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Paleo-vegetation studies show that even prior to anthropogenic influence, sage steppe communities were dynamic, and sometimes susceptible to replacement by other vegetation communities (including forests) under changing climatic conditions. Likewise, some forest communities (e.g. pinyon and juniper) have expanded northward in the past several thousand years with warming climate conditions. While fire has been a natural part of sagebrush steppe ecosystems (sage-steppe) from thousands to millions of years, human fire starts, land-use change and invasive species have substantially altered the natural fire cycle in recent times. Before Euro-American settlement in the western US in the1800's, fires in sage-steppe were generally smaller and less frequent than today. With settlement, widespread grazing reduced fine fuels and likely promoted expansion and densification of woody species such as sagebrush and juniper. This, along with fire exclusion, may have created a ‘fire deficit' (Marlon et al., 2012) that is now being aggressively remedied by a warming climate and invasive species. In the early 1900's, the arrival and subsequent expansion of cheatgrass (bromus tectorum), has produced an annually renewable continuous cover of dry fuel; in recent decades, fires exceeding 100,000 acres in rangelands are common; fires of this size were extremely unusual prior to the 1980's. Increased use and development in rangelands by people has increased human-caused fires, especially along roads and in recreation areas. Finally, a changing climate is driving longer and hotter fire seasons. These factors combine to create a vicious cycle: hot, dry, fire seasons and plenty of natural and human ignitions spark fires in sage steppe ecosystems, cheatgrass fuels larger and more frequent fires, and following fire, cheatgrass out-competes sagebrush to re-establish quickly in burned areas. These cheat-infested areas then provide more fuel for fires and further increase expansion of cheat at the expense of sagebrush.