RAPID: The Endless Summer: Implications of a 100-year drought for the functional biology of native Californian plants and ecosystems

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California is experiencing the most severe drought to occur in 160 years of state meteorological records. While the causes of the current drought are not yet fully known, it is similar to the warmer temperatures and more erratic rainfall patterns that are predicted to occur in California under future climate change scenarios. Extreme events such as the current drought are also anticipated to act as 'triggers' of change in ecosystem composition and function as the landscape adapts to warmer and drier conditions. Managing California's biodiversity and the services performed by its natural environment in the face of a changing climate is challenging because the response of species and ecosystems to drought (and other extreme climate events) is still poorly understood. The wide variety of plant species growing in complex soils, topography and geology mean that the same imposed drought conditions may lead to dramatically different outcomes in terms of the water stresses experienced by plants. This project takes advantage of the once-in-a century Californian drought to study the effects of water stress in different plant species growing in different habitats in order to evaluate how different plant adaptations lead to a spectrum of drought stress and susceptibility to ecosystem change. The research will contribute to the training of young scientists at multiple stages of their education, (postdoctoral scholars, graduate students and undergraduate students). The results will be widely shared with conservation and resource managers, providing a basis for enhanced planning of conservation priorities and possible interventions in response to drought.Although extreme drought events are becoming more common worldwide, detailed monitoring of plant performance during these events remains scarce. Quantifying the diversity of plant responses to extreme drought events provides an opportunity to advance our understanding of the underlying (mechanistic) reasons for how and why particular plant strategies may be either better or more poorly suited for coping with extreme physiological stress. Drought-induced changes are expected to drive the transient dynamics of vegetation communities, possibly triggering species transitions and pushing ecosystem-scale ecohydrology into novel states. The project will primarily draw on physiological measurements as indicators of drought stress, specifically leaf water potentials, stomatal conductance, native embolism and canopy area. These measurements will be made on a monthly basis at two intensive research sites in the San Francisco Bay Area. The effects of the drought on photosynthesis and plant carbon stores will be measured using carbon isotopes as an indicator. The sources of water used by the plants will be determined using oxygen and hydrogen isotopes of water. Previously installed soil moisture and meteorological equipment will be used to track site-specific microclimatic and hydrological conditions. Results will contribute to understanding of the physiological limits of native plant species to extreme drought and the suites of plant traits that mediate drought stress so that plants either survive or die.