Location: Great Basin Rangelands ResearchTitle: Multiple year effects of a biological control agent (Diorhabda carinulata) on Tamarix (saltcedar) ecosystem exchanges of carbon dioxide and water) Author
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/2012
Publication Date: 10/15/2012
Citation: Snyder, K.A., Scott, R.L., Mcgwire, K. 2012. Multiple year effects of a biological control agent (Diorhabda carinulata) on Tamarix (saltcedar) ecosystem exchanges of carbon dioxide and water. Agricultural and Forest Meteorology. 164:161-169. Interpretive Summary: An insect biological control agent, a leaf beetle, was released in several western states, in an effort to control the invasive woody species saltcedar. Saltcedar has invaded many river drainages in the western states. This study documents the effect of beetle herbivory and subsequent premature leaf fall on ecosystem exchanges of water and carbon dioxide. Carbon uptake and water lost via saltcedar transpiration was reduced for short time periods (two to three weeks) when the trees were leafless. However, over longer time frame 3.5 years of measurements there was not a reduction in carbon uptake or transpirational water. This may be in part due to the lower beetle density measured in the last year of data analyzed in this study.
Technical Abstract: 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 the 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 well correlated with ET during the summer months, indicating that these measures are useful for detecting beetle damage.