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Fuel Analysis in Upper Elevation Pinyon-Juniper Woodlands of Lincoln County, Nevada
AuthorCheek, Jonathan Wetherington
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Wildland fires are an important component of the Great Basin ecosystem, and their behavior is greatly controlled by forest fuels. Understanding changes in fuel conditions through time can enable managers to better manage fire use. Using data from permanent plots located within Mount Irish and the Clover Mountains of Lincoln County, Nevada, I studied current fuel conditions and their past changes in relation to historic stand composition and structure, climate variability, fire occurrence, and human impacts. My objectives were to quantify current surface and crown fuel, canopy bulk densities, and to use a regionally-specific vegetation simulator to: (1) reconstruct forest structure; (2) estimate changes in canopy fuels at each study site from time of settlement through the present (2007 at Mount Irish and 2008 at the Clover Mountains) and near future (2050); and (3) estimate changes in potential crown fire behavior over time. <italic>Pinus</italic> <italic>ponderosa</italic>, <italic>Pinus</italic> <italic>monophylla</italic>, <italic>Juniperus</italic> <italic>osteosperma</italic>, <italic>Juniperus</italic> <italic>scopulorum</italic>, and <italic>Abies</italic> <italic>concolor</italic> are tree species at the two study sites. Current fuel characteristics were quantified by: down dead woody debris (planar intercept method), litter and duff bulk density (collection and weighing), and canopy biomass and bulk density (allometric equations and Fuel Management Analysis Plus program). Percent cover for herbaceous and shrub vegetation was estimated using a Braun-Blanquet (1965) cover class system. The Clover Mountains have significantly higher amounts of 10-hr surface fuel and lower bulk densities of litter, and combined litter and duff (103.4 kg/m<super>3</super> at Mount Irish, 63.8 kg/m<super>3</super> at the Clover Mountains), which favor a higher rate of surface fire spread compared to Mount Irish. Both study sites have similar herbaceous cover percentages, but the Clover Mountains have higher percent cover of shrub vegetation, which also favors surface fire spread. Combining all species, canopy bulk density is significantly greater (P ≤ 0.05) at Mount Irish (0.195 kg/m<super>3</super>) compared to the Clover Mountains (0.085 kg/m<super>3</super>). This indicates that Mount Irish is more susceptible to a severe crown fire. Forest simulation modeling using USDA Forest Vegetation Simulator (FVS) began in 1900 at the Clover Mountains and in 1850 at Mount Irish, and modeled changes in canopy fuels (canopy biomass, canopy bulk density) and potential fire behavior (crowning index) through 2050. Simulations were relatively accurate, as assessed by comparing the simulation output in the year 2007 for Mount Irish and in the year 2008 for the Clover Mountains with field data collected in those years. I used a regionally calibrated simulator for the Great Basin (Utah variant) and I added regeneration by species and density in the correct historical sequence. Potential crown fire behavior was assessed with FVS in terms of crowning index (CI), the windspeed necessary to sustain a crown fire. Crowning index values decreased by 47.5% at Mount Irish and by 60% at the Clover Mountains over the modeled periods, indicating that both sites are becoming more susceptible to crown fire. If management goals are to prevent this type of destructive fire, then careful examination of available options to modify existing fuel loads is recommended.