Simulating future climate and land-use impacts on the Greater Sage-grouse

Background/Question/Methods

The Greater Sage-grouse (Centrocercus urophasianus) is a candidate species for listing under the Endangered Species Act and an icon for sagebrush conservation in the western US.  Threats to Greater Sage-grouse include habitat conversion and potential climate-induced changes in the distribution of sagebrush.  Typically, bioclimatic models that relate species’ current distributions to historical climate are used to project climate-impacts on future distributions.  These rarely incorporate land-use nor species associations with habitat, dispersal ability, or population responses.  Mechanistic simulation models address many of these gaps.  We explore the impacts of future land-use and climate change on Greater Sage-grouse using a spatially explicit individual-based simulation model, HexSim. We run the model with future land-use information simulated using the Forecasting Scenarios of Land-Cover (FORE-SCE) model and future vegetation information generated with a dynamic vegetation model incorporating downscaled output from five global climate models.  Our projections are based on the IPCC SRES A2 scenario reflecting continuous human population growth in the 21^stcentury and regional economic development.  This framework allows us to visualize annual, climate-driven changes in regional populations as well as the overall distribution of sage-grouse.

Results/Conclusions

Within a study area encompassing 97% of the Greater Sage-grouse’s current range across the interior western US, sagebrush-dominated shrublands are projected to decline by 6-27% from their current simulated extent (412,244 km²), depending on the global climate model considered.  Grassland steppe, which currently includes a sagebrush component, is also likely to change, with projections ranging from a decrease of 53% to an increase of 24% of its current extent (766,714 km²).  Land-uses unsuitable to sage-grouse, including urban and suburban development, mining, row-crop agriculture, and haylands, are projected to increase to 173% of their current extent (242,327 km²).  Projections of sage-grouse distributions track changes in available habitat, but with greater sensitivity to future vegetation cover than land-use.  Population-level responses include declines in regions projected to be more heavily impacted by climate change (e.g . the Great Basin) and land-use (e.g. the high plains of eastern Wyoming and Montana).  Regional conservation strategies focused on Greater Sage-grouse will need to adapt.  Many existing Important Bird Areas occur in sagebrush habitats projected to transition into grass-dominant systems.  Future designations should target projected sagebrush refugia in the Great Basin and Columbia Plateau.