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UNITED STATES DEPARTMENT OF AGRICULTURE

Contribution from the Forest Service
HENRY S. GRAVES, Forester

Washington, D. C. PROFESSIONAL PAPER December 21, 1917

EFFECTS OF GRAZING UPON WESTERN YELLOW-PINE
REPRODUCTION IN THE NATIONAL FORESTS OF ARI-
ZONA AND NEW MEXICO.

By Ropert R. HIL1, Grazing Examiner.

CONTENTS.
Page. Fage.
Importance of protecting pine reproduction. . 1 | Effects of grazing injuries upon western yel-
Scope and method of study. ...............- 2 low-pine reproduction ........-.---....... 16
Extent of damage to western yellow-pine SUM MAYA SSeS aga eee Gea See. es eee 23
reprogduct;onirom erazinge. = <..5-222-.- 2-56 4 | Application of results to range management
Factors influencing damage................. 9 11 THe: Sout WeStssse see seeeeee seme ee aise 25

IMPORTANCE OF PROTECTING PINE REPRODUCTION.

The best summer forage in Arizona and New Mexico is found
among the open stands of yellow pine, mainly at elevations above
6,000 feet, and covering more than 8,800,000 acres, or 6 per cent of
the total area of the two States. (See map, fig. 1.) Every economic
consideration requires that this forage, one of the region’s most
important resources, should be converted into meat. At the same
time, it is important that this should be done with the least possible
injury to the yellow pine, which is by far the most important timber
of the Southwest. In many.places the tree is not reproducing satis-
factorily, hence it is very necessary to protect the young growth
(which in any event has to contend with severe winters, dry springs,
and parasites and insects) from damage by stock.

The problem is especially important in the National Forests,
which are created primarily to conserve the timber supply and to
protect the vegetative cover on the watersheds. “In the Forests is
the bulk of the yellow pine in Arizona and New Mexico, and on the
National Forest range are grazed approximately 30 per cent of all
the range stock in the two States. Stock use the Forest range mainly
during the summer, from April to November.

This bulletin presents the results of a study to determine the
character and extent of the damage to young growth of western
yellow pine in the Southwest from the grazing of live stock, and to
find out the best means of keeping such damage at a minimum while
permitting proper utilization of the range.

4205°—17—Bull. 580-1

2 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.
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!
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I
1
CO |
ford
j I
|
eso, ’
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|
! \ oo
. r¢
: ey | yaa
=. \ ee ee ae
Se ee | © |APProx area of the iwo states_ I5L00Q000A
ee — Lt _Apprex area of WesternYellow Pine 8800,000A.

Fig. 1.—Yellow pine in Arizona and New Mexico.

SCOPE AND METHOD OF STUDY.

An intensive study was made on the Coconino National Forest,
in the north-central portion of Arizona, where grazing and timber
conditions are typical of the forests of the Southwest. and where
the problem of securing satisfactory timber reproduction is often
serious. This was supplemented by general observations, covering
a period of two years, on other Forests in Arizona and New Mexico.
The observations were confined chiefly to the yellow-pine type, but
for purposes of comparison some observations were made in the
Douglas fir and pifion-juniper types.

Early in the season of 1910 a preliminary reconnaissance was
made on the Coconino Forest. This was followed during that year
by a detailed study, in which observations were made upon 150 plots.
Further observations were made in 1912 on additional plots. Alto-
gether 250 plots were observed within a radius of 25 miles of Flag-
staff, in the heart of the Forest.

The plots were located so as to include the following range condi-
tions:

(1) Areas embracing all conditions of range normally grazed by
different classes of stock.

(2) Areas embracing all conditions of range overgrazed by dif-
ferent classes of stock.

(3) Areas supporting a good stand of forage normally grazed by
all classes of stock.

(4) Areas supporting a poor stand of forage normally grazed by
all classes of stock.

(5) Areas supporting chiefly bunch grasses, grazed by different
classes of stock.

(6) Areas where cattle congregate.

ST a a a

{
eee rh OC

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 3

(7) Areas where sheep congregate, ¢. ¢., along driveways and on
bed grounds. ‘

The plots were selected where representative rather than abnormal
injury was in evidence. In order to secure maximum results from a
limited amount of work, the plots were located where the stand of
seedlings was fair to good. They were laid out in quadrangles, vary-
ing in size from 10 feet by 30 feet to 30 feet by 90 feet, depending
upon the size and density of reproduction.

All seedlings and saplings of a size subject to grazing were
counted. An attempt was made at first to classify the damage ac-

cording to such divisions as “ leader destroyed,” “ needles removed,”
etc., but it was found that this did not give an accurate idea of the
amount of damage actually done without a great deal of qualification.
For this reason, it was decided to base the classification upon the
permanent effect upon the development of the tree which, in the opin-
ion of the observer, the damage would cause. Plants on which the
leader, side shoots, and needles had been so severely grazed that the
growth of the plant would be seriously interfered with for at least
a number of years, were classed as “injured.” Where the damage
was not so severe, but if continued would seriously interfere with the
development of the tree, the plants were classed as “severely
browsed.” Where the damage was severe enough to interfere to a
very considerable extent with the development of the tree for a period
of from one to three years, but not so severe as to affect its ultimate
development even though the usual amount of damage were to con-
tinue, the tree was classed as “moderately browsed.” Where the
damage was so slight that its effect would not be noticeable after the
current year, the plant was classed as “ lightly browsed.”

The trees were classified according to height by ocular estimate as
follows:

elon Grr ichesu es. Sean yeh eee ae eh ts VERO Seedlings:
Grineheswto; 1.) .feetenn = 22a eee ee acco pat 1-foot class.
GRLCEL LOe? oO tCCEBEMNIE): 2) ried 8 ee 2-foot class.

ah Tord oC ech Oe ety 2 ce ay ene ang ee REE a] 2 3-foot class.

SE OLECURtO. 4.9) TEC aan. TT. eae ee 4-foot class.

AS TSE fy Oty Ting RS, ol ee games cape ag is pe amg ey eee ey eet OE 5-foot class.

5.6 feet to as high as were subject to grazing____________. Above 5-foot class.

Four examinations were made in 1912 and in 1913 at intervals
during the grazing season to show the amount of seasonal damage.
The first examination was made during May, to record the amount
of damage at the beginning of the grazing period; the second ex-
amination was made early in July, to indicate the amount of damage
that occurred during the spring dry period; the third early in Sep-
tember, to determine the amount of damage done during the best
growing period; and the fourth early in November, at the close of
the grazing season, to record the damage done during the fall drying

4 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

period and also the total amount of damage during the entire graz-
ing season. An examination was made also at the close of the 1914
grazing season. Thus data on seasonal damage are available for two
years, and data on total annual damage for three years.

A supplemental study was undertaken in 1912 to determine the
effects of protection from grazing upon the establishment, growth,
and recovery of yellow-pine reproduction, and incidentally of forage
plants. In each of five areas subject to close grazing and represen-
tative of soil classes and forage types in the western yellow-pine
belt, 2-acre plots were fenced so as to exclude all grazing. Check
plots, established in the immediate vicinity of the fenced plots, were
left to the usual amount of grazing. The height and spread of
crown of the young trees within the plots were measured, and the
location of each tree was recorded. In addition, the severity and
probable date of past grazing injuries were noted. These data were
secured in 1912, 1913, and 1914. It is planned to repeat the exami-
nation every third year until a period of 10 years has elapsed, or
until conclusive results are obtained.

EXTENT OF DAMAGE TO WESTERN YELLOW-PINE REPRODUC- -

TION FROM GRAZING.

AVERAGE ANNUAL DAMAGE.

The average annual damage to western yellow-pine reproduction
due to grazing under existing practice is shown in Table I. The
figures are those obtained during the final examinations at the
close of the grazing seasons of 1912, 1913, and 1914. It will be seen
that 42 per cent of the total number of trees observed are damaged
to some extent annually.

