Much is unknown about the effects that climate change might have on the biota. To date, investigators have relied extensively on the use of species distribution modeling (SDM) to assess the potential impacts of climate change on species ranges and on extinction risks. SDMs are empirical models that relate field observations of species to environmental predictors based on statistically or theoretically derived response functions. Despite their extensive use in climate change impact analyses, however, SDM projections are largely untested. Data used in SDM development often are split into training and test sets, and goodness-of-fit is assumed to represent projection accuracy under novel climates. This research project will produce a temporally independent validation of SDM climate-change impact projections for vascular plant species of the mountain ranges of California. SDMs will be developed using a 75-year old dataset of vegetation distribution, and projections of these models under measured climate change will be compared to current data on the presence or absence of species. The investigators will use historic data from approximately 17,000 plots developed by Albert Wieslander from 1928 to 1940 as well as modern vegetation inventory data. This project will address several fundamental questions related to the development and interpretation of SDM projections: (1) Are SDM projections under novel climates accurate? (2) How does uncertainty in climate estimates affect SDM projections? (3) Do SDM accuracies vary by species and are they related to species ecological traits? (4) What is the influence of fire regime and land-use history on SDM predictive performance? (5) Is there systematic bias in SDM projections and is it large compared to the variability in projections introduced by model choice? The investigators will examine the predictive performance of SDMs across a number of species varying in ecological traits and through multiple modeling approaches.
Understanding biotic response to climate change is of major importance, with long-term implications for social welfare and biodiversity conservation. Concerns about climate change impacts have led to the widespread use of SDMs as tools for predicting species extinction risks and range shifts under climate-change scenarios. The potential impact of these studies on political and public debate is high. Consequently, determining whether SDM projections are accurate is of particular importance. This project will improve understanding of the predictive performance of SDMs in climate-change impact analysis. It will help to provide a backdrop for the interpretation of existing climate-change impact studies and a foundation for the development of future studies. Broader impacts of this work include the training and support of a diverse set of scientists and the education of students at the University of Montana and at the University of California,-Davis. Outreach will be conducted through an environmental education program in the central Sierra Nevada.
