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UCSB Biogeography Lab Publications Abstracts
Vegetation and Floristic Diversity in the Mojave Desert of California: A Regional Conservation Evaluation
Kathryn Alice Thomas
The Mojave Desert in California is currently the focus of conservation and ecosystem management planning efforts, all of which have a common need for biological data. One such effort, the Gap Analysis Program (GAP) provided a mechanism to examine both basic and applied biogeographical issues in the Mojave. Three objectives were accomplished: the development of a GIS based coverage of Mojave vegetation, a new analysis of a tabular database of Mojave flora, and a region-wide conservation assessment.
A Mojave vegetation coverage was created using existing subregional vegetation maps, updated with 1990 Landsat Thematic Mapper imagery. Vegetation classification for each mapping source was cross referenced to the Holland (1986) system. Extensive field checking was conducted to validate the cross-referencing and to update map units where necessary. The reliability of each map unit in the vegetation coverage was indicated with a qualitatively derived confidence score. A quantitative accuracy assessment was made for a subregion of the Mojave using existing plot data. The results of this accuracy assessment were used to calibrate the confidence score and provide an estimate of accuracy across the entire coverage. The vegetation coverage provides the most current regional view of Mojave vegetation.
The Lum database, which provides a description of the occurrence and various floristic properties of Californian species, was subsampled for the Mojave. Tabular analysis of the database shows the Mojave to support approximately 1150 species, which is proportional to its area compared to the rest of the state. Life-form distribution was shown to correlate with regional precipitation patterns: annuals predominate in the west and herbaceous perennials in the east and north. Cover types are distinct within subregions and often between subregions, as determined by Jaccard's similarity coefficient. Cluster analysis suggests that a two and/or five subregion division of the Mojave could serve to geographically represent species variation.
A conservation evaluation was made of the Mojave using the vegetation coverage, regionalized by floristic subregions. The coverage was overlain with a land ownership map that had been reclassified to three levels of biodiversity management. Management status of the various cover types was evaluated and eight vulnerable cover types were identified using a three part criteria. Seven areas were selected as candidate areas for further conservation effort.