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 ec osystems throughout the southwestern United States necessitates understandi ng its impacts on various ecosystem components, yet surface-active arthropo d communities in these systems remain largely unstudied in spite of their i mportance to ecosystem structure and function. We used pitfall-trap capture s to estimate taxonomic richness, abundance, and composition of surface-act ive arthropods in two cottonwood-dominated and two saltcedar-dominated ripa rian 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 var ied among taxonomic groups. Total richness was similar between the two salt cedar sites and one cottonwood site, but lower at the second cottonwood sit e. Cottonwood sites were distinguished by a greater abundance of exotic iso pods (Armadillidium vulgare and Porcellio laevis). but abundance of other k ey tara was generally similar or higher at saltcedar sites. Richness and ab undance 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 nat ive riparian vegetation, it does support a varied and abundant surface-dwel ling arthropod community that is available as prey to vertebrate species.