Projected Change in Rangeland Component Fractional Cover Across the Sagebrush Biome Through 2080.

Abstract:

Climate change has altered and continues to alter vegetation community composition and species distributions across rangelands in the western U.S. While a number of studies have projected the impacts of climate change using several modelling work-flows, none has evaluated impacts to fractional component cover at a 30-m resolution across the full sagebrush (Artemisia. spp.) biome. Sagebrush is a widespread shrub of significant ecological importance across the American West with many adaptive features that facilitate its occurrence across a range of climatic and biophysical conditions. We use fractional component cover data for rangeland functional groups and weather data from 1985 to 2018 in conjunction with soils and topography data to develop empirical models describing the spatio-temporal variation in cover across the sagebrush biome of the Western U.S. Our primary objective is to apply the models developed over the historical period to future weather conditions based on two emissions scenarios and three time periods (2020s, 2050s, and 2080s) to evaluate change in functional group cover and distribution. We then model component cover under these RCP scenarios and evaluate spatial and temporal patterns of change relative to the historical baseline. We tested both Generalized Additive Models (GAMs) and regression tree models, finding that the former was superior, both spatially and statistically. Our results showed a net decrease in sagebrush, herbaceous, and litter cover, and increase in shrub, annual herbaceous, and bare ground cover from the 1985-2018 baseline in both the RCP 4.5 and 8.5 scenarios. In general, both scenarios yielded similar results, but RCP 8.5 tended to be more extreme, with greater increases (or decreases) relative to baseline conditions. Spatially, the results suggest increasingly xeric vegetation across most of the study area, with an increasing dominance of non-sagebrush shrubs and bare ground over herbaceous and sagebrush cover. This information can be used to inform management to prepare for future vegetation composition and cover through the prioritization of conservation and restoration and shed light on species range shifts.