SOIL ORGANIC MATTER EFFECTS ON DOUGLAS-FIR GROWTH IN NORTHERN IDAHO SOILS

Deborah Page-Dumroese
Russell T. Graham
Alan E. Harvey

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 top-soil 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).

NUTRIENT AVAILABILITY

Timber harvesting, site preparation, and slash disposal systems can reduce the nutrient capital of forested 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).

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, play a 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.

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 lasiocarpa/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-cm 3 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.

TABLE 1 
Average soil bulk density (g/cc), after tamping soil into seedling cells, for each soil mix from each habitat type
Soil mix THPL/CLUN1
g/cc		 ABLA/XETE
g/cc
1Habitat types: THPL/CLUN = Thuja plicata/Clintonia uniflora, ABLA/XETE = Abies lasiocarpa/Xerophyllum tenax.
Organic 0.98a 0.98a
50/50 mix 1.00a 1.00a
Mineral 1.11a 1.13a

For complete detail of site description, materials, methods, and statistical analyses see Page-Dumroese and others (1990).

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.

TABLE 2 
Physical characteristics of Douglas-fir seedlings grown in three soil mixes
Soil source Soil mix Height
cm		 Top wt.
g		 Root wt.
g		 Root collar diameter
mm		 Bud length
mm		 Mycorrhizae per gram of root
No.
1Habitat types: THPL/CLUN = Thuja plicata/Clintonia uniflora, ABLA/XETE = Abies lasiocarpa/Xerophyllum tenax.
THPL/CLUN1 Organic 5.8a  0.14a  0.17a 1.1a  3.6a  0.8b 
50/50 4.8b  .09b  .13a 1.0a  2.9b  4.0ab
Mineral 4.6b  .06b  .08b .7b  2.8b  6.5a 
ABLA/XETE Organic 5.4a  .13a  .20a 1.2a  3.0a  2.5a 
50/50 4.4ab .09ab .12b .9ab 2.4ab  3.5a 
Mineral 4.0b  .05b  .07c .8b  2.2b  4.0a 

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).

TABLE 3 
Physical characteristics of Douglas-fir seedlings grown in three soil mixes
Soil source Soil mix Total N
Percent		 Total P
Percent		 Potassium
mg/kg
1Habitat types: THPL/CLUN = Thuja plicata/Clintonia uniflora, ABLA/XETE = Abies lasiocarpa/Xerophyllum tenax.
THPL/CLUN1 Organic 1.96a  0.38a  130.1ab
50/50 1.33ab .17b  123.4b 
Mineral 1.17b  .23ab 168.2a 
ABLA/XETE Organic 1.87a  .39a  120.0b 
50/50 1.28b  .13b  173.2a 
Mineral 1.10b  .11b  183.2a 

Seedling chemical properties also reflected the soil type in which they were growing (table 4). Total N and 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 N and 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.

TABLE 4 
Average soil chemical concentrations of each soil mix from each location
Soil source Soil mix Total N
Percent		 Total P
Percent		 Potassium
mg/kg		 pH
1Habitat types: THPL/CLUN = Thuja plicata/Clintonia uniflora, ABLA/XETE = Abies lasiocarpa/Xerophyllum tenax.
THPL/CLUN1 Organic 0.03a 0.27a 5.1  5.7a
50/50 .03a .24a 3.3a 6.0a
Mineral .01a .22a 2.4a 6.1a
ABLA/XETE Organic .10a .11a 3.0a 5.4a
50/50 .03b .12b 2.6a 5.4a
Mineral .03b .07a 2.5a 5.5a

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 N and 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 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.

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 clear-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 priorities. Gainesville, FL: University of Florida. 145 p.

Burger, J. A.; Kluender, R. A. 1982. Site preparation-Piedmont. 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 Society of America Journal. 49: 1041-1049.

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, Inter- mountain 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.

Graham, R. T.; Harvey, A. E.; Jurgensen, M. F. 1989. Effect of site preparation on survival and growth of Douglas-fir (Pseudotsuga menziesii Mirb. Franco) seedlings. New Forests. 3: 89-98.

Harvey, A. E. 1982. The importance of residual organic debris in site preparation and amelioration for reforestation. In: Site preparation and fuels management on steep terrain. Pullman, WA: Washington State University, Cooperative Extension: 75-85.

