data with which the deductions under the second class
of experiments were supported, were found on examination
not to be reliable, as they were taken from mixed crops of
Pine and Spruce of equal age (probably formed by sowing),
in which the struggle between them had been so keen as to
prejudice the development of both species. Hence, in the
Scots Pine wood classed as without underwood, the Spruce had
been removed in the thinnings ; whilst, in that shown as with
underwood^ the Spruces were not truly underwood, but were
suppressed poles still struggling for life with the Pines, which
therefore showed less increment than they would have exhibited
under normal conditions. In other data, the areas reported
on were so small that general deductions were not justifiable ;
moreover, the average height of the stems (which in general
affords a very sound means of judging of the quality of the
soil !) showed that the areas not underplanted were somewhat
better than the others subjected to consideration.

With regard to the third class of experiments, Michaelis

1 Grebe, Ertrags- und Betriebsregelung, 2nd edit. 1879, P- XI4-

CHAP, xi.] Effects of Underplanting 235

found J that in Oak forest, with an eighteen-year-old under-
growth, mostly of Hornbeam and Hazel in close canopy, the
increment was practically the same as was to be found on the
trees in another part of the same crop, which had been fenced
off as a game-park, and had been browsed on by deer to such
an extent that there really was no underwood to speak of. As
accurate details were not collected with respect to the nature
and physical properties of the soil and situation (as to depth,
moisture, exposure, &c.}, it would not be justifiable to argue
from such meagre data that undergrowth was unnecessary for
the retention of the productive capacity of the soil. It is,
indeed, quite true that the main food-supplies are derived
from the lower layers of soil only ; but, as those are only avail-
able whilst dissolved in water, and as the layer of mould
assists percolation by preventing the rapid off-flow of aqueous
precipitations, it can easily be understood how beneficial must
be the action of humus and of a good soil-covering on all such
soils as are apt to suffer from want of moisture.

Among the advocates of underplanting, Frombling in 1886
published 2 measurements made on Oaks of 1 60 years in age
growing on old grazing land, but which had been underplanted
for thirty-five years. In three stems growing close together and
not thinned, the breadth of the annual rings had sunk to their
minimum at the time of underplanting, but had broadened as
the undergrowth formed canopy, and became broader than any
of the annual zones during any of the previous fifty to sixty
years when the natural energy of growth of the trees was at its
maximum. Other stems, which had been thinned or partially
cleared, formed considerably broader zones at first in con-
sequence of the freer exposure to light ; but this fell off again
for three years, and then recommenced in response to the
improvement in the productive capacity of the soil consequent
on the formation of canopy by the underwood and of humus

1 Forstliche Blatter, 1884, p. 345.

* Zeitschrift fiir Forst- und Jagdwesen, 1886, p. 632.

236

Studies in Forestry

[CHAP. XI.

by its dead foliage. The deductions he drew were therefore
diametrically at variance with those previously arrived at by
Michaelis ; whilst the data on which they are based leave no
possibility of differences existing with regard to the quality and
physical conditions of the soil and subsoil.

But, before then, valuable data had already been contributed
by Riinnebaum1 respecting two areas under Scots Pine, one of
which (120 years) was underplanted with Beech, and the other
was without underwood (no years). The differences observ-
able as to mineral composition were inconsiderable ; but the
former had a thick layer of humose soil containing nearly
double the quantity of mineral nutrients that were found in
the thinner layer of humose soil on the area without under-
wood. The yield and returns from these areas (without
reckoning 343 cubic ft. of Beech sold from the former for
£27 13^-. od.} were as follows :

Age of Crop.

Outturn.

Annual average
Increment.

Selling price.

Rate per cb. ft

Years.

Cub. ft.

Cub. ft.

£, s. d.

Pence.

120
no

14,280
13,370

II9
I2l|

229 2 0
149 2 0

3-8
27

The slight difference in average annual increment in favour
of the younger crop (without underwood) is of course due, not
to differences in the soil and situation, or to greater increment
without undergrowth, but to the fact of the larger quantity of
timber removed in the thinning at the time of underplanting.
What must strike one most in the above data is the much
higher rate per cubic foot obtained from the standard Pines,
grown over underwood, in consequence of the stems being
straighter, smoother, less tapering, and with a proportionately
larger development of the summer zone in each annual ring.
Prof. R. Hartig of Munich was the first to enunciate the theory

1 Zeitschrift fur Forst- und Jagdwesen, 1885, pp. 156 et seq.

CHAP, xi.] Effects of Underplanting 237

that the underwood, by keeping the soil moist and cool in
early spring, delayed the early awakening of vegetation and of
assimilative processes for about a fortnight at least. This pre-
vents the commencement of growth until somewhat warmer
weather has set in, and thus stimulates the energy of the assimi-
lative organs, and leads to the formation of thicker cell-walls in
the woody fibrous tissue. To be unbiassed, it must be pointed
out that the comparative freedom from branches had nothing
to do with the undergrowth. It was due to the fact that the
crop was originally a mixed wood of Pine and Beech, from
which the latter was cut out about the sixtieth to seventieth
year, after the chief growth in height had already been com-
pleted, whilst a spontaneous undergrowth of Beech took
possession of the soil; for it is a well-known fact that this
species regenerates itself better under Scots Pine than under
the denser shade of parent standards.

The investigations conducted by the Munich authorities are
worthy of great respect ; for they were made in a truly scientific
spirit, free from bias either one way or another. They not only
take into account the breadth of the annual rings at various
heights above the ground, but also the superficial increment,
the increment in height, and the total increment in cubic
contents — without all of which reliable data are not obtain-
able. Where they are weak is that, although over 7,500 acres
of high forest have been underplanted and might be chosen
from, yet, unfortunately, areas without underwood, but abso-
lutely similar as to soil and situation, are wanting for accurate
comparison. Three sets of investigations were conducted, with
the following results.

The first series was made in Oak forest (Q. pedunculate?) of
eighty-two years of age, which had been underplanted with
Beech at fifty-four years of age (twenty-eight years previously).
The underwood had partly grown up into the crowns of the
standards, and the soil had a dense layer of dead foliage and
mould. The records of the Working Plan showed that at the

238 Studies in Forestry [CHAP. xi.

time of underplanting a heavy thinning or partial clearance had
taken place. This was of itself at first sufficient to stimulate
the trees to the production of broader annual rings, but only
in such a manner as to induce a tapering form of bole owing to
broader zones being formed near the base than higher up the
stem. But ten years later, when the underwood began to form
canopy, the breadth of the annual rings diminished consider-
ably ; and, in the case of four out of six sample stems, this was
succeeded by a slight increase again during the third decade.
During the second decade, whilst the increment was slightly
diminished, there was a distinct tendency to approximate in
mode of increment towards what obtains in close-canopied
forest. That is to say, in consequence of the underwood form-
ing canopy, the annual rings near the base of the stem
became relatively narrower whilst those near the top of the bole
became relatively broader, with the result that the bole became
less tapering and consequently better-shaped, technically more
useful, and financially more valuable. This improvement, often
a very slight one only, is due to the fact that, owing to the
soil, and consequently the root-system, being kept cool, the
latter is not stimulated to the extraction and absorption of such
large quantities of nutrients as if warmed by free insolation.
Hence the quantity of assimilated nourishment and construc-
tive matter which is conducted downwards to the base of the
stem and to the root-system is less in amount than under these
other circumstances ; and as the total amount of food-supplies
is diminished, whilst the demands of the top part of the bole
for nourishment practically remain constant, less remains to
be utilized for constructive purposes towards the base and
throughout the root-systems of the trees.

The second series of investigations was made on two Oak
standards of 105 years of^age, which, after having stood for
about twenty to thirty years with their crowns freely exposed
to light and air, were underplanted at sixty-five years of age
with Beech. The latter is now about forty years old, forms

CHAP, xi.] Effects of Underplanting 239

close canopy, and is already partially forcing its way into the
lower portions of the crowns of the standards. The Oaks were
rather short-stemmed; for not only was the soil somewhat
inferior, but the trees had also been allowed to develop without
forming close canopy. Records showed that the soil had
formerly been overgrown with whortleberries, though at the
time of the investigations it had a thick layer of dead foliage
and humus. The underwood was formed by sowing during
1843 to 1847, immediately after a thinning took place, which
was followed by a clearance of all diseased stems during
1853-1856.

The measurements made on the stems, when felled, showed
that (i) about eight years after the formation of the undergrowth
the rate of increment had sunk considerably, after having in-
creased at the time of its formation owing to the thinning; (2)
the effects of these two thinnings or partial clearances continued
for about two decades to induce tapering growth with larger
annual rings near the base than the upper part of the bole ;

(3) during the third and fourth decades after the formation of
the underwood the basal increment was lower in No. i and the
same in No. 2 as previously, whilst in both cases the increment
in the upper portions of the trees was somewhat enhanced; and

(4) finally, during the fourth decade, the superficial increment of
the various sections, and the total increment in cubic contents,
were practically about twice as great as they were throughout the
decade previous to underplanting. This last result completely
disposes of the argument that the growth of the standards is
prejudiced by the underwood consuming a large share of the
nutrients in the soil. At the same time it is hardly open to
reasonable doubt that the gradual improvement in the shape
of the bole is due to the underwood growing up into the
crown, and interfering more or less with the activity of the
foliage of its lower portion.

The third series of investigations was carried out in an Oak
wood eighty-eight years old, whose past history was accurately

240 Studies in Forestry [CHAP. xi.

traceable. Formed by sowing on old arable land, its growth and
development were good at first; but about its fortieth year the soil
became overrun with whortleberry, the increment of the crop
fell considerably, and its appearance was unpromising. Without
any thinning being made, beech-mast was sown out in 1840
for underwood, to which during 1844-1847 a heavy thinning
or partial clearance succeeded with simultaneous underplanting
(at forty-six years of age). Light thinnings were afterwards
made in 1853, 1859, 1873, and finally in 1887, when about
eighty stems per acre were removed, leaving about 300 per
acre on the average, which had formed canopy again. The
effect of the first thinning was hardly sufficient to affect the
breadth of the annual rings or the general shape of the bole ;
but it was still traceable in the predominant and dominant
stems till the third and fourth decades.

The measurements made on sample stems showed that the
increment in height diminished after the heavy thinning or
partial clearance, but eventually attained its former level, and
in some cases exceeded this. That is to say, the energy of
growth in height was diverted and utilized in the coronal
expansion, whilst it was re-directed into its original channel
when the crowns approached again to form close canopy.

Without giving any of the statistics and measurements
recorded — which can only be exhibited, for each series of in-
vestigations, in an extensive tabular form that might be out of
place here — the following are the results arrived at, as published
in a pamphlet by Dr. Kast, Lecturer on Forestry in Munich
University l. When crops of light-demanding forest trees are
underplanted, and the underwood begins to form close canopy,
the effect is to produce a diminution in the breadth of the
annual rings near the base of the stem, — but this only affects the
upper portion of the bole either to a less extent, or not at all, —
whilst the total annual increment is not always decreased.
If any such decrease be considerable, it is probably due to
1 Ueber den Unterbau und seine wirthschaftliche Bedeutung, 1889.

CHAP, xi.] Effects of Underplanting 241

re-formation of close canopy, and consequent sinking of the
assimilative power of the lower and inner foliage.

With regard to Prof. R. Hartig's theory, that heavier and
better timber is formed when underwood protects the soil,
Riinnebaum's experiments confirmed its correctness, at any
rate so far as Scots Pine is concerned, but without yielding
other final results of a satisfactory nature when criticised from
a purely academic point of view. In a general way, it might,
however, be deduced that the undergrowth, though in other
physical respects of favourable influence, does not (as has been
hitherto generally accepted) directly stimulate to enhanced
annual increment, — owing to the fact that it utilizes a portion
of the soluble nutrient salts contained in the soil for its own
growth and development. But the quantity of nutriment thus
diverted from the standards is, especially on the better classes
of soil, not sufficient to justify the objections of the opponents
of underplanting. Their argument, that after heavy thinnings
or partial clearance a spontaneous growth of grasses and weeds
covers the ground, and annually restores to the soil the
nutrients previously extracted from it, ignores the researches
of Vonhausen, who proved1 that a soil-covering of grass
extracts from four to five times as much mineral food (salts)
from the soil as is required by Beech underwood, whilst the
humus or mould formed by such herbage is almost entirely
consumed by the soil-covering of weeds annually without the
standard timber trees being able to reap any benefit therefrom.
It must also be remembered that the quantity of nutrients
annually extracted from the soil by the underwood is compara-
tively so small as hardly necessary to be taken into considera-
tion, at any rate on the better classes of soil, so far as the
food-supplies of the standard trees are concerned ; whilst the
influence that may thus be exerted on the productive capacity
of poorer classes of soil must be more than outweighed by the
greater increment due to the thinnings or partial clearances in
1 Allgemeine Forst- und Jagd-Zeitungt 1872, p. i.
R

242 Studies in Forestry [CHAP. xr.

tracts underplanted, as compared with similar woods not
treated in this manner. There are, of course, circumstances
and situations in which undergrowth might make relatively
higher demands on the soil than are made by the standard
trees, as, for instance, any endeavour to underplant Scots Pine
with Beech on poor, dry, sandy soils, — an attempt which, would
be diametrically opposed to the true sylvicultural characteristics
of the latter kind of tree.

Of at least equal importance to the amount of annual
increment on the standards, the quality of the timber produced
next demands consideration. Its technical utility is, apart from
such very special cases as formerly obtained when Oak-crooks
were in demand for ship-building, mainly determined by
(i) straightness of growth, (2) full-woodedness of the top end
or high-form factor, (3) freedom from knots and branches, and
consequent evenness of texture, (4) proportion of heartwood to
sapwood, and (5) height of specific gravity — for with regard to
any samples of wood of the same species the heaviest is
ceteris paribus the most durable1, as its specific gravity is
dependent on thicker deposits of ligneous substance on the
cell-walls. This last point is determined by the proportion of
the denser summer zone to the more porous spring zone in
the annual ring, the former being formed when the assimilative
process is carried out most thoroughly during the hottest
months of the year. And, as the practical effect of the under-
wood is to delay the awakening and commencement of active
vegetation for at least a fortnight, owing to its maintaining the
soil and the root-systems of the standard trees cool and moist
under its shade, it therefore exerts a most beneficial influence
on the timber produced. When heavy thinnings or partial
clearances have been made, this mechanical hindrance to
insolation and to early stimulation of active vegetation is all
the more important, as, from the comparative isolation of the
standards, an early commencement of the transpiratory and
1 Gayer, Die Forstbenulzung, yth edit., 1888, p. 66.

CHAP, xi.] Effects of Underplanting 243

assimilative functions would naturally be induced, which would
certainly lead to the production of a larger quantity of timber
but of lower specific gravity, and consequently of less technical
utility, than was being formed previous to the artificial inter-
ruption of the leaf-canopy.

And, at the same time, the underwood, as it gradually grows
up into the lower portion of the crowns, is of practical utility in
cleaning the boles by interfering with the vital functions of the
lower branches, and suppressing the activity of their foliage.
It thereby also helps to concentrate and confine the constructive
functions within the upper regions of the bole chiefly, so as to
increase the girth of the top-end relatively to that of the base,
and thereby enhance the technical and financial value of the
stem. These advantages must of course be counterbalanced
if the underwood be allowed to grow up so far as to interfere
with the normal development of the standards or to cause
partial suppression of the crowns.

The quantitative relation of the heartwood to the sapwood in
tree-growth is still an unread chapter in the great book of the
laws of nature. Up to the present, practically nothing is known
about this matter. Riinnebaum and others have shown that in
Pine woods underplanted with Beech the proportion of heart-
wood to sapwood is greater than in Pine standards growing
without underwood ; but as similar benefits can be proved in
the case of mixed woods of Pine, Spruce, Beech, &c., there is
as yet no sound basis for justifying the assumption that
underplanting specially favours any shortening of the period
of semi- activity which the older sapwood has to pass through
before attaining its full maturity as the kern or heartwood of
the tree.

Undoubtedly the greatest influences exerted by undergrowth
are to be found, firstly, in the richer stores of humus or leaf-
mould with which it provides and enriches the soil through
the decomposition of its annual fall of leaves and twigs, whereby
all the physical properties of ordinary woodland soils become

R 2

244 Studies in Forestry [CHAP. xi.

greatly improved, and the previously extracted nutrient salts are
again largely restored in a convenient, easily absorbed, soluble
form, and secondly, in the more thorough aeration of the soil
by means of the root-systems of the underwood. It is true that,
even when forming undergrowth and enjoying only compara-
tively limited exposure to light, air, and warmth, Beech under-
growth still transpires enormous quantities of moisture drawn
from the soil, and intercepts a high percentage of the precipita-
tions before they reach the ground ; but against this must be
duly weighed the greatly advantageous influence exerted by
the strongly hygroscopic humus in retaining the moisture
reaching the surface, and in allowing it facilities for entering
and percolating the soil, in place of running rapidly off into
the nearest water-channels, and of being quickly evaporated by
insolation and the freer play of winds. As a matter of practical
result Ramann found that, on the areas where Riinnebaum's
experiments were conducted, from the middle of May till the
end of August there was always more moisture immediately
underlying the humus in the Pine woods underplanted with
Beech than in those with no undergrowth ; and that, down to
2 ft. below the surface, the soil was moister in the former for
the first half of that time but drier throughout the later half,
whilst at a depth of about 28-32 inches the soil under the
pure Pine woods was always moister *. His deductions there-
from were that, under the light shade of the Scots Pine, the
spontaneous growth of berries, grass and other weeds exhausted
the superficial supplies of moisture to a greater extent than the
Beech underwood, whilst the layer about 20 to 24 inches below
the surface was called upon to furnish supplies to both Beech
and Pine ; whereas in pure Pine woods the lower soil received
larger quantities of moisture from above after the grasses had
completed their development than when a soil-covering of
Beech underwood existed. Wollny 2 also found, in independent

1 Zeitschrifi fur Forst- und Jagdwesen, 1885, p. 172.

2 Forschungen auf dem Gebiete der Agricultur-Fhysik, vol. x. p. 261.

CHAP, xi.] Effects of Underplanting 245

experiments, that the quantity of moisture under a soil-covering
of living plants is always less during the period of active vege-
tation than at a similar depth on naked soil (in consequence
of transpiration); that the influence is quite traceable down to
the lower layers; that the quantity found is less when the
plants stand densely (without being inversely proportional to
the density); and that a soil-covering of humus and dead
foliage, up to 2 inches in thickness, favours percolation from
above downwards as compared with naked soils.

As Beech, Hornbeam, and Silver, Nordmann's and Douglas
Firs have all very much the same sort of heart-shaped, mode-
rately deep root-system, the practical effects of underplanting
with these different species will ordinarily be about the same ;
whilst differences will be noted when the shallow-rooting
Spruce is selected as the underwood on soils for which it
seems best suited. In the latter case the woods will still
show more moisture than pure woods throughout the upper
layer of soil, for the Spruce undergrowth will draw its main
supplies of water from the layer from 12-18 inches below the
surface ; whilst, below that, the quantity of moisture will be
much the same, at any rate during the first half of the annual
period of vegetation. But, owing to the great density of an
underwood of Spruce, a large proportion of the atmospheric
precipitations will be intercepted without ever having any
chance of percolating to the lower soil; hence the deeper
layers will generally have less moisture than similar soils
without underwood. During the autumnal and winter period
of rest the soil under broad-leaved, deciduous underwood
must (ceteris paribus] show larger supplies of moisture than
under a coniferous undergrowth with persistent foliage, which
not only intercepts a larger percentage of the precipitations,
but also requires water from the soil for purposes of transpi-
ration.

Dense undergrowth throughout a whole wood will of course
withdraw larger supplies of moisture from the soil than that

246 Studies in Forestry [CHAP. xr.

which forms only a light canopy. Hence underwood may some-
times be utilized to the greatest practical advantage if only
formed here and there where there is no good layer of dead
foliage or moss ; for this may often give the most practical com-
bination of protection against sun and wind and of formation
of humus with least drawback on account of consumption of
soil moisture and soluble nutrient salts. And although the old
idea, that soils covered with underwood were invariably moister
than similar soils without undergrowth, has not proved itself
to be unconditionally correct, yet the advantages of the
undoubtedly better layer of dead foliage and humus have in
no way been overrated.

It is a well-known practical fact that the more valuable
classes of Oak and Pine timber cannot be profitably produced
merely by repeated thinnings and by delay in the utilization of
the crop l, since the increased growing-space demanded by the
crowns, and the consequent interruption of the leaf-canopy, are
incompatible with the conservation of the productive capacity
of the soil when it becomes exposed to the deteriorating influ-
ences of sun and wind. Strong thinning or partial clearance 2
of Oak crops about the sixtieth to the eightieth year, or of Scots
Pine about the thirtieth to the fortieth year, after their chief
growth in height has been attained on the different classes of
soils and situations, with simultaneous underplanting or under-
sowing of the shade-bearing species best suited to the soil in
question, is the only rational and profitable method of stimu-
lating the trees to further production of good annual incre-
ment. Mere enlargement of the growing-space will of itself
lead to enhancement of increment per individual stem ; but, as
has been above shown, its technical quality and its disposal will
not be so good or remunerative, whilst this increment will ulti-

1 Compare London, Arboretum et Fruticetum Britannicum, 1838,
vol. iii. p. 1809.

2 When up to 15 % of the basal area of the stems is removed, it is
a thinning, but beyond that it becomes a partial clearance \ see Chapter IX
on The Tending of Woods.

