Sagebrush dominated ecosystems are the largest semi-arid ecosystem in North America and face many threats leading to loss of native species, degradation of wildlife habitat, altered fire regimes, and decreased resistance to invasion and resilience to disturbance. Basin big sagebrush (Artemisia tridentata ssp. tridentata) ecosystems, in particular, are greatly reduced in distribution and are not well-studied. Most land previously dominated by basin big sagebrush has been converted to other land use types, particularly agriculture, due to the occurrence of these plant communities in fertile riparian floodplains. The natural fire regime in these ecosystems is not well defined. In particular, long-term fire effects in basin big sagebrush and the effects of repeated burns in sagebrush-dominated ecosystems are poorly understood. In this study, we revisited and resampled two studies that were burned and measured in the late 1980’s to gain a longer-term perspective of fuels accumulation following fire. Sites were on two different soil types, alluvial flood plain (Bear Creek) and pockets of deep fertile soil on north-facing slopes (John Day Fossil Beds National Monument [JODA]). The JODA site experienced a partial re-burn 10 years after the initial fire, providing an opportunity to quantify the effects of repeated burns on fuels accumulation.
Results/Conclusions
Intra-site variability at Bear Creek was high, ranging from 7-191% recovery of fuel in 25 years (prefire, 36.2-16.8 Mg ha-1; 25 years after fire, 69.1-2.3 Mg ha-1). In contrast, in upland JODA sites recovery of fuel mass 26 years after fire ranged from 113-209% (prefire, 6.2 Mg ha-1; 26 years after fire, 13.0-7.1 Mg ha-1). Repeated burns significantly altered fuels composition. 15 years post a single fire (15YPF), herbaceous fuels made up 44% and shrubs were 39% of total fuels. Twice burned sites (2xB) (burned 26 years and 15 years prior) had 71% herbaceous and 12% shrub fuel. Total fuel loads in 15YPF and 2xB sites ranged from 3.5-6.0 Mg ha-1 and did not differ by site (p=0.85). This suggests repeated burns in close succession could alter rates and trajectories of fuel succession in basin big sagebrush communities.