Effects of non-native plant removal on lizard abundance along the Middle Rio Grande in New Mexico

Many natural processes in the riparian cottonwood (Populus deltoides) forest of the Middle Rio Grande in the southwestern United States have been disrupted or altered, allowing exotic plants, such as saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) to establish. Numerous studies have examined the use of exotic plant-invaded ecosystems by birds, mammals, and arthropods but few have focused on herpetofauna. We sampled lizard populations at 12 study sites in exotic plant-invaded riparian forest along the Middle Rio Grande in central New Mexico for seven years (2000-2006). Sites were randomly assigned to one of three non-native plant removal treatments or as controls. We used a combination of pitfall and funnel traps from three trapping arrays per site to capture, mark, and release lizards June-September. A PCA analysis of 15 vegetation variables identified five factors that best explained the difference among arrays before and after non-native plant removal. Abundances of six common lizard species were related to vegetation components. Results suggested that abundance of lizards was greater at arrays with vegetation characteristics found in areas with non-native plants removed. This was confirmed with a paired analysis showing that, in the case of three lizard species, Chihuahuan spotted whiptail (Aspidoscelis  exsanguis), New Mexico whiptail (Aspidoscelis  neomexicana), and Eastern fence lizard (Sceloporus undulatus), relative abundance increased after non-native plants were removed. Overall, non-native plant removal treatments appear to be beneficial or at least, non-damaging, to the existing herpetofauna of the Middle Rio Grande riparian forest. Providing information on the habitat associations of the herpetofaunal community will help land managers to balance management objectives with other considerations, such as providing important wildlife habitat.