Taste I.—Annual damage to western yellow-pine reproduction from grazing.

Browsed.
Number Injured. :
Yur of trees sae Severely. Moderately. Lightly.
> ob- ioe A dey. onl | ee
served.

Num- | Percent} Num- | Percent| Num- | Percent; Num- | Per cent
ber. | of total. ber. of total. ber. of total.| ber. | of total.

NQUQ2E Ee ies ee ee 8, 945 853 9.5 1,035 11.6 2,240 25 896 10
igigt 232 55%, Pystitees 8,945 492 5.5 871 9.7 | 1,301 14.5 915 10.2
0 HOR ene ange aaa 8, 945 448 | 5. 0 589 6.6 | 698 7.8 382 4.3
Averageannual... 8, 945 | 598 [nos 6.7 | 832 | 9.3| 1,413 | 15.8|* 731 8.2

EFFECT OF GRAZING ON WESTERN YELLOW PINE. y

TasBLe I1.—Annual damage to western yellow-pine reproduction, etc.—Continued.

. Rubbed.
N Dead.
Year. Malco Severely. Moderately. Lightly.

ob- ee eee Rats Ae ee
SB Num- | Percent} Num- | Percent} Num- | Percent) Num- | Per cent
ber. | of total. ber. of total. ber. of total.| ber. of total.
TE RS a RE, gence 8, 945 10 Ont 5 0.1 1 0.0 50 0.6
MONS are wes 5 ote tet 8,945 6 46 5) 20 53) 94 1.0
RET Aes 2 ee Ue a 8,945 125 1.4 36 4 1 0 105 152
Average annual...| 8, 945 63 7 29 3 | 7 1 83 9

In order to arrive at the number of trees damaged to such an ex-
tent as seriously to retard their growth, it 1s necessary, under the
plan of classification, to include only the injured, the severely
browsed, and the severely rubbed trees. Estimated on this basis,
1,493 trees, or 16.7 per cent of the total number examined, are sub-
ject to severe damage by grazing. It is this class of damage, rather
than the total damage, that is of serious importance.

It is believed that the figures given represent fairly the actual
damage over approximately one-half of the yellow-pine type on the
Coconino Forest and that similar damage will occur elsewhere under
like conditions. Conditions under which the damage is greater or
less than the average are pointed out in the later discussions.

DAMAGE BY HEIGHT CLASSES.

The extent of damage done to trees of different sizes is shown in
Table II.

The conclusions drawn from this table are that damage is most
severe in the seedling class and gradually shades off as the plants
increase in size; that injuries and serious browsing constitute nearly
all of the important damage to trees below 3.5 feet high, but that
_above this height most of the serious damage is due to rubbing, which
becomes more acute with increase in height up to 5.5 feet.

Figure 2, which is constructed from the data in Table II, shows
eraphically the basis for these conclusions.

6 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

~

TABLE II1.—Damage by height classes.

Damage.
Average for three-year
Year. period.
|
Num-
REE 12
Height class. ber of | Character of injury. ental yee on
trees. | each class.
= oul
1912 | 1913 | 1914 Eel
See Dam- | Severe
= age dam-
of all age
classes. | only.!
Num- | Num- | Num- | Num-
ber. ber. ber. ber.
Tnyjored:.\. .fdoccseese =< 272 152 131 185 9}:
Severely browsed. .... 322 352 143 272 12
|| Moderately browsed... 166 212 43 140 7
Seedlings........--.--| 2,153 || Lightly browsed ...... 91 121 19 77 4 21
|) Severely rubbed <=.) 4 fa ek- | -teccee|a see)
Moderately rubbed 2 2|~ 25. - 2.2 |28- Sorel eect =o See eee
| Hiehtly cubbed ~ ~...2<s goa - Saeco feee -- |P ee ee
Injured styon. 3.8 2s22 385 232 203 273 8
Severely browsed. .... 365 365 229 320 10
|| Moderately browsed... 553 587 301 480 14
d=foot Class: 5. - 2-1 -.-% 3,294 || Lightly browsed ...... 293 351 119 254 8 18
Severely, rubbed. = 5)..- -2|_<ccrecdlescete | Seo ee ee eee
Moderately rubbed = 220. 2 ee eee eee ele ee a eee
Lightly.subbed &.¢ s3!-|ocs5 <0 35|f oe Sas Sores ce) ee Soe ee
LETT be 10 ey ey Arse onde 135 69 81 95 6 ||
Severely browsed. ...- 195 75 125 132 9 |;
Moderately browsed... 356 212 154 241 16 |;
2foot class......----- 1, 468 | Lightly browsed... bo7 |? 150°? a | ag re
Severely rubbed. .....|.......- 1 1 ho eee soe i
Moderately rubbed....|.....-..- dao Stel sce See Sees
Hightly Fubbed <<... slo soe wel aoe eee ee ee eee j
tnjared&..F. Feet! 55 37 32 41 3
Severely browsed. .... 104 73 96 91 8 |
| Moderately browsed... 238 229 156 208 17
3-foot class..-..------ | 1,212 |; Lightly browsed...-.. 165 183 84 144 12 12
Severely rubbed. ..... 2 23 26 17 | 1
Moderately rubbed... . 1 6 4 | 44-224
| Lightly TUDDEGe eae ce eee 7 ee lee vacenl | Sees
injured 5.2622 25- os s26 5 1 1 2 1
Severely browsed. .... 11 9 ii 10 3
Moderately browsed... 35 30 29 31 10
4-foot class........--- 324 || Lightly browsed...... 89 23 49 68 | 20
Severely rubbed...... 3 9 40 17 5
Moderately rubbed....}.......- 7 3 3 1
Lightly rubbed. .....- [aceatnee |aecpine <n ote tealen meee lesa ae
ANTE eee os oan Ir lee cee ce]: ete: | ee eee
| Severely browsed..... 3 2 5 3 1
| Moderately browsed .. 21 20 14 18 7
5-foot class..-.-..----- | 293 | Lightly browsed...... 40 36 42 39 15 9
Severely rubbed. ....-. 20 18 35 24 9
| Moderately rubbed... 9 7 6 7 3
Lightly rubbed. ...... 2 3. |Feaescee 2 1
| Tujurede eee 1 ig eset. tesoe
| Severely browsed =. -<-\oas i=-.| 2558-55.) Soba eee <3 oe
= Moderately browsed...}...-.-.--- 1 1 el eee es
Above 5-foot class... -) 201 || Lightly browsed......- 72 16 21 20 10 6
|| Severely rubbed... ---- 12 9 14 12 | 6
Moderately rubbed... - 25 20 22 | 22 | 11
Lightly rubbed. ...... 9 42 ates 7 | 3
|

1Determined by adding per cent injured, per cent severely browsed, and per cent
severely rubbed. =

~

i os
ee oe A oe

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 7

DAMAGE BY PERIODS.

To determine the damage caused during different periods of the
grazing season, four examinations were made of all plots during the
seasons of 1912 and 1913. The first examination was made at the
beginning of the grazing season; the second early in July at che

a7

ACC

.

‘\

Hs 3
A fv PER io iy

Damage —- Percent of Trees 1m each Class
AY
Y

5
|
ea

Height or a, Foot Classes

Vig. 2.—Extent of damage to reproduction of different heights.

close of the early summer drought; the third in the fore part of Sep-
tember, following the period of maximum plant growth; and the
fourth early in November at the end of the grazing season. Results
for the two years are summarized for the respective periods in
Table III.

8 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

TABLE III.—Periodic damage.