CHAP. XL] Affects of U nderplanting 247

mately be dearly bought through the deterioration that must
take place on any soils but those exceptionally circumstanced
with regard to insolation and winds.

In the above the underwood has been dealt with only as
regards its effects on the growth and development of the
standard trees ; it deserves, however, some consideration on
its own account. It will practically be found that even when,
at the time of the underwood being formed, all the standards
appear sound and healthy, individual trees become sickly or
lag behind in development to such an extent as to render
their utilization advisable without attempting to retain them
till the rest of the crop is mature. Where there is no under-
wood, this means that on such places the productive capacity
of the soil is either not utilized at all, or at any rate not utilized
to its full extent ; but with underwood already formed, it can
grow up into the blanks to be harvested along with the standard
crop when this attains its financial maturity. In such cases
Spruce, or Silver and Douglas Firs, although not in general
attaining first-class dimensions, will yield better results than
Beech or Hornbeam ; and, owing to the smaller growing-space
requisite for the normal development of their crowns, they can
often contribute a very fair return for the costs of formation
and the sub-tenancy of the soil.

When the standards are mature, the underwood has fulfilled
its duty, and may either be cleared away at once in order to
admit of their natural regeneration, or may be retained longer
and treated as high forest, at any rate in groups or patches show-
ing good promise of fair outturn in timber. But, in accordance
with the purely actuarial principles which should mainly guide
the owners of woodlands throughout Britain, and in view of
the comparatively small and unremunerative market for fire
wood, the clearance of the underwood will usually precede the
reproduction and utilization of the standards. Hence, for the
underplanting of the deciduous, light-demanding species of
our forest trees — Oak, Ash, Maple, and Sycamore — the Beech,

248 Studies in Forestry [CHAP. XL

and on moister localities the Hornbeam, are on the whole
preferable to Spruces or other Firs, for they accommodate them-
selves more to the natural habits of growth of the standards.
But, on the other hand, for Larch and Pine woods, though
Spruces, or on the better classes of soil and in mild sunny
situations Silver Firs, naturally conform more to the habits
and development of coniferous standards, an underwood of
Beech or Hornbeam is distinctly preferable when the con-
ditions of soil and situation permit of it, owing to the great
advantages conferred by them in respect of decreasing the
dangers arising from insect enemies and fungoid parasites.
In this matter the effect of the underplanting resembles the
advantages gained by an admixture of broad-leaved species
with the conifers ; and the benefits become more pronounced as
the underwood grows up nearer the level of the crowns of the
standards. Very often, however, the choice of the species to
be used for underplanting depends mainly on the nature of
the soil and situation, and is practically limited to the four
great shade-bearing genera, Beech, Hornbeam, Spruce and
Silver Fir — leaving out of consideration such exceptional
cases as favour coppice-growth of Alder under essentially light-
demanding species on moist, fertile, rather marshy soils.
Among exotics of comparatively recent introduction Nord-
mann's Fir seems best endowed with the requisite shade-
bearing and soil-improving capacity. If the Douglas Fir also
prove suitable, the timber of the latter holds out very enticing
financial promises to far-seeing landowners.

Of these genera, Spruce is the one which makes most
moderate demands as to the quality of the soil ; while it has
also the advantage of confining them to the upper layer of soil
through which the root-systems of deeper-rooted trees like Oak
and Pine do not ramify. The other shade-bearing genera not
only make greater demands for nutrients, but also tend to com-
pete with the standard trees in extracting them from the deeper
layers of soil. Speaking practically, Beech and Hornbeam

CHAP. XL] Effects of Underplanting 249

deserve the preference if the protection and improvement of
the soil is the main object in view ; whilst Spruce and Silver
Fir recommend themselves where it is desired to obtain fairly
marketable timber from the underwood as well as from the
standards. An underwood of Beech is productive of the greatest
improvement in the soil, owing to the rich fall of its dense
foliage and the fine quality of the humus formed therefrom.
But, owing to the demands it makes on potash and phosphoric
acid, it cannot be grown on the poorer classes of soil (just
where it is most wanted) ; and in damp localities under Oak it
is more apt than Hornbeam to suffer from late frosts in spring,
owing to its flushing into leaf about a fortnight sooner than
the standards. Where it is only advisable to underplant with
Spruce or Silver Fir, or where these may be admixed with
Beech or Hornbeam to form undergrowth, the Silver Fir
generally deserves the preference, even although its roots strike
deeper and its demands on mineral strength in the soil are
greater ; for it has on the whole a greater capacity for bearing
shade, forms better humus, and is not so apt to close the soil
to aeration and atmospheric precipitations, or to hinder the
percolation of water from the surface downwards to the sub-
soil. And, besides this, it has greater recuperative power later
on when the canopy over head becomes interrupted from
casual clearances of diseased or sickly stems among the
standards.

For the underplanting of Oak, Spruce is not to be recom-
mended, as it tends later on to interfere with the formation of
the crown. Beech, or on moister situations Hornbeam, should
form the major portion of the underwood, with Silver Fir
scattered in patches here and there wherever there is any
likelihood of its being allowed to develop into marketable
dimensions. Most of the eminent sylviculturists in Germany
condemn the use of Spruce as undergrowth to Oak, and urge, as
chief of the several reasons, that, by intercepting and utilizing
a considerable percentage of the atmospheric precipitations, it

250 Studies in Forestry [CHAP. xi.

induces stag-headedness among the standards, owing to in-
sufficiency of moisture in the layer through which the roots
ramify, and from which they extract their food-supplies. This
may, however, not infrequently be due to injudicious thinning or
partial clearance on soils that are below the average in quality
and are naturally rather deficient in moisture — though the evil
is then, of course, aggravated by the selection of Spruce as
underwood.

Although endowed with considerably greater capacity for
bearing shade than Scots Pine, the Weymouth and Black Pines
are not naturally adaptable for undergrowth ; far better results
are promised in this direction by Nordmann's Fir and perhaps
also by the Douglas Fir, which in many respects correspond
closely with the Silver Fir.

Although the richest fall of dead foliage takes place when
the whole of the standard crop is underplanted, yet the
advantages of partial underplanting, with reference to decreased
competition with the standards for the nutrient salts held in
solution by the soil-moisture (for it is only when soluble that
they can be imbibed by the rootlets), are so apparent as to
make this method preferable on soils of only average or inferior
quality. Because, whilst extracting smaller supplies of nutriment
from the soil, it permits of a larger percentage of the aqueous
precipitations reaching the soil, and of a somewhat speedier
decomposition of the dead foliage than under close canopy,
without endangering the quality of the soil through insolation
and wind. That, by arranging the underwood in patches, better
opportunities are given for studying the special character of
each particular piece of ground, and for selecting the shade-
bearing species best suited for it, with the additional advantage
of attaining a mixed growth of underwood, need hardly be
commented on ; nor the fact that, for the formation of under-
growth in patches, only a much smaller outlay will usually be
requisite than if the whole area be planted up or sown.

Whether the underwood should be formed by sowing or

CHAP, xi.] Effects of U nderplanting 251

planting depends mainly on local circumstances. Sowing is
usually cheaper, notwithstanding the fact that some measure
of preparation is always necessary to prepare the soil for the
reception of the seed ; but the object in view then takes
longer to attain than when planting is undertaken. Wherever
practicable, planting can be carried out with seedlings from
neighbouring crops, or with two-to-three-year-old seedlings or
transplants from temporary nurseries previously formed near
at hand. It should not amount to more than about 155". per
acre, if the soil permits of notching, and if the plants are not
put out closer than 4 x 4 ft. or 3^ x 3^ ft.

Oak, Larch, and Pine are the kinds of trees extensively
grown in pure forest in Britain, which stand most in need of
underplanting when once their growth in height has culminated,
and the individual stems have begun to assert their demands
for larger growing-space. The other light-demanding species,
like Ash, Elm, Maple, Sycamore, &c.,' are less frequently grown
in pure crops than as subordinate patches in mixed woods
where the ruling tree (which should usually be the Beech) can
protect the soil against deterioration.

And even if the costs of the formation of undergrowth under
pure woods of Oak, Larch, or Pine should locally exceed the
above-named sum, the advantages of the method are cheaply
obtained where the intention of the landowner is to obtain the
best financial returns from forests that are unable to protect
and enhance the productive capacity of the soil for themselves,
but which he does not wish to utilize at present so as to make
way for other timber crops. Many an Oak grove throughout
England, and many a Larch and Pine tract in Scotland, would
yield far more satisfactory returns from every point of view —
financially, sylviculturally, aesthetically — if proper measures
were taken for the protection and improvement of the soil
by means of thinning, or partially clearing, with simultaneous
formation of underwood and subsequent treatment of the crop
in accordance with the rational principles of scientific Forestry.

252 Studies in Forestry [CHAP. xi.

Brief Recapitulation. The Munich investigations showed
that it has not yet been proved that undergrowth exerts any
special and direct influence on the actual rate of increment of
light-demanding standard trees. But it unquestionably improves
the shape of the bole, by tending to make the stem less tapering
and therefore of greater technical and financial value, and also
the quality of the timber (at any rate so far as concerns the
light-demanding conifers) ; whilst by increasing the quantity of
dead foliage and preventing its being blown about by the wind,
it greatly favours the formation and increase of humus, and
thereby materially improves the physical properties of the soil,
and enhances its productive capacity.

CHAPTER XII

THE CONSERVATION OF THE PRODUCTIVE CAPACITY
OF WOODLAND SOILS

No kind of soil can be said to possess inherent productive
energy. The productivity or productive capacity of any land
for agricultural or sylvicultural utilization is a mere potentiality ;
whilst the light and warmth of the sun are the kinetic influences
which set this in action, and enable it to sustain organic life.

Only those kinds of woodland crops can be grown prudently
and economically, which merely utilize, but do not exhaust, the
productive capacity of the soil, — which in fact, to use a financial
simile, live on or within the annual income obtainable from
the land, and do not encroach upon its productive capital.
Whenever the form of crop is such as fails to safeguard the
productive capacity of the soil, any immediate advantage
promised by its retention is dearly bought at the cost of
ultimate deterioration of the land to a greater or less extent.
The rewooding of such deteriorated soils is often an extremely
difficult task, more especially when they are of a decidedly
limy nature.

I. Maintenance of, or Increase in, the Quantity of
Mineral Nutrients available throughout the Soil
in the form of Soluble Salts.

So far as concerns the actual withdrawal of sulphur, potash,
magnesia, lime, iron, and phosphoric acid — the most essentially

254 Studies in Forestry [CHAP. xn.

important constituents required for the growth of trees — it is
seldom the case that any given soil is deficient in any of these
minerals ; although it sometimes happens that it has not suffi-
cient moisture to enable it to offer them readily to the rootlets
in the shape of soluble salts, in which form alone they can be
imbibed by the suction-roots. With respect to the demands
they make on fertility, woodland crops differ essentially from
agricultural crops, and especially from the more exacting kinds
like tobacco, hops, and sugar-beet, which all demand the appli-
cation of manure in order to maintain the productive capacity
of farm-land at par, and to prevent its rapid exhaustion and
deterioration. In the majority of agricultural crops (hay, clover,
lucerne, barley, wheat) from 4 to 8 % of the dry tissue remains
behind as mineral ash on its combustion, and this even rises
to 1 7 % in the case of tobacco, hops, and sugar-beet ; whilst
for high-forest crops of timber the total requirements per acre
and per annum vary, according to Ebermayer's investigations,
with the different species of trees from 4 to 20 Ibs. as regards
lime, from 2 to 10 Ibs. as regards potash, and from about i to
4 Ibs. as regards phosphoric acid \ Say, for example, that any
given land contains only -05 % of potash in a soluble form
available for absorption throughout a soil of 1 8 to 20 inches in
depth ; then the total amount available per acre would be over
a ton and a half, or, roughly speaking, about 3,300 to 3,500 Ibs.
per acre (taking the specific gravity of the earth as 1-5). But as,
for Silver Fir, the tree which takes up most potash from the soil,
only about 10 Ibs. per acre are annually required for the forma-
tion of timber, even pure forests of this tree, if worked with
a rotation of 100 to 120 years, would only have withdrawn from
1,000 to 1,200 Ibs. by the time they attain maturity. They would
therefore still leave the soil with an abundance of soluble
potash for any kind of subsequent timber crop, even if in the

1 Article in Forstlich-naturwissenschaftliche Zeitschrift, 1893, p. 227.
See also Chapter IV on The Nutrition and Food-supplies of Forest Trees,
p. 83.

CHAP. XTI.] Protection of the Soil 255

meantime no fresh supplies had become available through the
continuous decomposition of the soil-particles, or if these had
sufficed merely to balance the annual loss due to soluble potash
being washed away out of the soil by the percolation of moisture.
And if this be the case with Silver Fir, it must a fortiori be true
of all other species of woodland trees, and for all mixed forests,
so far as potash alone is concerned. A similar argument
likewise obtains with regard to the various other mineral
food-supplies requisite for the growth of forest trees, either in
pure crops or in the preferable form of mixed woods. Hence
the conclusion must be arrived at that, wherever soils obviously
deteriorate under timber-crops, the reasons should first of all
be looked for in the physical conditions involved, rather than
in any excessive demands made by the crops with regard to
mineral nutrients.

So far as concerns any direct increase in the quantity of
mineral food supplies contained in an available (soluble) form
within the soil at any given time, the nature of the woodland
crop, and the treatment to which it is subjected, can of course
exert no influence. Great, however, is the influence which may
be indirectly made to act upon the quantity of nutrient salts
available for the rootlets, by maintaining such constant density
of canopy overhead as will break the violence of heavy rains
that might otherwise wash away the surface-soil, and as will
also prevent the soil-moisture from being rapidly evaporated
by sun and wind.

As most of the mineral food-supplies withdrawn from the
soil are, during the process of assimilation, concentrated in the
foliage, it follows that year by year the greater portion of what
has been withdrawn by tree-crops is restored again to the soil
when the decomposition of the leaves takes place. For when
humus is being formed from the defoliated leaves and other
dead parts of the tree-crops thrown down to the ground,
carbonic acid and ammonia are given off. The former of these
is essential to the solution of the mineral nutrients so as to

256 Studies in Forestry [CHAP. xn.

render them available for the rootlets ; whilst the latter is itself
an indispensable nitrogenous food. But this direct action of
humus is in reality of secondary importance to its enormous
influence in improving the physical conditions of soil, more
especially with respect to the regulation of the soil-temperature,
and with regard to its power of absorbing and retaining moisture,
in preventing the rain from rushing off the surface and in allow-
ing it to permeate gradually into the subsoil.

Though of itself affording no index to the mineral fertility
of the land, a favourable admixture of humus throughout the
upper layers of soils that are not of themselves fertile goes far
towards making them suitable for the more exacting kinds of
timber-crops. It is only when the normal progress of the
decomposition of the leaves and fallen debris is interfered
with by injudicious treatment of the crop — such as the mainten-
ance of an excessive density of leaf-canopy in crowded planta-
tions, or by allowing the leaves to be removed for litter, or to
be blown away by the wind— that there ever is any practical
danger of the humus and the upper layer of dead leaves having
an injurious effect upon the productive capacity of the woodland
soil which they cover.

But as a matter of fact, when the formation of humus goes
on under the most favourable combinations of moderate warmth,
moisture, and atmospheric oxygen — whose action is stimulated
by fungi like Cladosporium humifadens, Rostr., — the decompo-
sition takes place so continuously that but a slight covering
of leaves shed during the past, and partially also during the
previous, autumn litters the ground. Where the soil is exposed
so freely that the benefits, which would otherwise be derivable
from the humus, are diverted from the tree-crops and unprofit-
ably consume*d by a soil-covering of grass or weeds, care should,
in the interests of the productive capacity of the soil, be taken
to maintain a thicker canopy of foliage overhead, and thus
keep down the rank growth of weeds by cutting off the supplies
of light and warmth requisite for their growth. But where, on

CHAP, xii.] Protection of the Soil 257

the other hand, a deep layer of undecomposing leaves litters
the ground thickly, it prevents air from entering and circulating
within the soil, and induces an unfavourable condition with
regard to the moisture ; whilst it also tends to the development
of certain kinds of free acids of an injurious nature. Such
conditions indicate either wetness or want of aeration in the
soil, or an excessive density of canopy overhead. In our damp
insular climate, however, there is much less danger of the
productive capacity of the soil becoming endangered from this
cause, than from the opposite extreme, of having the timber-
crops more open and of a lighter canopy than is advisable for
the prudent husbanding of the means of stimulating the incre-
ment in the present crops, and for ensuring that those which
may succeed them will enter upon a heritage able to supply
the crops with sufficient supplies of nutriment.

Various tree-crops show different results with regard to the
capital in nutrient salts that they leave behind them in the soil
when they have reached maturity and fall to the axe. As has
been pointed out in a previous chapter (see p. 86), conifers in
general, but more especially the Spruce, and in even a more
marked degree the Scots Pine, make relatively smaller demands
on mineral nutrients than broad-leaved deciduous species,
both with regard to their foliage and their timber. Hence
tracts of woodland can be greatly improved by the rotation
of a coniferous crop, when once the soil has become exhausted
and deteriorated either by the free play of sun and wind, or by
growing light-demanding, thinly-foliaged kinds of trees (like Oak,
Ash, Maple, Larch, and Pine, when once they begin to get
broken in canopy) without an admixture of shade-bearing, soil-
improving kinds like Beech, Spruce, and Silver or Douglas
Firs. Under the good canopy maintained by all the evergreen
conifers (for even the light-demanding Scots Pine has a good
canopy till about the twentieth to thirtieth year, when its
special demands for increased growing-space make themselves
apparent) the rich fall of easily decomposed needles forms

258 Studies in Forestry [CHAP. xn.

a beneficial layer of humus. By means of the carbonic acid
and the ammonia evolved during the process of humification,
a stimulus is given to the formation of larger supplies of
nutrient salts within the soil. These are not required for the
annual production of foliage or timber; but as the density
of canopy overhead, and the mossy covering which often clothes
the soil under conifers, both combine in preventing the nutrients
being wasted by a rank growth of weeds, or being washed out
of the soil by the unbroken descent of heavy rainfall, it practi-
cally follows that the sum total of soluble nutrients is, at
the end of a coniferous crop that has been prudently managed,
considerably larger than it was at the time the planting with
Pines, Spruces, or Silver Firs was undertaken.

Many tracts throughout Germany, that half a century ago
bore fine woods of Oak and others of the nobler species of
broad-leaved trees, are to-day covered with Spruce and Scots
or Austrian Pine in consequence of imprudence in the manage-
ment of the former deciduous crops, and of the want of know-
ledge (since dearly purchased) that where a good leaf-canopy
is not maintained, an undergrowth is requisite for the safe-
guarding of the productive capacity of the soil, or for its
improvement if signs of incipient deterioration have already
made themselves apparent. And in England the same may
be said of many portions of the old Oak woods in the State
properties, the New Forest and the Forest of Dean, parts of
which have had to be transformed into coniferous woods in
consequence of neglect of the conservation of the produc-
tivity of the soil. In the low demands that it makes on mineral
nutrients, in the power of accommodation it exhibits with regard
to soil-moisture, and in its capacity for improving poor soil or
recruiting those that are temporarily deteriorated from exposure
to inimical influences, there is no tree of the forest that can
be more safely relied on to yield yeoman service than the
common Pine. On poor sandy land it can form a crop where
other trees fail to thrive ; and even on inferior classes of soil it

CHAP, xii.] Protection of the Soil 259

may be made to give fair returns in timber, whilst in reality
also making other payment for its tenure of the land by the
betterment of the soil and the improvement of its productive
capacity for the immediate future. Where land-improvements
of this nature can be made with mixed crops, these have such
estimable advantages of their own (see p. 118), that an admix-
ture of species should be effected wherever the circumstances
of soil and situation permit of it ; but where the soil is, for
the present, of such inferior quality that nothing but Scots
Pine seems likely to thrive, it will very often lead directly
and satisfactorily to the desired result, if the crops be tended
properly, and if no accidents occur from fire, snow, insects, or
epidemic outbreaks of fungoid diseases. A slight admixture
of Austrian and Corsican Pines should usually, however, be
tried experimentally.

For the re-wooding or the recuperation of limy soils that
have become exhausted through the action of sun and wind —
one of the most difficult of sylvicultural tasks — there is no better
method than first of all putting them under crops of Black or
Austrian Pine (Pinus Austriaca], Even this first step towards
the re-attainment of the high productive capacity characteristic
of good limy soils is often exceedingly hard to achieve. Excellent
results have at times been gained — even on hot southern hill-
sides exposed to the full blaze of the sun during a continental
summer — by sowing Lucerne and Black Pine seed together, and
allowing the crop of the former to decompose and humify on
the ground in order to assist the latter in maintaining itself for
the first year or two, until the young plants become established
in the soil. When once this is successfully effected, the rest
of the work is comparatively easy. From the time that such
crops have commenced to form canopy, the improvement
taking place in the soil not only becomes marked, but can
easily be maintained and enhanced by proper treatment of the
Pine, and by a rational choice and treatment of the species to
form the succeeding timber-crop.

S 2

260 Studies in Forestry [CHAP. xn.

The increase which may thus be made in the total quantity
of mineral nutrients stored up in an available form within the
soil cannot, however, be said to be directly due to any inherent
quality in tree-growth, but must be credited as primarily due
to indirect physical causes which give the sylviculturist an
opportunity of rectifying errors made during the past.

