Mule deer response to invasive annual grasses: implications for strategic management in sagebrush priority areas

Abstract

Invasive annual grasses (IAG) are a widespread threat to the sagebrush steppe (Artemisia spp. L) rangelands and associated wildlife of the western United States. Multiple ungulate species including mule deer (Odocoileus hemionus Rafinesque) rely on sagebrush steppe seasonally. While substantial efforts have been made to conserve critical mule deer habitat, less attention has been given to mule deer habitat affected by IAGs and there is limited information about how mule deer respond to IAG invasions. We evaluated mule deer resource selection in a sagebrush grassland community impacted by IAGs in northeast Wyoming. We then used empirical model estimates to forecast how IAG management could impact mule deer habitat in the future following a strategic IAG framework focused on defending and growing sagebrush core areas most threatened by IAGs. We found that mule deer responded to IAGs in a nonlinear pattern across all seasons and strongly avoided areas once cover exceeded approximately 20%. When projecting results 20 yr into the future, we found that over half of the study area is expected to experience significant declines in mule deer habitat quality if IAGs continue to spread at the same rate observed over the past two decades. However, with targeted IAG treatments, we predicted widespread improvements in mule deer habitat, particularly in priority areas where ecological integrity can be restored with future IAG management. Our findings reinforce the emerging notion that ecosystem-based frameworks designed to defend and grow intact sagebrush steppe through strategic management efforts also have the potential to benefit species of conservation interest. As current conservation efforts to mitigate IAGs are not progressing fast enough to address the magnitude of the IAG problem in sagebrush across the west, strategic management efforts will be necessary to maintain important habitats for numerous sagebrush occurring wildlife.