Period. Per cent | Average eee
of trees | per cent in =
| Total |-found | oftrees | 4. ar
; faa. Year. trees | damaged | damaged — k
No. of period. | Begit- | enaing. | Number observed.| ateach | each | PS “Ye
J 4 ning. * | of weeks. | exami- | grazing ss
| nation. | season. oe
| 19192 | 8,945 | 0.3 |
cp ae Se Apr. 15 | May 20 | 5 ji pees : 0.35 0.07
| Average., 8, 945 .35 |
| | [jim ol | 8,945 |) 44.04
Second......... May 21| July 8 | 7 ‘i teeeeeeeeee 8,985 | 7-228 17.6 2.5
| | Average. 8, 945 18.0 “
| 1] epee cpeisrsa 8,915 | 35.0 |
hind .-—.. be: July 9 | Sept. 12 Ty Be sos 8,95 | 36.0 aes 1.9
Average. 8, 945 35.5 |
; i
| "Cr ees ies 8,945 46.0 |
Wourth =... F Sept.13 | Nov. 6) g 1913.--..-----. 8, 945 40.0 7.5 .9
| Average. 8,945 43.0

The observations indicate that the greatest amount of damage
occurs during the latter half of June and early in July, or during
the severest portion of the early summer dry period, and that the
least damage occurs during the first few weeks of the grazing period,
or before June 1. A considerable amount of damage occurs during
the main growing season and a smaller amount during the fall drying
period.

The fact that a relatively small amount of damage occurred during
1914, which was unusually favorable for the growth of forage, gave
support to the theory that the severity of damage varies inversely as:
the amount of succulent feed available. The record of periodic
damage, however, indicates that there is an important factor besides:
the amount of available succulent forage which determines the
severity of damage. This is believed to be the condition of the cur-
rent year’s growth of pine shoots. All observations substantiate the
belief that, except in unusual cases, stock will not injure coniferous
shoots of a previous year’s growth. It has been noted particularly
that during the early summer practically no damage occurs until new
shoots appear, and that damage in any year is confined largely to
that year’s growth. Yellow-pine vegetative buds start active growth
on the Coconino Forest about May 15, and by June 20- have formed
succulent shoots with well-developed needles. From that time until
about the middle of August the shoots are tender and more palatable
than at other periods. Thus the season of best forage growth is also
the period when yellow-pine shoots are most palatable. This and
the probability that during the severe spring dry period stock develop
a taste for the pine shoots which continues during the early portion
of the summer growing period may explain the rather severe dam-

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 9

age that continues through the season of abundant forage growth.
The fact that the needles and stems become tough and therefore less
palatable by September seems to account for the relatively little
damage that is done during the fall period, when ordinary forage
becomes dry and usually is closely grazed.

In 1912 the time of making the first count extended until early in
June and in the preliminary study during 1910 until June 20. In
neither of these counts was serious damage recorded. In view of
this fact and of the indications based upon phenological observa-
tions, it is safe.to say that very little serious damage is done to the
reproduction before the middle of June.

. FACTORS INFLUENCING DAMAGE.

INTENSITY OF GRAZING.

Casual observations indicate that the amount of damage to repro-
duction is greater on heavily grazed areas than on those lghtly
grazed. In order to determine the extent to which this apparent
relation holds and the intensity of grazing which may be permitted
without causing an undue amount of damage, plots were observed on
ranges representing various degrees of utilization.

NORMAL GRAZING.

Normal grazing, as the term is used here, implies that the class
and number of stock are well adapted to the character and amount
of forage.

Observations during 1912, 1913, and 1914 on 92 plots, representing
a variety of forage types on ranges normally grazed by sheep, cattle,
and horses, showed that out of a total of 3,352 trees an average of
126 were injured, 258 were severely browsed, and 1,023 were moder-
ately to lightly browsed each year. Thus 384 trees, or 11 per cent
of the entire number, were severely damaged.

Observations on 14 plots, containing 571 trees, on ranges normally
erazed by cattle and horses only, showed no trees injured during the
three-year period, none severely browsed, and only 11 moderately to
lightly browsed. The number of plots in this series is perhaps
insufficient to form the basis of general conclusions, but extensive
observations elsewhere bear out the belief that cattle and horses,
under proper conditions of grazing, do a negligible amount of
damage to forest reproduction. |

OVERGRAZING.

By overgrazing is meant grazing by an excessive number of
stock, with consequent injury to the palatable forage. Of 1,792
trees on two plots on ranges overgrazed by all classes of stock, an
average of 298 were injured annually, 335 were severely browsed,

4205°—17—Bull. 580-—2

10 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

and 474 were moderately to lightly browsed. Thus 633, or 35 per
cent of the total number, were subject to severe damage.

Of 522 trees on 14 plots on an overgrazed range open to cattle
and horses only, an average of 11 were injured annually, 55 were
severely browsed, and 194 were moderately to lightly browsed. Thus
66 trees, or 18 per cent of the total number, were subject to severe
damage. This injury is not excessive in itself, but when compared
with the negligible injury which cattle and horses cause on nor-
mally grazed areas, it forms an additional reason for insisting upon
the protection of the range against overgrazing, especially on areas
where all of the established reproduction is needed.

The general conclusions from these observations are: (1) That
on ranges properly grazed by sheep as well as by cattlé and horses,
a very considerable amount of damage occurs, but that where only
cattle and horses graze under such conditions a negligible amount
of damage results; and (2) that where overgrazing occurs serious
damage is caused by any class of stock.

DENSITY, AMOUNT, AND CHARACTER OF FORAGE.
DENSITY OF FORAGE.

Since the intensity of grazing has a direct relation to the severity
of the injury to tree reproduction, the inference might be drawn
. that on a range supporting a scattered stand of forage plants the
percentage of trees damaged would be materially greater than on
a range where the stand of forage is good. In order to determine
whether this is so, observations were made on ranges where the
average density of forage plants was less than two-tenths, and on
ranges where the average density was four-tenths of the ground
surface. The plots were selected as representing all degrees of graz-
ing. On 39 plots supporting a good stand of forage and 1,010 trees,
31 trees were injured, 119 were severely browsed, and 255 were mod-
erately to lightly browsed. Thus 150, or 15 per cent of the total,
were subject to severe damage. On 92 plots, containing 3,678 trees,
on range poorly stocked with forage, 157 trees were found to be
injured, 500 severely browsed, and 882 moderately to lightly
browsed. Thus 18 per cent of the total were being severely damaged.

These comparisons indicate that under average conditions there
is not a great deal of difference in the amount of damage done on
ranges well stocked with forage plants and on ranges poorly stocked.
In general, therefore, it may be concluded that in a given forage
type, with the same amount of forage allotted each animal, the
density of the forage has little relation to the amount of damage to
pine reproduction.

ee etl ae

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 11
AMOUNT OF FORAGE BY SEASONS.

The fact that a greater amount of damage occurs during the dry
period of early summer, when ordinary forage is scarce, than during
other periods of the grazing season suggests the probability that dur-
ing a season when feed is unusually abundant the amount of damage
will be relatively small. This supposition is confirmed by a com-
parison of the damage done in 1914 with that done in 1913.

Ordinarily not enough precipitation occurs during May and June
to support the vegetative growth, and as a result not enough forage 1s
produced to meet the needs of stock. This was the case in 1913; but
in 1914 the dry period was broken in June by sufficient rainfall to
revive the forage, and this was followed by abundant rainfall in July
and August. Since the three months from June to August form the
main growing period, 1914 was an unusually favorable year for
the production of forage, and 1913 an unusually poor one. (See
Table IV.)

TABLE 1V.—Precipitation during the growing periods of 1913 and 1914.

Average for yellow-pine type. May. June. July. Aug. Sept.

Inches. Inches. Inches. Inches. Inches.
z 0. 01 0. 08 2. 25 2. 83 2:13
TAG Ue one ee EN 8 ee ar a a ee Sy ee eee -49 1.45 4. 54 2.47 714

1 The monthly rainfall is an average for the entire yellow-pine type, based upon the records at Fort
Valley, Flagstaff, and Walnut Canyon.

