Predicting fire-based perennial bunchgrass mortality in big sagebrush plant communities

Abstract

Maintenance and post-fire rehabilitation of perennial bunchgrasses is important for reducing the spread of exotic annual grass species in big sagebrush plant communities. Post-fire rehabilitation decisions are hampered by a lack of tools for determining extent of fire-induced perennial grass mortality. Our objective was to correlate post-fire characteristics with perennial bunchgrass mortality at the plant and plant community scales. We recorded basal area, percent char, depth of burn and soil colour for 174 bunchgrasses across four ecological sites after a 65 000 ha wildfire in south-east Oregon and assessed plant mortality. Mortality was correlated with post-fire soil colour and ecological site; soil colours (black and grey) associated with pre-fire shrub presence had up to five-fold higher mortality than brown soils typical of interspace locations. Models incorporating depth of burn and soil colour correctly predicted mortality for 90% of individual plants; cover of brown soil explained 88% of the variation in bunchgrass mortality at the plant community scale. Our results indicate that soil colour and depth of burn are accurate predictors of bunchgrass mortality at individual plant and plant community scales and could be used to spatially allocate post-fire bunchgrass rehabilitation resources.