COS 4-4
Exposure and simulated sensitivities of major vegetation types of California to climate change
Climate change is expected to impart a profound effect on California’s diverse vegetation. Studies project a broad pattern of reduction in evergreen conifer forests and expansion of mixed evergreen forests by year 2100, mediated by a complex interaction among vegetation types and disturbance regimes. Conservation organizations and government agencies are actively engaged in conducting vulnerability assessments of natural landscapes. Simulation results from dynamic general vegetation models (DGVMs) have provided regional-scale projections of vegetation change, but their outputs have been too coarse for effective integration into sub-regional planning. California Public Interest Energy Research Program has coordinated the evaluation, selection and the use of four SRES-based climate projections by researchers. Recently the climate projections were downscaled to 800m, making it suitable for National Forest planning and watershed-level planning. We calibrated and ran MC1 DGVM with this new data to create state-wide, fine-scale projections of climate impacts on the major vegetation types of California, and on carbon storage, runoff and fire. Using a vulnerability assessment framework, we quantified the exposure of every Bailey Ecoregion Section in California to climate change. We measured the simulated sensitivity of major vegetation types to climate change, and identified key drivers of vegetation change for each ecoregion section.
Results/Conclusions
Every ecoregion in the state is likely exposed to a 2-5°C rise in annual average temperature between now (1971-2000) and the end of the century (2070-2099). Exposure to changes in precipitation varies widely by the GCM rather than the emissions scenario. The greatest disagreement on precipitation projections are in the forested ecoregions. Northern California Coast, Coastal Ranges, and Interior Coast, along with the Sierra Nevada Foothills, have the highest simulated sensitivity to climate change, where MC1 results from all four climate projections agree that 60-70% of the area will change vegetation types. Not all moist ecoregions, nor the deserts, are highly sensitive to climate change. Climate variables do not drive vegetation change consistently across the major vegetation types, nor within one. A regression of response in NPP to changes in temperature and precipitation aggregated by ecoregion section suggests that although the effect of temperature and/or precipitation may be significant, their effects are probably weak in many ecoregions, and nearby ecoregions can exhibit opposite responses. Fire appears to decrease in the coastal ecoregions while mediating type-shifts in interior forested or shrubland ecoregions. Our results demonstrate that climate exposure and simulated sensitivities are spatially heterogeneous, and vegetation responses are complex and non-linear.