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Fire Patterns among Ecological Zones in the California Desert, 1984-2013

December 15, 2016

The California desert occupies the southeastern 27 percent of California (11,028,300 ha, 110,283 km2 or 27,251,610 ac). It includes two ecoregional provinces comprised of five desert regions ("ecological sections"; Miles and Goudy 1997). The American Semi-Desert and Desert Province (warm deserts) includes the Mojave Desert, Sonoran Desert, and Colorado Desert sections in the southern 83 percent of the California desert. The Intermountain Semi-Desert Province (cold deserts) includes the Southeastern Great Basin and Mono sections in the northern 17 percent of the region. Previous analyses of fire patterns across the California desert have used point occurrence data. Point occurrence data can have limitations because they can: (1) represent the containment area rather than actual fire area; (2) extend to include unburned areas as contiguous within the fire boundary; (3) be incomplete and estimated before the end of burning; and (4) be reported only in public agency boundaries. Point data also often contain errors associated with the initial recording, or subsequent transcription from paper to electronic records, of the point of origin of a fire. Point datasets also can contain redundancies, such as the same fire being reported by multiple responding agencies that can affect derived statistics such as fire area. Additionally, because points are one dimensional, the area they conceptually represent cannot be readily parsed using other spatial data (e.g. by desert regions and/or ecological zones). More accurate, detailed, and spatially-explicit fire data are available using Landsat satellite imagery from the Monitoring Trends in Burn Severity (MTBS) program. We used these data to precisely document fire area (area within fire perimeters) for fires greater than or equal to 405 ha (1,000 ac) between 1984 and 2013 in the California desert (www.mtbs.gov; accessed 6/30/2015). Previous fire analyses have also stratified analyses by ecological zones derived from 4 Kuchler potential vegetation types (barren, desert shrub, juniper-pinyon, sagebrush). That approach does not distinguish how the relative proportions of vegetation types comprising each ecological zone varies among California desert regions, or explain how the ecotones between the zones shift upslope with decreasing latitude moving from the cold deserts in the north to the warm deserts in the south. These limitations hinder their application to specific areas within the desert bioregion. We derived ecological zones derived from 43 LANDFIRE vegetation biophysical setting types, plus various non-wildland (e.g. developed urban/agriculture/roads) and non-burnable (e.g. open water/barren) areas (Rollins 2009). We also omitted from analyses non-wildland and non-burnable areas (2,003,148 ha [4,949,887 ac]), and focused instead on the remaining burnable wildland areas (9,025,152 ha [22,301,636 ac]). The 43 biophysical setting types were grouped into 13 general vegetation types, which were further grouped into four elevation-based ecological zones plus one riparian zone according to their constituent plant associations. The resulting 5 ecological zones were then intersected with the boundaries of the 5 desert regions of the California to create a map and associated burnable wildland area statistics. A diagram was also created illustrating the relative elevational positions of each ecological zone and vegetation type along a latitudinal gradient from cold deserts to warm deserts.

These data were developed to assess the distribution of wildfire regimes across California deserts for the chapter "Southeast Deserts Bioregion" in the book "Fire in California's Ecosystems, Second Edition" published by University of California Press.

Miles, S. R. and C. B. Goudy. 1997. Ecological subregions of California: section and subsection descriptions. USDA Forest Service, Pacific Southwest Region, R5-EM-TP-005, San Francisco, CA.
Rollins Matthew G. (2009) LANDFIRE: a nationally consistent vegetation, wildland fire, and fuel assessment. International Journal of Wildland Fire 18, 235-249.

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