The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council. |
Tuesday, January 29, 2008
27
Fire, Great Basin Sagebrush Rangelands and Vegetation Management
Brad Schultz and J.K. McAdoo. University of Nevada Cooperative Extension, 1085 Fairgrounds Road, Winnemucca, NV 89445
Sagebrush covers about 12.3 million ha (30.5 million acres) in Nevada and since 1999 about 2 million ha have burned. Fire is a disturbance mechanism that periodically reduces canopy cover from most woody species, which releases perennial herbaceous species, increasing their cover and biomass production. Large landscapes with spatially and temporally heterogeneous fires potentially can provide the suite of successional stages required to meet the year-long habitat requirements of Great Basin wildlife species. Fire history on Great Basin sagebrush rangelands, however, is poorly known. The few studies conducted have been in mountain sagebrush communities and had fire return intervals of 8-30 years. Return intervals on more arid sagebrush rangelands have been speculated to range from 50 to 125 years or more. Recent research about fire rotation has often been misinterpreted and used to speculate that fire return intervals may be 150 to 300 years or longer. Finally, some resource managers have touted that most fires were small, averaging only 15 to 20 ha (35-50 ac). An analysis of ha burned annually at different return intervals (50-125 years) and an average fire size of 20 ha found an impossibly high number of ignitions per day (52-131) were required to burn the projected acreage during the typical 90-day fire season (mid June to mid September). Further analysis found that a majority of sagebrush ecological sites in Nevada have annual biomass production levels similar to understory production in pondersoa pine forests with fire return intervals of 6-15 years. Lightning occurs less frequently in the Great Basin’s sagebrush region than in Arizona ’s ponderosa pine forests but similar fire frequencies have been documented despite a four fold difference in days with lightning. Fuel loads, fuel continuity and ignition data suggest large and frequent fires probably occurred on at least some sagebrush landscapes.