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Introduced annual grass increases regional fire activity across the arid western USA (1980–2009)


  • Jennifer K. Balch,

    Corresponding author
    1. Department of Geography, The Pennsylvania State University, University Park, PA, USA
    2. National Center for Ecological Analysis and Synthesis, Santa Barbara, CA, USA
    • Correspondence: Jennifer K. Balch, tel. + 202 360 0923, fax + 805 892 2510, e-mail:

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  • Bethany A. Bradley,

    1. Department of Environmental Conservation, University of Massachusetts-Amherst, Amherst, MA, USA
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  • Carla M. D'Antonio,

    1. Environmental Studies Program & Department of Ecology, University of California-Santa Barbara, Evolution and Marine Biology, Santa Barbara, CA, USA
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  • José Gómez-Dans

    1. Department of Geography, National Centre for Earth Observation and University College London, London, UK
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Non-native, invasive grasses have been linked to altered grass-fire cycles worldwide. Although a few studies have quantified resulting changes in fire activity at local scales, and many have speculated about larger scales, regional alterations to fire regimes remain poorly documented. We assessed the influence of large-scale Bromus tectorum (hereafter cheatgrass) invasion on fire size, duration, spread rate, and interannual variability in comparison to other prominent land cover classes across the Great Basin, USA. We compared regional land cover maps to burned area measured using the Moderate Resolution Imaging Spectroradiometer (MODIS) for 2000–2009 and to fire extents recorded by the USGS registry of fires from 1980 to 2009. Cheatgrass dominates at least 6% of the central Great Basin (650 000 km2). MODIS records show that 13% of these cheatgrass-dominated lands burned, resulting in a fire return interval of 78 years for any given location within cheatgrass. This proportion was more than double the amount burned across all other vegetation types (range: 0.5–6% burned). During the 1990s, this difference was even more extreme, with cheatgrass burning nearly four times more frequently than any native vegetation type (16% of cheatgrass burned compared to 1–5% of native vegetation). Cheatgrass was also disproportionately represented in the largest fires, comprising 24% of the land area of the 50 largest fires recorded by MODIS during the 2000s. Furthermore, multi-date fires that burned across multiple vegetation types were significantly more likely to have started in cheatgrass. Finally, cheatgrass fires showed a strong interannual response to wet years, a trend only weakly observed in native vegetation types. These results demonstrate that cheatgrass invasion has substantially altered the regional fire regime. Although this result has been suspected by managers for decades, this study is the first to document recent cheatgrass-driven fire regimes at a regional scale.

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