Detection of the spatiotemporal patterns of beetle-induced tamarisk (Tamarix spp.) defoliation along the Lower Rio Grande using Landsat TM images

The invasive Tamarisk (Tamarix spp.) has long been targeted for removal by land managers in the western United States. Biocontrol of the non-native tamarisk started in 2001 by introducing the tamarisk leaf beetle (Diorhabda spp.) to the riparian ecosystems. Since then, the beetles quickly established and substantial tamarisk defoliation was subsequently observed along river corridors in the western states. The ability to monitor and track the patterns of beetle-induced tamarisk defoliation across space and time is key to understand its impact on ecosystem functioning and processes. In the present study, spatiotemporal patterns of tamarisk defoliation caused by the subtropical tamarisk leaf beetle (D. sublineata) were successfully detected using a classification based method along the Lower Rio Grande in West Texas from 2009 to 2014. Our results indicated that the subtropical beetle species can sustain a dispersal rate of approximately 102kmyr−1 during the first year after release. Tamarisk abundance was the most important factor in directing beetle dispersal. We also found that the beetles preferred to forage within dense, connected tamarisk stands along wide sections of the riparian river corridors. These new findings of our study will help inform the land managers of the possible outcomes of tamarisk biocontrol to make effective management plans.