Mapping the Cheatgrass Caused Departure from Historical Natural Fire Regimes

Abstract—Cheatgrass (Bromus tectorum) is an exotic grass that has increased fire hazard on millions of square kilometers of semi-arid rangelands in the western United States. Cheatgrass aggressively outcompetes native vegetation after fire and signifi-cantly enhances fire size and frequency. To evaluate the effect of cheatgrass on historical natural fire regimes, we combined cheatgrass data mapped from Advanced Very High Resolution Radiometer images of the Great Basin with Fire Regime Condi-tion Class (FRCC) data mapped from plant succession data incorporated with several spatial data layers for the conterminous United States. These FRCCs depict the degree of departure from historical fire regimes resulting in alterations of key ecosys-tem components such as species composition, structural stage, stand age, and canopy closure. While the FRCC data layer adequately depicted forest communities, it insuf-ficiently depicted grassland and shrubland communities. By adding cheatgrass, FRCC 3 (areas that have been significantly altered from their historical range) increased by 20 percent on Federal lands to almost 60,522 square kilometers for the contermi-nous United States