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J.; Graham, R. T. 1987. Decaying organic materials and soil quality in the Inland Northwest: a management opportunity. Gen. Tech. Rep. INT-225. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 15 p.

Harvey, A. E.; Jurgensen, M. F.; Larsen, M. J. 1978. Role of residue in and impacts of its management on forest soil biology. Eighth World Forestry Congress; 1978 October 16-18; Jakarta, Indonesia. FAO Special Paper. Rome: Food and Agriculture Organization.

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

Jurgensen, M. F.; Harvey, A. E.; Graham, R. T.; [and others]. 1990. Soil organic matter, timber harvesting, and forest productivity in the Inland Northwest. In: Gessel, S. P.; Lacate, D. S.; Weetman, G. F.; Powers, R. F., eds. Sustained productivity of forest soils. Proceedings, 7th North American Forest Soils Conference; 1988 July 24-28; Vancouver, BC. Vancouver, BC: University of British Columbia, Faculty of Forestry: 392-415.

Kozlowski, T. T.; Torrie, J. H.; Marshall, P. E. 1973. Predictability of shoot length from bud size in Pinus resinosa (Ait.). Canadian Journal of Forest Research. 3: 34-38.

Leaf, A. L. 1979. Preface. In: Proceedings, impact of intensive harvesting on forest nutrient cycling; 1979 August 13-16. Syracuse, NY: State University of New York: ii.

Marx, D. H.; Krupa, S. V. 1978. Ectomycorrhizae. In: Dommergues, Y. R.; Krupa, S. V., eds. Interactions between non-pathogenic soil microorganisms and plants. New York: Elsevier Scientific Publishing: 373-400.

Page-Dumroese, D. S.; Loewenstein, H.; Graham, R. T.; Harvey, A. E. 1990. Soil source, seed source, and organic matter content effects on Douglas-fir seedling growth. Soil Science Society of America Journal. 54: 229-233.

Page-Dumroese, D. S.; Jurgensen, M. F.; Graham, R. T.; Harvey, A. E. 1987. Soil physical properties associated with three site preparation techniques and their effects on growth and survival of seedlings in northern Idaho. In: Kossuth, S. V.; Pywell, N. A., eds. Current topics in forest research: emphasis on contributions by women scientists. Gen. Tech. Rep. SE-46. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station: 66-70.

Page-Dumroese, D. S.; Jurgensen, M. F.; Graham, R. T.; Harvey, A. E. 1986. Soil physical properties of raised planting beds in a northern Idaho forest. Res. Pap. INT-360. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 6 p.

Parke, J. L.; Linderman, R. G.; Black, C. H. 1983. The role of ectomycorrhizae in drought tolerance of Douglas-fir seedlings. New Phytology. 95: 83-95.

Pehl, C. E.; Bailey, R. L. 1983. Performance to age ten of a loblolly pine plantation on an intensively prepared site in the Georgia Piedmont. Forest Science. 29: 96-102.

Pritchett, W. L. 1981. Site preparation in the coastal flatwoods. IMPAC Rep. 6(7). Gainesville, FL: University of Florida.

Reid, C. P. P. 1979. Mycorrhizae: a root-soil interface in plant nutrition. In: Todd, R. L.; Biddens, J. E., eds. Microbial-plant interactions. ASA Spec. Publ. 47. Madison, WI: Soil Science Society of America: 29-50.

Shoulders, E.; Terry, T. A. 1978. Dealing with site disturbances from harvesting and site preparation in the Lower Coastal Plain. In: Tippen, T., ed. Proceedings: a symposium on principles of maintaining productivity on prepared sites; 1978 March 21-22. Starkville, MS: Mississippi State University: 85-98.

Slankis, V. 1974. Soil factors influencing formation of ectomycorrhizae. Annual Review of Phytopathology. 12: 437-457.

Woods, R. V. 1981. Management of nitrogen in the P. radiata plantations of the southeast of Austrailia. In: Rummery, R. A.; Hingston, F. J., eds. Managing nitrogen economies of natural and man made forest ecosystems. Floreat Park, Western Australia: CSIRO Division Land Resource Management: 354-367.

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.