Effects of Coarse Woody Debris and Soil Depth on the Density and Diversity of Soil Invertebrates on Clearcut and Forested Sites on the Olympic Peninsula, Washington

Arthropod density and species richness were determined using high-gradient extraction for soil on clearcut and late successional forests on the Olympic Peninsula, WA. Study objectives were to compare the effects of harvesting at different soil depths and distances from coarse woody debris. Canonical correspondence analysis (CCA) was used to determine the effects of soil moisture, CO2 evolution, and 0 and A horizon depth on species composition. Soil depth had a greater effect on changes in density than did distance to woody debris. Densities of Acari, as well as total species richness, were significantly higher at 0–5 cm depths than at 5–10 cm despite significantly lower moisture content at the soil surface. Density of Acari and Coleoptera and species richness were significantly higher on forested sites than on clearcuts. There was a trend toward higher Collembolan density on clearcuts, but the difference was not significant because of the very different responses on dry and wet clearcuts sites. The results of CCA suggests moisture and O and A horizon depths were the most important quantitative environmental factors we measured in determining differences in species composition. Clearcutting appeared to have site specific-effects on wet and dry site locations. Low moisture and temperature extremes did not appear to limit microarthropod density. High rainfall accentuated by clearcutting was associated with lower O and A horizon depths and appeared to decrease Collembola and Coleoptera density on the wet clearcut.