Postfire shrub cover dynamics: A 70-year fire chronosequence in mountain big sagebrush communities

Abstract

Fire is natural in sagebrush (Artemisia L.) communities. In this study, we quantify effects of time since last burn (TSLB) on shrub cover over a 70-year (yr) fire chronosequence. We sampled mountain big sagebrush communities with very large-scale aerial (VLSA) imagery and measured sagebrush, antelope bitterbrush (Purshia tridentata [Pursh] DC.), and spineless horsebrush (Tetradymia canescens DC.) cover. We used segmented regression to describe two cover phases with respect to TSLB. Phase 1 was when cover responded to TSLB and Phase 2 was when cover had reached a steady state with respect to TSLB meaning that expected shrub cover did not change with increasing TSLB. In the first year after burning, total shrub cover was 5%. In Phase 1, total shrub, sagebrush, and bitterbrush cover increased with TSLB. Bitterbrush transitioned to Phase 2 in 6 yr, but 19 and 18 yr, respectively, were needed for sagebrush and total shrub to transition. Horsebrush cover decreased with TSLB from 2.1% to 0.2% over 27 yr. Steady-state cover for sagebrush, bitterbrush, and total shrub were 30.6, 2.8, and 39.8%, respectively. These data describe postfire shrub cover change in mountain big sagebrush communities that can be used in management plans that meet shrub cover objectives.