TABLE V.—Comparison of the serious damage caused by grazing during 19138

and 1914.
Trees seriously
damaged.
Year.

Per cent

Number. of total.

iC RES LES bs 9 BAUR Ee eS RS Me he te Oe eco Eels he ae re eee ee Oe iE 1,417 15.8
OTA e pig ek rae tea eh ees en oe Nace ots ide BOE ies cs hss oe cee hocces Le ekiaees 1,162 13.0

Table IV indicates that vegetation could not have made any con-
siderable growth in 1913 before July, and the record of periodic
damages shows that more than one-half of the total annual damage
for that year occurred during this dry period. No record of periodic
damage was kept in 1914, but a summary for the year (see Table V)
reveals 13 per cent of the entire number of trees seriously damaged,
as compared with 15.8 per cent for 1913. The lower per cent. of
damage for 1914 is believed to be due chiefly to the greater abundance
of feed during that year, particularly during June and early in July.

12 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

This suggests the conservative use of forage as a means of preventing
excessive injury to reproduction.

CHARACTER OF FORAGE.

Observations were made to determine the relative amounts of
damage to reproduction in the principal forage types of the yellow-
pine belt. .

Two main classes of forage are found in the yellow-pine type
of the Southwest. These are the mountain bunchgrasses (Muwhlen-
bergia gracilis, Festuca arizonica, and Blepharoneuron tricholepis)
and blue grama grass (Bouteloua gracilis), which occurs usually on
the more level mesas. Both types, with variations, are prominent
on the Coconino Forest. The blue grama is very palatable to all
classes of stock. The bunchgrasses, though very nutritious, are not
generally preferred by any class of stock because of their accumu-
lation of coarse, dry foliage.

The general conclusions regarding the relation of the intensity of
grazing to the amount of damage to tree reproduction are believed
to apply in the case of the grama range. But in the case of the
bunchgrass type, a serious amount of damage occurs on some por-
tions, even though the type is not grazed closely. A study was there-
tore made to determine which class of stock is responsible for such
damage.

Since no bunchgrass areas are grazed exclusively by sheep, it was
necessary, in order to determine the damage done by this class of

stock, to compare the amount of damage done on bunchgrass areas

by both sheep and cattle with that on similar areas grazed by cattle
only. Accordingly 72 plots were selected in the bunchgrass type
grazed moderately by both classes of stock. These plots contained

2,372 trees subject to grazing. During 1912 and 1913 counts on these ~

plots showed an average of 428 trees injured and 320 trees severely
browsed, or a total of 32 per cent which, if present conditions con-
tinue, may be expected to become seriously injured. On a number
of the plots practically every tree had been killed by grazing. As
compared with these figures there were no injuries or severe browses
on the 15 plots in this type located on areas grazed closely by cattle
only. Of the total of 618 trees only 7 were even moderately browsed.

The obvious conclusion that sheep are chiefly responsible for the
severe damage is substantiated by the fact that the serious damage
noted was characteristically that of sheep, that is, the needles were
cropped closely along the stems, instead of the end of the shoot
being eaten off.

It is not assumed that the injuries on the sheep-grazed areas are
representative of the bunchgrass type as a whole. All of the plots
studied were located in the north half of the Forest, where the bunch-

EFFECT OF GRAZING ON WESTERN YELLOW PINE. Le

grasses occur in much purer stand than over the remainder. In the
rest of the Forest blue grama, Gambel’s oak, and succulent weeds
form a considerable percentage of the vegetation comprising the
bunchgrass type. Extensive observations in this portion, supple-
mented by many others in the yellow-pine type in the Southwest,
bear out the conclusion that where sheep are not forced to depend
upon the rank growth of bunchgrasses for the main part of their
feed, but have access to plenty of browse and palatable weeds, they
will not cause such severe damage to yellow-pine reproduction in the
bunchgrass type. If, however, the browse and weeds are not suf-
ficient to supply the bulk of their feed, they are likely to cause very
severe injury to young pines.

The portion of the bunchgrass type on the Coconino Forest, over
which the damage is excessive, includes about one-third of the total,
or 130,000 acres. A circumstance which makes the injury to repro-
duction here a serious matter is the fact that where the worst damage
occurs reproduction is scattered, and for that reason is in special need
of protection.

CLASS 9F STOCK AND METHODS OF HANDLING.

CLASS OF STOCK,

It is comparatively easy to determine the amount of damage for
which cattle, horses, and burros are each responsible, because fre-
quently these classes of stock are handled in pastures where each may
be observed separately. In the case of sheep, however, which are not
handled in pastures on the Coconino Forest, but share the open range
with other classes of stock, it is difficult to determine the proportion
of the damage with which they can properly be charged. To arrive
at a conclusion it was necessary to compare the amount of damage
found on range occupied by both cattle and sheep with the amount
of damage under similar grazing conditions on areas from which
sheep are excluded and in pastures. This measure of sheep damage is
believed to be fairly accurate, since there is no evidence that cattle
do more damage to reproduction on a range which they share with
sheep than on a range which they graze alone. Sheep injuries,
furthermore, are characteristic and may be readily distinguished
from those of cattle and horses.

It is believed that horses and burros may be eliminated from the
classes of stock responsible for severe injuries to reproduction. The
many saddle horses, in all kinds of physical condition, ridden in the
yellow-pine type, have shown no disposition to eat coniferous repro-
duction. In a pasture 4 miles southwest of Flagstaff about 30 head

14 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

of horses were grazed from May until November, 1910. The only
other stock using the pasture were from three to five head of cattle
and two or three head of sheep. The number of stock was greater
than the carrying capacity warranted, and in the fall all forage was
cropped very closely and the horses were poor and rough. Counts
made in October showed that of 365 trees only 8 trees, or 2 per cent
of the total, were seriously browsed. In a grama-grass weed pasture
at Fort Valley, containing approximately 360 acres, about 12 horses
were kept during the grazing season of 1910. Observations on 15
plots showed practically no damage.

Burros form a very small proportion of the total number of stock
on the Forest. However, the fact that they often show little dis-
crimination in the selection of their feed raises the question of the
amount of damage which they do to forest reproduction. At the
Rees’s sheep-headquarters camp, located in the bunchgrass type on
the north slope of the San Francisco Peaks, five burros were run
during the seasons of 1913 and 1914 in a pasture containing about
160 acres. Observations made in October, 1914, upon 200 trees less
than 4 feet in height showed no damage whatever by grazing.

The amount of damage under different range conditions on sheep-
grazed areas and on areas from which sheep are excluded has already
been discussed. In order, however, to estimate the relative damage
chargeable to sheep and to cattle under average conditions in the

vellow-pine type, range conditions has been given a weight in per |

cent representing the importance of each to the whole. The per-
centage of severe damage attributable to cattle and to sheep has
been multiplied by the number representing the importance of each
range condition and an average arrived at which represents the
relative amount of damage for which these two classes of stock are

responsible and the total per cent of damage which each class is.

believed to be causing over the entire Forest. The results are given
in Table VI. :

TABLE VI.—Comparison of cattle and sheep damage.

Amount of Amount of
Com- | serious damage Com- | serious damage
(eae (per cent of eon (per cent of
Condition of range. povtance total stand). Condition of range. pone total stand).
Percent} mea aa ‘PeY CentilSecanaacei pes
of total: Cattle. | Sheep. of total: Cattle. | Sheep.
Normally grazed ......-- 38 0. 008 A187 || an Watsice eters cee re 0.92 | 0.20 | 0. 20
Overgrazed.......------- 6 - 78 2.10 || Around water and salt
Poorly stocked with for- {ike 205 It 0s a 08
APOr coy. eee ht eoee te 12 - 04 .31 || Corrals, ranches, and
Wellstocked with forage.| 28 - 08 - 62 bed grounds..........- - 03 - 02 - 02
Bunchgrass.ces.< 45 eee 15 001 1.50

TOU oon seeps 100.00 | 1.159 8. 96

a he es he ae ee x

Bul. 580, U. S. Dept. of Agriculture. PLATE I.

