Invasion of the exotic grasses: Mapping their progression via satellite

Abstract

Several exotic annual grass species are invading the Intermountain West. After disturbances including wildfire, these grasses can form dense stands with fine fuels that then shorten fire intervals. Thus invasive annual grasses and wildfire form a positive feedback mechanism that threatens native ecosystems. Chief among these within Nevada are Bromus tectorum (cheatgrass), Bromus rubens (red brome), and Schismus barbatus (Mediterranean grass). These grasses have an early phenology for both green-up and senescence that can be detected from the difference in greenness between two well-timed satellite images, allowing grass cover to be geographically modeled. The Nevada Natural Heritage Program is using imagery from Landsat and MODIS satellites to map annual grass invasion, and has completed a map of annual grass cover for the State of Nevada. The models and final map were developed from 806 training sites, remotely sensed data for two seasons from Landsat 5 TM and MODIS satellite sensors, and accessory geographic data. Accuracy of the final map was analyzed from two independent data sets: Southwest Regional Gap Analysis Project (REGAP) training data (15,318 plots) and California Department of Fish and Game vegetation plots from the Mojave region (939 plots). Root-Mean- Square-Error (RMSE) from the REGAP data was 10.33 percent; 75 percent of predictions for gap plots were off by 5 percent or less; and 95 percent of predictions were off by 21 percent or less. For the Mojave data set, RMSE was 7.48 percent; 75 percent of predictions were off by 9 percent or less; and 95 percent of predictions are off by 15 percent or less. Accuracy assessment on REGAP data suggests that annual grass cover is generally underestimated for sites with high cover, thus the map should be interpreted as an index of cover rather than an estimate of actual cover. Nevertheless, the map reveals the pattern of annual grass invasion across Nevada.

Parent Publication

• Proceedings-Shrublands under fire: disturbance and recovery in a changing world; 2006 June 6-8; Cedar City, UT

Citation

Peterson, Eric B. 2008. Invasion of the exotic grasses: Mapping their progression via satellite. In: Kitchen, Stanley G.; Pendleton, Rosemary L.; Monaco, Thomas A.; Vernon, Jason, comps. 2008. Proceedings-Shrublands under fire: disturbance and recovery in a changing world; 2006 June 6-8; Cedar City, UT. Proc. RMRS-P-52. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 33-39