Controls on spatial patterns of wildfire severity and early post-fire vegetation development in an Arizona Sky Island, USA

Context: Spatial patterns of vegetation change and fire severity are influenced by fire exclusion, topography and weather conditions during a fire. Since the late nineteenth century, fire exclusion has increased vegetation cover which could influence fire severity and post-fire vegetation composition. Objectives: We use field measurements and remote sensing of a 2011 wildfire to answer the following questions: (1) How did twentieth century vegetation change influence fire severity patterns? (2) What were the key drivers of wildfire severity? (3) Did initial post-fire development indicate stability or a shift in woody plant composition. Methods: Repeat aerial photography and pre and post fire field measurements were used to quantify twentieth century vegetation change and measure wildfire effects. Spatial controls on 2011 fire severity were determined using geospatial layers of vegetation type and change, topography, fire weather, daily fire extent, and fire severity. Results: Vegetation changes since 1935 increased area of closed woodlands and shrublands and the 2011 fire reversed this trend and increased heterogeneity of vegetation types. Vegetation in plots experienced a post-fire shift towards resprouting species. At the landscape scale, terrain and weather were the main variables controlling fire severity with modest contribution by vegetation type and areas with vegetation change since 1935. Conclusions: Our findings indicate that wildfire severity in this landscape is strongly influenced by weather and terrain and wildfires reverse the effects of fire exclusion. Using terrain based landscape compartments for prescribed and wildfire management would help maintain the heterogeneous effects of the 2011 fire into future.