Distribution of active ectomycorrhizal short roots in forest soils of the inland Northwest : effects of site and disturbance

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oe Distribution of Active
st Ectomycorrhizal aq Oe
pesearen Paper Short Roots in . |

Forest Soils of the =
Inland Northwest:
Effects of Site and
Disturbance

Alan E. Harvey
Martin F. Jurgensen
Michael J. Larsen
Joyce A. Schlieter

THE AUTHORS

ALAN E. HARVEY is a supervisory plant pathologist, Inter-
mountain Research Station, Forest Service, U.S. Depart-
ment of Agriculture, Ogden, UT, located in Moscow, ID.

JOYCE A. SCHLIETER is a statistician for the Intermoun-
tain Research Station, located in Missoula, MT.

MARTIN F. JURGENSEN is a professor of forest soils,
School of Forestry and Wood Products, Michigan
Technological University, Houghton.

MICHAEL J. LARSEN is a principal mycologist, Center for
Forest Mycology Research, Forest Products Laboratory,
Forest Service, U.S. Department of Agriculture, Madison,
WI.

RESEARCH SUMMARY

An examination of the distribution of active ectomy-
corrhizal short roots among soil components of eight
old-growth stands representative of the important timber
growing lands of the Inland Northwest revealed a dispro-
portionate concentration in surface organic materials. A
similar concentration in the forest floor was present in six
second-growth stands of various ages from the subalpine
fir and Douglas-fir habitat series of western Montana. Ex-
ceptions to this trend were noted only in an extremely dry,
old-growth, ponderosa pine stand and a highly disturbed
site regenerating to a pure stand of young western larch.
Even in these exceptional cases, ectomycorrhizal activities
were concentrated in shallow mineral horizons relatively
rich in organic materials. There was considerable variation
in the quantity of soil organic materials on the 14 sites. In
general, harsh and disturbed sites tended to have the
least. The relative proportions of soil organic components
(litter, humus, decayed wood) changed significantly both
within and between sites. Distribution of active ectomycor-
rhizal short roots among those components during the
early summer months was also significantly different, both
within and between sites. Approximately 75 percent of ac-
tive ectomycorrhizal short roots occurred in organic
materials that represented only the first 4 cm of the soil
depth. This disproportionate role of surface organic
materials in supporting critical symbiotic processes em-
phasizes the need to carefully manage this important soil
resource in forested ecosystems throughout the Inland
West.

Intermountain Research Station
324 25th Street
Ogden, UT 84401

Distribution of Active
Ectomycorrhizal Short Roots
in Forest Soils of the Inland
Northwest: Effects of Site
and Disturbance

Alan E. Harvey
Martin F. Jurgensen
Michael J. Larsen
Joyce A. Schlieter

INTRODUCTION

Recognition of the importance of symbiotic, ectomycor-
rhizal associations to survival and growth of forest trees
(Vozzo and Hacskaylo 1971) has provided impetus for ex-
tensive research on conditions required to maintain this
critical activity in forest soils. Soil conditions are of par-
ticular importance in altering the ability of ectomycor-
rhizal fungi and their hosts to start the association
(Bjorkman 1970). Any forestry operation likely to alter soil
conditions in a substantial way may change, perhaps
reduce, the ability of soil to support ectomycorrhizal asso-
ciations and attendant host growth. Because the fungi in-
volved in ectomycorrhizal associations are obligatorily
dependent on their host trees (Hacskaylo 1973), popula-
tions are reduced after harvest. Researchers have studied
disturbance-caused changes of mycorrhizal populations
(Danielson 1984) and reductions of mycorrhizal inoculum
potential (Pilz and Perry 1984). Even in the relatively
good soils of the Pacific Northwest, failure to initiate an
adequate level of ectomycorrhizal activity can limit sur-
vival and performance of young conifers (Christy and
others 1982; Trappe and Strand 1969).

Extensive examination of the distribution of forest tree
feeder roots (Herman 1977) and ectomycorrhizal short
roots (Fogel and Hunt 1979; Harvey and others in press;
Meyer 1973; Mikola and others 1966; Vogt and others
1981) have shown that (1) they tend to occur at a shallow
depth in the soil, and (2) they are usually associated with
organic soil horizons, particularly in older stands (Fogel
and Hunt 1979; Harvey and others 1976; Harvey and
others in press; Vogt and others 1981).

Frequently the association of ectomycorrhizal activities
with soil organic matter has specifically been with decayed
wood (Harvey and others 1976, in press; McFee and Stone
1966; McMinn 1963; Trappe 1965). Decaying logs and soil
wood are recognized as a unique ecosystem in North-
western forests (Harvey and others in press; Maser and
Trappe 1984) that represent an important source of
nutrients and moisture (Barr 1980; Harvey and others
1978; Larsen and others 1980; Place 1950). Harvey and

coworkers (1978, 1979) have shown that the distribution of
ectomycorrhizal activities in decayed soil wood, as com-
pared to the forest floor and mineral soil, changed with
both season and site. Decayed wood supported relatively
high mycorrhizal activity during dry seasons and on dry
sites. The levels of decayed wood in the Inland Northwest
may be affected by the trend toward greater use of har-
vesting residue, and this could have an impact on future
site productivity (Jurgensen and others 1977).

