||We request support to continue a study of the impact of environmental change on Southern California’s ecosystems. An ecosystem’s response to environmental change is determined by several mechanisms, including shifts in plant physiology, plant demography, plant competition and community composition, and biogeochemistry and nutrient cycling. Our goal is to understand how each of these mechanisms contributes to an ecosystem’s overall response to environmental change. Our ultimate goal is to be able to predict how a change in the external environment will affect an ecosystem’s function.
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 using a hybrid experimental design that simultaneously incorporates these approaches to better understand the effects of changing water balance on California’s ecosystems. We are working along a 150-km climate transect that traverses the Santa Ana, San Jacinto, and San Bernardino Mountains. We are working at three types of study sites. Gradient transect sites at 400’ elevation intervals. Year-round eddy covariance sites in grassland, coastal sage, oak/conifer forest, pinyon-juniper woodland, desert chaparral, and creosote bush desert. Factorial water manipulations in grassland and coastal sage, and that are being built in oak/conifer forest and pinyon-juniper woodland.
We are using observations of the effects of interannual climate variation at the eddy covariance sites to understand the short-term effects of climate on ecosystem physiology and ecosystem function. We are using comparisons among the gradient transect sites and among the eddy covariance sites to determine the long-term effects of climate on community composition and ecosystem function. We are manipulating 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. The manipulative experiments are also designed to determine whether severe disturbance, nitrogen fertilization, or the addition of seeds from other plant communities accelerates the effects of a change in water input on ecosystem function.
Our research is focused on high value ecosystems in a region where climate change is expected to have a major impact. Five considerations underscore the importance and relevance of this research. (1) California provides an excellent natural laboratory for understanding how climate controls ecosystem function. (2) Southern California’s location at the edge of the mean winter storm track increases the likelihood of pronounced future climate change. (3) Southern California’s semiarid climate and steep climate and vegetation gradients increase the likelihood that a change in climate will have a major impact on its ecosystems. (4) Southern California has experienced an extraordinary number of extreme weather-related events in the last 10 years, which are already impacting Southern California’s ecosystems. (5) The tight link between climate, ecosystem function and natural disasters in Southern California increases the likelihood that climate change will result in large socioeconomic impacts.