The dynamic global vegetation model MC1 simulates plant growth and biogeochemical cycles, vegetation type, wildfire, and their interactions. The model simulates competition between trees and grasses (including other herbaceous species), as affected by differential access to light and water, and fire-caused tree mortality (Bachelet et al., 2000; 2001). MC1 projects the dynamics of lifeforms, including evergreen and deciduous needleleaf and broadleaf trees, as well as C3 and C4 grasses. However, the model can also be parameterized for a particular dominant species of the associated lifeform. For this project we used two versions of MC1, both of which modified the standard code to improve the simulation of potential evapotranspiration (PET).For the western northern Great Plains (NGP) the model was calibrated to project the observed ecotone between ponderosa pine and grasslands at Wind Cave National Park in the Black Hills of South Dakota; full documentation of this version of the code is described by King et al. (2013a). In this case the evergreen needleleaf life form corresponds to ponderosa pine (Pinus ponderosa). For the eastern NGP we recalibrated MC1 so that the evergreen needleleaf lifeform corresponds to juniper; principally eastern redcedar (Juniperus virginiana), but also to Rocky Mountain juniper (Juniperus scopularum), which is present in the western and central NGP.