The strong participation of the forest floor and shallow
mineral horizons in nutrient cycling of many Inland North-
west forest ecosystems has led to concern regarding man-
agement (disturbance) of these important resources
throughout the Inland West (Harvey and others in press).
The purpose of this study was to investigate the involve-
ment of surface soil components in ectomycorrhizal pro-
cesses over (1) a wide range of mature ecosystems (habitat
types) distributed throughout the Inland Northwest and (2)
a range of site disturbance types within a local
geographical area on similar habitat types.

STUDY SITES

A summary of site characteristics is provided in table 1.

Sample Sites, Old-Growth

Eight old-growth sites were chosen to be representative
of a wide range of climatic and geographic conditions of
the Inland Northwest, with emphasis on habitat series
(Pfister and others 1977) most commonly associated with
commercial forests. These sites had no history of human
disturbance.

Site 1 (WH-M) is a western hemlock climax (habitat
series) in northwestern Montana on the Coram Experi-
mental Forest. It has a northwest aspect, a slope averag-
ing 15 percent, and an elevation of approximately 1,000 m
above mean sea level. The primary ectomycorrhizal host
on this site is 250-year-old western hemlock (T'suga hetero-
phylla (Raf.] Sarg.). Western larch (Larix occidentalis
Nutt.) and western redcedar (Thuja plicata Donn.), the
latter essentially a nonhost, also occur occasionally.

Table 1—A summary of site characteristics

Site
number and Slope Habitat Dominant
acronym Location Aspect percent series’ tree Age Treatment?
Years

1(WH-M)°* Western NW 15 Western Western 250 Undisturbed
Montana hemlock hemlock

2(SAF-M) Western E 55 Subalpine fir Subalpine fir 250 Undisturbed
Montana

3(DF-M) Western S 27 Douglas-fir Douglas-fir 250 Undisturbed
Montana

4(WH-1) Northern E 5-15 Western Western 250 Undisturbed
Idaho hemlock hemlock

5(WWP-1) Northern NW 0-10 Western Western 250 Undisturbed
Idaho hemlock white pine

6(GF-I) Northern W 30-40 Grand fir Western 250 Undisturbed
Idaho hemlock

7(SAF-WY) Northwestern N 15-25 Subalpine fir Lodgepole pine 165 Undisturbed
Wyoming

8(PP-W) Eastern W 15-35 Ponderosa pine Ponderosa pine 200 Undisturbed
Washington

9(MIX-i) Western E 40 Subalpine fir Douglas-fir 80 WF
Montana

10(LPP-i) Western W 5 Douglas-fir Lodgepole pine 50 WF
Montana

11(WL-y) Western N 10-20 Subalpine fir Western 15-25 CC-BB
Montana larch

12(DF-i) Western W 5-15 Douglas-fir Douglas-fir 60-120 I-SC
Montana

13(PP-i) Western SW 50-55 Douglas-fir Ponderosa pine 80-100 PC-UB
Montana

14(LPP-y) Western W 5 Subalpine fir Lodgepole pine 15 WF
Montana

‘Habitat series (Pfister and others 1977).

2Undisturbed = no history of human disturbance, WF = wildfire, CC-BB = clearcut-broadcast burn, I-SC = intermittent

selective cut, PC-UB = partial cut with underburn.

$Beginning letters denote primary ectomycorrhizal host, last letters indicate State (caps) and age (lower case); i =

intermediate age, y = young age.

Site 2 (SAF-WY) is a subalpine fir climax in northwest-
ern Montana on the Coram Experimental Forest. It has an
east aspect, a slope averaging 55 percent, and an elevation
of approximately 1,900 m. The primary ectomycorrhizal
hosts are 250-year-old Douglas-fir (Pseudotsuga menziesir
[Mirb.] Franco), western larch, subalpine fir (Abies lasio-
carpa [Hook.] Nutt.), and Engelmann spruce (Picea engel-
mannii Parry). Lodgepole pine (Pinus contorta Doug}.),
western hemlock, and western white pine (Pinus monticola
Dougl.) occur occasionally.

Site 3 (DF-M) is a Douglas-fir climax in northwestern
Montana on the Coram Experimental Forest. It has a
south aspect, a slope averaging 27 percent, and an eleva-
tion of approximately 1,150 m. The primary ectomycor-
rhizal host is 250-year-old Douglas-fir. Western larch occur
infrequently on this site.

Site 4 (WH-I) is a western hemlock climax in northern
Idaho near the Priest River Experimental Forest. It has
an east aspect, a slope averaging 10 percent, and an eleva-

tion of approximately 1,500 m. The primary ectomycor-
rhizal host is 250-year-old western hemlock. Western

redcedar occur frequently on this site.

Site 5 (WWP-I) is a western hemlock climax in northern
Idaho on the Deception Creek Experimental Forest. It has
a northwest aspect, a slope averaging 5 percent, and an
elevation of approximately 1,000 m. The primary ecto-
mycorrhizal host is 250-year-old western white pine.
Western hemlock, Douglas-fir, and grand fir (Abies
grandis [Dougl.] Lindl.) occur occasionally.

