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National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council Impacts in Southwestern Deserts Wildfire and Invasive Species • Nonnative grasses becoming established in deserts: – Red brome (in the Mojave) – Buffelgrass (in the Sonoran) • Grasses transform desert into flammable grassland: fire-adapted grasses re-establish quickly, pushing out native species like Saguaro cactus • Spread of grasses not directly a result of climate change, but warming may allow them to further spread in the desert and extend to higher elevations. Image courtesy T. Esque, USGS. National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council Impacts in Southwestern Deserts The Piñon Pine: Past a Tipping Point • Drought in 2000-2003 stressed a large swath of piñons, leaving them susceptible to infestation by pine bark beetles • This example shows how a stressful event can trigger dramatic ecological change when an ecosystem is subject to many interacting stresses 2002 2004 Images courtesy D. Allen, USGS.