Fire and the Great Basin

Fire regimes in Great Basin ecosystems have changed significantly since settlement of the region in the mid- to late 1800s. The following provides an overview of the nature and consequences of altered fire regimes, factors influencing the changes, and research and management questions that need to be addressed to maintain sustain-able ecosystems. For more detailed information, please see the list of references and recommended links. What are the consequences of altered fire regimes? Major changes are occurring in Great Basin vegetation communities—(1) In forested systems, a decrease in fire frequency due largely to fire exclusion has resulted in a shift in species composition from early-seral, shade intol-erant species to late-seral shade tolerant species. Increases in vertical stand structure (fuel ladders) and biomass (fuel loads) are resulting in more severe fires (Keane and others 2002). (2) In the pinyon-juniper woodland zone, decreased fire frequency due to fire exclusion, overgraz-ing through the mid-1900s, and climate change initially facilitated expansion and in-filling of pinyon and juniper trees. As stands mature and canopy closure occurs, the risk of higher-severity crown fires is increasing (Miller and others, in press). (3) In arid and semi-arid shrublands and lower-elevation pinyon-juniper woodlands, an in-crease in annual invasive grasses, coupled with higher fire frequencies, is resulting in progressive conversion of these ecosystem types to near homogenous grasslands dominated by invaders (Brooks and Pyke 2001). Changes occurring in vegetation communities are decreasing biodiversity and placing species at risk— Populations of many sagebrush-associated species are in decline, and approximately 20 percent of the ecosystem’s native flora and fauna are considered imperiled (Center for Science, Economics and Environment 2002). Fire exclusion in forests that historically experienced higher fire frequencies has resulted in increased landscape homogeneity and decreased patch diversity. Vegetation types that depend on more frequent and lower severit