Site 6 (GF-I) is a grand fir climax in northern Idaho on
the Priest River Experimental Forest. It has a west
aspect, a slope averaging 35 percent, and an elevation of
approximately 1,200 m. The primary ectomycorrhizal hosts
are 250-year-old western hemlock and Douglas-fir. West-
ern white pine, grand fir, and western redcedar occur
occasionally.

Site 7 (SAF-W) is a subalpine fir climax in northwestern
Wyoming near Union Pass. It has a north aspect, a slope

averaging 20 percent, and an elevation of approximately
2,800 m. The primary ectomycorrhizal host is 165-year-old
lodgepole pine. Subalpine fir and Engelmann spruce occur
occasionally.

Site 8 (PP-W) is a ponderosa pine climax located in
northeastern Washington near Spokane. It has a west
aspect, a slope averaging 25 percent, and an elevation of
approximately 700 m. The only ectomycorrhizal host is
200-year-old ponderosa pine (Pinus ponderosa Laws.).

Sample Sites, Second-Growth

Three of the six disturbed sites were chosen to provide a
uniform habitat series (subalpine fir climax type) from a
localized geographic area representative of a common com-
mercial forest in the Inland Northwest. The other three
were chosen to provide a comparison with drier conditions
(Douglas-fir climax type) from the same geographic area
(western Montana). To represent a variety of harvesting
and natural stand situations frequently found in the Inland
Northwest, treatments (disturbance type) were chosen to
provide a variation in time since disturbance and in
species dominance.

Site 9 (MIX-i) (i = intermediate-aged) is a subalpine fir
climax type in western Montana adjacent to the Hungry
Horse Reservoir. It has an east aspect, a slope averaging
40 percent, and an elevation of approximately 1,500 m.
This is an old wildfire-impacted site that now supports a
mixed-species, pole-sized, 80-year-old stand of primarily
Douglas-fir. Subalpine fir is also abundant. Western white
pine, grand fir, and birch (Betula papyrifera Marsh) occur
occasionally.

Site 10 (LPP-i) is a Douglas-fir climax type in western
Montana near Martin City. It has a west aspect, a slope
averaging 5 percent, and an elevation of approximately
1,200 m. This is an unharvested site with the previous
stand terminated by wildfire. The present stand is
50 years old. The primary ectomycorrhizal host is lodge-
pole pine. Douglas-fir occurs occasionally.

Site 11 (WL-y) (y = young-aged) is a subalpine fir climax
type in western Montana adjacent to the Coram Experi-
mental Forest. It has a north aspect, a slope averaging
15 percent, and an elevation of approximately 1,300 m.
This is a harvested site (clearcut and broadcast burned)
with a planted, 15-year-old stand of western larch. The
primary ectomycorrhizal species is western larch. No other
hosts occurred within the plot.

Site 12 (DF-i) is a Douglas-fir climax type in western
Montana on the University of Montana’s Lubrecht Ex-
perimental Forest. It has a west aspect, a slope averaging
10 percent, and an elevation of approximately 1,200 m.

_ The site has an extensive harvesting history (intermittent
selective cutting) and now has a mixed-size, intermediate-
aged stand (60 to 120 years old) of nearly pure Douglas-
fir. The primary ectomycorrhizal species is Douglas-fir. No
other host occurred within the sampled area.

Site 13 (PP-i) is a Douglas-fir climax type in western
Montana adjacent to the Hungry Horse Reservoir. It has a
southwest aspect, a slope averaging 50 percent, and an
elevation of approximately 1,300 m. This harvested site

(partial cut with an underburn) now has a residual stand
of ponderosa pine, 80 to 100 years old. The primary ec-
tomycorrhizal host is ponderosa pine. An occasional, small
Douglas-fir occurred within the sampled area.

Site 14 (LPP-y) is a subalpine fir climax type in western
Montana near the town of Hungry Horse. It has a west
aspect, a slope averaging 5 percent, and an elevation of
approximately 1,200 m. The previous stand originated as a
result of wildfire in 1929. The stand was harvested by
clearcut (with an occasional seed tree). At the time of sam-
pling there was a 15-year-old regenerating stand of lodge-
pole pine. Lodgepole pine was the only ectomycorrhizal
host, with no other hosts in the sampled area.

Climate

Thirteen of these sites are representative of the typical
Inland Northwestern climate characterized by cold wet
winters and warm dry summers. The weather on these
sites is generated primarily by Pacific frontal systems.
Site 7 is located on the east side of the Continental Divide
so is more often impacted by continental weather, in-
cluding frequent summer rainfall generated by thunder-
storm activity.

STUDY METHODS

Individual soil samples consisted of 10- by 38-cm soil
cores (Jurgensen and others 1977) taken randomly, five
from around each plot center, 10 plot centers scattered
evenly (approximately 30-m spacing) over 1 ha of uniform
conditions on each of the 14 study sites. Conditions evalu-
ated for uniformity included slope, aspect, soils, distur-
bance, stocking, and understory vegetation. Samples were
taken during late spring and early summer over several
years (1978 to 1982) to obtain maximum ectomycorrhizal
activity for each site (Harvey and others 1978). Each soil
core was subdivided in the field into the following com-
ponents or horizons: litter (O, horizon); humus (QO, hori-
zon); brown cubicle decayed soil wood, also referred to as
the O, horizon (Harvey and others 1979); surface mineral
soil (the first 5 cm); and the remaining mineral soil to a
depth of 30 cm. Each fraction was hand-separated and
placed in a plastic bag immediately after collection. Vol-
ume and depth occupied by each fraction was determined
by measuring its depth in the undisturbed core.