F-1! RRH

Fia. 1.—UNINJURED THRIFTY YELLOW-PINE REPRODUCTION FROM
4 INCHES TO 4 FEET TALL AND FROM 3 YEARS TO 14 YEARS
OLD.

F-—2 RRH

Fia. 2.—A YELLOW PINE 4% FEET TALL, WITH LATERALS
SEVERELY GRAZED BY SHEEP. LEADER OUT OF REACH OF
THIS CLASS OF STOCK.

Bul. 580, U. S. Dept. of Agriculture. ; PLATE Il.

F-3 RRH

Fia. 1.—TYPICAL SHEEP DAMAGE. SHOOTS EATEN AND NEEDLES PULLED.

F-—4 RRH

Fic. 2.—TYPICAL CATTLE DAMAGE. SHOOTS SEVERELY EATEN, BUT NEEDLES
LEFT LARGELY INTACT.

Bul. 580, U. S. Dept. of Agriculture. t PLATE I].

F-5 RRH

Fic. 1.—WESTERN YELLOW-PINE SAPLINGS, 4 FEET AND 6 FEET
TALL, SEVERELY INJURED BY CATTLE RUBBING.

F—6 RRH

Fic. 2.—A THRIFTY STAND OF REPRODUCTION IN A PASTURE AND A SCATTERED STAND
OF BADLY INJURED REPRODUCTION ON THE OUTSIDE.

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 15

According to this table the ratio between the severe damage caused
by cattle and that caused by sheep is approximately as 1 to 7.7
Striking variations from this ratio may be noted on the normally
grazed areas and on the bunchgrass range. Over these portions of
the type the damage caused by sheep is far out of proportion to that
caused by cattle. On the other hand, in flats, around camps, and
near water and salt licks the damage caused by each class of stock
is about the same. On areas representative of the rest of the yellow-
pine type the ratio of damage caused by cattle as compared with that
caused by sheep approximates the average ratio of 1 to 7.7. This
ratio is thought to be fair to the sheep. The proportion of reproduc-
tion severely damaged by both sheep and cattle is approximately 10
per cent. While this is not so high as the figure estimated for the
half of the yellow-pine type under observation, which, according to
Table I, amounts to 16.7 per cent, yet it is probably more nearly
representative of the yellow-pine type as a whole.

The foregoing data point to the conclusion that stock do not eat
yellow-pine reproduction through preference; that where the palatable
forage is sufficient, reproduction will not suffer seriously from graz-
ing; but that, on the other hand, where the palatable feed is not
sufficient for the class of stock using the range, yellow-pine repro-
duction is likely to be seriously damaged. |

METHODS OF HANDLING,

From the conclusions reached under the preceding heading it is
plain that the way stock are handled on the range has a most im-
portant bearing on the amount of damage that is done to reproduc-
tion. It has been pointed out, for example, that on bunchgrass
range, which, under the methods of handling stock on unfenced
range, at least is poorly suited to sheep grazing, this class of stock
is hkely to injure one-third of the stand of reproduction, as com-
pared with an injury of 10 per cent of the stand on range well suited
for sheep grazing and that the injury on an overgrazed range
varies from three times the amount of damage on a normally stocked
range to total destruction of the reproduction.

Further evidence as to the relation between the handling of stock
and the amount of damage to reproduction is brought out by a study
of the damage on areas where stock congregate.

Rubbing by cattle—Over the Forest, as a whole, the principal
damage caused by cattle is by rubbing. This damage is serious where
cattle are accustomed to congregate, principally at the edges of parks,
in alluvial flats, along drainage lines, and in the vicinity of watering
places, corrals, and salt licks.

16 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

Counts were made on 17 plots located in situations subject to this
kind of injury. Of 165 trees above 3 feet in height, and so of a size
subject to severe damage by rubbing, 36 were seriously injured. Fif-
teen were so badly rubbed that they would become worthless if the
rubbing continued, and 2 were moderately rubbed. Thus 22 per
cent of the trees subject to this class of damage had been severely in-
jured, and 9 per cent were being subjected to severe damage. In all,
a total of 31 per cent would in time be killed. This indicates a seri-
ous condition over certain parts of the yellow-pine type. The sites
on which such damage is most likely to occur support the best quality
of timber.

Damage along sheep driveways.—In the southern part of the Forest
the only places where pine reproduction seems to be injured are
around watering places, near the lower boundary of the yellow-pine
type where reproduction is scattered, and along the Mud Tank sheep
driveway. This driveway, with an average depth of 1 mile, extends
about 30 miles through the yellow-pine type. About 75,000 sheep
are driven over it each year. Besides its use as a driveway, the strip
is included in sheep and cattle allotments, and would be fairly well
grazed by stock throughout the season without the additional use by
transient stock. The first few bands find sufficient feed, but before
the total number have crossed the feed is so short that sheep are
forced to eat whatever growth is available, including a great deal of
yellow-pine reproduction. The damage caused in this way is so
severe that the boundaries of the driveway can readily be traced by
the line of severe damage. Conditions on this trail are typical of a
number of trails in Arizona and New Mexico. Good management re-
quires that this damage be reduced to the minimum.

Around watering places and ranches where stock are allowed to —
congregate it is very common to find a majority of the reproduction
badly deformed and stunted, as a result of browsing and rubbing.

EFFECTS OF GRAZING INJURIES UPON WESTERN YELLOW-PINE
REPRODUCTION.

ESTABLISHMENT OF REPRODUCTION.

INJURIOUS EFFECTS.

Abundant reproduction is often found in pastures, while just out-
side, with no apparent change in natural conditions, it is relatively
scarce. In all such cases observed the outside range had been subject
to severe grazing by all classes of stock for a number of years after
the pasture had been constructed. A comparison of the ages of
reproduction within and those adjacent to the pastures indicates that
the effect of severe grazing outside has been not only to prevent the
establishment of reproduction, but also to kill many of the trees
already established at the time the fences were built, This conclu-

EFFECT OF GRAZING ON WESTERN YELLOW PINE. Ay

sion is supported by detailed observations made on small fenced
areas on overgrazed ranges. One of these fenced areas, including
about 2 acres, is located near the Bottomless Pits, 6 miles southeast
of Flagstaff. At the time when the fence was constructed, in the
spring of 1912, all reproduction in the vicinity had been badly
injured by grazing for a number of years. During the three years
from 1912 to 1914 the trees inside the fence were entirely protected,
while those outside were subject to the same degree of grazing as
formerly. A record was kept of the reproduction located within the
inclosure and also of that on a check area of the same size near by.
Of 57 trees within the inclosure only 5 died during the three years,
whereas of the 45 trees on the check area 32 had died. Thus a loss
of 9 per cent occurred among the protected trees, as compared with a
loss of 71 per cent among the trees subject to continued grazing.
While this contrast is unusual, it indicates the possible effects of very
severe grazing.

Along most pasture fences which mark the line between good
reproduction and scanty reproduction are also areas which have
not been severely grazed. Where these begin the scanty reproduc-
tion ends.

It is asserted frequently that stock destroy a great many 1 and 2
year old seedlings. -While this doubtless is true, it is also a fact
that in inclosures entirely protected from grazing nearly all of the
reproduction that germinates is killed by adverse natural agencies.
Only during a series of favorable years does any considerable amount
of reproduction become established. Observations in pastures and
on sheep-excluded areas indicate that cattle and horses ordinarily
do very little damage to reproduction of the seedling class, even
though the larger trees suffer as a result of overgrazing. Though
sheep probably do more or less damage to young pines during the
first year, by far the greater number of such seedlings would die in
any event during the following winter or spring.

