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Fast-simulation models of gaseous exchange in Scots
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New Phytologist. 89: 165-178.
Delieu, Thomas J.; Walker, David A. 1983. Simultaneous
measurement of oxygen evolution and chlorophyll fluorescence from leaf pieces. Plant Physiology. 73: 534-541.
Landsberg, J. J. 1986. Experimental approaches to the
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assimilation by trees. Tree Physiology. 2: 427-444.
SOIL ORGANIC MATI'ER EFFECTS ON DOUGLAS·FIR
GROWTH IN NORTHERN IDAHO SOILS
Deborah Page-Dumroese, Russell T. Graham, and Alan E. Harvey
NUTRIENT AVAILABILITY
Regeneration of Douglas-fir (Pseudotsuga menziesii var.
glauca [Beissn.] Franco) usually depends on site manipulation and planting to achieve fully stocked stands. Seed
that produces superior survival and early growth is a
key factor in supplying quality Douglas-fir wood to meet
an increased demand for future timber-based products.
Planting success in the Intermountain West is hampered
by low soil moisture and nutrient stress (Duryea and
Lavender 1982). On sites where large amounts of topsoil and organic matter have been removed during the
harvest/site preparation sequence, initial tree growth
and survival is reduced and continues to be depressed
throughout the rotation (Glass 1976; Pehl and Bailey
1978). Douglas-fir can be considered an especially sensitive species in this regard (Graham and others 1989).
Soil, wood, litter, duff, and humus govern the quality
of many forest sites in the Inland Northwest because they
are an important source of moisture-holding capacity and
nutrient storage, which are essential for seedling survival
(Harvey and others 1976). Organic matter also provides
a favorable microsite for many microbes in the rhizosphere.
These microbes can be beneficial or deleterious to tree
survival and growth (Harvey 1982).
Timber harvesting, site preparation, and slash disposal
systems can reduce the nutrient capital offorested ecosystems (Clayton and Kennedy 1985). Nutrient loss is
greatest when intensive site preparation or utilization is
involved (Jurgensen and others 1990; Leaf 1979). Nutrient deficiencies induced by organic matter removal have
been blamed for poor yields and plantation failures on numerous sites (Burger and Kluender 1982; Pritchett 1981;
Woods 1981). In the steep, mountainous regions of the
Inland Northwest, this loss is often accelerated by erosion
and leaching after slash piling, burning, and organic matter removal (Clayton and Kennedy 1985). Site preparation techniques that mound the topsoil and organic horizons together have helped achieve greater conifer survival
and growth rates in several instances (Page-Dumroese
and others 1987; Shoulders and Terry 1978).
MOISTURE AVAILABILITY
Residual harvesting debris has many physical and
chemical properties that make it important to biological
processes (Harvey and others 1987). Dead plant materials tie up, then gradually release upon decay, substantial
quantities of nutrients and tend to retain more available
moisture. Available soil moisture is influenced by soil
temperature, moisture content, particle size distribution,
evaporative losses, and organic matter content (Cleary
1970). Of these five, organic matter is the most influential, since it represents a major component of soil moisture storage (Brady 1974).
Deborah Page-Dumroese, Russell T. Graham, and Alan E. Harvey are
Research Soil Scientist, Research Forester, and Principal Plant Pathologist, respectively, Intermountain Research Station, Forest Service, U.S.
Department of Agriculture, Moscow, ID 83843.
249
Table 1-Average soil
bulk density (glee), after tamping soil into
seedling cells, for each soil mix from each habitat type
MICROBIAL POPULATIONS
When the forest floor is exposed through harvesting,
there is a sharp increase in solar radiation and a concomitant reduction of transpiration. The previously stable
microclimate below the organic layer becomes subject to
large temperature, moisture, and nutrient fluctuations.
Changes in microsite lead to changes in microbial populations as well. Soil microbes, including mycorrhizae,
playa critical role in soil development and plant nutrition
and are perhaps an important contributor to seedling success. Harvey and others (1976, 1978, 1987; Harvey 1982)
have demonstrated that humus and brown cubical decayed wood are the major substrate for ectomycorrhizal
growth on Douglas-fir. These fungi tend to confer drought
resistance on seedling roots (Parke and others 1983).
Other benefits to the host plant include resistance to
pathogens, tolerance to environmental stresses, and an
increase in moisture and nutrient uptake (Marx and
Krupa 1978). Ectomycorrhizal colonization is highly dependent on inoculum source and environmental conditions surrounding the root system (for example, moisture
content, temperature, pH, and organic matter [Slankis,
1974]). Harvest and site preparation alter these factors
and may reduce the number of ectomycorrhizae and their
diversity (Amaranthus and Perry 1987). It follows, therefore, that soils high in organic matter affect plant rhizospheres through microbial activities and subsequent
changes in plant moisture and nutrition.