In the laboratory, each soil fraction was shaken for ap-
proximately 5 minutes in a standard 2-mm soil sieve.
Decayed wood, humus, or mineral aggregates were gently
crumbed before sieving. Soil and root material greater
than 2 mm were thoroughly washed in running water and
examined microscopically for ectomycorrhizal short roots.

Active ectomycorrhizal root tips were counted with the
aid of a dissecting microscope (10-50 x). Each active tip
was counted, even though in many cases it was part of a
complex structure. No attempt was made to count or dif-
ferentiate between root tips that were inactive and those
that were dead. The criteria used for identifying ‘‘active”’
ectomycorrhizal root tips have been described (Harvey and
others 1976).

RESULTS

The total quantity of soil organic materials varied sig-
nificantly between sites (table 2). In general, high-produc-
tivity, old-growth ecosystems had high organic reserves.
Low-productivity, old-growth and second-growth eco-
systems, particularly harsh ones, had low organic reserves.
The percentage distribution of organic fractions (litter,
humus, decayed wood) making up the organic mantle also
varied significantly. There were usually substantial
deposits of decayed wood in the forest floor on most sites.

The total number of active ectomycorrhizal short root
tips also varied significantly between sites (table 3). As
with soil organic matter, the high-productivity, old-growth
stands had high numbers of active short root tips, and the
low-productivity, disturbed second-growth stands, par-
ticularly harsh ones, had low numbers of active tips. There
were many significant differences in percentage distribu-
tion of active ectomycorrhizal short root tips among the
soil fractions, both within and between sites. The most
striking general trends were reduced short root tips in the
deep mineral fraction and high numbers in the organic
fractions, particularly humus and decayed wood. Only two
sites had the highest number of active short root tips in a
mineral fraction: old-growth ponderosa pine (site 8) and a
15-year-old stand of western larch (site 11). In both cases
it was the shallow (first 5 cm) mineral horizon that con-
tained most of the active tips (table 3).

Soil wood as an ectomycorrhizal substratum is particu-
larly interesting. A number of factors indicate that the
association between decayed wood and mycorrhizal ac-
tivities may be of importance to host trees. Todd (1979)

reports ectomycorrhizal fungi on Douglas-fir may be able
to break down certain organic materials directly, a means
for closed-cycle nutrient turnover. Selective concentration
of mycorrhizal inoculum in soil wood has been reported
(Kropp and Trappe 1982; Trappe 1965, 1962). Roots of
nonconiferous vegetation are seldom observed in soil wood
(Berntsen 1955; Harvey and others in press; Rowe 1955).
The apparent ability of mycorrhizal fungi to detoxify soil
phenolics (Zak 1971) may contribute to the ability of
conifer roots to thrive in decayed wood on and in forest
soils. Thus, soil wood provides a relatively competition-free
site for the growth of conifer feeder roots. In turn, this
provides a decided advantage to the conifers because they
are able to use this high-moisture material during drought
(Harvey and others 1978) and on dry sites (Harvey and
others 1979). Also, it is now apparent that some higher
plants have hydrotropic roots (Jaffe and others 1985).
Thus, the moisture contained in soil wood may be the
primary reason for the concentration of conifer roots
therein.

Although the number of samples taken on most of the
sites was not sufficient to show significant differences in
distribution of ectomycorrhizal activities among organic
matter classes (table 4), the trend toward low numbers of
short roots in the highest organic content class (> 45 per-
cent of the core) was striking. This was particularly evi-
dent in moderate- to low-productivity, old-growth stands
and in second-growth sites. This trend is likely related to
soil moisture availability. Periodic rainfall on these sites
may not be enough to wet deep organic matter deposits
sufficiently to maintain them above the permanent wilting
point, particularly during the normally dry growing

Table 2—Quantity and distribution of soil organic components from plots sampled

Distribution of organic matter

Site in forest floor
number and Total organic matter in
acronym soil core (x L/core) Litter Humus Decayed wood.
Liters) | a tesa iaees Percent ----------

Old-growth'

1(WH-M) 70.82" S123 38° Bile
2(SAF-M) fila FE 45° 48°
4(WH-l) 54% 122 30° 58°
3(DF-M) .50* 6* 58° 35°
5(WWP-1) 43% 30° 19° 51°
8(PP-W) .38* 31° 68° 2G
6(GF-I) 32 253 61° 14?
7(SAF-WY) mlog 34° 522 14°
Second-growth

10(LPP-i) .42* 19° 58° 23
9(MIX-i) .39” 19° 46° 36%
11(WL-y) 32% 2s 41° 39°
12(DF-i) .26* 22? 42° 35%
13(PP-i) al2z 27° 58° 15?
14(LPP-y) ales 467 40 14°

1See table 1 for explanation of abbreviations.

2Average includes all organic matter-containing strata. Differing letters indicate significant dif-
ferences down column (w-z), a = 0.05, ANOVA, Duncan’s multiple range test.

