Vertical and seasonal variation in canopy arthropod communities in an old-growth conifer forest in southwestern Washington, USA

Variation in canopy arthropod abundances and community structure were evalu ated in an old-growth (500-year-old) forest at the Wind River Canopy Crane Research Facility in southwestern Washington, USA. Arthropods were sampled at three canopy levels and two seasons in each of four tree species (Pseudo tsuga menziesii, Tsuga heterophylla, Abies grandis, and Thuja plicata). The four tree species had distinguishable arthropod species compositions and c ommunity organization. Thuja plicata (Cupressaceae) had a particularly dist inctive canopy fauna dominated by several mite taxa which did not occur on the other tree species (all Pinaceae). Pseudotsuga menziesii hosted a relat ively diverse arthropod fauna with greatest richness of taxa and functional groups. Distinct arthropod assemblages were not observed among canopy leve ls and sampling dates, but these factors significantly influenced abundance s of 63% of the arthropod taxa, either individually or interactively with o ther factors. These data indicate that forests managed for fewer tree speci es eliminate important components of arthropod diversity in Pacific Northwe st forests and that sampling for biodiversity assessment also should repres ent season and canopy level.