Post-fire succession in a Great Basin pinyon-juniper woodland: Importance of seed source availability and topographic heterogeneity

Vegetation succession following high-severity, extensive wildfire is considered to be strongly influenced by availability of seeds originating from unburned areas.  However, spatial heterogeneity in survival of seed banks and of belowground meristems is also important and can be expected to vary with topographic controls.  We investigated the relative influence of abiotic and biotic factors on the spatial pattern of post-burn vegetation, for a pinyon-juniper woodland wildland fire. Abiotic factors included topographic, edaphic and climatic variables across multiple spatial scales, obtained from field measurements and GIS analysis.  Biotic factors included pre-burn canopy cover and distance from unburned patches which provide sources for post-fire seed dispersal.  Pre-burn canopy cover, hypothesized to influence legacy effects associated with survivorship of resprouting perennial species and propagule availability, was classified using object-oriented classification algorithms applied to 1-m resolution orthophotography.  Our objectives were to (1) assess whether patches of similar micro-environment, pre-burn legacy of perennial plants and resources, and post-burn seed rain are likely to exhibit similar post-burn dynamics of plant community composition;  (2) develop recommendations for prioritizing restoration sites in pinyon-juniper woodlands following high-severity wildfire. A total of 102, 0.1-hectare, randomly stratified plots were surveyed across the 2800 hectare Wall Canyon burn in central Nevada to characterize plant succession within the 6-year-old burn, for unburned patches within the burn, and the surrounding unburned area.  Preliminary results indicate that topography and surviving seed banks, and not proximity to unburned seed sources, are major factors influencing the probability of rapid post-burn succession to native sagebrush grassland communities.