Whenever any woodland soil deteriorates, it is almost
certain that one or other, and usually two, three, or even all
four of the physical factors l — Cohesiveness or Tenacity \ Rela-
tion to Moisture, Relation to Warmth, and Depth — have been
affected in some prejudicial manner. These physical factors
determine, in a far greater degree than its mineral composition,
the capacity of any given soil for yielding to timber crops
abundant supplies of the nutrient salts requisite for their
normal growth, development, and reproduction. All these
physical factors, indeed, act and react so closely and essentially
on each other, as in point of fact to determine the general
quality of any particular soil for present sylvicultural utilization.
Whatever timber-crops, and whatever methods of treatment of
these, may be calculated to improve the condition of any one
of these factors, will therefore — provided always that it be not
altered to such an extent as to prejudice the utility of any of
the other three factors — be a step in the direction of conserv-
ing the productive capacity of the soil, and of stimulating this
when it is capable of being enhanced.

As was explained at the close of the chapter on ' The Nutri-
tion and Food-Supplies of Forest Trees ' (see page 88), Coppice-
woods in general, and more especially those in which the
crops consist of Ash, Elm, Lime, Oak or Willow, genera of
trees making the highest demands on the soil for nutrients,
tend more towards the exhaustion of woodland soils than
Copse or Coppice under Standards in which only the under-
wood is cleared away periodically at comparatively short

1 See Chapter V on The Characteristic Influences of the different Classes
of Soil, &°r., p. 102.

CHAP, xii.] Protection of the Soil 261

intervals, twenty to twenty-five years; while this composite
form of crop is in its turn less conservative of the productive
capacity than High-Forest timber crops.

The frequent deterioration of soils under coppice does not
arise on account of these kinds of trees making high demands
per se for food-supplies, although for young poles, shoots from
stools, and stoles of sucker-growth considerably higher demands
are continuously being made than would be the case if these
were to be allowed to develop into young trees having a larger
proportion of ripe wood to the foliage and bark in which the
mineral ashes are chiefly deposited ; but it is mainly ascribable
to the fact of the soil being laid bare to the exhausting influ-
ence of sun and wind every twelve to sixteen years on the hags
being cut over for the harvesting of the crops of poles, bark, or
small material.

So far, therefore, as considerations regarding conservation of
the productive capacity of the soil are concerned, high-forests
in general, and those formed of thickly-foliaged species in
particular, or copses of standard trees having a good protective
soil-covering of underwood, are certainly the forms of woodland
crops most thoroughly satisfying the first fundamental prin-
ciple of Sylviculture, viz. that the natural productive capacity
of the soil must be carefully conserved, in order that it may satisfy
continuously and uninterruptedly all rational demands made on
the land with regard to the production of timber or of other
forest crops. Both the quantitative yield and the qualitative
outturn in timber, or in other forest produce, are dependent
on the manner in which this fundamental principle is kept in
view. If, on merely average or inferior land, such kinds of
crops be formed, or methods of treatment be adopted, as
imperil the productivity of the soil, then any extra returns that
are promised in the immediate future must be dearly pur-
chased at the cost of the inevitable ultimate deterioration of
the land for timber-production. It would, in fact, be merely
discounting the future productivity of the land. The demands

262 Studies in Forestry [CHAP. xn.

for timber throughout the civilized world are steadily increas-
ing annually; while at the same time the total area under
forests is being reduced. More discrimination in the forma-
tion and the treatment of crops should, therefore, be exercised
generally than has hitherto been the case even in those coun-
tries that are furthest advanced in the art of forestry, and in
all scientific knowledge pertaining to Sylviculture.

II. Minor Climatic Influences affected by the nature
of the Treatment accorded to the Timber Crops.

Whilst influences regulating the productivity of large neigh-
bouring tracts of agricultural land can be affected beneficially
by the formation of extensive woodlands throughout districts
in which the annual rainfall is less than 40 inches l, and can
also be prejudicially altered through great total clearances of
forest growth, yet even on a very much smaller scale such
local climatic effects as early and late frosts are to a certain
extent within our control. Just as, in the case of coniferous
crops, the annual falls should, for the purpose of protection
against wind, succeed each other in the opposite direction to
the prevailing or most dangerous winds, so also in undulating
tracts and uplands, indented with coombs likely to collect the
cold, heavy air at night, consideration should be given to the
regeneration or the planting up of the endangered tracts first
of all, before similar operations are carried out round about
them. If their planting or natural reproduction be left till
that of the surrounding land is completed, then, when the
young crops on these have reached the thicket stage of
growth, the circulation of the cold night air becomes impeded ;
hence there is danger not only of the plants put out being killed
off, but also of these spots becoming frost-holes exceedingly
difficult to plant up again with any of the less hardy species

1 Endres, article Forsten in the Handworterbuch der Staatswissen-
schaften, Jena, 1892, vol. iii. p. 607.

CHAP, xii.] Protection of the Soil 263

of trees that may otherwise be best suited for the given soil
and situation.

On hillsides, therefore, the felling and regeneration should
take place from above downwards. On being cooled by
radiation of warmth from the surface of the soil, the air
becomes heavier and seeks a lower level ; and if its progress
down towards the valleys be hemmed or made to stagnate by
young thickets, the plants forming these are unduly exposed
to danger from late frosts in spring and early frosts in autumn.
On level stretches of land it suffices if the young crops are
fringed on one side at least by a lofty crop of trees ; for then
the cold air can circulate freely among the lofty stems in
that direction in place of being penned in by older, densely
foliaged thickets of somewhat higher growth. Hence, in natural
regenerations, it is an error to await the return of another seed-
year when patches here and there are deficient in seedling
growth. It is much more advisable to sow artificially, or to
plant, than to expose the ultimate seedling growth on such
patches here and there to subsequent danger from late and
early frosts on account of their being somewhat less in height
than the seedling growth around them. Similarly, when groups
of trees whose seedling growth is likely to suffer from frost, —
such as Oak, Ash, Beech, Maples, Silver Fir, and Spruce, —
occur of nearly mature age scattered among similar crops that
are fully mature, it is better to regenerate them along with the
latter, than to run the risk later on of developing frost-holes,
where only the hardier species of trees — like Birch, Elm,
Aspen, Alder, Larch, and Pines — will be able to outlive the
dangers constantly recurring for several springs and autumns
until the new crops of young plants get their head well above
the frost-line, below the level of which the chill night air
stagnates. And the quicker such spots are planted up, of
course, the less danger is there of frost-holes being formed.

In order that patches of this description may be utilized to
their full productivity, it is requisite that, if they are apt to be

264 Studies in Forestry [CHAP. XIT.

moist, they should either be drained or else planted up with
one of the genera of trees like Elm, Birch, and Larch, that
are at once hardy and capable of transpiring freely so as to
thrive on a moist soil.

III. The Manner in which the Cohesiveness or Tenacity
of the Soil may be affected by the Methods of
Treatment of Woodland Crops.

The productivity of any soil is dependent to no inconsider-
able extent on its cohesiveness. The whole relation towards
moisture and temperature is very directly and essentially influ-
enced by the fineness or coarseness of the individual particles
forming the soil. Whether the land be naturally binding and
tenacious, like heavy clays and argillaceous limes and loams,
or naturally light and porous, like many sandy soils, the main-
tenance of a good leaf-canopy throughout all the woodland
crops is of immense benefit in preventing the former class of
soils from becoming apt to get water-logged or else dried up
at different seasons, and the latter class from responding too
rapidly to changes in the atmospheric temperature, and from
running the risk of having portions of the soluble nutrient
salts washed out of the soil after heavy rainfall. Heavy soils,
that are insufficiently protected, are apt to become gradually
and imperceptibly caked in the upper layers, so that the
penetration, not only of the rootlets of seedlings, but also of
the atmospheric air, is rendered more difficult ; whilst sandy
soils rapidly sink below the freezing-point at night during the
cold seasons of the year, thereby exposing seedling crops to
late and early frosts, and become too easily heated during
summer days, thereby leading to excessive loss of moisture
through evaporation.

The great importance attached to aeration, or circulation of
air within the soil, is very practically recognized in agriculture

CHAP, xii.] Protection of the Soil 265

by the ploughing operations that are carried out annually. In
sylviculture similar operations are out of the question, except in
osier-holts, in nurseries, and in the preparation of patches or
strips of soil during natural regeneration or artificial reproduction
by means of sowing or planting. Nor are they required when
once the young seedlings have firmly established themselves
within the soil ; for the latter is not only aerated and mechani-
cally loosened by the humification of the dead foliage and the
cleaving and fissuring action of the roots, but is likewise pro-
tected from the soddening and setting action of rain by means
of the leaf-canopy overhead.

Actual experience shows that, except at the time of the
germination of seed, and the initial development of young
seedlings, so long as good canopy is maintained throughout
the crop no danger is run of the soil becoming set or hardened
on the surface by rainfall, as is so apt to be the case in fields
that lie fallow for any length of time. The humification of the
dead leaves and twigs, and of the roots of individual seedlings,
poles, or trees removed during the periodical processes of weed-
ing, clearing, or thinning, not only serves to improve the other
factors of influence as regards productivity, but most directly
acts on the cohesiveness of the soil-particles, by tending to
loosen binding soils, and to render more cohesive those which
are of a light sandy nature. This natural process is of course
aided by the action of the various organisms that are always
to be found more numerously in soils in which humification
is going on, such as Cladosporium humifaciens, Rostr., and
other fungi, insects, earth-worms, &c.

If the thorough aeration of the upper layer of woodland soil
could be periodically undertaken, there can be no doubt that
the productive effect of this measure would be speedily notice-
able in the more vigorous development and greater increment
of the crops. But, except on a small scale in osier-holts, this
is, for financial reasons, out of the question ; and besides this,
it is open to considerable doubt if the quality of the timber

266 Studies in Forestry [CHAP. xn.

produced would be so good as that which may now be grown
without any such artificial stimulation.

Soil that is exposed to the action of sun and rain is apt to
become rapidly heated, whereby the process of humification is
hastened on ; and, at the same time, the upper layer is apt to
cake or harden, whilst its nutrient salts are washed out into the
lower soil, in consequence of which the surface-soil deteriorates.
The best safeguards against such unproductive conditions are
undoubtedly the retention of a good normal canopy overhead,
and the prevention of the removal of dead foliage from the
ground either by wind or by any other means.

IV. The Manner in which the Quantity of Moisture
in the Soil may be affected by the Methods of
Treatment of Woodland Crops.

Unless care be taken to preserve the most advantageous
quantity of moisture throughout the soil, the productivity of
the latter becomes greatly prejudiced. For if, on the one
hand, too much moisture be allowed to remain in the soil,
this remains cold and inactive, the process of humification is
retarded, the solutions of the nutrient salts are weak and thin,
and the vital activity of the individual trees is below what it
otherwise would be if the soil-temperature of the layers per-
meated by the root-system were higher; and, on the other
hand, when there is an insufficiency of moisture throughout
the soil reached by the roots of the trees, the mineral food-
supplies, though perhaps contained potentially in a far greater
quantity than requisite for even the most exacting kinds of trees,
are often not available in that soluble form in which alone
they can be utilized by timber-crops. The former condition,
implying excess of moisture, can often be remedied by drain-
age, or by the choice of kinds of trees for crops like Alder,
Ash, Willow, Maples, Elm, and in a less degree pedunculate
Oak, Birch, Aspen, Larch, Spruce, and Weymouth Pine, all

CHAP, xii.] Protection of the Soil 267

of which are species that require to transpire a considerable
amount of water through their foliage before they elaborate
the requisite amount of mineral food necessary for carrying on
active vegetation and building up their ligneous tissue. The
latter condition, however, implying an insufficiency of water for
the transpiratory requirements of many of the above species,
and even of the other less exacting kinds like Beech, sessile
Oak, Silver Fir, and Douglas Fir, and generally involving along
with this but scanty supplies of mineral food, necessarily limits
the choice of trees from among which it is for the time being
possible to form woodland crops. As has previously been
shown (see page 79), deciduous trees make far higher demands
on soil-moisture than conifers ; and among the latter the most
suitable species for forming crops on dry soils are the Pines,
more especially the Scots and Black Pines on sandy tracts, and
particularly the Austrian Pine on land of a limy character.

In order that the most advantageous degree of soil-moisture
may be retained continuously throughout extensive woodland
areas, it is necessary that the soil should be protected as well as
possible from becoming exposed to the drying and evaporating
effects of sun and wind. This object may be best attained by
a judicious choice of the trees to form the crop, by avoiding
the formation of coppice-woods on soils tending to dryness, by
the maintenance of good leaf-canopy without overcrowding
(which would act most injuriously on the soil-moisture), by
regenerating the woods naturally — in place of making large
clearances or clear fellings of all the trees on the annual fall,
to be followed by sowing a planting artificially, — and by taking
the ordinary sylvicultural precautions for preventing the dead
foliage from being blown away and the normal process of
humification being interfered with — for, owing to its extremely
favourable hygroscopic qualities, humus is of invaluable in-
fluence in absorbing, in retaining, and in regulating the dis-
posal of the atmospheric precipitations throughout the upper
layers of the soil.

268 Studies in Forestry [CHAP. xn.

The nearer any soil approaches to dryness, the more neces-
sary, and at the same time the more difficult, it is to husband
the soil-moisture. It is a fact that very many species of trees,
like Oaks, Elms, Maple, Sycamore, and indeed all essentially
light-demanding trees, are more intolerant of shade on soils
from which they have difficulty in obtaining their requisite
supplies of water for transpiration, than on those which yield
them an abundance of moisture and food. Hence, on dry soils,
there is not only greater necessity for maintaining close canopy
overhead in the interest of the productivity of the soil, but also
at the same time a much stronger natural tendency on the
part of the trees to have thinly-foliaged crowns, and to strive
after an increase in growing-space. Under these latter circum-
stances the only proper sylvicultural treatment that can be
adopted is to cut out and dispose of the kinds of trees that
soon attain their maturity (such as Birch, Aspen, Willow, Ash,
Maple, Sycamore), thin out individual trees of the nobler
genera not likely to develop ultimately into valuable stems,
and then underplant the Oak, Larch, or Pine retained with
the species of underwood best suited to the given soil and
situation. By this means the soil is not only afforded a good
mechanical protection against the evaporating and drying effects
of sun and wind, but considerable masses of dead foliage are
thereby provided for humification, and for the improvement of
the soil generally (see last Chapter, page 243). It may here be
remarked that the Spruce is less adapted for forming the
underwood on dry soils than any of the other shade-bearing
species (Beech, Hornbeam ; Silver, Douglas, and Nordmann's
Firs), for its shallow roots are apt to interlace and form
a network throughout the upper layers of the soil, and to
intercept the aqueous precipitations, thus hindering the per-
colation of a fair proportion of the water down into the lower
soil, whence the deep-seated roots of the standard trees
draw by far the greatest portion of their supplies of food and
moisture.

CHAP, xii.] Protection of the Soil 269

Where woodlands are exposed to the action of dry winds,
care should be taken to favour the growth of branches down
to the very ground along all the outer lines of trees, so as to
protect the dead foliage and prevent evaporation of the soil-
moisture as much as possible. In coniferous crops a fringe of
Spruce, Douglas Fir, Silver Fir or Black Pine, is to be recom-
mended as forming the thickest mantle of foliage towards the
open ; but in crops of broad-leaved trees a very effective pro-
tective mantle can be formed by cutting the first few rows of
trees back to the stool, and letting them spring up as coppice.
Plantations in fields, or bordering on fields, should be fenced
in with good thick live hedges. On dry hill-sides, and more
particularly on those of a sandy nature and little retentive of
moisture, care must also be taken not to make large clear
annual falls of timber, but to regenerate naturally so far as
possible. When once the seedlings have established them-
selves, however, the parent standards have to be rapidly
removed ; for on such inferior situations the young growth can
ill bear any overshadowing that deprives them of the beneficial
dews at night. On such localities a certain amount of soil-
preparation for the reception of the seed is almost a necessity,
as without that the seedlings find difficulty in establishing
themselves, and are apt to be delicate. When this soil-pre-
paration takes the form of horizontal rills along the hill-sides,
it is more favourable towards water-catchment than any other
method ; consequently it tends to increase the amount of
soil-moisture, and thereby to enhance the productivity of the
land. Anything like irrigation of the soil can of course only
take place in osier-holts, and in nurseries. But wherever it is
feasible on dry hill-sides or on slopes covered with oak-bark
coppices, a good deal of benefit may be derived at a com-
paratively small outlay by leading off water from any water-
courses or ditches into small rills formed almost horizontally
along the slopes by means of a light plough.

In order to prevent light sandy soil near the sea-coast from

270 Studies in Forestry [CHAP. xn.

being blown about so as to form dunes of shifting sand, and in
order to hinder the formation of a thin impermeable subsoil layer
of xnoorpan by dry heather mould, quartz-sand, and a slight
admixture of oxide of iron, the retention of a fairly good canopy
and the preservation of all the foliage for humification are
essential. When stretches of moorpan soil have been reclaimed
by subsoil ploughing and planting up with Scots Pine, the
undecomposed layer of heather-humus is often turned into
mould of a more ordinary nature. And on reclaimed dunes,
the layer of dead needles under the Pine trees not only acts
as a mechanical hindrance to the lifting of the sand, but
yields to it the beneficial humus that helps to bind it and
to keerj it moist. Such light sandy soils are unfortunately
too poor to bear densely foliaged crops, or to permit of any
underwood being formed with a view to the improvement of
the soil.

V. The Manner in which the Relation of the Soil
towards Warmth may be affected by the Nature
of the Crop or the Method adopted for its
Treatment.

The manner in which woodland soils respond to variations
in the atmospheric temperature is determined more especially
by the quantity of moisture contained in them, than by the
specific warmth of the different kinds of soil. Colour, Conduc-
tivity, Porosity, Composition, and other physical factors all
exert direct influence in this direction ; whilst the nature of the
soil-covering is also of no little importance. That the quantity
of moisture contained is of so much influence may be easily
understood from the great latent power that has to be overcome
in effecting changes in the temperature of water. And as
regards colour, soils prove no exception to the law of radiation
and absorption, viz. that dark bodies respond more quickly to
variations than those of a similar texture but lighter in colour.

CHAP, xii.] Protection of the Soil 271

The more porous the soil, the larger the individual particles,
and the greater the extent to which stones occur throughout
the finer earth, the higher is the general conductivity of the
soil.

Soils which are retentive of moisture, like clay and stiff loams,
remain cold and inactive in spring. Porous, sandy, and gravelly
soils become easily warmed, but are liable to the danger of
radiating their warmth too rapidly, and are thus apt to sink
below the freezing-point at the most critical times in spring,
and again in the autumn to a less important extent.

Even a small admixture of moisture in sandy soils makes
them less apt to respond closely to sudden diurnal and noc-
turnal changes in the atmospheric temperature ; hence any
sylvicultural measures likely to increase the amount of moisture
in light porous soils are beneficial. And in the same way what-
ever tends to remove anything approaching to excessive moisture
in heavy land likewise stimulates the root-systems ramifying
throughout it to a more active imbibition of nutrients ; for the
rootlets are stimulated into activity far more by the soil-tem-
perature than they possibly could be merely by the atmospheric
warmth that is conducted down the stem. Apart from such
extreme cases of wetness as make drainage advisable to a
greater or less extent, it will be at once recognizable what
an important influence may be exerted both on light and on
heavy soils by an admixture of humus. Humus is strongly
hygroscopic in absorbing and retaining moisture It acts as
a non-conductor, not only in keeping out sporadic warmth from
the lower layers of soil early in spring before the warm changes
in the weather become settled, but also in retaining it well into
the autumn when diurnal variations again become marked.
It is, however, needless to recapitulate its good qualities, as
they have already been commented on in each of the previous
sections of the present Chapter. A good admixture of humus
in the upper layers of soil, and a soil-covering of foliage under-
going the process of humification, will therefore, by tending

272 Studies in Forestry [CHAP. xn.

to keep the soil fresh or at most slightly moist, and by causing
it to respond gradually to actual periodic variations, and not
to mere sporadic daily changes of temperature, prevent the
commencement of the annual vegetative activity till the general
warmth is greater and the assimilative process can be carried
on with greater energy, and without risk of the young flush
of leaves and shoots being killed by late frosts. But the
advantages derivable from delaying the early awakening of
vegetative activity in timber crops have previously been con-
sidered l '} and it is only necessary to point out here that the
relation of soil towards warmth will be most favourable when
the timber-crcps are of such a nature as to favour the formation
of a good layer of humus, and when they are subjected to such
methods of treatment as will not interfere with the normal
process of humification. Thus soils naturally of a moist descrip-
tion can most advantageously be utilized for crops of Ash,
Alder, Oak, Elm, Maple, Sycamore, Willow, or Birch, where
the more densely foliaged species of trees, with their heavier
fall of dead foliage, might be apt to litter the ground with so
thick a layer of dead leaves as to interfere with the progress
of humification and to impede the entrance of air into the soil,
or where, by their greater density of canopy and their lower
capacity for transpiration through their foliage, they might tend
to keep the soil too moist and inactive. On land of this class
the more lightly foliaged trees have not only a better leaf canopy
than on dry soils, but the action of the sun may be even
beneficial where there is any tendency to excess of moisture.
On dry soils, however, there exists a necessity for the mainten-
ance of good canopy, for admixture of Beech along with Oak,
and of Douglas Fir, Silver Fir, or Black Pines along with Larch
and Scots Pine, or for underplanting when the crop of timber
trees is unable for itself to maintain the soil against the action
of sun and wind, and unable to prevent the upper layers from

1 See also chapter on Underplanting. pp. 236, 237.

CHAP, xii.] Protection of the Soil 273

being robbed of their soluble salts by weeds and useless
growth.

