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The ecosystems of the west are adapted to a long history of wildland fires that varied in frequency and severity. Over the last 100 years or more, though, fire suppression efforts, human settlement patterns and other land use practices have changed the composition and structure of the forests and grasslands of the West. Where once we typically had periodic low-intensity fires of low severity, we now experience damaging fires that can be both intense and severe. Severe fires can substantially affect the environment. Lack of vegetation on burned hillsides increases the likelihood of flooding and soil erosion from rain and snowfall. In turn, the water quality of streams and rivers is degraded, which affects fish populations. Wildlife populations are disrupted. However, the most environmentally and economically damaging impact of wildfires is the post-fire invasion and aggressive reestablishment of noxious weeds, which compete aggressively with desired native species for space and nutrients. Minimizing the impact of noxious weeds requires good post-burn weed management. Many kinds of native plants will survive and reinitiate growth soon after a fire. The ability of these plants to reestablish, thrive and reseed in subsequent years will be reduced by the presence of noxious weeds. Unfortunately, noxious weeds can thrive in recently burned areas. Fires expose ground surfaces, reduce shade and increase light, and create a flush of nutrients. All of these conditions favor weeds. Wildlife habitat, livestock grazing, watershed stability and water quality may be compromised. Large-scale infestations of noxious weeds are difficult, and costly, to manage.