VEMAP vs VINCERA: A DGVM sensitivity to differences in climate scenarios

The MC1 DGVM has been used in two international model comparison projects, VEMAP (Vegetation Ecosystem Modeling and Analysis Project) and VINCERA (Vulnerability and Impacts of North American forests to Climate Change: Ecosystem Responses and Adaptation). The latest version of MC1 was run on both VINCERA and VEMAP climate and soil input data to document how a change in the inputs can affect model outcome. We compared simulation results under the two sets of future climate scenarios and reported on how the different inputs can affect vegetation distribution and carbon budget projections. Under all future scenarios, the interior West becomes woodier as warmer temperatures and available moisture allow trees to get established in grasslands areas. Concurrently, warmer and drier weather causes the eastern deciduous and mixed forests to shift to a more open canopy woodland or savanna type while boreal forests disappear almost entirely from the Great Lakes area by the end of the 21st century. While under VEMAP scenarios the model simulated large increases in carbon storage in a future woodier West, the drier VINCERA scenarios accounted for large carbon losses in the east and only moderate gains in the West. But under all future climate scenarios, the total area burned by wildfires increased especially in C4 grasslands under all scenarios and in dry woodlands under VINCERA scenarios. The model simulated non-agricultural lands in the conterminous United States as a source of carbon in the 21st century under the VINCERA future climate scenarios but not VEMAP. However, the magnitude of this carbon source to the atmosphere could be greatly reduced if the CO2 growth enhancement factor built in the model was enhanced but evidence that all mature forests across the entire country will respond positively to increased atmospheric CO2 is still lacking.