3Differing letters (a-c) indicate significant differences (2 = 0.05) within treatments, between
individual strata, detected by two-sided t-test on actual volume measurements.

Table 3—Number and distribution of active ectomycorrhizal root tips in soil strata;
all samples taken during June to July peak activity period (Harvey and

others 1978)

Percent distribution of

Number ectomycorrhizal root tips in
Site ectomycorrhizal
number and roots (x) all Decayed Shallow Deep
acronym strata combined Litter Humus wood mineral mineral
No./liter = -------------- Percent --------------

Old-growth'
5(WWP-1) 21:20" 34108° 572 26°” 6: 19
4(WH-I) 95" Gade "672 16° 8° 3°
1(WH-M) 93” 6° 32° 51°° 1103 12
7(SAF-WY) 65* 6° 37° 28° 28° 12
8(PP-W) 60* ile BF Tee 74° 10°
2(SAF-M) 21’ 0 74? 19b 6° AP
6(GF-I) 14’ 26° 113? 31? 20° 10°
3(DF-M) 11Y 14? 30° 3 213 2
Second-growth
9(MIX-i) 49” Ge 47° gba 10° 28
10(LPP-i) 41* 102° 15? yao oe 2
13(PP-i) 29* 0 25? 61° vial 2
14(LPP-y) 14Y 0 36° 40° 2c 3°
11(WL-y) 7? 1? 232 fi 57° ala i
12(DF-i) 4? 20° 0 46° 33? Ae

1See table 1 for explanation of abbreviations.

2Differing letters indicate significant differences (a = 0.05) between sites, down column (w-2z),
and within strata and site, across (a-e), based on two-sided t-test of numbers of short root

tips/liter.

3Ectomycorrhizal distribution in individual strata shown as a percentage of the total to

facilitate between site comparisons.

seasons. Also, many sites with limited organic matter pro-
duction have few substantial deposits accumulated, and
those that do are likely to be disrupted by harvesting-
related disturbances and natural wildfires. These results
appear to support a management recommendation to
maintain 2.4-3.6 tons/ha (10-15 tons/acre) (based on the 31
to 45 percent volume class) of woody residues to maintain
soil organic reserves (Harvey and others 1981).

The concentration of ectomycorrhizal short root tips in
shallow organic horizons (table 5) makes them extremely
vulnerable to external perturbation. Even moderate
physical disturbance or heating is likely to produce high
mortality of short roots from nearby trees. Also, because
it is now apparent that moisture laden with air pollutants
(acid rain) can inhibit ectomycorrhizal activities (Reich and
others 1985), their concentration in shallow horizons of In-
land West forests may make them extremely vulnerable to
air pollution damage. A shallow distribution of feeder
roots from conifers has been noted (Fogel and Hunt 1979;
Maser and Trappe 1984; Mikola and others 1966; Vogt and
others 1981).

In the two instances reported here where the most ecto-
mycorrhizal short root tips were not concentrated in the
organic horizons (table 5, sites 8—old-growth ponderosa
pine—and 11—second-growth western larch), they were
concentrated in the topmost mineral layer (table 4). In one
of these instances the dominant host (ponderosa pine) is a
relatively deep-rooted species (Steinbrenner and Rediske

1964) growing on an extremely dry site where surface
moisture is episodic and rare during the growing season.
In the other instance, the dominant host was young
western larch, a well-adapted pioneer species growing on a
highly disturbed site with little surface organic matter
present.

When soil organic matter content was grouped into
volume classes for each site, numbers of active short root
tips compared between classes showed no significant dif-
ferences in distribution (table 4). However, a strong trend
toward low numbers in the highest organic matter class
(> 45 percent of the core) was evident. Also evident was
the low percentage volume of the cores represented by
organic fractions in all but the most productive ecosystems
(table 2, table 4). When the comparison between organic
classes was made on a larger sample base (150 cores), sig-
nificant differences between classes within the Coram Ex-
perimental Forest sites in Montana for old-growth western
hemlock, subalpine fir, and Douglas-fir (sites 1, 2, 3) were
found (table 4).

A comparison of the distribution of ectomycorrhizal
short root tips in all organic versus all mineral soil frac-
tions (combined) showed a strong, frequently significant
trend favoring organic fractions for all but the old-growth
ponderosa pine and second-growth western larch sites
(sites 8, 11) (table 5). A direct measurement of the depth
of organic horizons (litter, humus, and decayed wood com-
bined) showed the extreme shallow nature of organic

Table 4—Distribution of active ectomycorrhizal root tips (percentage of total in core)
among organic matter (litter, humus, decayed wood) volume classes
within and between sites; all samples taken during June to July peak
activity period (Harvey and others 1978)

Organic matter volume class

Site (percent)
number and Mean percent
acronym of core organic 0-15 16-30 31-45 >45
tort t rc ee ee Percent -----------

Old-growth'
1(WH-M) 31 ales 45° 23° 19°
2(SAF-M) 30 12? Be 2M 53
4(WH-1) 28 20 49 21 10
3(DF-M) 19 fia 36° 5b 4°
5(WWP-l) 17 12 20 40 27
8(PP-W) 15 39 44 17 0
6(GF-I) 13 44 43 13 0
7(SAF-WY) 6 58 0 42 0
Second-growth
10(LPP-i) 17 W/ 12 31 0
9(MIX-i) 17 42 36 22 0
11(WL-y) HS 57 20 22 0
12(DF-i) 12 0) 100 0 0
13/PP-i) 5 39 44 17 0
14(LPP-y) 5 100 0 0) 0

1See table 1 for explanation of abbreviations.

