As hotter temperatures intensify the natural summer drought period in Mediterranean climate forests over the next century, they are likely to experience increased tree mortality, and changes in species interactions and composition. Such shifts would impact carbon storage and a wide range of other ecosystem services. We have parameterized SORTIE-ND, and individual-based, spatially explicit forest model, for diverse Mediterranean climate forests in the Sierra Nevada mountains of California. We tested the model's ability to reproduce past patterns (1999-2014) for several long-term forest plots. We then used downscaled GCM projections (RCP 8.5) for key climate variables (annual precipitation, July maximum temperature, and January minimum temperature) to project forest dynamics to the end of the century under different scenarios.
Results/Conclusions
The model reproduces past observed patterns in density and basal area well. In the 2014-2100 simulations, the low-elevation plot is projected to experience a decrease in tree density but an increase in basal area, especially under climate change scenarios, with increased dominance of black oak. The higher elevation plots are projected to experience increases in basal area and/or density in both control and climate change scenarios, with different species being favored by warm-wet versus warm-dry conditions. We identify several model behaviors that may account for divergence between empirical data and SORTIE-ND projections in particular cases - particularly early seedling survival - and suggest additional empirical studies that could reduce such discrepancies. Future model developments will include addressing these elements and allowing heritable variation in climate responses to test the potential impact of evolution on forest climate responses.