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

Authors: Boyd, Chad; Davies, Kirk; Hulet, April

Submitted to: International Journal of Wildland Fire
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2014
Publication Date: 3/26/2015
Citation: Boyd, C.S., Davies, K.W., Hulet, A. 2015. Predicting fire-based perennial bunchgrass mortality in low elevation big sagebrush plant communities. International Journal of Wildland Fire. 24:527-533. https://doi.org/10.1071/WF14132.
DOI: https://doi.org/10.1071/WF14132

Interpretive Summary: Empirical knowledge of how to predict fire-based mortality of perennial bunchgrasses is extremely limited which hampers post-fire vegetation rehabilitation decision-making. Our objective was to correlate post-fire environmental characteristics with perennial bunchgrass mortality at the plant and plant community scales; we recorded post-fire basal area, percent char, depth of burn, and post-fire soil color for 174 bunchgrasses across four ecological sites within a 65,000 ha summer wildfire in southeast Oregon and related these characteristics to perennial bunchgrass mortality one year post-fire. Individual bunchgrass mortality was highest on black-colored soils (which are associated with pre-fire under shrub canopy locations) and with increasing depth of burn within the plant crown, and 88% of the variation in bunchgrass mortality at the plant community scale was explained by soil color. Our results indicate that soil color and depth of burn are accurate predictors of bunchgrass mortality at individual plant and plant community scales and could be used to determine spatial allocation of post-fire bunchgrass rehabilitation effort.

Technical Abstract: Maintenance and post-fire rehabilitation of perennial bunchgrasses is important for reducing the spread of annual grass species in low elevation 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 post-fire basal area, percent char, depth of burn, and soil color for 174 bunchgrasses across four ecological sites within a 65,000 ha summer wildfire in southeast Oregon and assessed plant mortality one year post-fire. Mortality varied by post-fire soil color and ecological site; soil colors associated with pre-fire shrub presence (black and gray) had up to 5 fold-higher mortality than brown soils typical of interspace locations. Models incorporating depth of burn and soil color 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 color and depth of burn are accurate predictors of bunchgrass mortality at individual plant and plant community scales and could be used to determine spatial allocation of post-fire bunchgrass rehabilitation effort.