A Summary of the Joshua Tree National Park: Vegetation Mapping Project

La Doux, Tasha; Lea, Chris; Babich, Erin; National Park Service

Characterization Program initiated a project at Joshua Tree National Park (JOTR or Park) in 1996 to classify, describe, and map the vegetation communities of the Park. The project, including the final map, classification, and report, was completed in 2012. Initial mapping, photo-interpretation, and field work was conducted between 1996 and 2005. Final reports for these efforts were generated by 2005, including a map, ecological descriptions, classification, key, and photo-interpretation guide. Following this, a total of 1,313 accuracy assessments were conducted in 2007 and 2008, the results of which spurred additional field relevés and a reworking of the map and classification. An additional 111 relevés were conducted in 2009 targeting problematic associations and alliances; these data were used in conducting additional analyses to produce a revised vegetation map and classification. Photo-interpretation was also redone during this time for a subset of the problematic associations and the classification was updated to match the most recent vegetation classification presented in the Manual of California Vegetation Second Edition (Sawyer et al. 2009). Between 2010 and 2011 data analysis was completed and incorporated into the final map and classification. By February 2012 the ecological descriptions were updated and completed to match (as best as possible) the most recent version of the U.S. National Vegetation Classification and the map was updated to reflect the final nomenclature. The 2012 version of the vegetation classification for the Park includes 51 Alliances (including Provisional Alliances, Semi-Natural Stands, and Special Stands) and 78 Associations (including Provisional Associations). There are eight map classes that have less than 2% absolute vegetation cover, these include Disturbed/Built-Up, Water, Dunes, Playas, Recent Burns, Rock Outcrops, Desert Pavement, and a generic Non-vegetated Habitat type. The largest amount of land cover is classified under the Larrea tridentata — Ambrosia dumosa Shrubland Alliance, which is classified into seven Associations. This Alliance covers a total of 1,130 km2, representing 35% of the total area within JOTR (3,208 km2). On the other hand, there are eight Alliances, mostly associated with riparian habitats, which have less than 1 km2 mapped, these include: Washingtonia filifera Woodland Alliance, Salix gooddingii Woodland Alliance, Prosopis glandulosa Woodland Alliance, Populus fremontii Forest Alliance, Justicia californica Provisional Shrubland Alliance, Ericameria nauseosa Shrubland Alliance, Cylindropuntia bigelovii Shrubland Alliance, and Ambrosia salsola Shrubland Alliance. Overall map class accuracies for the JOTR map are 41.0% at the U.S. National Vegetation Classification association level, 61.0% at the alliance level, 82.0% at the group level, 87.3% at the macrogroup level, 92.5% at the formation level, and 92.9% at the class level. The goals of this report are three-fold: 1) to summarize the events and products that resulted from the 16-year effort; 2) to describe and present the results of the accuracy assessment phase of the project; and 3) to present the final vegetation classification, ecological descriptions, and a geospatial vegetation classification map of the Park.