VI. The Manner in which the Depth of the Soil may
be affected by the Nature of the Crop, and the
Method adopted in its Treatment.

So far as sylvicultural operations are concerned, but little can
practically be done with a view of directly increasing the depth
of the earthy soil throughout woodland tracts. The natural
processes of the disintegration and decomposition of rocks,
stones, &c. are gradual and slow. Much can certainly be done
to improve the productive capacity, as has already been men-
tioned with reference to the planting up of poor limy soils ;
and there is no doubt that the gradual humification of the dead
foliage not only adds to the depth of the upper layer of soil,
but also favours the processes of further decomposition, which
again lead to increase in depth. In the majority of cases, how-
ever, the existing depth of the soil is taken as one of the
concrete factors, to which the choice of the crop and of the
method of treatment must accommodate themselves.

Wherever the sylviculturist has to deal with shallow soils,
he must naturally select species of trees for cultivation that
are able to develop normally within the depth available for the
ramification of the root-system. To attempt, for instance, to
grow high forest of Oak on a soil of only a couple of feet
in depth, with a subsoil of an impenetrable nature for the tap-
root and the main side-roots, could not reasonably be expected
to prove a success, however fertile the land might be. If the
land were good enough, and there were reason to anticipate
better returns from such than from any other crop, then Oak-
coppice might be cultivated for the sake of tanning-bark.
Wherever the soil under timber is shallow, any measures must
be avoided that may probably lead to interference with the
amount of moisture contained in it, or with the normal process

T

274 Studies in Forestry [CHAP. xn.

of humification of the dead foliage shed from the crop, and
consequently with the stimulation of the formation of fresh
nutrients within the soil. Thus, gradual natural regeneration
under parent standards, though perhaps merely in groups or
patches here and there, will prove much more prudent than
extensive clear-fellings laying bare large areas at one time ;
and this precaution is all the more necessary on steep and
on rocky slopes, where, in addition to the powerful inimical
influences of sun and wind, there also comes the mechanical
danger of the surface-soil being washed away by heavy rainfall.

All of the above considerations, individually and collectively,
lead to the simple result that the fullest utilization of the
soil and the most effective safeguarding of its productivity
are obtainable by one and the same means, viz. by the continuous
protection of the soil through the maintenance of a good leaf-
canopy of normal moderate density^ and through the retention
of the soil-covering of dead foliage for the beneficial formation
of forest mould by the usual process of humification. Where the
timber-crops stand too thin, as seems to me the general fault
in British woods, the productive capacity of the soil is neither
utilized to its fullest extent for the formation of the longest and
straightest boles of timber, comparatively free from branches,
nor is it husbanded as it should be in accordance with the first
fundamental principle of Economy in general, and of Sylvicul-
ture in particular. Where, on the other hand, the timber-crops
are too thick or crowded, nutrients may be drawn in excessive
quantity from the soil, and squandered in the individual struggle
for existence, instead of being utilized to anything like the best
advantage in the more rapid development of the predominant
individual stems ; and at the same time the process of humifi-
cation of the dead foliage is interfered with. These dangers
are of course greatest on poor lands that are either too moist
or too dry. Just, in fact, where an admixture of humus is
most requisite, its formation is most difficult.

A good canopy of foliage protects the soil from any excessive

CHAP, xii.] Protection of the Soil 275

evaporation through the action of sun or wind, and helps to
maintain the advantageous, non-conducting soil-covering of
dead foliage, which gradually becomes of greater benefit to
the soil itself and to the growing timber-crop as the process
of humification advances. Hence woodland soils, that are
judiciously utilized, provide for themselves the very best means
of maintaining their productivity, so long as they are treated
in such manner as will endow or retain them with the most
advantageous degree of freshness or moisture ; for along with
this will, from the very nature of the factors upon which this
is dependent, certainly be favourably combined the other
physical properties and organic conditions which work together
in order to produce the highest quantitative and qualitative
returns obtainable from any given soil and situation. It stands
to reason that these highest results can hardly be expected
from the small patches, and clumps, and groves of woodland
so often to be found dotted about large estates, more often
really for the protection of game than for timber-production,
but that they will be most easily and most effectively attained,
the larger and the more compact the areas are, which may be
set apart for the express purpose of growing timber in a rational
manner in accordance with the Principles of Sylviculture.

T 2

CHAPTER XIII

THE FUNGOID DISEASES OF FOREST TREES, AND
THEIR PREVENTION

No small proportion of the disturbances which take place in
the growth of plants, and which vary from comparatively trifling
ailments up to serious injuries resulting in the death of trees,
is directly ascribable to the influence of parasitic, cryptogamous,
vegetable organisms called Fungi, which live on or in the
plants in question.

Fungi are plants of lowly organization, consisting only of
cells and containing no chlorophyll. They consequently
cannot elaborate organic substance for themselves, and there-
fore only obtain their requirements in this respect by with-
drawing organic nutriment from other living or dead organ-
isms belonging either to the animal or the vegetable kingdom.

Until the last few decades this pathological branch of phy-
tology received scant attention, so far as woodland growth was
concerned. Many of the fungal diseases of trees were unknown
and contemptuously disregarded ; whilst, with respect to some
others of a more prominent and widespread nature, cause and
effect were confused. The appearance of many fungi, e.g.
species of Polyporus causing red and white rot, was regarded
as the consequence of the rot in place of its cause ; and not
a few of the phenomena are still a sealed book to sylviculturists.
The Pasteur of this branch of Forest Science is Professor
Robert Hartig of Munich.

CHAP, xiii.] Fungoid Diseases of Trees 277

Fungi may be either saprophytic or parasitic. The former,
fortunately including most fungi, are only to be found on dead
and decomposing substances, and are therefore the accom-
paniment or consequence of sickly growth and disease, and
not its cause. Those belonging, however, to the latter class,
attack healthy living plants, and are a direct cause of disease,
often terminating in death; but many of them continue in
a sort of saprophytic growth when once the disease they have
occasioned has terminated the life of the plant attacked. All
the fungi called rusts ( Uredineae] are parasitic.

The reproductive organs of fungi are developed in or on
receptacles, sporangia, sporophores, or spore-producers, and
consist of germinative cells of different kinds roughly classi-
fiable as Spores, Sporidia } and Gonidia or Conidia.

Spores (including ordinary spores, and also Uredospores,
Aecidiospores, Teleutospores &c., according to the different
circumstances relative to their formation and development),
are the generic name for these germinative cells without dis-
tinction ; whilst Sporidia are secondary spores formed on
a Promycelium developed by the germination of hibernating
or resting spores ; and Gonidia or Conidia are those formed
at the point of usually erect-growing mycelial threads.

When any spores that settle on plants find the conditions
(damp and warmth) favourable to their development, germina-
tion follows, i. e. they develop delicate, thin-walled, mostly
colourless, tube-like processes (mycelial filaments or hyphae\
sometimes filled with a golden-yellow oily fluid. These tubes,
though often undivided, are as a rule divided into simple
cells (septated), their contents being protoplasm and cell-sap.
With the exception of the mildew-fungi, which merely vege-
tate on the exterior, the infection of leaves, fruits, bark and
wood always commences from the outside by the hyphae
pushing their way either through the stomata or the epidermal
cells of young leaves or bark, or effecting an entrance into
the interior of the plant through the unprotected portions of

278 . ' Studies in Forestry [CHAP. xin.

the roots, or at any wound-surfaces like those of broken
branches.

These hyphae either insinuate themselves between the
cellular walls of the parenchym or the prosenchym, and vege-
tate in the intercellular spaces or the resin-ducts, whilst they
send single short off-shoots or suction-roots (haustoria) into
the interior of the cells, or else they bore through the cell-
walls, and thus force their way from one cell to another. By
extending in length, and at the same time throwing out side-
processes — less frequently by ramifying — they at length form
a filamentous network or Mycelium, which represents the
complete vegetative body of the organism. Masses of myce-
lium form Sclerotia, containing stores of food-supplies (chiefly
proteids and oil) which, under favourable conditions, produce
either new mycelium or sporophores of the fungus.

Receptacles or spore-producers spring from the mycelium and
produce the reproductive organs, the spores. One and the
same fungus often produces sporophores of the most varying
shapes, and the form of these is much more characteristic (e. g.
mushrooms, toad-stools, &c.) than the hidden mycelium, which
is much alike in all fungi.

When the sporophores are only single threads from the
mycelium they are called spore-hyphae, but in other cases the
sporophores or receptacles are of the most varying forms, and
have different names. Carpospores are spores which produce
a second generation differing from the original form, whilst
Gonidia or Conidia only reproduce the form on which they
occur. Gonidia therefore multiply one form of fungus very
rapidly within the annual period of vegetation, whereas carpo-
spores perpetuate the species from one year to the other.

The spread of infectious diseases can take place either by
mycelial infection from root to root under the ground (as in
Trametes pini, Agaricus melleus, and Rosellinia quercina in
plantations, and Dematophora necatrix in vineyards), or by
spores and gonidia wafted about by the wind or conveyed

CHAP, xjii.] Fungoid Diseases of Trees 279

mechanically by animals or other agencies (as in the case of
Phytophthora omnivora on seedlings, new outbreaks of Tra-
metes radiciperda at the base of the stem, and the rust on corn
occasioned by species of Puccinia] \

The consequences of such infection with fungal hyphae are
interference with the normal transpiration and the decompo-
sition of the carbonic acid in the part infected, gradual destruc-
tion of the cells and consumption of the cellular substance
and contents, with chemical disturbance and morphological
alteration, generally accompanied by more or less hypertrophy
or morbid enlargement, and resulting finally in death. In
consequence of the sickly state of the plant, insects are often
attracted and assist in the work of destruction. From the
mycelium at length proceed the various forms of spore-bearing
organs characteristic of the different kinds of fungi, breaking out
and appearing sometimes on leaves, twigs, or on the surface of
the bark, at old branch-holes, or even from holes through which
bark-beetles have previously made their exit from the stem.
Millions of reproductive spores are produced, and the cyclus
of generation begins anew. Some fungal species of sylvi-
cultural importance deviate from this normal type in having
frugiferous organs (Rhizomorpha) without any fructification of
the mycelium (e.g. in Agaricus melleus, a species closely allied
to the common mushroom).

Many fungi complete their life-cycle within a few weeks or
months, whilst in other species the spores hibernate, and in
others again the mycelium retains its vital energy for two,
three, or more years ; most of the species occasioning diseases
of forest trees belong to this last-named category.

The polymorphic tendency of many fungi, or the change of

1 Smut on wheat is occasioned by Puccinia graminis, which in its aecidial
form, occurs as Aecidium berberidis on the leaves of the Barberry. This
shrub should therefore be treated as a very noxious weed in all hedges, &c.,
throughout corn-growing districts in which rusts and smuts are in the
slightest degree prevalent.

280 Studies in Forestry [CHAP. xin.

generation, demands special mention. It not infrequently
happens that the spores of one fungus do not produce an
individual resembling the parent, but something which appears
quite a different kind of fungus ; and the spores of this again
may perhaps produce what seems a third kind of fungus not
resembling either of the two previous forms ; but ultimately
the spores of the second or third forms produce, or throw back
to, the original parent type, and the cycle re-commences.
Accurate observations have thus shown, and are still showing,
that many fungi previously reckoned as belonging to different
genera are merely different stages in the development of other
well-known species. Those genera are of course most highly
organized, in which sexual processes can be proved. The
regular change of form is called change of generation ; the change
in the shape of the regenerative organ is known as pleomorphy;
and the change in the choice of a host, i. e. of the plant
infected, is termed heteroecy. This change of generation finds
its complete parallel among certain gall- wasps (Cynipidae] in
the insect world. Thus Cynips aptera, producing galls on Oak-
roots, gives birth to Cynips terminalis^ forming galls at the ends
of the twigs, whose progeny throws back to the original form
C. aptera, and the cycle commences anew.

The occurrence and the spread of fungal diseases are specially
favoured by certain conditions of climate and situation. Damp-
ness and warmth are requisite essentials, whilst light is of less
importance, as their peculiar processes of assimilation proceed
without the agency of chlorophyll, inasmuch as they cannot,
like green plants, assimilate carbonic acid; hence, if light were
essential, they could not grow underground, and in the inside
of timber trees, as they do. In damp seasons, and in humid
localities with heavy, stagnant air, fungoid growth is more
favoured than in dry years, or in exposed situations with free
play of winds. Nitrogenous substance favours their growth,
as the plasmic contents of the mycelial threads contain a large
proportion of Albumen. In timber-work, the quantity of nitro-

CHAP, xiii.] Fungoid Diseases of Trees 281

genous matter contained in the wood determines its liability
to decay from fungoid causes (Merulius lachrymans, &c.) ; hence
Beech or Willow wood is far less durable than Oak or Pine.
But if there were no albuminous substance in woody tissue, or
if it could be kept absolutely dry, fungoid decay would not
take place in wood-work ; for moisture is an absolute necessity
to fungoid growth.

In woodlands, fungoid disease may sometimes be noticeable
as epidemic or somewhat general simultaneously throughout
the crop, otherwise it may be merely sporadic or distinctly
localized in places here and there. In the former case it is due
to conditions closely connected with soil and situation or with
climatic factors unsuited for the species of trees forming the
crop, and can usually only be prevented by change of crop to
a more suitable species ; whilst in the latter case it can generally
be eradicated by excision, root and branch, of the infected
individuals so as to obviate the spread of the disease.

Within the short space here at disposal it is impossible to
undertake the detailed descriptions of any but the more
important and frequent fungal diseases of our forest trees ;
and, in considering them, it will be advantageous to discard any
attempt at the natural classification according to reproductive
peculiarities in orders and families, and merely to group them
together according to the general tendencies they show with
respect to the infection of Foliage, of Stem and Branches, and
of the Roots and the base of the Trunk.

It may be remarked, generally, that (as will also be seen
to be the case as regards injurious forest insects) fungoid
diseases do much more damage in coniferous crops than in
woods formed of broad-leaved species. This may be accounted
for not only by the natural attraction they seem to offer to the
different kinds of fungi, but also partly on account of the much
weaker recuperative power the conifers possess in comparison
with deciduous, broad-leaved species of trees.

Studies in Forestry [CHAP. xin.

General Classifications of the Chief Fungoid Diseases
of Sylvicultural Importance.

I. ON FOLIAGE.

A. Of Conifers:—

1. Hysterium pinastri. Pine scab or scurf. Mainly attacking
Scots Pine.

2. Chrysomyxa abietis, Spruce needle-rust or blight. Mainly
attacking Spruce.

3. Aeddium pini, var. adcola, Pine needle-rust or blight.
Mainly attacking Pines.

4. Trichosphaeria parasitica. Silver Fir needle-blight. Mainly
attacking Silver Fir and Spruce.

Minor disorders are occasioned by Hysterium nervisequium
on Silver Fir, H. macrosporum on Spruce, Caeoma laritis on
Larch, C. abietis pectinatae on Silver Fir, Aeddium columnare on
Silver Fir, A. abietinum on Spruce, and A, strobilinum on the
bracts of Spruce cones.

B. Of Broad-leaved Trees : —

i. Phytophthora omnivora, Beech-seedling fungus. Mainly
attacking Beech, Maples, Ash; Spruce and Scots Pine (in
nurseries and young seedling growth).

Minor disorders are due to Melampsora Hartigii on Willows
(especially ,S. caspicd) ; M, tremulae on Aspen, M. Betulina
on Birch, and M. salidna on Sallow, also Rhytisma acerinum
on Maples and Sycamores \

1 It may here be remarked that there is reason to believe that Caeoma
laricis and C. pinitorquum can both of them pass through their aecidial
stage either as Melampsora tremulae on Aspen or as M. Betulina on Birch ;
and that the spores of either of these latter forms may infect the shoots of
Scots Pine with Caeoma pinitorquum or the foliage of Larch with C. laricis.
Hence Birch and Aspen should be treated as weeds and cut out, wherever
either of these diseases is prevalent among Pine or Larch woods.

CHAP, xiii.] Fungoid Diseases of Trees 283

II. ON STEMS AND BRANCHES (in the bark or in
the wood).

The cankerous diseases which belong to this section may be
divided into two main groups. In the first of these are
comprised all such diseases of the bark and the cambium as
cannot be healed without human interference, because of their
influence annually extending, so that when it has encircled the
stem all above this zone dries and dies off. And in the second
group are comprised disorders which only, as a rule, spread
through the bark during a single period of vegetation ; but if
within that time the disease has not completed its circuit round
the stem the infected place becomes cicatrized and heals over.
Unfortunately the only one of the chief cankerous diseases
below mentioned which belongs to this latter group is Nectria
cucurbitula.

A. Of Conifers : —

1. Trametes pini. Pine fungus. Mainly attacking Scots Pine,
Spruce, Larch, Silver Fir.

2. Aeddium pint, Pers. var. corticola^ Pine-canker or bark-
fungus. Mainly attacking Pines.

3. Caeoma pinitorquum, Pine-shoot fungus. Mainly attack-
ing Pines *.

4. Aeddium elatinum, Silver Fir fungus. Mainly attacking
Silver Fir.

5. Nectria cucurbitula. Spruce-bark fungus. Mainly attack-
ing Spruce.

6. Peziza Willkommii, Larch canker. Mainly attacking
Larch.

Minor disorders are occasioned by Cladosporium entoxylinum
and C.penidllioides on Scots Pine, and Pestalozzia Hartigii on
Spruce and Silver Fir (seedlings in nurseries).

1 See foot-note on opposite page.

284 Studies in Forestry [CHAP. xm.

B. Of Broad-leaved Trees : —

i. Nectria ditissima. Beech canker. Mainly attacking
Beech, Oak, and all other similar trees (except Birch ?;.

Minor disorders are due to Nectria cinnabarina on Maples,
Elm, Lime, and in particular Horse Chestnut, and Polyporus
sulphureus on Oak, Poplar, Tree Willows, Birch, and Larch.

III. ON ROOTS AND BASE OF TRUNK.

A. Of Conifers : —

1. Agaricus melleus^ the Honey fungus, an edible mushroom.
It mainly attacks conifers, but especially Spruce, or Scots
and Weymouth Pines.

2. Trametes radidperda^ Root-fungus. It mainly attacks
Scots and Weymouth Pines, Spruce, and Silver Fir.

B. Of Broad-leaved Trees: —

i . Rosellinia querdna, Oak-seedling fungus, occurring in one
to three-year-old Oaks principally.

Details with regard to the Appearance, Causes and
Effects of the Chief Fungoid Diseases, and the Pre-
ventive Measures adoptable against their spread.

I. FUNGOID DISEASES OF THE FOLIAGE.

A. On Conifers: —

i. Hysterium pinastri, Schrad., the Pine scab or scurf, is
one of the principal causes of leaf-shedding in young plantations.
During late summer and autumn small brown spots, which
contain the characteristic mycelium of this fungus, make their
appearance on the young foliage of Pines. Early in the following
spring the needles wither, redden, and drop off. If the winter
has been mild and the spring is wet, the blackish fruits or

CHAP, xin.] Fungoid Diseases of Trees 285

apothecia are developed in May ; but they can only burst when
favoured by long-continuous rain. Hard winters and dry
spring weather therefore tend to prevent the spread of the
disease. This disorder is of very frequent occurrence in
nurseries and young plantations.

In Germany thirty years ago this disease of the Scots Pine
was merely ' an interesting observation,' but now it has practi-
cally become a widespread calamity *. Similar appearances of
leaf-shedding in the Pine may, however, easily be occasioned by
other causes. Although R. Hartig and Prantl have shown it to
be due to H. pinastri in a great many cases, Ebermayer has
proved that it can be caused by a process of drying up or
exhaustion owing to excessive transpiration in early spring ;
whilst Alers and Nordlinger proved that it was frequently due
to autumn frosts in rapid contrast with sunny days owing to
strong radiation of warmth from unprotected soils, more
especially after wet, cold summers unfavourable to the
hardening of the shoots.

This disease attacks Scots Pine chiefly, and also the Austrian
Pine, between the ages of one to five years, although it is like-
wise found on plants up to about twenty years of age. Damp,
misty localities favour its spread, hence it is more frequently
found in plains and valleys, than in hill-side woods. The
best measures adoptable to prevent its spread consist in the
admixture of Spruce with the Pine, in the avoidance of delay
in pricking out seedlings in the nursery beds, in the formation
of Pine nurseries in places free from infection — amid broad-
leaved woods if possible, — and in the burning of all plants
infected.

Some similar disorders are occasioned by H, macrosporum
on the two-year-old foliage of Spruce plantations from ten to
thirty years of age, and by H. nervisequium on two-year-old
and older foliage of Silver Fir.

1 See Chapter VI. p. 130.

286 Studies in Forestry [CHAP. xm.

2. Chrysomyxa abietts, Ung., the Spruce needle-rust or
blight.

Pale yellow spots break out here and there on the needles
of one-year-old shoots about the end of May or the beginning
of June, which increase and become of an intense yellow whilst
the uninfected parts remain normally green. Towards autumn
brown longtitudinal marks make their appearance along the
underside of the needles on both sides of the midrib, which
become ruddy and slightly swollen during the autumn. These
beds of Teleutospores become enlarged in the following spring ;
the epidermis bursts along the middle of the swelling in April
or May ; and the spore-bed makes its appearance as a velvety,
bright orange pustule, which scatters its spores about the
middle of May over the new flush of needles. The green
parts of the foliage attacked soon withers, and the needles fall
off in June and July.

