Spatial Analysis of Historical Fire Regimes and Landscape Structure in Sagebrush Ecosystems of the United States

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Reconstructing evidence of historical fires is difficult at the large spatial extent required to understand whether recent large wildfires like the 652,358 acre Murphy Complex fires of 2007 in Idaho and Nevada sagebrush, are unprecedented or also occurred historically, prior to widespread EuroAmerican land uses. This limitation is particularly problematic in sagebrush ecosystems, which cover about 47 million ha of the western United States, as tree-ring evidence of historical fires is limited to forests and woodlands on the margin of these ecosystems. As a consequence, little is known about the structure of historical sagebrush landscapes or the rates and patterns of historical wildfires in these landscapes. Professor William Baker at the University of Wyoming will reconstruct historical fire regimes and landscape structure in sagebrush ecosystems in the United States using the General Land Office Surveys of the late 1800s. Surveyors recorded the location of wildfires and early-successional postfire vegetation as they laid out section lines. Section-line information can be computerized and converted into maps of historical vegetation to allow spatial analysis of historical fires and landscape structure. The study will acquire, process, and analyze survey records for sample sagebrush landscapes of about 2,223,900 acres in each of four major floristic provinces spanning the range of sagebrush in the United States, and use these records to reconstruct historical fires and landscape structure. The research will address nine specific hypotheses about historical fire regimes and landscape structure in sagebrush. These hypotheses center on (1) historical fire-size distributions, (2) the patchiness of historical fires, (3) the frequency at which fire historically burned across landscapes, (4) the structure and size of historical landscapes, and (5) geographical variation in historical fire regimes and landscape structure. Sagebrush is the sole habitat for a host of sagebrush-obligate species, some that are declining or are already listed as threatened or endangered, for example Sage Grouse. Sagebrush is also key forage for major populations of native ungulates, such as deer and elk, on their winter ranges. This study will substantially enhance basic understanding of spatial variation in a key natural wildfire disturbance and its historical influence on the structure of large landscapes representing a major western ecosystem. Improved information on historical wildfires will help understand if there is a wildfire contribution to declining species and how to manage wildfires and sagebrush on key winter ranges.