Climate Cahnge Effects on Vegetation Distribution, Carbon Stocks, and Fire Regimes in California

We simulated the response of vegetation distribution, carbon, and fire under two constrasting scenarios of future climate change in California. The simulations were generated by MC1, a vegetation model that simulates vegetation succession at large spatial extents through time while estimating variability in the carbon budget and responses to episodic events such as drought and fire. The results for the historical climate compared favorably to independent estimates of vegetation distribution, carbon density, and the fire regime. However, validating the historical simulation was complicated by the lack of land use effects in the model. The results under the future climate scenarios showed ecosystem sensitivities and interactions likely to be features of the response of natural and semi-natural systems to a rise in temperature and changes in precipitation. The response to increases in temperature was characterized by shifts in the relative dominance of tree lifeforms, and by changes in the productivity of trees. The response to changes in precipitation was more complex, involving direct effects on vegetation productivity associated with changes in available soil moisture, but also changes in tree-grass competition that were mediated by fire. The persistence of a Mediterranean climate with dry summers was a key feature of the modeled response. The summer months were warmer and persistently dry under both scenarios, so differences in the modeled fire behavior and effects were primarily a response to differences in simulated fuels.