Surface-active arthropod communities in native and exotic riparian vegetation in the middle Rio Grande Valley, New Mexico

The rapid naturalization of exotic saltcedar (Tamarix) trees in riparian ecosystems throughout the southwestern United States necessitates understanding its impacts on various ecosystem components, yet surface-active arthropod communities in these systems remain largely unstudied in spite of their importance to ecosystem structure and function. We used pitfall-trap captures to estimate taxonomic richness, abundance, and composition of surface-active arthropods in two cottonwood-dominated and two saltcedar-dominated riparian forests along the Middle Rio Grande of central New Mexico during 1991 through 1993. Arthropod communities at cottonwood sites were generally more similar to each other than to those at saltcedar sites, but similarity varied among taxonomic groups. Total richness was similar between the two saltcedar sites and one cottonwood site, but lower at the second cottonwood site. Cottonwood sites were distinguished by a greater abundance of exotic isopods (Armadillidium vulgare and Porcellio laevis). but abundance of other key tara was generally similar or higher at saltcedar sites. Richness and abundance of spiders was greater at saltcedar sites. Predators were the most speciose trophic group at all sites, although detritivores had the greatest numbers of individuals due to the abundance of isopods. Although saltcedar has greatly altered riparian ecosystems and may be less desirable than native riparian vegetation, it does support a varied and abundant surface-dwelling arthropod community that is available as prey to vertebrate species.