Consequences of climate and land-use change for vernal pool hydrologic regimes in the Central Valley of California

By

Christopher R. Pyke

Ecological systems are sensitive to the spatial and temporal distribution of environmental variability. They respond to changes in variability with changes in population processes, species interactions, and, ultimately, species persistence. The distribution of environmental conditions available to species across a region is a function of interactions between ecological tolerances and the spatial and temporal distribution of climate and habitat. Climate and land-use change may alter these relationships, and assessing their impact requires an understanding of the mechanisms linking environmental conditions to ecological processes. I explored these relationships for rain-fed, ephemeral, depressional wetlands (vernal pools) in the Central Valley of California. Ecological processes in these habitats are strongly influenced by their hydrologic regimes, and they may be particularly sensitive to climatic change. They are also disproportionately affected by habitat loss due to development and land conversion, and consequently, they contain a large number of rare and endangered species. This research combined simulation modeling, statistical analysis, and fieldwork to: (1) evaluate hydrologic regimes under historic climates, (2) test the sensitivity of hydrologic regimes to regional climate predictions, and (3) evaluate hydrologic regimes with respect to land-use, climate, and the range of endemic fairy shrimp (Anostraca). Results suggest that vernal pool hydrologic regimes exhibit non-linear changes over geographic space and reflect more intense changes in ecologically-relevant conditions than might be suggested by climatic trends alone. Consideration of climate change impacts in the absence of land-use change (i.e., habitat loss) indicates that vernal pools could experience either a small reduction in annual hydroperiod (cool and dry condition) or a substantial increase in the annual duration of flooding (warm and wet conditions). These ecoregion-wide responses change significantly when potential land-use change and associated habitat loss are considered. A bias in the distribution of reserve lands toward drier areas in the Central Valley results in a net shift toward drier, shorter-lasting, and less predictable vernal pools even under wetter climatic conditions. This research demonstrates that interactions between land-use and climate change can result in significant differences in the magnitude and direction of impacts compared to those predicted for either variable alone. These findings suggest that the combination of climate and land-use change may create additional threats to species endemic to vernal pools, and demonstrate that climate change impact assessments should explicitly consider the interactions between climate and land-use in evaluating future scenarios.

More information is available at http://www.biogeog.ucsb.edu/