At 2 years of age a seedling may be said to be well enotigh
established to give it an even chance of survival against adverse
natural agencies. For this reason the influence of grazing injuries
after this period increases in importance. Table II indicates that
injury to trees of the seedling class or to trees between the ages of
2 years and 6 years is more serious than in the case of larger trees.
The fact that 21 per cent of trees of the seedling class are severely
damaged indicates that grazing seriously handicaps young trees in
becoming thoroughly established. Thus, though grazing is not a
prime factor in the establishment of a seedling during its first or

-second year, it may seriously interfere with its growth after that

age,

18 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

BENEFICIAL EFFECTS.

Probably the only important ways in which stock aid in the
establishment of reproduction are by helping to plant the seeds and
by reducing the fire menace.

Sheep aid very materially in covering the seeds of grasses, thus
helping to insure their germination... It is reasonable to suppose
that they aid in planting the seed of yellow pine. However, this aid
is not very important, because the important problem in establishing
a stand of reproduction is not to secure germination but to resist
freezing during the following winter and starvation during the
long dry period of the following spring.

Grazing, by preventing the accumulation of rank growth, plays
no small part in preventing severe ground fires.

HEIGHT GROWTH.

The extent to which the growth of young trees is retarded forms
the most obvious index of the severity of the effects of grazing
injuries. The effects upon height growth, however, indicate the
immediate results of injuries and may or may not be a guide to the
more permanent effects.

On Taylor’s ranch, 9 miles northwest of Flagstaff, is a pasture
in which the reproduction is abundant and free from injury. Just
outside of the pasture damage by grazing has been very severe.
Measurements of the height growth of saplings for the last five years
within and outside the pasture gave the results shown in Table VII.
Twenty trees form the basis for each height class.

TasBLleE VII.—Comparison of height growth of trees in and outside of pasture.

Rees of the av-
erage tree a

be PRO E oe ae oe ae
|
ing last 5 years.
Height
class.
In Sulside
pasture ee
Feet Feet. Feet
1 1.02 0.6
2 1.45 84 =
3 1. 97 97
4 2.53 1. 26

The growth outside of the pasture is scarcely more than 50 per
cent of that inside.

Measurements of 75 representative trees selected from three of the
inclosures fenced in connection with this project in 1912 revealed an

1 Journal of Agricultural Research, Department of Agriculture, Vol. III, No. 2, “ Natu-

ral Revegetation of Range Lands Based upon Growth Requirements and Life History of
the Vegetation,” by Arthur W. Sampson.

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 19

average growth of 0.7 foot for the three-year period, 1912-1914.
Measurements of a similar number of trees growing in the check
plots just outside these fenced areas showed an average height growth
of 0.2 foot for the three-year period.

The rate of growth of 46 badly grazed saplings at Fort Valley, 9
miles northwest of Flagstaff, and 59 uninjured saplings of the same
age in a pasture on Observatory Hill, just outside of Flagstaff, the
two sites being very similar, are given in Table VIII.

TABLE VIII.—Comparative growth of trees in pasture and on overgrazed range.

Average
he Number | Average | Average
Location. : annual
of trees. age. height. growth.
Years. Feet. Feet.
Vj) FOE SATUS eh A ey ee I a he he al ON ea Nae eg 59 Lee, 5. 2 0. 86

Oiererazedsran o Green see ere es nr ery cS a rec Ae LIA | 46 17.0 2.1 -12

The foregoing comparisons, which are believed to be representa-
tive, indicate that grazing injuries decrease the rate of growth of
young trees from one-half to two-thirds.

From the standpoint of the production of a crop of timber this
check in the growth of reproduction is not a serious matter, provided
the trees have a chance to outgrow the injuries before their vitality
is destroyed. The addition of 20 or 30 years to the period of rota-
tion is not in itself a vital consideration in the management of yel-
low pine. Retarded growth is a serlous matter, however, when it
is considered that grazing conditions are generally stable and that
where severe damage occurs the trees have no opportunity to out-
grow their injuries, but are slowly killed.

FORM OF TREE.

It is generally thought that the bole of a young tree that is severely
injured is likely to become crooked or forked. This belief appears
to have little basis in fact. The probable cause of crooked boles in
nearly all instances is that the trees have at some time been over-
topped or suppressed and in that condition have grown at an angle
toward the strongest light, later becoming dominant or codominant
and attempting to grow upright. Forked boles serious enough to be
objectionable are formed at a height above that affected by grazing.
Observations of a great many young trees recovering from severe
injuries revealed no deformities that promised to be at all prominent
when the trees mature. Nearly all grazing injuries occur at a height
of less than 44 feet, and the trees, when protected, very quickly de-
velop a leader which gradually outstrips all others. The laterals of

20 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

young trees made bushy by injuries contribute to the more rapid
growth of the main bole.

PERMANENT EFFECTS.

It is important to know what becomes of the seriously injured sap-
lings. If they recover and become normal trees, then the ultimate
effects of such damage are unimportant. But if a considerable por-
tion of them die, and if others remain dwarfs or develop into -de-~
formed trees, then the need for applying protective measures is ap-
parent. Owing to the slow growth of yellow pine, effects of grazing
injuries upon the later development of reproduction requires a good
many years to determine. Observations so far made, however, indi-
cate clearly the effects that may be expected where injured reproduc-
tion is protected and where it remains subjected to continued severe
grazing.

Observations of a great many trees formerly injured but later pro-
tected from grazing indicate conclusively that young injured pines
have remarkable recuperative powers. Even though they have been
eaten off repeatedly for as long as 10 years, a few years’ protection
will enable them to recover. Unless the injuries are particularly
severe, the subsequent growth is as rapid as in the case of younger
uninjured trees of the same height. Ordinarily, trees subjected to
repeated grazing develop many laterals capable of supporting vigor-
ous height growth at the first opportunity. When protection is
afforded to such trees, the ultimate effects of the injuries appear to be
simply the retardation of growth equivalent to the period of serious
injury plus 5 to 10 years required for the plant to regain its normal
vitality and to develop a well-defined leader. if, however, the young
trees are defoliated. as is characteristic of severe sheep injuries, recu-
peration is necessarily very slow.

The ability of injured trees to recuperate if protected is well illus-
trated at the Fort Valley Ranger Station pasture. Previous to three
years before the observations were made, the pasture had been greatly
overstocked with cattle during certain portions of the year, but since
that time it has been grazed only moderately. Reproduction is
abundant, but during the period of overgrazing the saplings were
severely damaged. Practically no damage was done in the three
years preceding the observations. A comparison of the last three
years’ growth of saplings in the pasture previously injured, but
showing no damage during this period, and of the growth during
the same period of injured saplings just outside the pasture where
severe grazing conditions prevailed, gave the results presented in
Table IX. Twenty trees in each of four height classes were ex-
amined.

EFFECT OF GRAZING ON WESTERN YELLOW PINE. 91

TABLE IX.—Comparative growth of protected and unprotected saplings.

Average growth é
during 3 years.

Height classes.
I Outside
a of
pastures. | nostures.
Feet. Feet. Feet. '
TL eR a ae hae ee 0.8 OFZ
PAE IS RSS Sere eae Hout a.
a a oe eh ae ee lee ait
AD yh ee 1.4 4
1 soe

| Average...... 1h

The results show that the growth of the protected saplings is more
than three times as rapid as that of the unprotected ones and indi-
cate a marked ability of young pines when protected to recover from
injuries. This conclusion is substantiated by the results of measure-
ments of trees previously injured within the fenced plots and of
trees outside subject to continued injury (p. 18). As stated in that
case, the ratio of growth between protected and unprotected trees
was as 7 to 2.

