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SOIL PROPERTIES AS A FACTOR IN REGENERATION FAILURES
IN THE GRAND FIR MOSAIC-PRELIMINARY RESULTS
Mark Sommer, David Adams, and Robert Mahler
The grand fir mosaic (GFM) consists of a patchwork
arrangement of several forest plant communities located
in an elevation range of 4,000 to 5,800 feet above sea
level. The grand fir mosaic is found primarily in Idaho's
Clearwater and Nez Perce National Forests. The plant
communities (habitat type from Cooper and others 1987)
are:
variability, the cores were taken from areas that had similar relief, parent material, and climate. Fifteen samples
from each area were taken to a I-foot depth. Soil analysis
was completed at the University of Idaho's Analytical Services Laboratory and Soil Fertility Laboratory.
RESULTS
1. Forested stands where the grand fir/wild ginger
Clearwater National Forest soil chemical properties are
given in table 1; physical properties are not yet characterized. More thorough soil sampling, in addition to foliar
sampling, is planned for 1990. Statistical analysis as well
as finalized results will be presented after these data have
been received.
(Abies grandis / Asarum caudatum) habitat type
predominates.
2. Bracken fern (Pteridium aquilinum) glades that
appear to be climax communities.
3. Alder glades where the Sitka alderlbroadleaved
montia (Alnus sinuata/ Montia cordifolia) habitat type
predominates.
DISCUSSION
As the forested areas are harvested, bracken glade
communities can invade and exclude most woody vegetation, including conifers. This occurs despite attempts at
natural and artificial regeneration. The pocket gopher
(Thomomys talpoides) also invades the harvested areas
and rapidly multiplies. Current research indicates
bracken fern allelopathy and damage by pocket gophers
as major factors in the poor regeneration success (Ferguson
and Boyd 1988). The alder glades expand slightly, causing few problems.
The bracken fern produces a large amount of biomass,
which dies in the fall and is buried by snow in the winter.
When spring arrives, a surface of almost bare soil is revealed. Thus rapid decomposition and mineralization
rates may be taking place beneath the snow.
This study compares forest and natural bracken glade
soils. It also examines soils from cutover areas where
bracken fern has invaded to see if soil properties are
changing.
The soil chemical properties of the uncut forest and
the bracken glade appear to be somewhat different. Soil
chemical properties of the bracken-invaded areas differ
from both the uncut forest and the bracken glade. However, they seem most similar to bracken glade soils.
The most striking change in the bracken glade-invaded
areas is the decrease in pH and increase in extractable
aluminum. Within the bracken glades and brackeninvaded areas there are high amounts of composition,
mineralization, and nitrification during the winter and
early spring. During this time there is little active uptake
by plants, and nitrate and cations can be leached from
the soil. This process lowers the pH, which could cause
aluminum to be released. Bracken fern is also high in
phenolic acids, which may aid acidification. Apparently
the soil's buffering capacity is not able to neutralize the
increased acidity.
The increased amount of decomposition and mineralization could be due to several factors:
METHODS AND MATERIALS
1. The bracken glade community produces a greater
annual turnover of biomass than the forest community
it replaced.
2. A change in microclimate where lack of shade in
early spring and late fall causes soil to be warmed to
higher temperatures.
3. Warmer and wetter environments than normal
for these elevations.
The study area is located about 15 miles northeast of
Headquarters, ID, in the North Fork Ranger District of
the Clearwater National Forest. Portions of the area's
forests were clearcut about 25 years ago. Within the
study area there is uncut forest, natural bracken fern
glades, and harvested areas invaded by bracken fern.
A randomized block design was used for sampling.
Soil cores were taken from the uncut forest, bracken
fern glades, and the bracken-invaded areas. To reduce
Mark Sommer is a Soil Scientist Trainee, Nez Perce National Forest, Forest Service, U.S. Department of Agriculture, Route 2, Box 475, Grangeville,
ID 83530. David Adams and Robert Mahler are Professor of Silviculture
and Professor of Soil Fertility, respectively, University ofIdaho, Moscow,
ID.
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Preventive measures can be based on an understanding
of the mechanism that causes this process. In addition,
a search for methods of prevention without awareness of
the mechanism must continue. Different types of silvicultural practices need to be examined to determine which
are least likely to lead to this process.
Table 1-Clearwater National Forest soil chemical properties-
CONCLUSIONS
means (standard deviations)
Uncut
forest
Sample area
Bracken
Invaded
Bracken
glade
Phosphorus
uglg
NaOAC
1.56 (0.75)
2.95 (1.50)
4.25 (1.93)
Potassium
uglg
NaOAC
209 (57)
214 (73)
502 (188)
CEC
meql100 9
NH40AC
24.9 (3.8)
30.2 (6.2)
31.6 (3.8)
Exch. Ca
meql100 9
NH40AC
5.6 (1.9)
5.0 (1.5)
3.9 (1.8)
Exch. Mg
meql100 9
NH40AC
0.80 (0.19)
1.12 (0.35)
1.21 (0.46)
Exch. K
meql100 9
NH40AC
0.80 (0.18)
1.15 (0.32)
1.75 (0.51)
Zinc
uglg
OTPA
0.73 (0.67)
1.66 (1.14)
2.05 (1.32)
Manganese
uglg
OTPA
45.4 (17.3)
28.6 (15.7)
32.0 (14.2)
Copper
ug/g
OTPA
0.32 (0.09
0.36 (0.15)
0.41(0.13)
Extrac. AI
uglg
KCL
35 (43)
197(128)
211(101)
pH
pH units
1:1 water
5.93 (0.26)
4.95 (0.38)
4.79 (0.30)
Carbon
percent
CHN analyzer
4.n (0.95)
5.18 (1.79)
6.14 (1.53)
Nitrogen
percent
CHN analyzer
0.28 (0.05)
0.41 (0.12)
0.45 (0.09)
Property,
units,
method
1. The different plant communities lead to formation
of different soils on what otherwise appear to be areas
with the same relief, climate, and parent material.
2. When bracken fern invades harvested areas, soil
chemical properties can be altered. Thus, in addition
to allelopathy and pocket gophers, a change in soil properties may be contributing to the poor regeneration success.
A NOTE ON THE MOSAIC
The introduction stated that the grand fir mosaic (GFM)
exists in both the Clearwater and Nez Perce National Forests. However, as more information is gathered, it seems
that the GFM is not the same ecosystem in each Forest.
For instance:
1. The "climax" bracken fern glades are almost nonexistent in the Nez Perce National Forest.
2. After harvest, bracken fern is the primary invader
in the Clearwater National Forest, but in the Nez Perce
National Forest the primary invader is coneflower (Rudbeckia occidentalis).
3. Soil chemical properties have not changed after harvest in the Nez Perce National Forest.
Because of this, this poster paper was largely focused
on one National Forest. The Clearwater was chosen
because it is more interesting from a soils standpoint.
However, from a forestry standpoint, both Forests are
important because regeneration failures in the GFM
have been noted in each.
REFERENCES
Cooper, S. V.; Neiman, K. E.; Steele, R.; Roberts, D. W.
1987. Forest habitat types of northern Idaho: a second
approximation. Gen. Tech. Rep. INT-236. Ogden, UT:
U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 135 p.
Ferguson, D. E.; Boyd, R. J. 1988. Bracken fern inhibition
of conifer regeneration in northern Idaho. Res. Pap.
!NT-388. Ogden, UT: U.S. Department of Agriculture,
Forest Service, Intermountain Research Station. 11 p.
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