Northern tamarisk beetles (Diorhabda carinulata) were released in the Upper Colorado River Basin in 2004–2007 to defoliate introduced tamarisk shrubs (Tamarix spp.) in the region’s riparian zones. The primary purpose was to control the invasive shrub and reduce evapotranspiration (ET) by tamarisk in an attempt to increase stream flows. USGS scientists evaluated beetle-tamarisk interactions with MODIS and Landsat imagery on 13 river systems, with vegetation indices used as indicators of the extent of defoliation and ET. Beetles are widespread and exhibit a pattern of colonize-defoliate-emigrate, so that riparian zones contain a mosaic of completely defoliated, partially defoliated, and re-foliated tamarisk stands. Based on satellite data and ET algorithms, mean ET before beetle release (2000–2006) was 416 mm/year compared to post-release (2007–2015) ET of 355 mm/year (P
Major sampling sites for defoliation trends and evapotranspiration across the Colorado River Basin.