Influence of forest-clearcut edges on fungal fruiting, litter decomposition and seedling growth in low elevation second-growth conifer forests in western Washington

Extensive timber harvesting in the Pacific Northwest has resulted in forest landscapes that include numerous edges, where patches of older forests are bounded by more open areas. Mature second-growth Douglas-fir/western hemlock stands adjacent to very young stands resulting from recent clearcutting are particularly common at low elevations. In this study, thirteen forest interior to clearcut center transects were used to investigate soil and fungal-related edge effects on both sides of edges.; Moisture content of surface forest floor material varied more strongly with distance from edge than did moisture content of mineral soil. Moisture levels tended to be lowest just inside forest edges, and highest just outside them, for transects running through edges facing east, north or west. Soils near south-facing edges were drier than soils in clearcut centers. Forest floor moisture content was negatively correlated with soil temperature. Decomposition of Douglas-fir needles occurred more quickly on cooler, moister portions of transects. Needles in such areas were covered with more fungal hyphae and microinvertebrate debris than needles from warmer, drier plots. Regional differences in soil type appeared to be more influential than distance from edge on soil pH.; Patterns in sporocarp taxa richness and biomass production with distance from edge varied with fungal functional group and appeared to primarily reflect availability of an appropriate carbon source. Overall taxa richness of ectomycorrhizal sporocarps was high throughout forests, and declined exponentially in the first 10 m into clearcuts. Decomposer species that produced large, fleshy fruiting bodies appeared much more abundantly in clearcuts than inside forests. Despite these general patterns, individual fungal genera appeared to respond to edge conditions in unique ways. Some only fruited deep in forest interiors, while fruiting of others occurred more frequently near edges.; Results from trenched plots at edges indicated that most ectomycorrhizal fungal fruiting there required photosynthate supplied by adult trees. Western hemlock seedlings in trenched plots grew more rapidly than those in untrenched soil, which was drier, suggesting that competition with roots of adult trees might strongly influence growth of seedlings at edges of clearcuts.; These results indicate that belowground edge effects can be substantial. It seems clear that in order to understand edge effects in forest ecosystems, we need to more fully incorporate belowground organisms and the processes they mediate into edge research.