This fungus only attacks the young needles, hence one-year-
old or older needles are exempt ; and the upper portions of the
crown are much less liable to the disorder than the central
and lower portions. Spruce plantations of from ten to twenty
years of age, in damp, close situations with southern and south-
western exposures suffer most, although the disease is also
found in woods of thirty to forty years old. Its spread is said
to be much more prevalent on limy than on other soils.
Warm, damp spring weather favours its increase, whilst all
atmospheric influences checking the early flush of the foliage
militate against it. The direct injury done to the plantations
is only considerable when the disease has obtained a foothold
on the foliage for several successive years ; but indirectly it is
of real importance, as it vastly increases the danger of attacks
from Bark-beetles. The only means of preventing attacks is
to avoid planting Spruce in pure forests on wet soils and close,
confined situations ; whilst remedial measures are confined to
the removal of all twigs infected, and to the regular conduct
of thinning operations.

CHAP, xin.] Fungoid Diseases of Trees 287

Somewhat similar appearances of rust or blight are caused
by Caeoma laricis on the needles of Larch, and by C. abietis
pectinatae, and by Aecidium columnare on Silver Fir.

3. Aecidium pint ^ Pers., var. adcola, the Pine needle-rust or
blight.

During April and May, on the one and two-year-old
foliage of young Pine, minute orange-yellow blisters (Peridia}
are often to be seen in a row, either on one or both sides of
the needles, between which the Spermogonia lie. These turn
brown when mature, as also do the Peridia before they burst in
the middle and scatter their spores. The mycelium develops in
the inside of the needle without killing it, and again produces
Aecidia in the following year. The foliage is only killed off
and shed when the disease infects the plants extensively ; in
this case its marks may be traced by small, blackish, warty
spots with light edging.

Although mainly confined to Pines (and in particular to Scots
and Black Pines) of from three to ten years of age, it may be
found in woods up to thirty years old, but always on needles of
the last or of former years, and never on the new flush of
foliage. Here again the formation of mixed in place of pure
woods, careful clearing and thinning, the removal of infected
twigs, and the removal of groundsel plants (species of Senecid]
on which the other generative form Coleosporium senetionis is
produced, constitute the only practical measures for obviating
the spread of the disease.

Somewhat similar disorders are caused on one-year-old
Spruce foliage by A. abietinum. To one of the same genus,
A. strobilinum, is also due the fungoid disease common on the
bracts of Spruce cones.

4. Trichosphaeria parasitica^ R. Hrtg., the Silver Fir needle-
blight.

The thin, colourless mycelium is generally to be found on
the lower side of the last sprays of Silver Fir, whence it usually
attacks the needles pointing downwards, forming close white

288 Studies in Forestry [CHAP. xin.

pustules on the whitish streaks along the under surface. In
consequence of infection the needles change colour, turn
brown, and drop off from the twig, to which they remain
suspended by the mycelium. The pustules turn brown after
the drying-up of the needles; and about November small,
round, blackish-brown, hairy Peritheda are formed containing
the dirty grey spores, which germinate easily on Silver Fir
foliage and thus spread infection. But the mycelium hibernates
on the sprays and needles, and extends to the new shoots
developing in spring, whose foliage it attacks as well as the
needles that may hitherto have escaped on the old sprays. In
addition to scattering abroad myriads of spores, this fungus
never relaxes its attacks or quits the foothold it may once have
attained on any young tree, until the latter has been killed. This
disease occurs most frequently in twenty to forty-year-old crops
of Silver Fir, especially on the lower foliage and on individuals
of most forward development ; but it is also to be found on
Spruce. The best remedial and protective measures consist in
the cutting out of infected twigs, and in careful tending so
as to maintain a good canopy and keep the woods as free as
possible from tangled growth.

B. On Broad-leaved Trees : —

i. Phytophthora omnivora, de Bary, the Beech-seedling
Fungus.

The effects of this disease were first noticed in the cotyle-
donous leaves of Beech-seedlings. They manifest themselves
in the withering of either the slender stalk or the rootlet, and
in black spots at the base of the cotyledons or on the pri-
mordial leaves when these appear. Within about a week of
the first symptons of disease the whole seedling exhibits its
effects, especially when May and June are damp months. In
dry seasons the seedlings infected have a blackened, scorched
appearance.

Infection primarily takes place by means viovispores (pospores]

CHAP, xin.] Fungoid Diseases of Trees 289

dormant in the soil. As the mycelium is formed, it spreads
throughout the whole stalk as well as within the cotyledons ;
whilst numerous hyphae break through the epidermis from
within, or force their way through the stomata, and develop
into sporangia-bearers. After the detachment of the citron-
shaped sporangia their receptacles become prolonged and
again form sporangia; whilst the older ones drop off and
either at once germinate, or scatter in all directions the Conidia
which they contain. The development of this fungus is so
rapid that in rainy weather, and in close, damp situations, new
sporangia-bearers are formed within three to four days of the
first appearance of infection. Ovispores (oospores) are at the
same time formed by the sexual process of fructification. These
become incorporated within the soil when the infected parts
rot away, and retain germinative power for three to four years,
or even longer. When once this fungus establishes itself in
nurseries, or in areas being naturally reproduced, it may occa-
sion very serious damage, as in addition to infection from
ovispores (oospores) that are easily carried from place to place
by wind and passing animals, the mycelial filaments produce
infection subterraneously by entering into the rootlets and
suction-roots of neighbouring seedlings.

Besides the Beech, the seedlings of Ash, Maple, and Syca-
more are most liable to its attacks, as well as those of all
conifers, but especially Spruce and Scots Pine. So long as the
infection only takes place at the tip of the seedling, recovery is
possible ; but where, coming from below, it begins to make its
appearance in the stem, the case is hopeless. In consequence
of this fungus whole seed-beds covered with rills of coniferous
sowings may be killed off even before the germinating seed-
lings have made their appearance above the soil.

Preventive measures include the careful removal of infected
seedlings whilst the disease is as yet merely sporadic. Any
seed-beds which have been attacked should only be used for
the schooling of transplants during the two or three following

290 Studies in Forestry [CHAP. xiu.

years ; if possible a different species of plant should be pricked
out from what has previously been sown there. Watering
the seed-beds with a solution of 4! Ib. of copper vitriol (blue-
stone) and one quart of ammonia in fifty gallons of water is
said to yield good results in checking the spread of the
disease.

Minor disorders are occasioned by Rhytisma acerinum — which
causes the yellow spots (Xyloma acerinum, the summer form),
that change in autumn and winter to black, on Maple and
Sycamore foliage, — Melampsora tremulae on Aspen, and M.
Hartigii on the leaves on the one-year-old shoots on Willows :
this last disorder is often serious on S. acutifolia and S. caspica.
A similar fungus, M. salidna, is also found on Willows, on S.
caprea chiefly, and M. Betulina on the Birch. In all these cases
the burning of infected foliage should be seen to during autumn
and winter; whilst in osier-hags infected shoots should be cut
away and burned wherever the disease manifests itself.

II. FUNGOID DISEASES OF THE STEM OR BRANCHES
(in the bark or in the wood).

A. On Conifers : —

i. Trametes pini, Fr., the Pine Fungus.

This disease is to be found chiefly in Pine stems from about
forty years of age onwards, although it also occurs on Larch,
Spruce, and Silver Fir. The spore-tubes insinuate themselves
into the woody tissues on wound -surfaces or wherever green
branches have been broken off. When the germination of the
spores begins, the hyphae push forward, destroying the cell-walls
and forcing their way into the heart-wood of the tree. Here the
mycelium develops, and forms ring-shakes or heart-shakes
extending down from the crown and leading to the rapid
decomposition of the timber in consequence of the rapid
increase of the mycelial filaments, whilst as a rule the sapwood
remains untouched. The mycelium next makes its appearance

CHAP. XTII.] Fungoid Diseases of Trees 291

at branch -holes of the trees attacked, or else direct out of the
bark, where it forms a brown, woody, bracket-like receptacle
or hymenium ; and the spores scattered from this infect other
wound-surfaces, unless these are protected by resinous outflow,
or by having been tarred after any pruning of the Scots Pine.
The technical value of Pine stems often becomes much reduced
owing to this disease. It often happens that these spore-
producers live for a long time (up to fifty years, according to
R. Hartig l) and gradually assume large dimensions.

The immediate removal of trees attacked by the fungus
appears advisable, not only in order to be able to utilize the
timber before decomposition has proceeded too far, but also
in order to prevent the spread of the disease by the scattering
of the spores produced in immense numbers in the receptacle.
The removal of Scots Pine branches in which heart-wood has
already begun to form should be avoided ; or, if pruned, then
the wound-surfaces should be coated over with tar.

2. Aeddium pini, Pers., var. corticola, the Pine Canker or
Bark-fungus.

This is a disease to which Pines in general, and Scots Pine
in particular, are liable both as poles and trees, but principally
as young poles about fifteen to twenty years of age. The fungus
appears first on portions of the tree that are of at least two
years' growth, mostly at the whorls, and near the top of the
tree.

Some kind of wound in the bark is necessary before the
spores of this fungus can effect an entrance ; but when once
this has been gained, the presence of the disease is first noticeable
by the appearance of small bright semi-spherical or oval orange-
reddish pustules (aetidia) protruding from the' bark of branches
and stems in June, which swell up and burst, scattering the
spores they contain. The colourless, septated hyphae of the
fungus live intercellularly between the parenchym cells of the
bark, the liber, and the medullary rays, and send haustoria or
1 Op. dt., p. 164.
u 2

Studies in Forestry [CHAP. xiu.

short side-branches through the cell-walls into the inside, in
search of nourishment.

When the mycelial filaments come in contact with the starch
contained in the cells, this becomes transformed into turpentine,
which collects on the inner wall and saturates the tissue itself,
so that a process of resinification or inspissation of turpentine
sets in and interrupts the circulation of sap throughout the
portions affected. These not only extend far up and down the
stem, but also reach to a depth of three to four inches in large
stems. As the mycelium annually increases in size, the can-
kerous parts clogged with resin also increase ; whilst the stems
assume an eccentric form of growth owing to increment taking
place only where the bark is not yet infected. Sometimes the
upper portion of the crown is killed off within a year, when
infection has taken place nearly all the way round the stem ;
but at other times decades sometimes pass before the crown
becomes dry and death ensues. Warm, dry summers favour
the advances of the disease owing to the stimulus given to
transpiration through the foliage, with which the partial sup-
plies of sap yielded by the uninfected portion of the stem
cannot maintain a due balance.

The spores scattered by the aeridia haye a change of genera-
tion with Cokosporium senecionis, having species of Senecio as
their host. The mycelium hibernates on these, and in the
following spring develops new spores by means of which the
canker of the Pine is produced.

When once this disease has been noticed, the best measures
adoptable are to cut out all the stems attacked before the
fungus has had time to develop fully, and to destroy, so far as
possible, all two-year old species of Senecio before they flower
in April ; this must be done by rooting them out, otherwise
the stalks removed are replaced by new stool-shoots.

3. Caeoma pinitorquum, de Bary, the Pine-shoot Fungus.
This fungus is mostly to be found on Scots and Weymouth
Pines of from one to ten years of age, although young crops

CHAP, xiii.] Fungoid Diseases of Trees 293

are not safe against attack until about thirty years old. It
occurs principally on wet soils, and after cold damp springs.

The mycelium of this fungus develops itself in the green
parenchym of the bark of the youngest shoots, within which
it is perennial, and extends itself into the new shoots when they
flush in May. Shoots thus taken possession of by the mycelial
filaments show a brownish discolouration of the woody tissue
right into the pith. Before the shoots have attained their full
length, pale yellow spots, bearing within the bark-parenchym
the spermogonia of the fungus, become apparent about the
end of May or the beginning of June, from the middle towards
the end of the shoots. With the development of the sporidia
under the bark the light yellow spots turn reddish-yellow, and
become raised like pustules until the epidermis at last fissures
longitudinally, and the spores are scattered. Each such fissure
produces slight hypertrophy ; and, as the cellular tissue dies
down as far as the woody substance, this necessitates a bend
in the shoot, which becomes concave at the diseased part, and
at the same time naturally shows an outflow of resin. If the
damage is only slight the wound cicatrizes and in time becomes
obliterated ; but when eruptions of spermogonia take place, as
often happens, on alternate sides, a peculiar twisted form of
growth is characteristic of this disease. When damp weather
in May and June favours the development of the fungus during
successive years, the shoots of the young Pines often become
completely deformed ; portions of them die off wherever the
disease extends all round the shoot so as to stop the circula-
tion of sap, and the young plants assume a somewhat frost-
bitten appearance. The side-shoots which endeavour to
assume the place of the leading shoots also usually become
infected.

This fungus has an undoubted change of generation with
Melampsora tremulae occurring on Aspen, whose teleutospores,
produced in the following spring, develop the original form
Caeoma pinitorquum.

294 Studies in Forestry [CHAP. xin.

Dry warm weather retards and checks the development of
this disease ; but when, for several seasons, the spring and
early summer months are wet, it often occasions damage whose
traces never become obliterated.

Prevention of this disease is confined solely to the selection
of suitable soil and situation for the different species of Pine ;
whilst remedial measures include the removal and burning
of all shoots infected, and the cutting out of all Aspen on
the foliage of which the change of generation as Melampsora
tremulae may be carried out (see also note to p. 282).

4. Aeddium elatinum, Link., the Silver Fir Fungus. To
this fungus are due not only the peculiar cankerous, diseased
swellings occurring on the stems at a greater or less height,
but also the deformities or diseased twig-clusters, called ''witches-
brooms ' in Germany, often formed in the crowns of Silver Firs.

The canker makes its appearance on the stem at all heights
as well as on the branches. It is most frequent on loamy
soils and low-lying localities, where the progress of the disease
is more rapid than on sandy soils and upland tracts. It forms
spindle-shaped excrescences — usually extending all round the
stem, though sometimes only on one side, — on which the
bark fissures longitudinally, so that the wood is laid bare and
begins to rot. This process is hastened by insects becom-
ing attracted, and by other fungoid diseases (Polyporus]
effecting an entrance at the wounds; whilst the mycelium
asserts itself throughout the bark-parenchym and the neigh-
bouring sap-wood, — the same kind of mycelium as is found
occasioning the twig-deformities. Infected stems become more
or less unsuited for technical purposes according to the part
attacked and the number of cankers, of which two or three
may sometimes be seen on one tree ; such stems also often
break at the diseased parts during stormy winds. The canker
may continue active in trees for fifty years or more, although
during very hot summers it is apt to become fatal to the tree.

Another form of the disease occasioned by this fungus is

CHAP, xiii.] Fungoid Diseases of Trees 295

the occurrence of yellowish-green loranthus-like deformities
or twig-clusters of a more bushy appearance than the normal
branches from which they protrude at right angles ; the yellow-
ish-green needles, growing closely and all round the twigs, are
shed during the first autumn. These deformities always have
their origin in a swelling or node within which the mycelium
of the fungus infests the bark, liber, and young wood, and
from which it annually extends to the young twigs and needles
till the disease dies out.

Whether a canker-spot or a twig-deformity will be produced
by the fungus depends on the nature of the place in which the
mycelium develops. Should the latter in extending itself effect
an entrance into a bud still capable of development, a deformed
twig-cluster is the result; but when the shoots are already
formed, the mycelium is principally confined to the bark, and
a cankerous swelling is there produced. In either case infec-
tion seems only possible at wound-surfaces. The receptacles
(spermogonia and stylospores) develop in the diseased leaves of
the youngest shoots, appearing on the lower side of the needles
in June in the shape of red or orange cups (aecidia\ which
burst and scatter their spores. All attempts hitherto to pro-
duce the disease directly by means of infection with these
spores have failed, as a heteroecious change of generation is
necessary ; but the intermediate form of the fungus and the
host on which it produces itself remain, for the present,
unknown to mycologists.

The formation of mixed forests is the best prophylactic
measure against this disease; whilst the removal of twig-
clusters in June and July, and the cutting out of cankerous
stems, should be undertaken, wherever possible, in order to
check its spread.

5. Nectria cucurbitula, Fr., the Spruce-bark Fungus. This
is a cankerous disease occurring principally on the stems of
young Spruce from about 3 to 15 ft. in height, especially in
localities exposed to danger from frost. Infection can only

296 Studies in Forestry [CHAP. xiu.

take place when the spores obtain a foothold on wound-
surfaces occasioned by insects, hail, &c. ; hence the spread of
the disease is greatest in places where the young crops are not
vigorous in growth, where insects are likely to be attracted,
and where any slight wounds inflicted take longest to heal.

The first symptoms of the disease are bleaching of the
needles, and drying up of the bark and cambium which
become brown, more particularly near wounds caused by the
caterpillars of the Spruce-bark Tortrix (Grapholitha pactolana).
This is followed by the appearance of numerous groups of
small red concave peritheda on the bark which contain the
tube-spores. Throughout the winter months these are scattered
abroad, and spread the disease wherever they happen to land
on open wound-surfaces.

The branching mycelium extends principally throughout the
vessels of the new sap-wood and among the intercellular spaces.
The whole development of the fungus takes place quickly,
although it appears to be accomplished only during the period
of rest, and not whilst the cambial layer is in full activity
during the summer months. When the disease proceeds round
the whole stem, the crown, and often the whole plant, dies off;
but, if a strip of bark still remains sound, a cortaceous formation
takes place at the edges. This prevents the further spread of
the disease ; and after the dead bark of the other part has been
shed, the ordinary process of cicatrization begins.

The only means of combating this disease is to remove
and burn, during autumn and the early months of winter, all
shoots or young stems attacked. In doing this, care should
be taken to remove them in the manner least likely to scatter
the spores abroad.

6. Peziza Willkommii, R. Hartig, the Canker of the Larch.
Although a diseased condition of the Larch is caused by bad
attacks of the Larch aphis (Chermes /aria's) or the mining moth
(Coleophora laricelld), yet the cankerous ailment occasioned
primarily by this fungus is widespread and very serious in every

CHAP, xiii.] Fungoid Diseases of Trees 297

respect. It occurs chiefly in damp, close localities, or on low-
lying tracts, wherever mists and late frosts in spring are apt
to prevail. It is most frequent in young crops from ten to
twenty years in age, though stems are still liable to become
infected up to about forty years. Hartig states l that the very
great extent to which this disease occurs in the forests of
northern Germany, Scotland, &c., is due to the more luxuriant
development of the fungus, and to the less vigorous growth of
the Larch ; for, though the Peziza is also to be found through-
out the alpine home of the Larch, the fruits of the fungus
generally dry up there without attaining maturity, whilst at the
same time the tree is better able to resist the attacks of this
parasite 2.

The first signs of the disease consist in the appearance of
smooth, lustrous spots or slight swellings on the stem or
branches, and the formation of longitudinal fissures in the bark
from which a slight resinous outflow takes place. This fissuring
soon becomes more general, and bits of bark begin to scale
off from the stem ; whilst small fungi appear from the fissures
with cup-shaped apothecia having white felty edges and bright
red centres. The dead, diseased parts gradually grow scurfy
and black ; whilst the wounds appear to deepen as the bark
curls up at the edges of the fissures, and the canker gradually
spreads up, and down, and round the stem.

It is only at damaged parts, such as wounds from insects
(principally tree-lice and the mining moth), hail, bending of
the branches under snow or ice, &c., that the spores can
find a favourable germinating bed, from which the mycelium
may penetrate into the cortex during the non-active period of
vegetation. Its advance is checked during the active time of
the year by the formation of a tough corky layer around the
diseased part ; but, during the following autumn, the mycelium
again penetrates from the cambium into the bark, and enlarges

1 Lehrbuch der Baumkrankheiten, 2nd edit. 1889, P- 45-
3 See Chapter II, p. 43.

298 Studies in Forestry [CHAP. xm.

the canker. If the cankerous spot finally extend all round the
stem the tree dies off above the diseased ring, though otherwise
the struggle between the disease and the vitality of the stem
may often be continued for decades. But, in large cankers,
the mycelium is apt to penetrate through the medullary rays
into the heart-wood of the stem, and to assume such propor-
tions as to interfere considerably with the circulation of the
sap, in which case the tree begins to sicken and die.

Dry situations and warm sunny exposures are unfavourable
to the maturing of the sporophores ; whilst humid localities
favour the ripening of the spores. The disease is also of more
frequent occurrence in pure crops of Larch, and whenever the
canopy is close. The best preventive measures are therefore
to be found (i) in careful choice of the soil and situation most
suitable to Larch, and (2) in its growth in mixed forests only
— along with broad-leaved trees, if possible, in preference to
other conifers. Remedial measures are practically confined to
the removal of all cankerous individual stems during the
operations of thinning.

B. On Broad-leaved Trees: —

i . Nectria ditissima, Tul. , the Canker of the Beech. Cankerous
places on Beech-stems may be occasioned by tree-lice (Lachnus
and Chermes), or by frost, or by sun-burn, or by fungoid
disease; but in the latter case the disease is recognizable
through the small white Gcmidta-pustules which first of all
appear, to be followed afterwards by numerous - dark-red
globular sporophores on the cankerous spots.

Although occurring also on Oak, Ash, Hornbeam, Alder,
Lime, Maple, and Sycamore, as well as on Apple and Cherry
trees in orchards, this disease chiefly attacks the Beech. It is
not confined to any particular period of the development of
the tree, being met with in mature crops, as well as in very
young thickets, and sometimes on the one-year-old shoots, or
sometimes on the bark of much older portions of the stem.

