Potential natural vegetation and NPP responses to future climates in the US Great Plains

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.