2Within the sample used for these calculations (50 cores) no significant differences between
treatments could be detected. However, on the three sites for which a larger sample was
available (150 cores, Harvey and others 1981) significant differences were detected within the
three sites (2 = 0.05), two-sided t-test, differing letters indicate significant differences.

Table 5—Cumulative depth (centimeters) of organic soil strata and distribution of
active ectomycorrhizal short roots in organic and mineral strata within and
between sites; all samples taken during June to July peak activity period
(Harvey and others 1978)

Total ectomycorrhizal
short root tips in

Site -
number and Cumulative depth/core Organic horizons Mineral horizons
acronym of organic horizons (all) (all)
Cm ww we ee ee Percent -----------

Old-growth'
1(WH-M) 3.8 289 he
2(SAF-M) 3:5 93? 1
4(WH-I) 2.5 89? ie
3(DF-M) 23 76° 24°
5(WWP-1) 2.0 93? 7
8(PP-W) Usd 16° 84°
6(GF-1) 1e5 70? 30°
7(SAF-WY) 7 TAN 29°
Second-growth
10(LPP-i) 1.9 82° 18*
9(MIX-i) 1.8 89? We
11(WL-y) fe 312 69°
12(DF-i) ie 66° 34
13(PP-i) 6 86° 14°
14(LPP-y) i) z 76% 24°

1See table 1 for explanation of abbreviations.
2Differing letters indicate significant differences (a = 0.05) within site, based on two-sided
t-test of numbers of short root tips in combined strata.

horizons (less than 4 cm) in these forests, particularly low-
productivity, harsh, or disturbed sites (table 5). The same
trend was shown for percentage of the core (table 4) and
total volume of sample (table 2) represented by organic
horizons.

DISCUSSION

The tendency to accumulate soil organic matter in the
mature, productive stands studied is probably a simple
reflection of biomass production (table 2). However, the
significantly greater accumulation on the western hemlock
and subalpine fir sites in western Montana (sites 1 and 2)
as compared to the western hemlock, white pine, and
grand fir sites in northern Idaho that have higher produc-
tivity (sites 4, 5, 6—Pfister and others 1977) may indicate
that the cool Montana climate slows decay of organic resi-
dues enough to offset higher biomass production in Idaho.
The thin organi¢ horizons on low to moderate productivity
habitat series are commensurate with their production.
The low to extremely low organic reserves (organic com-
ponent volume by depth) on the variously disturbed sites
likely reflect mixing, transport, and loss of the forest floor
due to harvesting and site preparation (tables 2 and 5).

The distribution of soil organic components was highly
variable in both combined total and individual quantity
(table 2). However, substantial reserves of decayed wood
were present in most of the old-growth stands, except
those likely to have a frequent fire history (sites 6, 7, 8).
Similarly, substantial reserves of decayed wood were pres-
ent in most second-growth sites except where site prepara-
tion had been extensive (sites 18, 14). The relatively good
balance between the long-lived organic components (wood
and humus) on most of these sites may result from a
usually infrequent or low-temperature fire history that
allows production of the large woody residues required to
produce soil-wood deposits.

Numbers of ectomycorrhizal short root tips also gen-
erally reflected site productivity, particularly of the undis-
turbed stands. On the second-growth sites, short root tip
numbers were moderate in intermediate-aged stands and
low in young stands (table 3). These numbers likely reflect
the root density of host trees. However, reduced organic
horizons may also be a contributing factor. Organic
materials contain most of the soil nutrients (Harvey and
others in press) and moisture (Barr 1930; Harvey and
others 1978; Place 1950) and are a highly favorable
substrate for ectomycorrhizal activities (Fogel and Hunt
1979; Harvey and others 1976, 1979, in press; Maser and
Trappe 1984; Mikola and others 1966; Vogt and others
19S) 58

The highly significant distribution patterns of active ec-
tomycorrhizal short root tips among the various soil com-
ponents, both within and between sites (table 3), are likely
brought about by the individual nature of these compo-
nents as conditioned by the climate and fertility of the site
(Harvey and others in press). For example, humus is an
attractive substrate for feeder roots because of its high
nutrient content, but its shallow depth limits moisture
retention. On the other hand, soil wood is moderately
supplied with nutrients but usually occurs in large enough
volumes to be a significant source for moisture.

CONCLUSION AND APPLICATIONS

Perhaps the most striking effect (or lack thereof) of site
or disturbance on numbers of ectomycorrhizal root tips, in-
cluding differences in host species and time (age), was the
generally similar distribution of ectomycorrhizal roots
among organic versus mineral soil horizons. In most cases
short root tips were concentrated in organic horizons. On
the two sites where this did not occur, the forest floor was
thin and root tips were most numerous in the surface
mineral layer. Thus, the surface soils, particularly the
organic horizons, were universally important for support-
ing this important feeder root activity on all 14 sites. This
is a clear indication that management methods likely to
impact soil surfaces, particularly mechanical site prepara-
tion and broadcast burning, should be applied with caution
to minimize loss or disruption of surface soil horizons,
organic and mineral. The extremely shallow distribution of
most ectomycorrhizal activity (4 cm or less) emphasizes a
critical need to protect this valuable resource.