CHAP, xin.] Fungoid Diseases of Trees 299

Infection appears invariably to take place at wound-surfaces
occasioned by causes of the most various nature (hail, removal
of standards, snow-pressure, injuries during clearing, weeding,
thinning, &c.). From such spots, frequently at the fork of
young branches, the mycelium penetrates into the woody tissue
and spreads quickly in a longitudinal direction up and down
the stem, when the wood infected becomes brown and dead.
As the mycelium develops, the canker seems to deepen into
the wood ; whilst the edges round the diseased part become
raised, and a hypertrophic condition ensues, which results in
spindle-shaped excrescences along the part attacked. The
branches or stems infected gradually become more and more
cankerous, until finally the pole or young tree is killed off.

In order to prevent the spread of this disease, care should be
exercised in the felling and removal of standards, or of parent
trees above young seedling growth ; whilst all cankerous Beech
and Oak should be removed during the weedings and thinnings,
so far as possible without interrupting the leaf-canopy.

Minor diseases are also occasioned by Nectria cinnabarina,
a fungus very frequently occurring as small bright-red pustules
on the twigs and buds of Maple, Sycamore, Elm, Lime, and in
particular Horse Chestnut — also by species of Poly poms, the
most important of which is P. sulphureus occurring on Oak,
Poplar, Tree Willows, Birch, and Larch. These species of
Polyporus, which also occasion red and white rot in timber, are
partly saprophytic, living only on dead wood, and partly true
parasites causing disease. In the latter case the mycelium
develops in the interior of the stem; whilst the well-known
fructification of different shapes, often bracket-like, are situated
on the outside of the stem. The timely removal of trees thus
infected with fungus is advisable, not only in order to have
any use from the timber itself, but also for the purpose of pre-
venting the further spread of the disease through the formation
and scattering of spores.

300 Studies in Forestry [CHAP. xm.

III. FUNGOID DISEASES OF THE ROOTS AND THE BASE

OF THE TRUNK.
A. On Conifers: —

i. Agaricus melleus, L., the Honey Fungus, one of the
edible Mushrooms. This is a very common and, in many
localities, a very dangerous parasite in young coniferous crops,
especially on Spruce, Scots and Weymouth Pines, and Larch,
though seldom to be found on Black Pines. It also occurs
extensively as a saprophyte on dead stools and roots of old
trees, particularly on Beeches. It appears mostly in young
crops of from four to fifteen years of age, but may also be
found in mature stems of 100 years old. Close sowings and
plantations formed with wisps of seedling Spruce suffer most
from the disease. It is apt to be frequent in localities where,
owing to deterioration of the soil, a coniferous crop is formed
after a fall of broad-leaved timber, on the roots and stools
of which the mushrooms or 'toad-stools' have developed
saprophytically.

The first symptoms of the disease consist in the gradual
yellowing, withering, and shedding of the needles. This is
followed by withering of the shoots, swelling of the root-stool,
fissuring of the bark, resinous outflow on the ground, rotting
of the cambium, and finally the death of the plant, which
usually occurs either between the middle of April and the
middle of June, or else between the middle of October and
the middle of November.

The blackish-brown mycelial filaments of this partly sapro-
phytic fungus, by extending themselves under the bark of the
stool and roots, and throughout the soil, manage to effect
a foothold on the roots with which they may come in contact ;
and then, boring their way through the bark, they commence
their attacks as a parasitic fungus by forming long, white, flat
rhizomorphous mycelial filaments developing between the
sapwood and the cambium. Such rhizomorphous develop-

CHAP, xiii.] Fungoid Diseases of Trees 301

ments of the mycelium only occur in a limited number of
fungi. In Agaricus melleus they assume the forms of Rhizo-
morpha fragilis var. subterranea so long as they are blackish-
brown and lie outside the bark ; but they become Rhiz. frag.
var. subcorticalis when the mycelial filaments develop below or
within the bark. The sporophores of the former, appearing here
and there above the soil, are less numerous, and less apt to
attain maturity, than those of the latter variety, which make
their appearance in thick clusters near the neck of the root.
The blackish-brown filaments of the former are generally round,
and ramify throughout the soil like fine rootlets ; whilst those of
the latter are whitish and ribbon-like.

Concerning this fungus, Professor Vines makes the following
remarks * :

' The most remarkable sclerotia are those of Agaricus melleus, a Fungus
which is very destructive to timber. The mycelium gives rise to dark-
coloured compact strands of hyphae, of the pseudo-parenchymatous
structure characteristic of sclerotia ; but they are peculiar in possessing
continued special growth, and by this means they soon become long
filaments, known as Rhizomorpha. It is in this way that the Fungus
spreads from tree to tree : the Rhizomorpha-filaments grow under-
ground from the roots of an infected tree to those of a healthy tree
(usually a Conifer) ; it penetrates into them and spreads in the tissues
external to the wood in the form of a white fan-shaped mycelium. The
compound gonidiophores (Agaricus melleus) are borne either on the
subterranean Rhizomorpha-filaments, or on the parasitic mycelium ; in
either case the gonidiophores come to the surface.'

Young plants, when attacked, usually die off during the first
year of the attack. A microscopic examination of them will
then show that all the cambial layer and the resin-ducts have
been invaded by the mycelium, robbed of their contents, and
gutted to form empty hollows, the starchy matter in the cells
being transformed into turpentine, which causes the resinous
outflow on to the soil. The receptacles, mushrooms, or toad-
stools (pilei\ make their appearance in October, being developed

1 A Students' Text-book of Botany, 1894, p. 314.

302 Studies in Forestry [CHAP. xin.

most numerously during damp seasons. They are of a dirty-
brown or honey colour, with darker scales ; whilst the lamellae
are yellowish-white, with reddish-brown spots forming later on.

Characteristic features of this disease are its occurrence
here and there in patches, and the rapidity with which it kills
young plants in full vigour, after they have made good growth
in height during the season ; hence damage from this cause
is easily distinguishable from death caused by insects, drought,
or the like, when the plant only succumbs after a longer or
shorter period of sickly growth. To prevent the occurrence
of the disease, the stumps of broad-leaved species should, if
possible, be carefully grubbed up, before sowing or planting
coniferous crops.

The best practical means of preventing its spread consists
in the pulling up of the plants attacked with all their roots,
and burning them ; whilst the isolation of these places may be
arranged for by digging small trenches round them to a depth of
i-ij ft. in order to hinder the subterraneous extension of the
mycelium. Careful collection of the older saprophytic mush-
rooms on old stumps is also advisable, and none the less so on
account of their being edible. Where blanks have been
occasioned in young coniferous crops by this disease, it is best
to fill them with transplants of broad-leaved species, as conifers
are more exposed to a recurrence of the disorder.

2. Trametes radiciperda, R. Hartig, the Root Fungus. This
is one of the most serious of fungoid diseases in coniferous
woods. Scots and Weymouth Pines and Spruce suffer in
a much greater degree from it than Silver Fir and other species.
Young plants, poles, and trees, are seen to rot away suddenly
near the roots and die off; whilst other individuals near them
are also attacked and succumb, often causing serious inter-
ruption of the canopy and sometimes blanks of considerable
size.

Infection proceeds as a rule from the diseased roots of
a neighbouring stem ; but it may also take place direct from

CHAP. xiii.]. Fungoid Diseases of Trees 303

gonidia or spores conveyed easily on the furry coats of mice,
&c., or by wind. The colourless mycelium develops through-
out the cambium as well as the woody tissue of the roots and
the base of the stem. The walls of the cells are penetrated and
destroyed by masses of mycelial filaments, so that the whole
root-system seems at times to be in a rotten, damp condition.
This rottenness spreads from the roots upwards into the stem —
except in the case of the Scots Pine, whose morbid formation
of resin is so great as to check the upward progress of the
mycelium. The disease is also noticeable externally by the
mycelium protruding from the fissures of the bark in the shape
of small yellowish white pustules. The sporophores or spore-
producers, of a yellowish-white or pure white colour, are mainly
to be found on the roots or at the base of the stem in charac-
teristic, large, flat, excrescences which sometimes assume a
bracket-like shape ; in the old days of flint and steel these
fungi made excellent tinder.

Against direct infection by spores, preventive measures can
hardly be taken. Hence protective and remedial measures are
alike to be found in the grubbing up and removal of all
diseased material before it has time to produce the conidia,
and in the more general introduction of broad-leaved species
of trees into the coniferous woods. Isolation of the patches
infected by means of ditches leads to prolific development of
sporophores on the roots cut through ; this measure can, there-
fore, only be recommended where these latter can be duly
removed and burned before there is any chance of their burst-
ing and scattering fresh spores abroad.

B. On Broad-leaved Trees : —

i. Rosellinia quercina, R. Hartig, the Oak-seedling Fungus.
This disease attacks the roots of young one- to three-year-old
seedling Oaks, especially in nursery-beds and during damp
years. It occasions fading and drying up of the plants. The
roots appear to be woven round with fine filaments, in the

304 Studies in Forestry [CHAP. xin.

vicinity of which the bark-tissue turns brown ; whilst small,
round, dark-brown or blackish pustules, about the size of a pin-
head, make their appearance here and there on the main root.
The drying-up process begins at the terminal leaves and con-
tinues downwards. The small round pustules on the tap-root
are fruits (sderotia) from which numerous brown thread-like
rhizomorphous filaments proceed, encircling the roots and
extending throughout the soil. By means of these sclerotia,
a perennial form of mycelium, the fungus can retain its
vitality from year to year, thus withstanding the effects of dry
summer periods which would be fatal to the ordinary myce-
lium, to the development of which damp warm weather is
essential. As the tap-root is protected against infection by
a corky epidermis, the mycelial filaments usually effect an
entrance by means of the tender side-rootlets, whence they
push into the main body of the seedling. The spread of the
disease can, however, also take place through the gonidia
developed by the mycelium above the soil, or by means of
the spores of the black, spherical peritheda produced on the
surface of the soil or in the stems of the diseased Oak-plants.

This disease is best combated by the removal of all diseased
seedlings from the nursery-beds, and by isolating all parts
infected by means of narrow, trenches about i foot deep.

The Changes in Generation which not infrequently take
place have already been alluded to briefly ; the more important
of them may be here named, although space prohibits any
details being given concerning their life-history. They are
specially characteristic of the rusts ( Uredineae\ all of which are
parasitic.

In forming spore-producers portions of the mycelium of
Agaricus melleus develop into Rhizomorpha fragilis, of which
there are two varieties, viz. subterranea, where the mycelial
strands remain under the ground, and subcorticalis^ where they
are under the bark of trees.

Aeddium pini becomes Coleosporium senedo on species of

CHAP. XITL] Fungoid Diseases of Trees 305

groundsel (Senetio), the spores from which scatter in the follow-
ing spring, spreading abroad the germs of the Pine needle-
rust and the Pine canker ; hence it is advisable to remove
groundsel before it flowers in April. Aeddium abietinum has its
Teleutospore form as Chrysomyxa rhododendri on rhododen-
drons, and Aeddium columnare its change of generation with
the Calyptospora Goeppertiana on cranberries. What form is
assumed by the aecidial spores of Aeddium elatinum, or on
what plant they occur, has not yet been discovered.

Caeoma pinitorquum becomes Melampsora tremulae on
Aspen foliage, hence Aspen should be cut out of Pine woods
to prevent the development of the Pine-shoot fungus. The
Larch blight, Caeoma larids^ has also its Melampsora form on
Aspen foliage.

M. Betulina on Birch probably stands in relation with some
form of Caeoma. Melampsora Hartigii, the Willow-rust, has
first its Uredo-form, Uredo salids, and then its Teleuto-form,
Caeoma ribesii^ on gooseberries and raspberries; but this last
form is not absolutely necessary for its regeneration. Melam-
psora salidna on the Goat-willow similarly becomes Caeoma
evonymi on the Spindle-tree.

Prevention and Cure of Fungoid Diseases in Trees.

The great sylvicultural authority on this matter, Professor
R. Hartig, expresses the following opinions 1 : —

' The best prophylactic measures against the outbreak and spread of
epidemics is the formation of mixed woods. Subterraneous and super-
terrene infections are best obviated when each tree is, as it were, isolated
by neighbours of different species. A change in the species of tree may
even seem advisable, under certain circumstances, on soils which have
been taken possession of by root-parasites, or which contain Teleuto-
spores retaining their vitality for many years. Avoidance of the conveyance
of fungus spores by men and animals is recommended, especially during
operations in young tree-forest. The therapeutic measures adaptable after
any outbreak of fungoid disease occasioned by root-parasites consist

1 Op. cit., pp 55, 56.
X <

306 Studies in Forestry [CHAP. xin.

partly in the timely pulling or digging up of the sickly plants, and partly
in isolation of the infested patch by means of narrow trenches. But the
best and most important general measure to be recommended is the
immediate removal of all diseased plants from the woods, so as to hinder
further infection being spread by their spores. Keeping the woods clean
is an essential condition to the maintenance of their health.'

Even a very superficial study of the character and life-history
of the more important fungi causing diseases among our forest
trees cannot fail to show the immense importance of the main-
tenance of close canopy, so as to hinder a rank growth of
shrubs, berries, and weeds on the soil, which may tend to
reproduce and spread heteroecious fungi. The necessity for
keeping the woods clean and free from suppressed material in
a more or less sickly condition will also be evident, as also for
cutting out the soft-wooded trees like Aspen and Birch when-
ever it may be suspected that Pine or Larch trees in the
vicinity are suffering from fungous disease. But even if con-
siderations as to fungoid diseases alone are not sufficient to
urge that woods should be kept clean and free from sickly
growth, it should also be borne in mind how very much
greater and more frequently disastrous are the dangers at the
same time incurred from noxious insects.

CHAPTER XIV

THE PROTECTION OF WOODLANDS AGAINST INSECT
ENEMIES

Sylvicultural Entomology, a branch of the Protection of
Woodlands thoroughly taught at all the Universities and
Academies in Germany which provide for instruction in Forest
Science, relates not only to the injurious Forest Insects, but
also to the useful species which prey upon these and tend to
restrain their increase in large numbers likely to damage the
growth of timber crops. Under noxious Forest Insects gene-
rally, all the species which may perhaps be found at any time
on woodland trees are not included, but merely such as occur
more or less frequently in large numbers, and do perceptible
damage to the growth and development of the timber crops.

The nature of the injuries inflicted on woodland crops by
insect enemies is manifold ; and neither the seedling growth,
nor the young pole-forest, nor the mature crop, is safe from
injuries varying from slight attacks on foliage, bark, and roots,
occasioning merely temporary disturbance, up to the total
destruction of crops over enormous areas. Even when exten-
sive devastations do not take place, both young crops and trees
may be so seriously disturbed in normal growth, as to occasion
loss of increment, and the formation of blanks necessitating
outlay for re-filling and improving.

X 2

308 Studies in Forestry [CHAP. xiv.

The Life-history of Forest Insects.

Insects (Insectd] are animals with jointed feet (Arthropodd],
which have a body consisting of three main sections, six legs
(three pairs), and usually also four or two wings (two pairs or
one), and which pass through various stages of growth. Most
insects undergo four stages of development or Metamorphoses,
each distinctly distinguishable from those which precede and
succeed it. These are in turn (i) Ovum or egg, (2) Larva, grub
or caterpillar, (3) Pupa or chrysalis, and (4) Imago or mature
insect. When all these separate stages are passed through an
insect is said to have a complete metamorphosis; whilst the
comparatively few instances (forming the orders Hemiptera and
Orthopterd] in which a distinct pupal stage is not apparent,
as the larva gradually becomes transformed into the imago,
are termed an incomplete metamorphosis. The former are called
metabolian (insecta metabold], and the latter ametabolian (insecta
ametabola\ whose pseudo-chrysalides are known as nymphae.
The metabolic class comprises about 95 % of all insects, and
the ametabolic only about 5 %. The Ova or eggs vary
greatly in shape, size, and colour. Ovideposition may take
place singly, or in clusters or nests on different parts of trees ;
they are sometimes protected by some sort of covering. The
Larva often makes its appearance from the egg within the
course of a few weeks ; but in many other cases it hibernates
within the shell, and only issues during the following spring.
Different kinds of larvae have special names. Those of most
beetles, partly six-footed, partly without feet, are called larvae,
except in the case of cockchafers (Melolontha), where they are
termed grubs ; the sixteen-footed larvae of butterflies and moths
— those of Spanners (Geometridae) have only ten, and a few
Mining-moths (Tineidae] have none — are called caterpillars \
the eighteen- to twenty-two-footed larvae of Sawflies (Tenth-
redinidae) with their tail-like extremities are named tailed cater-
pillars ; and the feetless larvae of flies (Dipterd]^ which show

CHAP, xiv.] Insect Enemies 309

no complex structure of the head are called maggots or strigs.
Several changes of skin take place in the larva before it enters
into the pupal state of rest. In the case of beetles (Coleoptera)
the structure and different sections of the mature insect are
externally distinguishable ; whilst in moths and butterflies
(Lepidoptera^ they are masked or indistinct. The pupa is some-
times to be found lying unprotected on the soil, under moss,
in fissures or under scales of the bark, and at other times it is
covered by a woven cocoon, often of large size, as in the case of
some of the Bombycidae; whilst with flies (Diptera), in place of
any cocoon, the last larval skin forms a protective case. The
stage of development which lasts longest is that in which the
insect hibernates. This is usually the larval stage, although
many injurious beetles hibernate as imagines. Except in
genera which hibernate either as ovum or pupa, these two
stages usually last only from two to four weeks. Thus the
devastating Spruce moth (Liparis monacha] appears after two
to three weeks' rest; whilst the destructive Pine moth (Gastro-
pacha pini} remains as a chrysalis for six to eight months from
autumn till spring, and the cockchafer (Melolonthd) even so long
as for four years. According to the Morphology ', or structure of
the Imago or mature insect, it is classified among the beetles
(Coleoptera], butterflies or moths (Lepidopterd], hymenopters
(Hymenopterd), flies (Dipterd), neuropters (Neuropterd], hemip-
ters (Hemiptera\ and orthopters (Orthoptera}.

As soon as the imagines appear, they begin to swarm and
reproduce themselves. The male generally dies soon after
having entered in copula, although this is not the case with
beetles, which very often hibernate as imagines, nor with bees,
which live for four to five years.

The complete cycle from ovum to ovum is termed the
Generation of any insect; this varies greatly in different
genera and species. Thus it is said to be multiple or manifold
as in the case of plant-lice (Aphides], and ichneumon-flies
(Ichneumonidae), of which several generations are produced

310 Studies in Forestry [CHAP. xiv.

within the year ; two-fold or double in the case of bark-beetles
(Scolytidae] and Saw-flies (Tenthredinidae\ which produce two
generations in each year ; single, simple, or annual in the case
of most butterflies and moths (Lepidopterd), which yearly pro-
duce one generation ; biennial or two-yearly in wood-wasps
(Uroceridae\ the Pine Resin-gall Tortrix (Tortrix resinelld),
and many longicorn beetles (Cerambyddae] \ or finally mult-
annual or poly annual in the case of the cockchafer (Melolontha
vulgaris), which takes three, and sometimes four years to com-
plete its generative cycle. Occasionally two generations take
place in three years, as in the case of Tomicus bidens ; but this
is most probably only exceptional.

Metabolic insects feed merely as larvae and mature insects,
and in some exceptional cases (e. g. Spanish Fly, Lytta vesica-
toria^ Pine weevil, Hylobius abietis, &c.) are only injurious to
woodland growth as imagines ; but with ametabolic insects the
nympha also requires food-supplies. In both groups the de-
structive power of the larvae is often excessive, as numerous
species daily consume many times their own weight of foliage.

Classification of Injurious Forest Insects.

The scientific or morphological classification of insects is of
comparatively little use to the sylviculturist, for whom a bio-
logical method of grouping them together is in many ways
preferable. Thus they may be classed with reference to the
species of trees on which they feed, as Spruce insects, Pine
insects, &c. ; this is, however, open to the objection that many
insects are not monophagous merely, but also polyphagous, or
even pantophagous, devouring everything (like Liparis monacha
when occurring in vast swarms). Or they may be classed with
reference to the nature of the damage they do, which may be
either physiological^ interfering with the imbibition, transpira-
tion, or assimilation of the food-supplies and nourishment, as

CHAP, xiv.] Insect Enemies 311

in the case of bark-beetles and moths, or technical, interfering
with the utilization of the timber for technical purposes, as in
the case of wood-wasps (Siricidae\ longicorns (Cerambycidae),
and certain Scolytidae ; but this would be met by the objection
that in such cases the damage depends on too many different
factors (species and age of tree, time of attacks, surrounding
local circumstances, &c.) to be convenient. Or classification
may be made with reference to the extent of the damage
usually done; but this would be a very unsafe guide, for
some of the most destructive species (e.g. Liparis monacha]
are often for many years seldom to be seen, until at last cir-
cumstances favour their development in such enormous masses
that they devastate woodlands over large tracts of country.
Or they may be grouped with reference to the age of the
crops generally attacked (seedling-growth, thickets, pole-forest,
tree-forest) ; yet this would also be unsatisfactory, as many
species are dangerous throughout all stages of the development
of the crop. Finally, and preferably, they may be classified with
reference to the portion of the tree on which they principally
effect injuries. Adopting this last-named biological method of
classification, and commencing with the roots, we may group
the most dangerous species as follows : —

Root-destroyers, including the grubs of the mole-cricket
(Gryllotatpa vulgaris) and the cockchafer (Melolontha vul-
garis), and the caterpillars of the Seed Owlet-moth (Agrotis .

Wood-borers, comprising the larvae of wood-wasps (Siri-
cidae), cervicorn beetles (Cerambycidae), and certain Scolytidae
like Tomicus lineatus, T. monographus, and T. dispar, also the
caterpillars of certain moths like Cossus ligniperda and Zeuzera
aesculi.

