Future transition from forests to shrublands and grasslands in the western United States is expected to reduce carbon storage

Climate change is expected to impact vegetation in the western United States, leading to shifts in dominant Plant Functional Types and carbon storage. Here, we used a biogeographic model integrated with a biogeochemical model to predict changes in dominant Plant Functional Type by 2070–2100. Results show that under the Representative Concentration Pathway 4.5 scenario, 40% of the originally forested areas will transition to shrubland (7%) or grassland (32%), while under the Representative Concentration Pathway 8.5 scenario, 58% of forested areas shift to shrubland (18%) or grassland (40%). These shifts in Plant Functional Types result in a net overall loss in carbon storage equal to −60 gigagram of carbon and −82 gigagram of carbon under Representative Concentration Pathway 4.5 and 8.5, respectively. Our findings highlight the need for urgent action to mitigate the effects of climate change on vegetation and carbon storage in the region.