Environmental Change in Southern California

Researchers have used various approaches to investigate the ecological effects of environmental change, including manipulations, interannual observations, and gradient studies.  Each of these approaches provides a key piece of the puzzle, but no single approach provides a complete picture of ecosystem response. We are initiating an experiment that uses a hybrid design that simultaneously incorporates manipulations and interannual and gradient observations to better understand the effects of changing water balance on California’s ecosystems. We will work along a 150-km climate transect that traverses the San Joaquin Hills and the Santa Ana, San Jacinto, and San Bernardino Mountains. We will establish two types of sites: Natural Gradient Sites in grassland, coastal sage, chaparral, evergreen hardwood forest, pine forest, pinyon pine woodland, and creosote bush desert, where we will measure ANPP, litterfall, LAI, community composition, nitrogen mineralization, plant water status, and the fluxes of CO2, energy, and water vapor, and Experimental Sites in grassland, coastal sage, pine forest, pinyon woodland, where we will manipulate the environment.

We will use observations of the effects of interannual climate variation within the individual gradient sites to understand the short-term effects of climate variability on ecosystem physiology and ecosystem function. We will compare across the sites along the gradient to predict the long-term effects of climate on community composition and ecosystem function. To test whether predictions based on gradients match how a system will respond to rapid change, we will manipulate water input at the experimental sites to understand how a change in moisture balance affects NPP, plant community composition, nutrient cycling, and plant water use. We are manipulating fire, nitrogen availability, and propagule input at two of the experimental sites (coastal sage and grassland at Irvine Ranch Land Reserve) to further understand how multiple environmental changes interact to control the rate and direction of ecosystem response.