All these interrelated processes (microbial activity, nutrient and water release) are crucial for the maintenance
of conifer plantations in the Inland Northwest and are of
particular concern for Douglas-fir. Soil manipulation, in
the form of site preparation and harvesting activities, can
be a controlling factor for stand establishment or failure.
Because field trials of site preparation techniques have
difficulty in separating the influence of organic matter on
seedling performance and independent conflicting variables (Graham and others 1989; Page-Dumroese and
others 1986, 1989), this study was established.
Soli mix
THPUCLUN1
ABLAlXETE
- - - - - - - - - - - - -glee - - - - - - - - - - -
Organic
mix
Mineral
50/50
0.9Sa
1.00a
1.11a
O.9Sa
1.00a
1.13a
1Habitat types: THPUClUN = Thuja plicatalClintonia uniflora, ABLAI
XETE =Abies lasiocarpa/ Xerophyllum tenax.
RESULTS
Organic matter plays an important role in the growth
and performance of Douglas-fir seedlings. Soils containing high organic matter levels had a greater water-holding
capacity (Page-Dumroese and others 1986) and, therefore,
a greater available water content than soils consisting of
only mineral soil. The available water in the organic matter may help bring the seedlings through critical drought
periods during the growing season.
Seedlings grown in organic mixes grew significantly
better than those grown in only mineral soil (table 2).
Height, top weight, root weight, root collar caliper, and
terminal bud length were all significantly greater for
seedlings grown in the organic mixes. Terminal bud
length was used as an indicator of both current season
conditions and seedling potential (Kozlowski and others
1973). Seedlings grown in the organic mix soils had a significant growth advantage, not only for the current year,
but also for the following season, over their mineral soil
counterparts. The improved seedling morphological properties likely can be attributed to the additional moisture
and nutrients available in soil organic matter.
The most notable difference between seedlings grown
in the various mixes was the number of ectomycorrhizae.
Seedlings grown in mineral soil generally had more ectomycorrhizae than those grown in organic mixes. Seedlings grown in the more fertile environments (more moisture and nutrients) may have less need for extensive
ectomycorrhizal colonization (Brainerd and Perry 1987).
However, seedlings grown in mineral soil did not seem to
derive benefit from colonization; neither seedling physical
nor chemical properties (tables 2 and 3) were improved.
Under this particular circumstance, ectomycorrhizae may
represent a carbohydrate cost to seedlings deficient in factors not improved by ectomycorrhizal colonization (Reid
1979).
Seedling chemical properties also reflected the soil type
in which they were growing (table 4). Total Nand P in
seedlings were significantly higher in those grown in
100 percent organic matter than in the 50/50 mix or in
mineral soil. This was probably a reflection of the amount
of Nand P released from the soils during the growing season. Potassium levels did not follow these same trends.
This was due to high initial K levels in the mineral soil
and subsequent release from exchange sites during the
growing season.
SITES, MATERIALS, AND METHODS
Soil organic matter, mineral soil, and seed were collected from two dissimilar habitat types in northern
Idaho. A low-elevation site (750 m) in the Thuja plicata/
Clintonia uniflora (Cooper and others 1987) habitat type
and a high-elevation site (3,500 m) in the Abies lasiocarpal
Xerophyllum tenax habitat type (Cooper and others 1987)
were selected. Soil was sieved to pass a 2-mm mesh sieve.
Planting media consisted of 100 percent organic soil, 100
percent mineral soil, and 50 percent mineral/50 percent
organic soils. Soil was tamped into 163-cm3 cells and seed
was sown. Bulk densities of the cells were kept constant
(table 1). Seed was sown in April and seedlings were
grown until October.
For complete detail of site description, materials,
methods, and statistical analyses see Page-Dumroese
and others (1990).
250
Table 2-Physical characteristics of Douglas-fir seedlings grown in three soil mixes
Soil source
Soli mix
Height
THPUCLUN1
Organic
5.8a
4.8b
4.Bb
Topwt.
cm
50/50
Mineral
Organic
ABLAlXETE
- - - - - - - - g- - - - - - - 0.14a
.09b
.0Bb
5.4a
4.4ab
4.0b
50/50
Mineral
Rootwt.
.13a
.09ab
.05b
Root collar
diameter
Bud
length
- - - - - - - - - mm- - - - - - - - -
Mycorrhlzae
per gram of root
No.