Even though protection against severe grazing may enable seri-
ously injured saplings to recover, such protection may not be advis-
able unless the loss of young trees on unprotected areas is excessive.
Reference to Table I shows that an average of only 0.9 per cent of
the total number of trees were found dead during the three years
covered by the study. While this loss probably represents the aver-
age mortality from grazing over the Forest as a whole, yet it does
not adequately express the seriousness of the losses in certain impor-
tant parts of the Forest. Areas exist where more than 50 per cent
of the total number of young pines have been killed. Such areas
include many sections of the bunchgrass type south and west of
Lake Mary, the edges of parks, bedgrounds, driveways, the vicinity
of headquarter ranches and water holes, and range areas that have
been overgrazed for a long period.

It is estimated from a comparison of the age and height of 265
trees that a yellow pine will ordinarily, if uninjured, reach a height
of 4.5 feet—above which it can withstand severe grazing injuries—
when 15 years old, but that if it is subject to repeated grazing injuries
it may require 35 years to reach this height. If it may be assumed
that under average conditions which prevail over the Forest it re-
quires 17 years for reproduction to reach a height of 4.5 feet, and
that, as shown in Table I, 0.9 per cent of all trees observed die an-
nually as a result of grazing injuries, it is safe to conclude that the
loss of trees during the period when they are subject to severe grazing
is approximately 15 per cent of the stand, or nearly as many as are

22 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

seriously damaged each year in the north half of the yellow-pine

type.

This poor showing of the injured trees would not be such a serious
matter were it not for the fact that even though an injured tree does
not die immediately, the needles, after repeated grazing, become
dwarfed and turn yellowish, and the whole plant becomes stunted.
If injury is continued the vitality is so weakened that a severe season
or an attack by natural enemies is very likely to kill the tree. It is
not uncommon to find saplings so impoverished by continued defolia-
tion that they can readily be pulled out of the ground by hand.

The destruction of young trees is not such a serious matter where
more reproduction has become established than is necessary to insure

a complete regeneration of the stand. But where the reproduction -

is more or less scattered. the loss of a considerable percentage of young
_ trees becomes decidedly important.

SUSCEPTIBILITY TO FUNGOUS AND INSECT ATTACKS.

It is commonly supposed that young trees injured by grazing are
more susceptible to attack by fungi and by insects than are unin-
jured trees. The extent to which this danger actually exists, and
under what circumstances. is a subject which deserves careful con-
sideration. :

Dr. W. H. Long, forest pathologist for Arizona and New Mexico.
who has made a special study of fungi attacking western yellow pine,
has expressed the opinion that—

The fungi and diseases Known at the present time to cause serious damage

to yellow pine in the Southwest normally do not enter trees through ordinary -

injuries caused by grazing. The spores of certain species of rust (Perider-

mium spp.) May enter through wounds in the living bark of pines, and it would —
be entirely possible for such spores to enter through wounds caused by grazing.
However, the total damage due to such a rust entering through grazing wounds —

and finally girdling the trunks of yellow pine is probably very small.

_ No heart-rotting fungus is known which issapt to start growth through grazing
wounds other than in cases where the bark“is removed or where the heartwood
and sapwood are exposed by breaking and twisting. Since injuries of this
character form a very small part of the total amount of damage. the danger of
fungus attack due to them does not require serious consideration. Injuries that
favor this kind of rot are caused by lightning, fire. deep blazes, ete.

It might be presumed that mistletoe (Razoumofskya spp.) would be liable
to attack grazing wounds, but a knowledge of the circumstances under which
this parasite attacks tissue leads to the conclusion that this danger is relatively
unimportant. for while it is true that mistletoe berries start growth where
new tissue is exposed, such as on the calloused edges of blazes, and while the
wounds to tender shoots such as are caused by grazing might afford favorable
conditions for germination of these berries, the conditions are probably no
more favorable than they are on the tips of uninjured stems.

:
d

|
q
|

EFFECT OF GRAZING ON WESTERN YELLOW PINE. Ze

Certain needle diseases exclusive of rusts are believed to attack dwarfed
and unhealthy needles more readily than vigorous needles. Since the effect of
moderate grazing wounds is to stimulate the growth of plant tissue, these needle
diseases are not apt to secure a foothold more readily because of them. How-
ever, when persistent and severe wounds reduce the vitality of the trees until
the needles reflect the weakened condition, certain needle diseases are apt to
find favorable hosts. The total amount of damage caused by needle diseases or
the increase in this character of damage which may be attributed to grazing
is not known, although it is believed to be relatively unimportant.

During the last two years studies of the extent of damage by in-
sects on the Forests of Arizona and New Mexico have been made a
special study by A. J. Jaenicke, forest assistant in charge of insect
studies. Mr. Jaenicke has expressed the opinion that grazing in-
juries are not responsible for a serious amount of insect damage to
western yellow-pine reproduction. He states that—

Western yellow-pine reproduction in Arizona and New Mexico suffers particu-
larly from the following insects: ;

1. Tip moths of the genus Retinia. These kill the terminal shoots of the
reproduction, causing it finally to assume a bushy form, but rarely kill it.

2. Engraver beetles of the genus Ips, particularly Ips confusus Leo. These
insects are responsible for the death of considerable reproduction in various
parts of the district, particularly on cutting areas.

3. Small scolytid beetles, which work in the thinner bark of the young trees
and occasionally cause their death.

4. Flat-headed borer of the family of Buprestide. These were found doing
serious damage on only one Forest in the district.

During the past field season careful attention was given the relation of graz-_
ing injuries to attacks by the above-named insects. It was found that only in
localities where serious overgrazing has taken place for a number of years is
there ever any material increase in insect damage.

The tip moth kills the terminal shoots of healthy and unhealthy reproduction
with equal ease. Grazing injuries, therefore, are an unimportant factor in
infestations by this insect.

Wherever the vitality and health of reproduction has been seriously lowered
by overgrazing or any other cause, particularly on areas recently cut over, en-
graver beetles may become responsible for the rapid death of the injured seed-
lings. The same is true of attacks by various small scolytids. Both the en-
graver beetles and small scolytids breed in slash, and so it is on the areas where
there has been recent cutting that reproduction injured by grazing suffers most
from these insects. It is not believed that attacks by fiat-headed -borers are
increased by grazing injuries.

The minor injuries caused by regulated grazing, therefore, are of little
importance in augmenting insect attack. Even serious injuries are rarely
responsible for insect damage of any consequence, except on recently cut-
over areas.

SUMMARY.

(1) Of 8,945 trees of a size subject to grazing, observed over a
period of three years, 1,493, or 16.7 per cent, were severely damaged
each year and 1,442, or 16.1 per cent, were moderately damaged.

24 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

(2) The most injured are the seedlings, 21 per cent of which are
seriously damaged. The damage gradually decreases with an increase
in the size of the trees. Trees above 4.5 feet in height are free from

severe injuries from browsing, but those between 3 feet and 6 feet -

in height are likely to be rubbed severely.

(3) The greatest amount of damage occurs during the latter half
of June and the first part of July, or when the effects of the spring
dry period are most pronounced. The least damage occurs during
the first few weeks of the growing period, or before June 15. A
very considerable amount of damage is done during the main grow-
ing season and during the fall drying period.

(4) Under normal conditions of grazing cattle and horses, and
incidentally burros, do an inconsiderable amount of damage to
reproduction. Sheep under the same conditions may be responsible
for severe injury to 11 per cent of the total stand.

On overgrazed areas all classes of stock are apt to damage small
trees severely. Cattle and horses may damage about 10 per cent of
all reproduction. Where sheep are grazed along with them, how-
ever, at least 35 per cent of the total stand may be severely damaged.

Cattle and sheep are responsible for practically all of the grazing
damage to yellow pine on the Coconino forest. Ordinarily sheep
cause about:seven and a half times as much damage as cattle.

(5) The density of forage does not affect the amount of damage
that may be caused on a given area.

(6) The suitability of the forage to the class of stock using a
range has an important influence upon the amount of damage to
timber reproduction. Because of the suitability of the pure bunch-
grass type to sheep grazing, the reproduction over approximately
one-third of the bunchgrass type on the Coconino Forest, or over
130,000 acres, is being seriously injured. .

