Through a collaboration with the National Park Service, CNPS and NatureServe ecologists compiled over 9,000 new and existing vegetation surveys and analyzed over 4,000 surveys from three parks and other areas in the Mojave Desert and related ecoregions. A vegetation classification was developed, identifying approximately 105 alliances and related types from Lake Mead National Recreation Area, Mojave National Preserve, and Death Valley National Park. This project’s data analyses of three park areas spanned more than 4 million acres of area, plus enabled cross-analyses with other parks and preserves such as Joshua Tree National Park in California and Red Rock Canyon National Conservation Area in Nevada. We used classification and ordination methods such as cluster analysis, indicator species analysis, and Nonmetric Multidimensional Scaling (NMS) to inform the vegetation classification of the park areas.
This dynamic analysis process allowed for broad development and interpretation of the National Vegetation Classification (NVC) hierarchy, resulting in an evaluation of and updates for the NVC hierarchy especially at the macrogroup, group, alliance, and association levels. This project also enabled ecologists to increase both exposure to and peer review of the NVC standard, and to promote the networking of ecologists in the western U.S. Various examples of the revised NVC hierarchy and expansion of the classification at the alliance and association levels are elucidated in this project. For example, the Pleuraphis rigida Desert Grassland Alliance was previously placed in a mid-elevation mixed desert scrub group and has now been moved into a desert dune & sand flat group within a different macrogroup, while another alliance of Cylindropuntia acanthocarpa / Pleuraphis rigida Shrubland Alliance has been accepted within that former desert scrub group.