NORTHERN TAMARISK BEETLE (DIORHABDA CARINULATA) IMPACTS ON TAMARISK (TAMARIX SPP.) WATER USE
Authors: Pamela Nagler, Uyen Nguyen, Heather Bateman, Christopher Jarchow, Edward Glenn, William Waugh, Charles van Riper III.
Tamarisk beetles (Diorhabda carinulata) were first introduced on the Colorado Plateau in 2002. The beetles feed exclusively on tamarisk leaves, resulting in episodic defoliation events with some mortality of shrubs after several cycles of defoliation. The primary purpose of the releases were to reduce water loss by reduction of tamarisk evapotranspiration (ET) with a secondary goal of improving riparian ecology by allowing the return of native trees to floodplains. The beetles are now widespread throughout the riparian zones of the Upper Colorado River Basin and have moved into the Lower River Basin at migration rates of about 40 km per year. The beetles have now been active on the Colorado Plateau for 14 years. Based on satellite data and ET algorithms, mean ET before beetle release (2000-2006) was 416mm yr-1 compared to post-release (2007-2015) ET of 355mm yr-1 (P < 0.05) for a net reduction of 61mm yr-1. This is lower than initial literature projections that ET would be reduced by 300-460mm yr-1. Reasons for the lower-than-expected ET reductions are because baseline ET rates are lower than initially projected and ET reduction is low because tamarisk stands tend to regrow new leaves after defoliation and other plants help maintain canopy cover. Overall reductions in tamarisk greenness during the study are about 21% based on reductions in ET. This talk will provide a comprehensive assessment of the status of tamarisk and tamarisk beetles and identify research and management needs to cope with the new conditions on rivers colonized by tamarisk.