Bark-beetles, including most bark-beetles (Scolytidae) i.e.
most of the true bark-beetles (Bostrychini), and the cambial
beetles (Hylesinini\ and several weevils (Curculionidae\ which,
often in both active forms, either destroy the cambial layer of
the bark and the sapwood (e. g. most Bostrychini and several

312 Studies in Forestry [CHAP. xiv.

Curculionidae], or else hollow out the pith from young shoots
(e. g. some Hylesinini and Tortriddae).

Leaf-destroyers, including the caterpillars of most moths
(Lepidoptera) and Saw-flies (Tenthredinidae), also leaf-beetles
(Chrysomelidae\ cockchafers (Melolontha , and Spanish fly
(Lytta\

In addition to these main groups, there are also Bud-
destroyers, consisting of several weevils {Curculionidae) and
some leaf-roller caterpillars ( Tortriddae), Seed-destroyers like
the acorn-borer (Balaninus) and the larvae of Grapholitha
strobilella and species of Anobium in Spruce cones, and also
Producers of hypertrophic Deformities and various Mal-
formations on foliage, shoots and fruits by gall-wasps (Cyni-
pidae\ gall-midges (Ceddomyidae), plant-lice (Aphidae), whJch,
though frequently more easily noticeable, are as a rule in
reality of such comparatively trifling physiological and technical
consequence that they may almost be left unnoticed.

Although a biological classification according to the ages
of the crops attacked seems less preferable than that above
sketched, it may nevertheless be remarked that most weevils
or rostral-beetles ( Curculionidae\ some leaf-rollers (Tortriddae),
and the grubs of the cockchafer (Melolontha) genus of the
lamellicorn beetles (Scarabidae) usually attack seedling growth
and young plantations; whilst crops that have outgrown the
thicket stage and have developed into pole-forest or tree-forest
are most exposed to attacks from the majority of species of moths
(Lepidoptera\ and then of the many bark-beetles (Bostrychini}
and cambial-beetles (Hylesinini) which follow in their wake
when once physiological disturbances have been occasioned
and the young trees grow sickly in consequence. Many moths,
however, exhibit an unquestionable amount of choice between
pole-forest and tree-forest in commencing to feed. Thus, for
instance, the caterpillars of the Pine owlet-moth (Trachea pint-
perdd) and the Pine Span-worm (Fidonia piniarid) are always
to be found in pole-forest crops first of all, whence they migrate

CHAP, xiv.] Insect Enemies 313

to older crops only when they have greatly increased in number ;
whilst on the other hand the Spruce moth (Liparis monacha)
and the Pine moth ( Gastropacha pint] attack the older woods
first, and then on rapidly increasing proceed to devastate the
younger crops also.

And though the rough classification, slightly injurious,
noticeably injurious, and very injurious, is extremely indefinite
and elastic (for Liparis monacha, one of the most destructive
of moths, is often for decades a comparatively rare insect), yet
sylvicultural experience abroad has shown that the Spruce
bark-beetle ( Tomicus typographies^, the large brown Pine weevil
(Hylobius abietis\ the cockchafer (Melolontha vulgaris], the
Spruce moth (Liparis monacha), and the large Pine moth
{Gastropacha pirn) must certainly be classified as very injurious
species ; whilst it would not be at all incorrect to include in such
a category also the Pine Beauty (Trachea piniperda\ the Bor-
dered White moth (Fidonia piniaria\ the Pine Sawfly (Lophyrus
pint), the small brown, white-spotted weevil (Pissodes notatus\
and others which, under ordinary circumstances, are usually
regarded as merely noticeably injurious. The debateable
ground between this latter class and those that would have to
be termed slightly injurious is also very vague and indefinite.
It depends entirely on circumstances ; and whenever the only
safe motto relative to injurious insects — Principiis obsta —
is neglected, any comparatively rare or innocuous species may
ultimately develop into a downright scourge, especially where
large pure forests of Pine or Spruce are their feeding-grounds.
The monophagous species then become polyphagous, and
with still greater increase pantophagous, devouring everything
within their reach.

The places in which the greatest number and variety of insects
will usually be found are the warm plains and uplands, espe-
cially those with sandy soil. Southern exposures, frost-holes,
and crops on inferior soil or of poor growth from any cause, are
usually the places where the danger of a rapid increase in the

314 Studies in Forestry [CHAP. xiv.

number of noxious insects is chiefly to be feared ; hence the
additional importance of keeping such woods or portions of
woods carefully thinned and tended so as to remove any sickly
stems before they become breeding-places for the insects.

As a rule conifers are much more exposed to attacks from
noxious insects than broad-leaved species of trees. And as they
are at the same time comparatively deficient in recuperative
power, owing to their not being able to set apart such good
reserves of starchy and nitrogenous matters, the damage suffered
by them is usually much greater. Spruce and Pine suffer far
more from insects than any other species of forest trees ; whilst
among broad-leaved kinds Oak, Beech, Poplar, and Willow are
more damaged than the Birch, Alder, Ash, Elm, Maple or
Sycamore. But there can really be no comparison between the
devastations sometimes occurring in coniferous woods and the
attacks to which broad-leaved crops are exposed. Even after
Oak standards have been defoliated in June by armies of cater-
pillars of the Processionary moth (Cnethocampa processionea\
the trees, thanks to their nutrient reserves, flush into leaf again
in July ; whereas, when about four-fifths of the foliage of Scots
Pine and Spruce have been devoured, the ultimate recovery
of the former is extremely doubtful, and the death of the
latter is certain owing to the much smaller reserve supplies
it stores up.

Whatever the species may be which forms the crop, damage
done to young growth is, for obvious physiological reasons,
more serious than when it occurs on older poles and trees ;
whilst attacks made in spring are more injurious than those
taking place in summer or near the close of the active period
of vegetation, when the buds have been formed and the
nutrient reserves secreted for the succeeding year's growth.
The extent of the damage often also varies according to the
parts injured. If the foliage alone be attacked the loss may
perhaps be confined to the mere deficiency in increment;
whereas when the roots and the cambium are extensively

CHAP, xiv.] Insect Enemies 315

damaged, the injuries usually result in the wilting and death
of the seedling, pole, or tree.

The Numerical Increase of Injurious Insects.

The reproductive capacity or prolificness of forest insects
varies considerably according to the species. But, fortunately,
the most prolific varieties are not among the most injurious
kinds, as the average rate of reproduction of the latter does not
exceed from 100 to 200 ova, according to Ratzeburg.

Hard winters are not particularly fatal to insects, and on the
whole may be said to favour their increase, especially with
regard to beetles protected by their tough outer casing of
chitin ; for severe cold works greater havoc among the insecti-
vorous song-birds than amongst the insects. The most sensi-
tive to damp cold weather and raw winds are the naked larvae
which have no hairy or protective covering; these are often
killed off in great numbers during the processes of changing
their skins. Warm, dry, genial weather, ungrubbed stumps
remaining in the ground over extensive falls of mature timber,
sickly crops of seedlings, saplings, poles, or trees, and sup-
pressed or unhealthy individuals with a weakly flow of sap —
such as may be found in woods that have suffered from wind-
fall, snow, or ice-accumulations — also want of clearing, thinning,
and proper tending of the woodland crops, are all exceedingly
apt to encourage the speedy numerical increase of noxious
insects, which often multiply with exceeding rapidity in such
breeding-centres. Bark-beetles (jBostrychini) and cambial-
beetles (Hylesinini] select for ovi-deposition stems that have
been thrown or broken by wind, or newly-felled trees, or those
already brought into a more or less unhealthy condition by
reason of attacks of moth-caterpillars on the foliage ; whilst
the large Pine weevil (Hylobius abietis) chooses for its feeding-
ground, when available, crowded crops raised from seed or
sickly plantations, and at the same time selects the stumps

3i 6 Studies in Forestry [CHAP. xiv.

of newly-felled trees for its breeding-place. Moths also, when
laying their eggs, frequently give the preference to crops of
backward growth on inferior qualities of soil, which are thus
all the more liable to succumb entirely to the ravages of
the caterpillars during the following spring. Such favourable
breeding- and feeding-places will usually be found to be the
centres from which swarms of noxious insects spread to other
woodland tracts. Hence the necessity for careful tending even
in crops where such outlay does not seem likely to prove
directly remunerative. Slovenly, negligent treatment of any
one portion of an extensive wooded estate endangers the well-
being of all the growing-stock of timber throughout the whole
area under forest within a wide circuit.

All circumstances, therefore, tending to the formation of such
breeding-centres are only too favourable to increase in the
number of injurious insects ; whilst hot dry summers and long-
continued drought, by reducing the woodland growth to a
somewhat weakly condition, decidedly add to the prolificness
of moths and saw-flies.

Amongst the influences inimical to the numerical increase
of noxious insects may first of all be noted damp, rainy, cold,
raw, ungenial weather, while caterpillars are changing their
skins, and when beetles and moths are swarming and entering
in copula^ although the influence exerted by cold in winter is
comparatively slight even in the case of species which hibernate
in the larval or the chrysalid stage. But as, before any species
can make its appearance in unusual and excessive numbers,
the balance of nature must of necessity have been in some
way or another disturbed (e. g. by bad breeding-years amongst
insectivorous birds and insects which may happen to be
its particular enemies) a natural readjustment would always
of itself take place, although this might not happen until
irreparable damage had been done to the woodland crops.
Thus, experience in Germany has shown (i) that bad devasta-
tions by moth-caterpillars as a rule last for three years, to which

CHAP, xiv.] Insect Enemies 317

a previous and a succeeding year of minor damage may be
added (without, however, counting the subsequent ravages of
the Scolytidae and Curculionidae, that have also to be reckoned
with owing to the sickly state in which the still existing crops
are left), and (2) that then parasitic insects (Ichneumonidae\
fungoid diseases, and insectivorous birds also increase nume-
rically to such an extent as to decimate and finally exterminate
the plague in a very short time. Under ordinary circum-
stances, however, and especially in mixed woods (as compared
with pure or mixed crops of coniferous species only) with their
larger numbers of insectivorous song-birds, the tendency to
excessive reproduction and increase of noxious insects is held
in check by the presence of their natural enemies. So far, there-
fore, as may be compatible with other and sometimes more
important considerations, all these natural enemies of injurious
insects should be preserved and their numerical increase
encouraged. The chief of these are : —

A. Among Mammals.

Bats (species of Vesperugo\ which consume large numbers of
cockchafers and moths; moles (Talpa europea] that destroy
grubs and mole-crickets (Gryllotalpa vulgaris)-, Shrew (Sorex
vulgaris\ Hedge-hog (Erinaceus europaeus\ Squirrels (species of
Sciurus\ Weasel (Putorius vulgaris\ Pole-cat (P. foetidus), Stoat
(P. ermineus\ Badger (Metes taxus\ and Fox ( Vulpes vulgaris\
which devour large numbers of beetles and chrysalides, as has
often been proved by the examination of their stomachs and
excreta.

B. Among Birds.

The most generally useful are the Cuckoo (Cuculus canoris]
— which is the only bird that eagerly devours the hairy cater-
pillars of species like the Pine moth (Gastropacha pini} — the
Starling (Sturnus vulgaris\ Flycatchers (Muscicapa^ Tits or
Titmice (Paridae), Tree-creepers (Certhia familiar is], Swallows
(species of Hirundo\ and most singing birds ; then Thrushes

3i 8 Studies in Forestry [CHAP. xiv.

(species of Turdus\ Rooks ( Corvus frugilegns), the Stannel-
hawk (Tinnunculus alaudarius\ and Wasp-buzzards (Perm's
apivorus\ Woodpeckers (species of Picus\ Sparrows (Passeres)
and Finches (Fringillidae\ Crows or Ravens (Corvus corax\
Jackdaws (Monedula turrium) and Larks (Alaudidae\ which
are only of minor utility in this manner.

C. Among Insects.

The class of useful forest insects is, on the whole, of consider-
ably more importance in keeping a check on the abnormal
increase of injurious kinds than either mammals or birds.
They comprise not only the various predatory species which, often
both as larva and imago, prey on the ova, larvae, pupae, and
imagines of noxious insects, but also the parasitic species, whose
eggs are generally deposited on the ova and larvae, or less
frequently on the pupae, or imagines, of the injurious kinds,
that thus become the hosts, on which the maggots prey when
they issue from the ovum. By the careful observer these
species will usually be found to exist in woodlands in much
larger number and variety than might be imagined. Hence
when anything like abnormal increase of the noxious kinds
takes place, so also do these, their natural enemies, multiply
in consequence of the greater amount of available nourishment
and the more frequent opportunities of reproduction thus
offered to them.

i. The Predatory Species include, among the Coleoptera, the
sand-beetles (Cicindetidae), the predaceous land-beetles (Cara-
bidae)— a large family among which many species of Carabus
and the tree-climbing Calosoma sycophanta and C. inquisitor
are particularly useful in killing the caterpillars of the Pine,
Spruce, and Processionary moths — the dung-beetles (Staphylin-
idae\ the carrion-beetles (Silphidae\ the hister-beetles (Hister-
idae\ the nitid or shining beetles (Nitidulidae\ the thread-beetles
( Colydiidae), the soft beetles (Malacodermatd), the gold-beetles
(Cleridae) — especially Clerus formicarius, which is so frequently

CHAP, xiv.] Insect Enemies 319

to be found in the larval galleries of the Pine-beetle (Hylurgus
piniperda] under the bark of Scots Pine — and the lady-birds
{Cocrinellidae\ of which Coccinella septempunctata and C. bi-
punctata are of most frequent occurrence, whilst several species
of the genus Halyzia are only to be found in the woods,
particularly in Spruce and Pine woods.

Among the Hymenoptera, the digging wasps (Sphegidae) stun
caterpillars, beetles, plant-lice, &c., with their stings, drag them
to their holes, and then utilize them for breeding places (so
that they are both predatory and parasitic); the wasps
( Vespidae), and in particular the hornet ( Vespa crabro] — itself
injurious to Ash — prey on moths and flies ; whilst the ants
(Formicidae\ which live in colonies of thousands in their
breeding-mounds, consume enormous numbers of larvae of
various descriptions.

Among the Diptera, the predatory flies (Asilidae), which
breed principally in sandy localities, attack and feed on many
other kinds of insects ; whilst the humming or chirping flies
(Syrphidae) are more frequently to be found in orchards than
in the woods.

Although the Neuroptera contribute the scorpion-fly (Pan-
orpa\ the camel-necked flies (Rhaphidia\ the gold-eyed fly
(ffemerobia perla\ and the ant-lion (Myrmeleori), which are all
useful in preying on noxious insects (the last-named un-
fortunately also diminishes the number of useful ants), whilst
the Hemiptera furnish the scaly and other bugs (Pentatomidae
and Reduviidae)) and the Orthoptera produce the dragon-
flies (Libellulidae], yet the predatory species among these
three orders are comparatively inactive as compared with
those in the first-named three.

2. The Parasitic Species, the chief insect enemies of the
noxious varieties, are to be found among the ichneumon-flies
(Ichneumonidae] of the Hymenoptera, and the parasitic-flies
(Tachinmae), a group of the Muscidae family of the Diptera.
In fact, it is mainly to fungoid diseases and to the Ich-

320 Studies in Forestry [CHAP. xiv.

neumonidae that the suppression of the occasional enormous
plagues of devastating insects raised in the pure coniferous
forests of Germany, Russia, and Austria is ascribable.

Of about 5,000 species of ichneumon-flies nearly 1,000 are
parasitic on noxious insects1. The female is provided with
a long ovi-depositor by means of which her eggs can be laid
either singly in the case of large species, or in considerable
numbers for smaller genera (290 larvae of Microgaster globatus
have been counted in a single caterpillar of the Pine moth,
Gastropacha pini]. The eggs are more frequently deposited on
the ova or the larvae than on the pupae or the mature insects.
The tiny larvae subsist on the vital fluids of the hosts they are
parasitic on, and then work their way out to the surface, where
their cocoons may be seen thickly studding the dying cater-
pillars. As the generation of the Ichneumonidae is only partly
simple, and in other cases manifold, they increase with
enormous rapidity when the number of hosts is large. The
larvae attacked become even more voracious than previously in
order to maintain supplies of nourishment for their parasites,
but perish during the pupal state when they succeed in
passing through the larval stage of development.

The Tachininae are chiefly parasitic on the larvae and pupae
of moths and saw-flies. The principal species are Tachina
monachae on the caterpillars of the Spruce moth (Liparis
monachd], and Echinomyia fera on those of the Spruce moth
and the Pine Owlet or Pine Beauty (Trachea piniperdd). They
are easily distinguishable from other flies by the rough, brush-
like hairs on their abdomen.

It would perhaps be asserting far too much to say that
enormous swarms of insects might quite well be suppressed by
Ichneumonidae and Tachininae unaided ; for there can be little
doubt that, in addition to killing larvae outright, the fungoid
diseases predispose caterpillars to attacks from these parasitic

1 Hess, Der Forstschutz, vol. i. 1887, p. 213.

CHAP, xiv.] Insect Enemies 321

insects. Experience of past calamities, collated with the recent
investigations made in Bavaria owing to the devastations of the
Spruce moth, have shown that the chief fungoid diseases, by
means of which nature reasserts the normal balance obtaining
before any plague begins, are produced by species of Botrytis
(which occasions Muscardine, B. bassiana, in silkworms) Micro-
coccus, Bacterium, Isaria, Cordiceps, Saccharomyces, and Torula.

Preventive Measures.

As a numerical increase of injurious insects is most of all to
be feared in crops of backward development or sickly growth,
all prophylactic measures for warding off any predisposition to
disease or to interference with the normal transpiratory and
assimilative processes must tend to their repression, and obviate
any inducement to abnormal reproduction favoured by increase
in the quantity of material offered as suitable feeding-grounds
and breeding-places. The careful clearing, weeding, thinning,
and general tending of all kinds of woodland crops at the
different stages of their development are therefore necessary in
order that all suppressed, unnecessary, diseased, or damaged
individuals may be eliminated before they offer attractions
to insects which may ultimately be fatal to the more vigorous
and healthy portions of the crop. Such measures of tending
will, of course, be least needed wherever, at the time of the
formation of the woods, due consideration has been given to
the choice of the species of trees best suited for the varying
conditions of soil and situation throughout the area to be
brought under timber, and to the invaluable advantages to be
gained by the formation of mixed woods1 of broad-leaved species
and conifers (wherever possible with any given conditions
of soil and situation) in place of pure crops, or of mixed crops
of conifers only. The crops should be inspected frequently ;

1 See lecture On the Advantages of Mixed Woods over Pure Forests^
para. 7, p. 135.

322 Studies in Forestry [CHAP xiv.

whilst thinnings should take place as often as funds permit, and
considerations relative to the maintenance of a full leaf-canopy
and the safeguarding of the productive capacity of the soil
dictate. Wherever damage has been done by frost, snow, ice,
wind, or fire, measures should not be delayed in rectifying it,
so far as may be possible ; and care should be taken to have
the injured timber either barked, or, better still, removed from
the vicinity of the woods as soon as convenient, in order that
species of Bostrychini and Hylesinini may not become attracted
to them as favourable breeding-places. Felling of coniferous
crops during the summer and careful removal of the bark from
the stems are therefore to be recommended. But when, from
one reason or another, winter fellings have to be made, then
some of the logs should be left here and there with the bark
on, in order to act as decoy stems. These should be peeled
during the following May, and the bark burned so as to destroy
the various broods of Scolytidae that may have been deposited
in it.

Wherever any possible market for firewood makes it feasible
to grub up the stumps of coniferous species of trees, without
incurring much outlay, this should be done immediately after
the fall of the timber, so as to diminish the number of natural
breeding-places offered to the dangerous classes of weevils
( Curculionidae) and cambial-beetles (Hylesinini}. Even casual
examinations of palings formed of coniferous poles will show
how many breeding-places Bostrychini and Hylesinini find in
the bark and cambium. Barking of the poles, therefore, before
they get dry, would not only help to reduce the number of
insects generated, but would also otherwise contribute to the
durability of the wood, and to its protection against attacks
from saprophytic fungi.

But, whilst mixture of different kinds of trees in the forma-
tion of the crops, and careful tending, are the principal means
of preventing the abnormal increase of any kind or kinds of
injurious insects, everything should at the same time be done

CHAP, xiv.] Insect Enemies 323

to promote the increase of their natural enemies, most par-
ticularly amongst the class of insectivorous birds. These are,
however, naturally of somewhat infrequent occurrence in dark,
sombre coniferous woods as compared with broad-leaved and
mixed crops. And amongst these insectivorous birds there is
none which deserves so much encouragement as the Starling
(Sturnus vulgaris\ for whose convenience and protection
nesting-boxes should be hung or nailed up in the woods, to
protect their eggs and young against cuckoos, cats, and other
enemies. Since the recent devastations of the Spruce moth in
Bavaria (1890-1892) there have been many thousands of such
starling-boxes distributed throughout the State Forests in order
to promote the breeding of these most useful birds.

Exterminative Measures.

