PARENT SESSION
Poster Session #50: Climate Change.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Climate change effects on vegetation distribution, carbon stocks, and fire regimes in California.

Lenihan, James^*,2, Bachelet, Dominique¹, Drapek, Raymond², Neilson, Ronald², ² US Forest Service Pacific Northwest Research Lab, Corvallis, OR¹ Oregon State University, Corvallis, OR

ABSTRACT- The objective of this study was to dynamically simulate the response of vegetation distribution, carbon stocks, and fire regimes under two contrasting scenarios of climate change in California over the next century. The simulations were generated by MC1, a dynamic vegetation model developed to simulate 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 of the model simulations for the historical climate compared favorably to independently observed estimates of vegetation distribution, carbon density, and different aspects of the fire regime. However, attempts at validating the historical portion of the simulation were complicated by the lack of land use effects in the model. The results of the future climate simulations demonstrate ecosystem sensitivities and interactions that are likely to be features of the response of both natural and semi-natural (e.g., managed forests and rangelands) systems to a relatively certain rise in temperature and to less certain changes in precipitation. The response to an increase in temperature was characterized by shifts in the relative dominance of needle-leaved and broad-leaved lifeforms, and by changes in the potential production of trees. The simulated response to changes in precipitation were more complex, involving not only a direct effect 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. The results of the simulations underscore the potentially large impact of climate change on California ecosystems, and the need for further use and development of dynamic vegetation models using various ensembles of climate change scenarios.

KEY WORDS: climate change, carbon, vegetation distribution, fire