Fuel Analysis and Potential Fire Behavior in Mixed Conifer Woodlands of the Great Basin, Nevada, Usa

Abstract

The Great Basin contains mountain woodlands characterized by a mixture of conifer species (mainly Pinus monophylla, Pinus ponderosa, and Juniperus osteosperma) whose interaction with wildland fire may be affected by climatic changes. To determine expected wildfire behavior at these semiarid mountain sites, we analyzed fuel conditions at Mount Irish and the Clover Mountains, in southeastern Nevada. Current fuels were quantified by herbaceous and shrub vegetation cover, down dead woody debris, litter and duff bulk density, canopy bulk density (CBD), and biomass. At Mount Irish, CBD was about twice that at the Clover Mountains, indicating a potential crown fire behavior of higher severity. On the other hand, continuity of surface fuels, and associated surface fire spread, were greater at the Clover Mountains. To reconstruct canopy fuels at each site, all woody stems on twelve 0.1 ha plots were mapped, measured, and cored. Increment cores were processed using dendrochronological methods; establishment dates and reconstructed DBH were then used as input for simulation models. Canopy fuels and potential fire behavior over time were modeled using the Forest Vegetation Simulator (FVS) and its Fire and Fuels Extension. A transition from surface to crown fire conditions was uncovered at both sites, but at the Clover Mountains it occurred 20-30 years post Euro-American settlement, while at Mount Irish it took place 70-80 years prior to settlement. Because patterns and processes of fuel accumulation and potential fire behavior are not spatially or temporally homogenous in Great Basin mixed-conifer woodlands, conservation targets for these ecosystems cannot simply replicate those designed for either pinyon-juniper vegetation or for ponderosa pine stands in other regions of North America.