Canopy arthropod communities in relation to forest age and alternative harvest practices in western Oregon

Arthropod community structure and herbivory were compared inreplicate Douglas-fir and western hemlock canopies in intact old-growth (>400 yr old), and Douglas-fir only in partially-harvestedold-growth, natural mature (150 yr old) stands, and regenerating
plantations (10-20 yr old) in a 15,000 ha including the H.J.Andrews Experimental Forest in western Oregon. Species diversityand abundances of several taxa, especially predators anddetritivores, were significantly lower in plantations, comparedto older forests. Mature, old-growth, and partially-harvestedstands showed few significant differences, but principalcomponents analysis (PCA) suggested some differences in communitystructure and indicated that old-growth was least variable(tighter clustering) in arthropod diversity and abundance,whereas partially-harvested stands were most variable.Defoliation was higher in the mature stands, probably becausethese stands were composed of relatively dense and pure Douglas-fir. Although old-growth appeared to be the source of greatestarthropod biodiversity in these forests, arthropod communities inDouglas-fir canopies may largely recover old-growth structure by150 years, and partially-harvested stands retain substantiallygreater arthropod diversity than do regenerating plantations.
Key Words: Diversity, herbivory, disturbance, succession,
Pseudotsuga, Tsucra