REFERENCES

Barr, P. M. The effect of soil moisture of the establish-
ment spruce reproduction in British Columbia. Bulletin
26. New Haven, CT: Yale University, School of
Forestry; 1930. 57 p.

Bjorkman, E. Forest tree mycorrhizae—the conditions for
its formation and the significance for the growth and af-
forestation. Plant and Soil. 32: 589-610; 1970.

Berntsen, C. M. Seedling distribution on a spruce-hemlock
clearcut. Research Note PNW-119. Portland, OR: U.S.
Department of Agriculture, Forest Service, Pacific
Northwest Forest and Range Experiment Station; 1955.
7p.

Christy, J. E.; Sollins, P.; Trappe, J. M. First year sur-
vival of Tsuga heterophylla without mycorrhizae and
subsequent ectomycorrhizal development on decaying
logs and mineral soil. Canadian Journal of Botany. 60:
1601-1605; 1982.

Danielson, R. M. Ectomycorrhizal association in jack pine
stands in northeastern Alberta. Canadian Journal of
Botany. 62: 932-939; 1984.

Fogel, R.; Hunt, G. Fungal and arboreal biomass in a
western Oregon Douglas-fir ecosystem: distribution pat-
terns and turnover. Canadian Journal of Forest
Research. 9: 245-256; 1979.

Hacskaylo, E. Dependence of mycorrhizal fungi on hosts.
Bulletin of the Torrey Botanical Club. 100: 217-223;
1973.

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J. Seasonal
distribution of ectomycorrhizae in a mature Douglas-
fir/larch forest soil in western Montana. Forest Science.
24: 203-208; 1978.

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J. Organic
reserves: importance to ectomycorrhizae in forest soils
of western Montana. Forest Science. 27: 442-445; 1981.

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J.;

Graham, R. T. Decaying organic materials and soil qual-
ity in the Inland Northwest: a management opportunity.
General Technical Report. Ogden, UT: U.S. Department
of Agriculture, Forest Service, Intermountain Research
Station; [in press].

Harvey. A. E.; Larsen, M. J.; Jurgensen, M. F. Distribu-
tion of ectomycorrhizae in a mature Douglas-fir/larch
forest soil in western Montana. Forest Science. 22:
393-398; 1976.

Harvey, A. E.; Larsen, M. J.; Jurgensen, M. F. Com-
parative distribution of ectomycorrhizae in soils of three
western Montana forest habitat types. Forest Science.
25: 350-358; 1979.

Herman, R. K. Growth and production of tree roots: a
review. In: Marshal, J. K., ed. The belowground
ecosystem: a synthesis of plant associated processes.
New York: Dowden, Hutchinson, and Ross; 1977: 7-28.

Jaffe, M. J.; Takahashi, H.; Biro, R. L. A pea mutant for
the study of hydrotropism in roots. Science. 230:
445-447; 1985.

Jurgensen, M. F.; Larsen, M. J.; Harvey, A. E. Effects of
timber harvesting on soil biology. In: Proceedings, an-
nual meeting, Society of American Foresters. Washing-
ton, DC: Society of American Foresters; 1977: 244-250.

Kropp, B. R.; Trappe, J. M. Ectomycorrhizal fungi of
Tsuga heterophylla. Mycologia. 74: 479-478; 1982.

Larsen, M. J.; Harvey, A. E.; Jurgensen, M. F. Residue
decay processes and associated environmental functions
in Northern Rocky Mountain forests. In: Environmental
consequences of timber harvesting. General Technical
Report INT-90. Ogden, UT: U.S. Department of Agri-
culture, Forest Service, Intermountain Forest and
Range Experiment Station; 1980: 157-174.

Maser, Chris; Trappe, J. M., tech. eds. The seen and un-
seen world of the fallen tree. General Technical Report
PNW-164. Portland, OR: U.S. Department of Agricul-
ture, Forest Service, Pacific Northwest Forest and
Range Experiment Station; 1984. 56 p.

McFee, W. W.; Stone, E. L. The persistence of decaying
wood in the humus layers of northern forests. Soil
Science Society of America Proceedings. 30: 513-516;
1966.

McMinn, R. G. Characteristics of Douglas-fir root systems.
Canadian Journal of Botany. 11: 105-122; 1963.

Meyer, F. H. Distribution of ectomycorrhizae in native and
man-made forests. In: Marks, G. C.; Koylowski, F. F.
Ectomycorrhizae: their ecology and physiology. New
York: Academic Press; 1973: 79-105.

Mikola, P.; Hahl, S.; Tornianen, E. Vertical distribution of
mycorrhizae in pine forests with spruce undergrowth.
Annals of Botany Fenn. 3: 406-409; 1966.