(7) The amount of palatable feed available during the grazing
season, and especially during June and July, has an important bear-
ing upon the amount of damage that grazing will cause to reproduc-
tion. During a favorable year the damage may be 18 per cent less
than during a subnormal year.

(8) The manner in which stock is handled has much to do with
the severity of grazing damage. Cattle are likely to injure 22 per
cent of the trees between 3 feet and 6 feet in height that grow on
areas where they are accustomed to congregate. Sheep severely
injure reproduction along driveways and on bed grounds. |

(9) Grazing is believed to have a largely neutral effect upon the
germination and early establishment of reproduction, but to have an
important effect in reducing the destruction of reproduction by fire.

— ee ee

i ,
a a ee

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—f EFFECT OF GRAZING ON WESTERN YELLOW PINE. 25

(10) The effect of grazing upon the height growth of reproduc-
- tion is marked. Severely injured trees grow only from one-half to
one-third as fast as uninjured trees.

(11) Grazing injuries are not responsible for the common deform1-
ties of mature trees.

(12) The permanent effects of grazing injuries upon the develop-
ment of the trees damaged are not serious, provided the damaged
trees have a chance to recuperate. If grazing is unrestricted, about
15 per cent of the total stand is likely to be killed during the period
required for reproduction to become established.

(18) Reproduction that has been impoverished greatly by grazing
is more likely to be attacked by some fungi and insects than unin-
jured and vigorous reproduction. However, the ordinary grazing
injuries are not believed to increase seriously the danger of such
attacks.

APPLICATION OF RESULTS TO RANGE MANAGEMENT IN THE
SOUTHWEST.

The conclusions arrived at in this study are believed to be appli-
cable over the entire yellow-pine type of the Southwest. Since for-
age composition, class of stock using a range, intensity of grazing,
and methods of handling stock vary on different Forests, it is not
advisable to attempt to prescribe specific suggestions for certain areas,
but rather to prescribe definite remedies for certain conditions.

Under present conditions all reproduction should be protected
against severe damage by grazing. Where immediate cutting of the
mature stand is contemplated, the reason for protection is obvious,
since the prime purpose should be to insure a stand of reproduction.
Where reproduction on an area not to be cut over in the near future

is being injured, protection is needed to assist nature in maintaining
a forest cover. Reproduction generally occurs naturally in openings
made by the death of mature trees. Unless this reproduction is pro-
tected, the gaps will tend to increase and the regeneration of the
forest be made constantly more difficult. Moreover, under the most
favorable conditions it is only through the combination of a good
seed year with two or more good growing years following that any
considerable amount of reproduction becomes established. Such a
combination is so rare that it is not safe to depend upon it.

The grazing of stock on National Forests must be so regulated that
the number of stock shall not decrease, but, if possible, shall increase.
Under proper grazing management reproduction does not suffer an
unwarranted amount of damage; in fact, the advantages of conserva-

tive grazing in reducing the loss of reproduction by fire probably
offset the injury from stock. The application of conservative graz-
ing throughout the western yellow-pine type, then, is the basis for
the protective recommendations which follow.

26 BULLETIN 580, U. S. DEPARTMENT OF AGRICULTURE.

Since overgrazing is the cause of the most severe grazing damage.
it should be avoided by all means. An overgrazed condition may
exist even though the general appearance of the range does not
indicate it, as, for instance, on a bunchgrass range allotted to sheep.
The principal grasses may be largely uneaten, while sheep feed, con-
sisting of palatable weeds and grasses, and, too often, of yellow-pine
reproduction, may be largely destroyed. Overgrazing may result
from allotting too many stock to a range, or from poor distribution
of a proper number of stock due to lack of sufficient well-located
watering places, poor salting arrangements, or, in the case of sheep,
to poor herding. In any case the cause should be determined and
removed. ,

Sheep should not be depended upon primarily to utilize the bunch-
grass range. This type should be utilized chiefly by cattle and
horses, held in pastures if possible. On this type, wherever the
bunchgrass species occur in nearly pure stand during early spring,
sheep should be run in May and the fore part of June while the
grasses are tender and most palatable. Where the succulent weeds
and browse species occur In mixture with the bunchgrasses, sheep
may be grazed season long together with cattle and horses.

Sheep should be excluded from cutting areas on which they are
causing severe damage until reproduction is well established. usually
for a period of from 15 to 20 years. They should be excluded also for
a period of from two to five years from cutting areas where the stand
of reproduction is deficient but has been supplemented by an abun-
dant crop of seedlings which, having survived the first winter and
spring, promise to become established, even though injury to the
reproduction already established is not severe.

All stock should be worked and handled as little as possible around
watering places, salting grounds, and headquarter ranches. Sheep
should be bedded as seldom as possible on any one bed ground, prefer-
ably for one night only.

It is very difficult to avoid the damage caused by cattle rubbing.
In exceptional cases, where complete reproduction is desired within
a short period, as on a cutting area, flats might be fenced and cattle
excluded from them during the fly season. However, if overgrazing
and excessive handling are avoided, it is believed that the damage
caused by cattle will not be excessive. .

One of the most serious menaces to reproduction as well as to
forage occurs on stock driveways. Even at best, an excessive number
of stock must use these strips of range and injury can not be avoided.
However, all practicable means should be used to conserve the stand
of forage and by furnishing sufficient feed for the stock using the -
driveways to reduce the injury to reproduction to a minimum. In
order to accomplish this, it is recommended that driveways be used

+

EFFECT OF GRAZING ON WESTERN YELLOW PINE. oi

as little. as possible; that, wherever practicable, they be closed to
grazing except by passing stock; that a sufficient number be estab-
lished to prevent overgrazing; and that water be furnished in abun-
dance at proper intervals along them.

Every effort should be made to protect yellow-pine reproduction in
the “twilight” zone between the yellow-pine type and the juniper-
pinion type. Conditions here are unusually unfavorable for yellow-
pine reproduction, and such seedlings as become established should by
all means be protected against grazing.

Stock, especially sheep, should not be held in the yellow-pine type
during the winter, when they would be forced to eat reproduction.

Advantage should be taken of grazing as a means of fire control
by securing proper utilization of all range where at present an
accumulation of inflammable unused feed occurs each year. Such
areas are common on the bunchgrass type and on other types of
range far removed from water or located on rough ridges and slopes.

PUBLICATIONS OF THE UNITED STATES DEPARTMENT OF
AGRICULTURE RELATING TO THE SUBJECT OF THIS
BULLETIN.

PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BY DEPARTMENT OF
AGRICULTURE.

That Improvement by Deferred and Rotation Grazing. (Department Bulletin
No. 34.)

Native Pasture Grasses of the United States. (Department Bulletin No. 201.)

Carrying Capacity of Grazing Ranges in Southern Arizona. (Department
Bulletin No, 367.)

Improvement and Management of Native Pastures in the West. (Separate
No. 678 from Yearbook, 1915.)

PUBLICATIONS FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GUVERN-
MENT PRINTING OFFICE, WASHINGTON, D. C.

The Reseeding of Depleted Grazing Lands to Cultivate Forage Plants.
(Department Bulletin No. 4.) Price, 10 cents.

Grazing Industry of the Bluegrass Region. (Department Bulletin No. 397.)
Price, 5 cents.

The Utilization of Logged-off Land for Pasture in Western Oregon and West-
ern Washington. (Farmers’ Bulletin No. 462.) Price, 5 cents.

Stock-watering Places on Western Grazing Lands. (Farmers’ Bulletin No.
592.) Price, 5 cents.

Grazing and Floods: A Study of Conditions in Manti National Forest, Utah.
(Forestry Bulletin No. 91.) Price, 10 cents.

v

WASHINGTON : GOVERNMENT PRINTING OFFICE ; 1917

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