Invasive woody plants affect the composition of native lizard and small mammal communities in riparian woodlands

Nonnative Tamarix spp. (saltcedar) is among the most invasive and common trees along riparian habitats in the western U S, impacting native plant communities and habitat quality. Tamarix dominance causes a reduction in habitat physiognomic heterogeneity in riparian habitats. Animal abundance, diversity and habitat associations in monotypic stands of saltcedar remain largely unexplored for non-avian communities. We sampled small vertebrate and ground arthropod communities in monotypic Tamarix stands and in mixed stands of Tamarix and native (Populus, Salix, and Prosopis spp.) trees in riparian habitats along the Virgin River in the Mojave Desert. Our survey of faunal communities suggests that many species of arthropods, reptiles and small mammals utilize both Tamarix-dominated and mixed habitats along the Virgin River. Small mammal and lizard communities were dominated by generalist species. Mixed stands had greater arthropod abundance, lizard abundance and small mammal diversity; whereas, monotypic and mixed stands had similar lizard diversity. The habitat of mixed sites was characterized by 'nativeness' (areas with native riparian trees) and less 'shady exotic thickets' (areas with Tamarix and high overstory cover) compared to Tamarix-dominated stands. There were species-specific responses to habitat physiognomy. Peromyscus maniculatus (deer mouse) was associated with shady exotic thickets. Sceloporus magister (desert spiny lizard) and Neotoma lepida (desert woodrat) were associated with native trees and woody debris. Seven rodent and lizard species' abundances were explained by habitat physiognomy variables. Rare and specialist species were more impacted by nonnative vegetation. These results contribute to the body of research on animal utilization of nonnative habitats and relation to habitat physiognomy. Management of nonnative plants should consider how control activities could impact habitat physiognomy and native animal communities in riparian habitat.