0.17a
.13a
.08b
1.1a
1.oa
.7b
3.Sa
2.9b
2.8b
0.8b
4.0ab
B.Sa
.2Qa
.12b
.07c
1.2a
.9ab
.8b
3.0a
2.4ab
2.2b
2.Sa
3.Sa
4.oa
1Habitat types: THPUClUN = Thuja plicatalClintonia uniflora, ABLA/XETE =Abies lasiocarpalXerophyllum tenax.
horizon destruction and enhance seedling growth through
organic matter conservation. Along with maintaining
organic matter levels, careful consideration of microsite/
seedling relationships is also very likely to improve stand
conditions throughout the rotation.
Table 3-Chemical characteristics of Douglas-fir seedlings grown
in three soil mixes
Soli source
Soil mix
Total N
Total P
mglkg
- - - - Percent- - - THPUCLUN1
Organic
50/50
Mineral
ABLAlXETE
Organic
50/50
Mineral
Potassium
1.96a
1.33ab
1.17b
O.38a
.17b
.23ab
130.1ab
123.4b
168.2a
1.87a
1.28b
1.10b
.39a
.13b
.11b
120.0b
173.2a
183.2a
REFERENCES
Amaranthus, M. P.; Perry, D. A. 1987. Effect of soil
transfer on ectomycorrhiza formation and the survival
and growth of conifer seedlings on old nonforested
c1ear-cuts. Canadian Journal of Forest Research.
17: 944-950.
Brady, N. C. 1974. The nature and properties of soils.
8th ed. New York: McMillan. 639 p.
Brainerd, R. E.; Perry, D. A. 1987. Ectomycorrhizal
formation in disturbed and undisturbed soil across
a moisture/elevation gradient in Oregon. In: Sylvia,
D. M.; [and others], eds. Mycorrhizae in the next
decade-practical applications and research priorties.
Gainesville, FL: University of Florida. 145 p.
Burger, J. A.; Kluender, R. A. 1982. Site preparationPiedmont. In: Kellison, R. C.; Gingrich, S. A., eds .
Symposium on loblolly pine ecosystems (East region).
Raleigh, NC: U.S. Department of Agriculture, Forest
Service, and North Carolina State University, Raleigh:
58-74.
Clayton, J. L.; Kennedy, D. A. 1985. Nutrient loss from
timber harvest in the Idaho batholith. Soil Science
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Cleary, B. D. 1970. The role of moisture stress and
temperature in the growth of seedlings. In: Regeneration of ponderosa pine. Paper 681. Corvallis, OR:
Oregon State University School of Forestry: 64-68.
Cooper, S. T.; Neiman, K; 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.
Duryea, M. L.; Lavender, D. A. 1982. Water relations,
growth and survival of root wrenched Douglas-fir
seedlings. Canadian Journal of Forest Research.
12: 545-555.
Glass, G. G.1976. The effects of rootraking on an upland
Piedmont loblolly pine (Pinus taeda L.) site. Tech. Rep.
56. Raleigh, NC: North Carolina State Forest Fertilization Cooperative. 44 p.
1Habitat types: THPUClUN = Thuja plicatalClintonia uniflora, ABlAI
XETE = Abies lasiocarpalXerophyllum tenax.
Table 4-Average soil chemical concentrations of each soil mix from
each location
Soli source
Soli mix
THPUCLUN1
Organic
Total N
Total P
- - - - Percent- - - - -
50/50
Mineral
ABLAlXETE
Organic
50/50
Mineral
Potassium
pH
mglkg
0.03a
.03a
.01a
0.27a
.24a
.22a
5.1
3.3a
2.4a
B.Oa
B.1a
.10a
.03b
.03b
.11a
.12b
.07a
3.0a
2.Sa
2.Sa
5.4a
5.4a
5.Sa
5.7a
1Habitat types: THPUClUN = Thuja plicatalClintonia uniflora, ABlAI
XETE =Abies lasiocarpel Xerophyllum tenax.
CONCLUSIONS
Increased nutrient and moisture availability associated
with organic soil components, although in many cases not
sufficient to be statistically significant in this study, likely
resulted in increased uptake and provided the basis for increased seedling growth. This is a strong indication that
organic residues left on a site after harvesting could determine the performance of succeeding stands by providing critical moisture and nutrients, especially on harsh
(dry) sites low in Nand P.
In the Inland Northwest most harvested areas are being planted to achieve adequate stocking levels. This provides an opportunity for land managers to minimize soil
251
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Woods, R. V. 1981. Management of nitrogen in the
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In: Rummery, R. A.; Hingston, F. J., eds. Managing
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in the Inland Northwest: a management opportunity.
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252