Canopy arthropod assemblages in four overstory and three understory plant species in a mixed-conifer old-growth forest in California

We compared canopy arthropod assemblages among overstory conifer and understory angiosperm species at Teakettle Experimental Forest in the Sierra Nevada in California during 1998-2000. Arthropods were sampled from upper, middle, and lower crown levels of one overstory tree of each of the four dominant conifer species (Jeffrey pine, sugar pine, white fir, and incense cedar), and from three understory plants of each of the major understory species (California black oak, manzanita, and white-thorn ceanothus) in each of five replicate plots during June and Aug. in each of the 3 years to represent seasonal and annual variation in abundances. Many taxa differed significantly in abundance among plant species, with one to five taxa being significant indicators for each plant species. Five to eight taxa on each plant species showed significant differences in abundance among years. Aphids and scale insects, predaceous mirids, and some detritivores showed peak abundances in 1999, a particularly dry year, whereas most other taxa showed lowest abundances during 1999 or declining abundances during this period, suggesting association with wetter conditions. Nonmetric multidimensional scaling (NMS), supported by multi-response permutation procedure (MRPP), showed that arthropod assemblages differed significantly among the seven plant species, especially between overstory conifers and understory angiosperms, and among the 3 years. These data indicate that the diversity and structure of arthropod communities depend on vegetation structure and/or condition, perhaps as modified by annual variation in weather conditions.