PHYSIOLOGICAL RESPONSE OF TAMARIX RAMOSISSIMA (TAMARICACEAE) TO A BIOLOGICAL CONTROL AGENT

Within the last century, the floristic composition of riparian communities in the Southwest has drastically changed following introduction of the exotic tree Tamarix ramosissima. In an attempt to control Tamarix populations, the tamarisk leaf beetle (Diorhabda carinulata) has been utilized as a biological control agent. Three years of data collection at our study sites along Fountain Creek (Fountain, CO) allowed us to characterize the response of Tamarix to invasion by the biological control agent. In analyzing data collected before, during, and after the beetle invasion, we observed a significant effect of foliar herbivory on Tamarix physiology and life history strategy. Associations between flower number and functional traits changed before, during, and after the beetle invasion. Before the invasion, reproductively fit individuals exhibited high stomatal conductance and used relatively more water. During and after the invasion, fit plants had higher foliar chlorophyll content, but conductance was not significantly correlated with fecundity. Tamarix responded to defoliation by increasing water use, which may have been an attempt to sustain photosynthate allocation to reproductive structures. Therefore, the leaf beetle may increase the water use of Tamarix during the growing season.