Projections of Contemporary and Future Climate Niche for Wyoming Big Sagebrush (Artemisia tridentatasubsp.wyomingensis): A Guide for Restoration

Abstract

Big sagebrush (Artemisia tridentata) is one of the most widespread and abundant plant species in the intermountain regions of western North America. This species occupies an extremely wide ecological niche ranging from the semi-arid basins to the subalpine. Within this large niche, three widespread subspecies are recognized. Montane ecoregions are occupied by subspecies vaseyana, while subspecies wyomingensis and tridentata occupy basin ecoregions. In cases of wide-ranging species with multiple subspecies, it can be more practical from the scientific and management perspective to assess the climate profiles at the subspecies level. We focus bioclimatic model efforts on subspecies wyomingensis, which is the most widespread and abundant of the subspecies and critical habitat to wildlife including sage-grouse and pygmy rabbits. Using absence points from species with allopatric ranges to Wyoming big sagebrush (i.e., targeted groups absences) and randomly sampled points from specific ecoregions, we modeled the climatic envelope for subspecies wyomingensis using Random Forests multiple-regression tree for contemporary and future climates (decade 2050). Overall model error was low, at 4.5%, with the vast majority accounted for by errors in commission (>99.9%). Comparison of the contemporary and decade 2050 models shows a predicted 39% loss of suitable climate. Much of this loss will occur in the Great Basin where impacts from increasing fire frequency and encroaching weeds have been eroding the A. tridentata landscape dominance and ecological functions. Our goal of the A. tridentata subsp. wyomingensis bioclimatic model is to provide a management tool to promote successful restoration by predicting the geographic areas where climate is suitable for this subspecies. This model can also be used as a restoration-planning tool to assess vulnerability of climatic extirpation over the next few decades.