As previously stated, endeavours must be made to put an
end to every abnormal increase in the appearance of any noxious
insect, before it acquires the power of reproducing itself in count-
less swarms. This requires some knowledge of the appear-
ance, habits, and life-history of injurious species generally.
It also involves constant attention being paid to all areas where
plantations or fellings have been recently made, or where
damage has occurred from wind or snow, as well as to all sickly
and backward crops, which might easily develop into extensive
breeding-places. The frequent revision of Pine and Spruce
woods is indeed an absolutely indispensable measure. The
discovery of noxious insects may take place by many different
kinds of observations. Bore-holes on the stems, bore-dust, or
cobwebs, or drops of resin on the bark or at the foot of poles
or trees, all indicate their presence in the stems of standing
crops ; whilst excreta or damaged foliage along paths and in
the ruts of cart-tracks, and a gradual thinning of the foliage,
indicate the presence of moth-caterpillars in the crowns of the
trees. Even before these last signs become distinct, the

Y 2

324 Studies in Forestry [CHAP. xiv.

presence of more insectivorous birds than usual conveys a
plain hint to the thoughtful observer. Towards evening any
abnormal swarming of moths serves to put one on guard ;
whilst threatened large attacks of the Pine moth (Gastropacha
pint) may be foretold by the frequency with which the hiber-
nating caterpillars may be found under the layer of moss
covering the soil.

Whenever thus forewarned, or when called upon to annihi-
late swarms of any injurious species that may have acquired
numerical strength enough to seriously threaten or interfere
with the vigorous growth and development of timber crops,
the exterminative methods adoptable vary according to the
habits of the insect occasioning the trouble and anxiety,
Some knowledge of its life-history is requisite in order that the
easiest point of attack against it on a large scale may be fixed
on. As, however, the methods usually adopted against beetles
differ essentially from those in use against moths, these two
great classes may be treated separately as forming two distinct
groups comprising the chief species of destructive insects.

A. Annihilation of Beetles (Coleoptera).

So far as many of the bark-beetles (Scotytidae) and weevils
(Curculionidae) are concerned, which chiefly breed in conifers,
the felling and barking of stems attacked, and the burning
of the bark whose cambial layer contains the ova, larvae,
pupae, and often imagines, are the first steps to be taken.
The foresters and woodmen should be carefully trained to find
out such infected stems, and should also be taught the
principle and the practice of felling a tree here and there so as
to form a decoy-stem, and thus prevent the beetles selecting
healthy stems for ovideposition in default of sickly ones. The
careful revision and subsequent burning of the bark must of
course be duly arranged for, and not on any pretence over-
looked.

CHAP, xiv.] Insect Enemies 325

Such decoy-stems should be felled and laid in position early
in the season, before the insects are likely to swarm, as many
species naturally seek after diseased and recently felled trees
before attempting to deposit their ova in healthy stems, whose
strong resinous exudation to a considerable extent threatens the
well-being of their brood. Stems that have thus been placed as
decoys in winter or early spring must be barked and removed
during May and June ; and fresh decoy-stems must be made to
take their place in summer, so as to catch the second brood of
species having a double generation. For such decoys, domi-
nated or suppressed, but still healthy, poles or trees should be
selected, and not half-dry stems that are already nearly dead ;
otherwise these present no great attractions to the females in
search of breeding-places. It is also well to support them upon
rests so as to raise them off the ground and let the beetles and
weevils have full access to the lower side, which remains fresh
and sappy after the upper half is becoming dry. The branches
(which may also be used for decoy purposes for many species)
should be lopped off the stems in order to obviate the evapora-
tion which would otherwise be continued through the foliage.
Timber from the winter fall may thus be used for decoy pur-
poses ; but it must be removed and carefully barked not later
than the middle of May. Its removal alone is not sufficient ;
for then the broods develop normally, and increase prolifically.

The decoy-stems should be examined from time to time
to see if they have been successful in luring insects to deposit
their ova there. This may be noted by small drops of resin or
heaps of bore-dust near the punctures and bore-holes; but pieces
of the bark should also be removed occasionally to see how
far the young brood has developed. When the largest larvae
appear about half-grown the proper time has come for the bark
to be stripped and burned, as until then there would always
be the danger of beetles, whose ovi-deposition was not yet
completed, being able to continue their reproduction elsewhere.

Attempts to collect the larvae can only be made in the case

326 Studies in Forestry [CHAP. xiv.

of cockchafer grubs in nurseries ; whilst the collection of the
mature insects is practically confined only to beetles of the
larger kinds, like cockchafers and Spanish flies (Lytta vesica-
torta\ which may be shaken down from the crowns of poles or
young trees. Smaller species of beetles may also be caught by
means of decoy bundles of twigs or bark, which are burned
when infested ; whilst the large Pine weevil (Hylobius abietis]
is entrapped in narrow, upright-walled ditches, and then killed
by treading on them or pouring boiling water over them.

B. Annihilation of Moths (Lepidoptera).

True day-butterflies (Papilionidae] are practically innocuous
to woodlands. The various injurious species, Sphyngides,
Spinners, Spanners, Leaf-rollers, &cv are all moths or night-
butterflies. It is chiefly during the larval stage that successful
efforts can be made for the extermination of swarms of moths,
although something can also be done to reduce the number
of ova, pupae, and imagines.

Sometimes the caterpillars may be collected merely by hand
(the workmen being provided with old gloves in the case
of hairy caterpillars like those of the Pine moth). This is the
case with those which hibernate under the moss, or which may
be brought down to the ground by shaking the poles or knock-
ing on the branches of trees with padded mallets or the flat
heads of axes, or which may be caught in isolating ditches.
By shaking and knocking, the caterpillars of the Pine Beauty
( Trachea piniperda) and the Pine Span-worm (Fidonia piniaria]
may be brought to the ground for collection ; and the shaking
or tapping is most effective during cool weather, or early in
the morning, when their foothold on the foliage is looser than
during warm sunshine. In the case of the Spruce moth (Liparis
monacha] the newly developed larvae may easily be killed in
large numbers, whilst they are still clustered together in schools
of about ten to twelve, before wandering upwards to the crown

CHAP, xiv.] Insect Enemies 327

in search of food. The so-called nests of caterpillars of the
Lackey moth ( Gastropacha neustria) may also easily be crushed
or burned, as well as the cocoon-like clusters containing those
of the Processionary moth ( Cnethocampa processioned].

When the attacks are severe but confined to small areas,
the migration of the caterpillars to neighbouring crops may be
prevented by isolating the infested portions by means of narrow
ditches — a method which, of course, can only be efficacious
if the leaf-canopy overhead be also interrupted. The deepest
ditches are required for the large Pine moth, when they are
made nearly 2 feet deep; but, in general, a depth of 12 to
15 inches is sufficient, care being in every case taken to ensure
the walls being cut perpendicularly, whilst holes should be
made here and there (also with clean-cut, upright sides) along
the sole of the ditch to catch the caterpillars and lessen their
chance of escaping up the sides. It is also advisable to cut
several traverse ditches within the area thus isolated, in order
to make the work of extermination as complete as possible.

One of the great lessons taught by the recent ravages of the
Spruce moth in Bavaria — third in importance only (i) to the
great advantages derivable from the formation of mixed woods,
and (2) to the necessity for taking active steps against injurious
insects whenever there is the slightest sign of the balance of
nature having been disturbed in any such manner as to permit
of their abnormal frequency — is the efficacy of forming rings or
girdles of patent glue * or viscous tar around all stems in infested
tracts, for the purpose of hindering caterpillars from ascending
to their feeding-grounds on the foliage, or, if once up, from
descending the stems for the purpose of entering into the pupal
state of rest, or for any other purpose. It has thus become by
far the most efficacious method of combatting bad attacks
of dangerous enemies like the Pine and Spruce (Nun) moths.

1 Leim (Ger.) means glue, and not lime, as was the incorrect translation
given in the Foreign Office report on The JVun Moth (Liparis monacha] in
Bavaria, published in 1891.

328 Studies in Forestry [CHAP. xiv.

The caterpillars of the former are thus prevented from ascend-
ing the stems in spring after hibernating under the layer of
moss on the ground ; whilst the same is also the case when the
latter spin themselves down to the ground on cocoon-like
threads (like some of the Tortriddae]. This they practically do
at least once before they lose the power of spinning their
gossamer filaments or get too heavy to be supported and
borne downwards by the latter; and these transformations
occur simultaneously, though gradually, about the third time
of changing their skins.

The essential requirement about good viscous tar is that it
should remain sticky, and without either running or getting
hard and dry from exposure to rain and sun. Its efficacy is not
dependent on the mechanical action of its stickiness, but on
some inherent smell of one or more of the ingredients that is
exceedingly repulsive to the caterpillars till the ring becomes
hard and dry. Even if individual caterpillars can be found
to face and cross it, their feet and mandibles get clogged with
the gluey composition, and they die of inability to procure
food for themselves. It is therefore essential that the rings or
narrow girdles should remain sticky until the larval state of
development has been completed, that is to say, for at least
six to eight weeks (although practically good patent tar remains
active about three times as long) without the surface oxydizing
or becoming covered with a skin. It is a patent composition,
whose ingredients must, however, be a very open secret, as
over a dozen firms advertise it throughout Germany for delivery
at about 75. 6d. per cwt. This quantity suffices for about
2\ acres on the average, although of course young crops
require more per acre than older woods \

Previous to the application of the patent viscous tar the
bark of the stem requires to be cleaned, or cleared of loose

1 For the benefit of those who may wish to try the effects of this patent
tar or ' Raupenleim/ the following addresses of manufacturers may be
given : — L. Polbora, I Kohlenufer, Berlin S. ; Schindler and Miitzel, Stettin ;
and J. M. Witzemann, Stuttgart.

CHAP, xiv.] Insect Enemies 329

bark, so that the glue may bite well on to the stem evenly all
round without so much being required as on rough-barked
stems. This cleaning, or ' reddening ' as it is called in the
case of the Scots Pine, takes place with iron scrapers at about
breast-height, where a girdle about 4 inches is cleared, care
being taken not to injure the stem by too rough treatment.
This preparation should take place in winter and early spring
in all crops where inspection has shown that Pine moth cater-
pillars are hibernating under the moss, or that deposits of
Spruce moth ova are noticeable on the stems. About the end
of March or the beginning of April the formation of the rings
of patent tar should take place before any mild spring weather
has quickened the ova to life or the caterpillars to renewed
activity. It may be applied with hard brushes ; but the best
results were attained in Bavaria by the use of small wooden
spuds about i to ij inches broad, the rings or bands being
smoothed off with similar spuds hollowed to a depth of about
Jth of an inch. Wherever convenient, a thinning out of the
crop should first take place so as to remove all individual
poles or stems not actually necessary for the maintenance of
the full leaf-canopy or of the productive capacity of the soil.
This not only reduces the cost of the operation materially,
but also removes the class of stems most likely to favour the
increased propagation of the insects.

Even in the case of species whose caterpillars hibernate
on the ground (e. g. Pine moth) the removal of the soil-cover-
ing of moss has been found to do more harm than good, as it
rapidly exposes the soil to deteriorating influences.

The collection of the chrysalides by hand is only practicable
when they are formed on shrubs or in fissures of the bark
near the base of stems, and can hardly be carried out on any
large scale. A much more efficacious method consists in the
driving in of swine into the woods. They eagerly devour all
smooth-skinned pupae like the Pine Beauty and the Pine
Span-worm lying under the moss, although they will not touch

33° Studies in Forestry [CHAP. xiv.

hairy kinds like those of the Pine moth, owing to the irritant
properties of the hairs.

It is only when deposited low down on the stem that the
ova of species like the Spruce moth can practically be col-
lected and destroyed ; but under any circumstances, and espe-
cially on the fissured bark of Pine trees, many eggs and clusters
of ova are apt to be overlooked. Prof. Altum, a celebrated
sylvicultural entomologist of Northern Germany, recommends
a daub of viscous tar as efficacious in killing the clusters of
ova of species like the Spruce and Gipsy moths (Liparis
monacha and L. dispar) and the Beech-spinner (Dasychira pudi-
bunda).

Attempts to collect and destroy the restless moths them-
selves can in no way be considered at all satisfactory. A good
many experiments were made in Bavaria in 1891 with strong
electric lights placed before powerful exhaustors, but without
any practical results being attained with the Spruce moth.

As previously remarked, bad attacks of moths seldom last
for longer than three years in their full destructive intensity*.
But within that time enormous damage may be committed,
and vast sums may have to be incurred for fighting against the
moths. The latter are also almost always followed by enormous
numbers of bark-beetles, cambial-beetles, and weevils, whose pro-
lificness is stimulated by the vast quantities of dead, felled, and
sickly timber which litters the woods in quantities not removable
all at once. These vast breeding-places, sooner or later, attract
such large flights of insectivorous birds, that market-gardeners
and orchard-owners in other localities begin to complain of
insect pests owing to the departure of starlings, finches, &c. ;
whilst at the same time the balance of nature re-asserts itself
by epidemics of fungoid diseases and through any unusual
prolificness among the Ichneumonidae and Tachinidae.

Too much stress cannot be laid on the importance of the
early discovery of any, even apparently slight, increase in the

CHAP, xiv.] Insect Enemies 331

usual number of injurious insects, and of the necessity that
then exists for adopting exterminative measures. Enemies
that might during the first spring be annihilated at a moderate
outlay, may necessitate a vastly greater expenditure in the
following and subsequent years, not to mention the monetary
losses involved by having to fell and reproduce crops that repre-
sent considerable capital but have not yet attained their normal
marketable or financial maturity. Thus, during 1892, no less
than £75,000 was spent in the State Forests of Bavaria on
ringing stems with patent viscous tar for fear of a recrudescence
of the attacks of the Spruce moth, whose devastations during
the previous three years had involved the loss of hundreds of
thousands of pounds in the destruction of the timber crops.
Large quantities of timber had to be thrown on markets that
were soon glutted, and in which prices sank very low; and
immature crops had to be felled and removed in order to
try and hinder the otherwise inevitable appearance of enormous
plagues of bark-beetles, cambial beetles, and weevils, that would
have been bred within the sickly stems and the stumps in the
ground.

It is true that, with our comparatively limited woodland
areas, we are not exposed to anything like these extensive
calamities in Britain. But it is worth while learning the lessons
which such devastations teach ; and these are, firstly, that the
formation of mixed woods should be favoured to as great an
extent as convenient (especially in the case of conifers), and
secondly, that dangers from insect enemies are minimized when
the woods are kept properly tended throughout all the
various stages of their development.

INDEX

A.

Acacia, 74.

Advantages of Mixed Woods, 12,

115.
Aecidium elatinum, 294.

— pini, 287, 291.
Agaricus melleus, 300.
Agricultural Depression, results of,

ii.

— Schools, Forestry at, 17.
Agriculture, University Chairs of, 16.
America, forests of, 8.
Appreciation of Timber, 8, 24.
Arboricultural Society, Royal Scot-
tish, 15.

Arboriculture, 18.

Artificial Reproduction, 166.

Aspect, 112.

Assessment of Quality of Soil, 114.

B.

Beech, 37, 72, 77, 79, 85, 146, 149,

187.

Beetles, annihilation of, 324.
Black Arches or Nun, 132, 326.
British Sylva, 27.

— Woodlands, area of, i, 4, 12.

C.

Caeoma pinitorquum, 292.
Canopy or Leaf-Canopy, 32, 40,

274.

Carbonic Acid, 70.
Changes of Generation in Fungi,

304-
Characteristic Flora of certain Soils,

105.

Chlorine, 81.

Choice of Species of Trees, 158.
Chrysomyxa abietis, 286.

Clayey Soils, 98.

Clearances, partial, 182, 196, 220,

224.

Clearing, 180.
Committee (Parliamentary) on

Forestry (1885-87), 12.

— Woods and Forests (1889-90),
14.

Configuration of Soil, 113.
Conservation of Productivity of

Soil, 253.

Cooper's Hill College, 19.
Coppice-woods, 88, 167, 260.
Copse or Coppice under Standards,

88, 167, 260.

D.

Density of Crop, choice of, 165.

— of Woods, 34, 37, 167, 188.
Department of Woods and Forests, 9.
Dependent Species of Trees, 30, 36.
Depth of Soil, 106, 273.
Distribution of Cultivated Area in

Britain, i, 10.
Dunes, 270.

E.

Ebermayer's "Investigations, 72, 83,

79» 93, 254.

Excess of Nutriments, effects of, 81.
Exposure, 112.

F.

Financial Considerations, 162, 175,

221.

Food-Supply of Trees, 67, 79, 83.
Forestry in Britain, i.

— Parliamentary Committee (1885-
87) on, 12.

— Instruction required in, 21.

334

Index

Forestry, Proposed Edinburgh Chair
of, 19, 25.

— Various Branches of, 27.
Forests, Parliamentary Committee

on Woods and, 14.
Forked Growth in Plantations, 177.
Form of Crop, choice of, 165.
Formation of Crops, choice of, 171.

— of Mixed Woods, 138, 143.

— of Pure Crops, 141.
Form-factor, 168.
Frosts, 50, 262.

Fungoid Diseases, 129, 172, 180,
276.

— Prevention and Cure of, 305.

Gradient, 113.

G.

H.

Heartwood of Trees, 243.

Height, rate of growth in, 91.

High-Forest, 88, 167, 261.

v. Honel's Investigations, 78.

Humidity, HI.

Humus, 71, 96, 101, 104, 250, 255,

268, 271.
Hysterium pinastri, 130, 284.

I.

Imports of Timber into Britain, 5.
Improvement of Land (Scotland)

Act, 1893, ii.
Increment, 59, 190, 200.
Insect Enemies, 129, 167, 180.
Insects, classification of injurious,

310.

— Extermination of, 323.

— Natural Enemies of, 317.

— Preventive measures against, 321.
Irrigation, 269.

Larch, 43, 79, 83, 154, 227, 231,

251.

— Canker, 44, 130, 296.
Law of the Minimum, 67, 87, 92.
Leaf-Canopy, 32, 40.
Leaf- Shedding of the Pine, 130, 284.
Light, relation of Trees towards,

54, HI.

Light-demanding Species of Trees,

36, 55» !54> i7i» 268-
Lime, 80, 253.
Limy Soils, 99.
Loamy Soils, 100.

M.

Magnesia, 81, 253.
Management of Woodlands, 27, 33.
Maturity of Woodland Crops, 65.
Mineral Food of Trees, 80.
Mixed Woods, 40, 115, 146.

— Formation of, 138, 143.
Moisture in Soil, 103, 266.
Moths, annihilation of, 326.
Mycorhiza, 71.

N.
National Economic Importance of

Forests, 4.

Natural Degeneration, 167, 177.
Nectria cucurbitula, 295.

— ditissima, 298.
Nitrogen, 73.

Normal Density, 34, 37, 169.
Normal Age attainable by Trees, 65.

— Shape of Stem and Crown, 56.
Nutrient Reserves, 71, 216.
Nutrients in Soil, 253.
Nutriment, excess of, 81.
Nutrition of Trees, 67.

O.

Oak, 38, 79, 85, 150, 224, 231, 245,

251.
Oxygen, 72.

P.

Partial Clearances, 182, 196, 220,

224.

Peziza Willkommii, 130, 296.
Phosphorus, 81, 253.
Phytophthora omnivora, 288.
Physical Properties of Soils, 102,

260, 264.

Planting, 170, 172, 177.
Potash, 80, 253.
Principal Species of Trees, 30, 36,

146.

Productivity of Soil, 253, 274.
Protection of Soil, 38, 253.

— of Woodlands, 27.

Index

335

Pruning, 203.

Pure Forests, 42, 115.

— Formation of, 141.

R.

Rate of Growth, 59, 91.
Regeneration or Reproduction of

Crops, 171.

Removal of Branches, 203.
Reproductive Capacity of Trees, 62 .
Requirements of Trees as to Climate,

— Light, 54.

— Soil and Situation, 50.

— Soil-moisture, 79.

— Water, 75.

Reserve Nutrients, 71, 216.
Returns, Agricultural, for 1892, 4, 10.

— Customs, for 1892, 5.
Rosellinia quercina, 303.

Ruling Species of Trees, 30, 36, 146.

S.

Sandy Soils, 97.
Sapwood in Trees, 243.
Scots Pine, 37, 79, 85, 153, 226,

231, 246, 251.
Shade-bearing Species of Trees, 36,

54, 146, 170.
Silva, Evelyn's, 10, 46.
Silver Fir, 37, 79, 85, 146, 187, 228,

254-

Situation, 108.
Slope, 113.
Soda, 81.
Soil, 90.

— Classification of, 96.

— Conservation of, 253.

— Depth of, 1 06.

— Quality of, 114.

— Physical Properties of, 102.
- Warmth of, 106, 270.

Soil-moisture, 103, 266.

Soils, Flora characteristic of various,

105.

Sowing, 173.
Species of Trees, choice of, 158.

Spruce, 37, 79, 85, 146, 187, 228.
Stagheadedness, 219.
Stimulation of Increment, 210.
Stoles or Suckers, 64.
Stool-shoots, 64.

Subordinate Species of Trees, 30.
Subsoil, 90.
Sulphur, 81, 253.
Sylva, British, 29.
Sylvicultural Chemistry, 67, 92.

— Entomology, 307.
Sylviculture, 18, 27, 46, 93, 261.

T.

Temperature, 67.
Tending of Woods, 179.
Thinning, 40, 169, 175, 182, 185,

211, 225.

Total Clearance of Crops, 166.
Trametes pini, 290.

— radiciperda, 302.
Transpiration, rate of, 48, 76.
Trichosphaeria parasitica, 287.

U.

Undergrowth, influence of, 243.
Underplanting, 214, 218, 230.
Utilization of Woodland Produce,
27.

V.

Valuation of Timber Crops, 2, 4, 27.

W.

Warmth of Soil, 106, 270.
Water, 75.
Weeding, 183.
Weeds, 180, 293, 294.
Winds, protection against, 180.
Woodlands, area of British, i, 4.

— value of British, 2, 4.
Wood-pulp Industry, 8.

Woods and Forests, department
of, 9.

— Parliamentary Committee (1889-
90) on the Administration of the
Department of, 14.

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