14. Climate Change Trends for Chaparral

Chaparral vegetation is a dominant and unique feature of California’s Mediterranean-type climate. The evergreen shrubs that characterize chaparral are well adapted to long, hot, dry summers and extreme fluctuations in inter-annual precipitation. Despite the ability of chaparral species to tolerate climatic extremes, the integrity of the chaparral ecosystem is currently being challenged by rising temperatures, increased variability in precipitation, and longer and more persistent droughts. Climate scenarios for California project continued warming through the century leading to increased physiological stress, canopy thinning, and mortality of chaparral vegetation across portions of the state. In some instances, however, chaparral vegetation may expand into forested landscapes. Climate change forecasts suggest enhanced fire activity, including an extended fire season and more frequent large fires. In this already stressed system, non-climate stressors, like increased fire frequencies, can lead to decreased shrub biomass, loss of species diversity, and conversion to other vegetation types. Chaparral in southern California is already trending toward conversion to dominance by non-native annual grasses, and climate projections suggest that this trend will continue in the future. In this chapter, we evaluate historical and projected climate trends in California and explain how they might directly and indirectly affect the integrity and persistence of chaparral on the landscape. We show that the interaction of climate and non-climate stressors can drive landscape level conversion of shrublands to non-native annual grasses leading to the loss of social and ecological benefits provided by the ecosystem. We provide a detailed review of projected changes in carbon storage for one of the (under-valued) ecosystem services provided by chaparral. We conclude by highlighting key management lessons from our review, and point to a few high priority information gaps that must be filled by future research.