The potential effects of climate change on net primary productivity (NPP) of U.S. rangelands were evaluated using estimated climate regimes from the A1B, A2 and B2 global change scenarios imposed on the biogeochemical cycling model, Biome-BGC from 2001 to 2100. Temperature, precipitation, vapor pressure deficit, day length, solar radiation, CO₂ enrichment and nitrogen deposition were evaluated as drivers of NPP. Across all three scenarios, rangeland NPP increased by 0.26 % year⁻¹ (7 kg C ha⁻¹ year⁻¹) but increases were not apparent until after 2030 and significant regional variation in NPP was revealed. The Desert Southwest and Southwest assessment regions exhibited declines in NPP of about 7 % by 2100, while the Northern and Southern Great Plains, Interior West and Eastern Prairies all experienced increases over 25 %. Grasslands dominated by warm season (C4 photosynthetic pathway) species showed the greatest response to temperature while cool season (C3 photosynthetic pathway) dominated regions responded most strongly to CO₂ enrichment. Modeled NPP responses compared favorably with experimental results from CO₂ manipulation experiments and to NPP estimates from the Moderate Resolution Imaging Spectroradiometer (MODIS). Collectively, these results indicate significant and asymmetric changes in NPP for U.S. rangelands may be expected.

As the future climate becomes hotter or drier, forests may be exposed to more frequent or severe droughts. To inform efforts to ensure resilient forests, it is critical to know which forests may be most exposed to future drought and where. Longer duration droughts lasting 2–3 years or more are especially important to quantify because forests are likely to experience impacts. We summarized exposure to 36‐month drought for forests across the conterminous United States using the Standardized Precipitation‐Evapotranspiration Index (SPEI) overlaid on forest inventory plot locations. Exposure was quantified under 10 scenarios that combined five modeled climates and two Representative Concentration Pathways (RCPs, 4.5 and 8.5) through 2070. Future projections indicate a tripling of the monthly spatial extent of forests exposed to severe or extreme drought—38% of forests were exposed on average by mid‐century as opposed to 11% during 1991–2020 (2041–2070). Increases in drought exposure were greatest under hotter (HadGEM2‐ES), drier (IPSL‐CM5A‐MR), and middle (NorESM1‐M) climate models, under either RCP. Projections agreed that forests in portions of the western United States, especially the southwestern United States, could face high levels of exposure. Forest types including pinyon/juniper, woodland hardwoods, and ponderosa pine were projected to be exposed to drought more than 50% of the time on average across all scenarios by mid‐century, when no forest type was exposed more than 25% of the time under any scenario during the recent period. Projections agreed less for the eastern United States, but in some scenarios, particularly under RCP 8.5, large portions of the East could be exposed to drought nearly as often as parts of the West. Moreover, a substantial portion of oak/hickory forests occur in eastern regions, where projections agree on increased drought exposure. This study provides novel insights about the changing conditions forests face in both the eastern and western United States. Our results can be combined with information about the sensitivities and adaptive capacities of forest ecosystems to prioritize drought adaptation efforts.

Asymmetric climate projections throughout the U.S. Great Plains may intensify the existing latitudinal temperature gradient and magnify the longitudinal precipitation gradient. These potential changes present a unique challenge to understanding the ecological consequences of future climates in the region. Here we investigate how climate change may affect the spatio‐temporal patterns of potential natural vegetation types (PVT) and net primary production (NPP) throughout the 21st century with the global dynamic vegetation model MC2. Simulations were driven by projected climate variables from five global climate models under representative concentration pathway (RCP) 8.5. MC2 simulated C3 and C4 grassland, shrubland, forest, and woodland (shrubland + forest) PVTs, and total NPP for each PVT. The largest increases in woodland and grassland NPP occurred in the Northern Plains (17.5% and 4.7%), followed by the Central Plains (10.6% and 0.0%), while NPP in the Southern Plains remained unchanged compared to historic means (1981–2010). A shift from grassland to woodland in the Northern and Central Plains further affected regional NPP; regional woodland NPP increased 72% and 26% in the Northern and Central Plains, respectively, while regional grassland NPP decreased 18% and 12%, respectively. The most pronounced shift in PVT was associated with increasing, rather than decreasing, mean annual precipitation in the Northern Plains where grassland contracted in response to westward expansion of woodland. C3 grassland was gradually replaced by C4 grassland in the Northern Plains by 2080, and only a trace remained at centuries end. C3 grassland decreased to a trace amount ca. 2060 in the Central Plains, while C4 grassland increased slightly. The relative stability of PVTs in the Southern Plains suggests that species and functional trait diversity may buffer grassland responses to future climates by providing the capacity for species reordering. The asymmetric response of simulated vegetation and NPP to 21st century climate change suggests that the provision of ecosystem services—beef cattle production, carbon sequestration, and grassland bird habitat—will be modified in distinct ways along a latitudinal gradient throughout the Great Plains.