Influence of forest harvesting on soil organisms and decomposition in western Washington.

Abstract Clearcutting has created a fragmented landscape with many forest edges in the Pacific Northwest—a condition different from that created by natural disturbances. Recently ecosystem management has been proposed as an alternative method to clearcutting whereby coarse woody debris (CWD) (snags and logs) and green trees are retained to provide important structures. Knowledge of how harvesting practices affect soil microbiology is far from complete. The objectives of this paper are to discuss (1) the influence of clearcutting on respiration of forest floor/soil and coarse woody debris and invertebrate density; (2) the influence of forest edges on litter decomposition and nitrogen release, soil moisture, and fruiting of epigeous mycorrhizal fungi; and (3) the influence of ecosystem management practices on soil moisture and temperature, microbial biomass, and Douglas-fir seedling growth and survival in western Washington. Sites on the Olympic Peninsula and in the Puget Sound region were studied. Clearcutting influenced microclimate, soil respiration, decomposition, nitrogen release, and invertebrates to varying degrees, but the mild environment of this area tended to dampen the effect. Decomposition and nitrogen release, soil moisture, temperature, and the patterns of fruiting of mycorrhizal fungi are strongly influenced by forest edges. Ecosystem management, specifically green-tree retention treatments, generally created an intermediate microclimate between forests and clearcuts, but did not strongly influence soil microbial biomass. Douglas-fir seedlings were successfully grown under tree canopies for 1 year, but survival and growth need to be evaluated over time.