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 tlie 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 1930; 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 (Tsuga hetero- 

 phylla [Raf.] Sarg.). Western larch {Larix occidentalis 

 Nutt.) and western redcedar (Thuja plicata Donn.), the 

 latter essentially a nonhost, also occur occasionally. 



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