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Conserving Listed and At-Risk Plants in a Non-Stationary World: A Predictive Framework for Assessing Risks and Guiding Management
Dr. Dov Sax | Brown University
Given plausible levels of climate change over the next several decades, it is likely that changing conditions will place new strains on already listed or at-risk species. One group of particular concern are federally-listed and candidate species of plants in the contiguous United States. Nearly 500 of these species occur and many are present on lands owned and operated by the Department of Defense (DoD). Although changes in climate will provide increased risk for many of these species, these risks will not be uniform. Indeed, ample evidence exists to suggest that though some species are highly sensitive to climate and dependent on narrowly specific conditions, other species can actually thrive in climate conditions considerably different from those they currently experience. At present, however, there is no predictive framework for distinguishing these different types of species: i.e., no ability to make reliable judgments about which species will tolerate plausible changes in climate and which will be unable to survive in their current habitats. Traditional ecological approaches can investigate one or a small group of species through experimentation and exposure to alternative climate conditions, but doing this is not feasible for the large number of species for which determinations must be made. The objective of this project is to develop a predictive framework, based on species characteristics (such as region of origin, native range size, seed dispersal mechanism, and soil requirements), that can inform the extent to which species are likely to thrive, be moderately impacted, or perish in their current locations given likely changes in climate over the next several decades. This effort will inform extinction risks from climate change, provide guidance on alternative management options, and provide an educated jumping-off point for additional studies that can test the hypotheses generated by the framework for any particular species.
Species Distribution Models (SDMs) are a powerful approach for forecasting risks species face from climate change. These models, however, make the simplifying assumption that the climate experienced in a species’ native range represents the sum of conditions in which a species can survive. This assumption is false, but the extent to which it is false (as will be demonstrated via this project) has previously not been appreciated. This project will take advantage of a species’ native, naturalized, and horticultural occurrences to document species-specific relationships with climate, specifically by characterizing the realized, fundamental and tolerance niches of a species. To begin, a preselected group of 200 woody plant species native to the United States will be studied that are naturalized and planted in horticulture in regions of the United States where they are not native. A complementary group of 1,000 species also will be studied that are randomly selected from among U.S. natives. Finally, the 468 federally-listed and candidate species previously mentioned will be studied. The project will include field work to confirm the status of purportedly naturalized populations and extensive database development for native, naturalized, and horticultural occurrences. Data collected from various portions of the geographic distributions of all three groups of species, together with species characteristics, will be used to develop a predictive framework for characterizing the size and relative placement of species’ niches. For federally-listed and candidate species, SDMs will be generated based on realized niche conditions and extinction risk and management options will be predicted under alternative forecasts of climate change over multiple time periods. The ground-breaking element of the work will be to evaluate and improve these predictions using: (1) empirically-generated niche relationships (when such data exists for individual species) and (2) niche relationships generated from the predictive framework (that will be generated for each species).
This work will provide a major advance in our scientific understanding of how species’ distributions are related to climate. This work will provide species-specific determinations of risk from climate change for many federally-listed species on DoD land. For instance, the work will address when a species is unlikely to be impacted by warming temperatures or when a species is likely to be impacted, but not so much that it couldn’t still be protected in place with management. The work also will address when the most likely means of a species’ survival involves its movement off-site. In such cases, the regions with climate suitable for its long-term persistence will be identified. Finally, this work will identify key hypotheses for each species that could be tested with additional targeted work. It will provide key information for making determinations for a great number of species for which we currently lack any reasonable basis for inferring their responses to changes in climate. (Anticipated Project Completion - 2018)