Park, J. L.; Linderman, R. G.; Trappe, J. M. Effects of
forest litter on mycorrhizae development and growth of
Douglas-fir and western red cedar seedlings. Canadian
Journal of Forest Research. 13: 666-671; 19838.

vv U.S. GOVERNMENT PRINTING OFFICE: 1986—791-032/41,033 REGION NO. 10

Pfister, R. D.; Kovalchik, B. L.; Arno, S. F.; Presby, R. C.
Forest habitat types of Montana. General Technical
Report INT-34. Ogden, UT: U.S. Department of Agricul-
ture, Forest Service, Intermountain Forest and Range
Experiment Station; 1977. 172 p.

Pilz, D. P.; Perry, D. A. Impact of clearcutting and slash
burning on ectomycorrhizal associations of Douglas-fir
seedlings. Canadian Journal of Forest Research. 14:
94-100; 1984.

Place, I. C. M. Comparative moisture regimes of humus
and rotten wood. Silviculture Leaflet 37. Ottawa, ON:
Canadian Department of Research and Development,
Forest Research Division; 1950. 2 p.

Reich, P. B.; Schoettle, A. W.; Stroo, H. F.; Troiano, J.;
Amundson, R. G. Effects of 03, S05, and acid rain on
mycorrhizal infection in northern red oak seedlings.
Canadian Journal of Botany. 63: 2049-2055; 1985.

Rowe, J. S. Factors influencing white spruce reproduction
in Manitoba and Saskatchewan. Technical Note 3. Winni-
peg, MB: Canadian Department of Northern Affairs and
National Resources, Forestry Branch, Forest Research
Division; 1955. 27 p.

Steinbrenner, E. C.; Rediske, J. H. Growth of ponderosa
pine and Douglas-fir in a controlled environment. Paper
Number 1. Centralia, WA: Weyerhaeuser Forest; 1964.
31 p.

Todd, A. W. Decomposition of selected soil organic matter
components by Douglas-fir ectomycorrhizal associations.
In: Abstracts of the 4th North American conference on
mycorrhizae. Fort Collins, CO: Colorado State Univer-
sity; 1979.

Trappe, J. M. Fungus associates of ectotrophic mycor-
rhizae. Botanical Research. 29: 588-606; 1962.

Trappe, J. M. Tuberculate mycorrhizae of Douglas-fir.
Forest Science. 11: 27-32; 1965.

Trappe, J. M.; Strand, R. F. Mycorrhizal deficiency in a
Douglas-fir region nursery. Forest Science. 15: 381-389;
1969.

Vogt, K. A.; Edmonds, R. L.; Grier, C. C. Seasonal
changes in biomass and vertical distribution of mycor-
rhizal and fibrous-textured conifer fine roots in 23- and
180-year-old subalpine Abies amabalis stands. Canadian
Journal of Forest Research. 11: 223-229; 1981.

Vozzo, J. A.; Hacskaylo, E. Inoculation of Pinus caribaea
with ectomycorrhizal fungi in Puerto Rico. Forest
Science. 17: 239-245; 1971.

Zak, B. Detoxication of autoclaved soil by a mycorrhizal
fungus. Research Note PNW-159. Portland, OR: U.S.
Department of Agriculture, Forest Service, Pacific

Northwest Forest and Range Experiment Station; 1971. 4 p.

Harvey, Alan E.; Jurgensen, Martin F.; Larsen, Michael J.; Schlieter, Joyce A.
Distribution of active ectomycorrhizal short roots in forest soils of the Inland North-
west: effects of site and disturbance. Research Paper INT-374. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Intermountain Research Station; 1986.

8p.

Approximately 75 percent of ectomycorrhizal activities that occurred in soils from
eight undisturbed and six variously disturbed sites occurred in shallow organic
horizons. These horizons represented only the first 4 cm of soil depth. This dispro-
portionate participation of surface organic materials emphasizes a need to conserve
them in forested ecosystems of the Inland West.

KEYWORDS: soil microbial activity, soil quality, soil productivity, soil management,
fire management, site preparation, site protection

INTERMOUNTAIN RESEARCH STATION

The Intermountain Research Station provides scientific knowl-
edge and technology to improve management, protection, and use
of the forests and rangelands of the Intermountain West. Research
is designed to meet the needs of National Forest managers,
Federal and State agencies, industry, academic institutions, public
and private organizations, and individuals. Results of research are
made available through publications, symposia, workshops, training
sessions, and personal contacts.

The Intermountain Research Station territory includes Montana,
Idaho, Utah, Nevada, and western Wyoming. Eighty-five percent of
the lands in the Station area, about 231 million acres, are classified
as forest or rangeland. They include grasslands, deserts, shrub-
lands, alpine areas, and forests. They provide fiber for forest in-
dustries, minerals and fossil fuels for energy and industrial develop-
ment, water for domestic and industrial consumption, forage for
livestock and wildlife, and recreation opportunities for millions of
visitors.

Several Station units conduct research in additional western
States, or have missions that are national or international in scope.

Station laboratories are located in:

Boise, Idaho

Bozeman, Montana (in cooperation with Montana State
University)

Logan, Utah (in cooperation with Utah State University)

Missoula, Montana (in cooperation with the University of
Montana)

Moscow, Idaho (in cooperation with the University of Idaho)
Ogden, Utah
Provo, Utah (in cooperation with Brigham Young University)

Reno, Nevada (in cooperation with the University of Nevada)