An Index of Threat: Mapping Climate Change in High Sierra Nevada Communities.


Climate change is already affecting the distribution of species, and the ranges of high mountain species are shifting. This thesis creates an Index of Threat for high mountain communities in the Sierra Nevada that is spatially-based and will indicate threat to the persistence of the communities where they are found in order to prioritize areas for conservation. Using three climate change scenario projections (A2, A1b and B1) and 30-year averages for maximum summer temperatures, known summertime occurrences for three species that share high-mountain habitat, and regional vegetation maps, index measures as D-1 were made to compare areas in the north, central and south sections of the Sierra Nevada, and potential refugia were indicated. A temperature-only species envelope model was made in ArcGIS ( and Maxent models were also utilized ( to estimate species persistence. Model agreement was tested with Kappa Statistic. The results showed that Maxent was useful used in concert with ArcGIS modeling to estimate the index of threat (Average Kappa for three scenarios = 69%). Greatest threat was found for the northern area (Index .83 on a scale of 0-1). (Central area threat was 0.06, south was 0.45). More available refugia were located adjacent to the northern area than the others. Limitations to this study include the biased of observational field data. The index of threat measures loss and does not reflect distribution expansion.