OOS 41-6
A new project to evaluate vegetation response to Tamarix control and restoration across 4 states during the last 20 years
Efforts to control Tamarix invasion in the US have been very intense during the last two decades. Years of trials and errors with a diversity of techniques employed for Tamarix eradication, including the biocontrol agent Diorhabda carinulata, have gradually increased the effectiveness in keeping stable and even reducing Tamarix populations in many watersheds. However, even though Tamarix removal effectiveness is today higher than when these efforts began decades ago, most of the restoration works that have been done have not been evaluated systematically. When this evaluation has occurred, it has been usually local (river reach), limiting the finding of general patterns that may guide restoration elsewhere. Only two works have evaluated success of multiple Tamarix removal projects at large spatial scales (Harms and Hiebert, 2006 and Bay and Sher 2008). Harms and Hibert’s work was based on data collected in 2003, only two years after the first release of D. carinulata. Bay and Sher (2008)’s field work was done in 2005 and focused on restored sites where active revegetation, a less frequently used restoration practice, had taken place.
Results/Conclusions
We recently launched a new project to implement an integrative evaluation of Tamarix control efforts in the Southwest of US for the last two decades. A database of more than 250 sites (reference, control, biocontrol and removal) in different river reaches of the Upper, Lower Colorado, and Rio Grande catchments is currently being collected. The database includes information on plant composition and three potential groups of factors determining success: (1) hydrology, (2) site history and (3) meteorology. Preliminary analyses of these data reveal that even though Tamarix populations are being controlled, riparian plants do not readily colonize restored sites. Here we present our approach to using asymmetric eigenvector maps and constrained ordinations to describe the contribution of the different group of factors in determining success as well as a conceptual model to understand the different successional trajectories after Tamarix control. This project is intended to provide guidelines that will optimise resources devoted to riparian restoration in the future. Further, understanding plant community succession after significant disturbances associated with weed control is important in the context of how we view plant invasions and our response to them.