Infestation by the non-native tree Tamarix spp. has made habitat restoration projects necessary to maintain the ecological integrity of many riparian communities in the Southwest. These restoration projects may include Tamarix removal, manipulation of hydrographs, and active revegetation of native species. There is no single strategy for achieving success in these projects; rather success will vary by site based on specific site characteristics and methods used. Revegetation success, plant species diversity, and vegetative cover were evaluated at 28 sites in New Mexico, Arizona, and Nevada where active revegetation was completed after Tamarix removal. These data were incorporated into regression tree models with predictor variables that included number of years since removal (1-18 years) and multiple management, climate, soils, and hydrological variables to determine success of Tamarix control, revegetation success, and plant community responses. Our results suggest that there are easily measurable site characteristics that lead to greater native cover and richness, planting success, and Tamarix control. Lower soil salinity and pH and coarser soil texture as well as proximity to permanent water, sufficient precipitation, and good drainage all favored native species. Additionally, success increased with time since Tamarix removal, both increasing native cover and richness and decreasing Tamarix cover. Overall, those site characteristics that promoted native species success were the same as those that contributed to a lower cover of Tamarix. These quantitative models are intended to assist researchers and land mangers to design more effective riparian restoration efforts in this critical arid lands ecosystem.
