Multiple year effects of a biological control agent (Diorhabda carinulata) on Tamarix (saltcedar) ecosystem exchanges of carbon dioxide and water.
Biological control of Tamarix spp. (saltcedar) with Diorhabda carinulata (the northern tamarisk beetle) is currently underway in several western states U.S.A. through historical releases and the natural migration of this insect. Given the widespread dispersal of this biological control agent and its many unknown consequences, this study examines a variety of ecohydrological effects of the beetle on a Tamarix invaded ecosystem in the Great Basin Desert, Nevada. Nearly four years of ecosystem carbon dioxide (CO2) and evapotranspiration (ET) fluxes, measured with an eddy covariance system, are examined in relation to normalized difference vegetation index (NDVI) from Landsat imagery and on the ground measures of leaf area index (LAI) with a light attenuation instrument. We predicted that successive years of beetle herbivory should result in a trajectory of reduced ET and reduced CO2 uptake. We found that three and a half years of beetle herbivory and the resulting defoliation events produced short-term decreases in ET and C uptake. However, total ET and C fluxes over multiple growing seasons were not affected in a clear directional trajectory of reduced ET loss and reduced CO2 uptake, perhaps due to variability in beetle density. LAI and NDVI were fairly well correlated with each other and NDVI was correlated with ET during the summer months, indicating that these measures are useful for detecting beetle damage to the canopy.