Studies for this RVDE activity encompass four phases.

• Phase 1—Remeasure perennial vegetation on the Beatley plots. Using Beatley's original methods, remeasure as many of the existing plots as is feasible. Resulting data will be evaluated to determine if they are adequate to address questions about the long-term stability of perennial vegetation assemblages.

• Phase 2—Remeasure annual vegetation on an annual basis in selected undisturbed plots and in all plots where disturbance was part of Beatley's original sample design.

• Phase 3—Remeasure rodent populations, with particular emphasis on plots where disturbance recovery from fire was the focus of the plot design.

• Phase 4—Analyze recovery in perennial vegetation in plots where burns and other severe disturbances were part of the original plot design. Other permanent plot measurements (for example, the Becamp plots) will be incorporated where feasible.

Morningstar gold mine, a small heap-leach mine. Photo by David Miller, USGS.

The objective of this study is to quantitatively define the recovery of perennial vegetation using several recovery benchmarks:

• Visual recovery (ability to recognize a disturbance from a distance)

• Recovery of total cover of perennial vegetation

• Recovery of density of perennial vegetation

• Recovery of species composition

Dated disturbances such as ghost towns, roads, or pipeline right-of-ways were measured to develop quantitative projections of recovery of vegetation cover and density and species composition after a variety of disturbances. By statistically examining dated disturbance data compiled from field work and literature with respect to total vegetation response and individual species response, transfer functions can be developed to define recovery rates. The rate of recovery may vary by the type of vegetation assemblage in which the disturbance occurs, the size and type of disturbance, the surficial geology and topography of the site, and climatic events. Each of these parameters is investigated.

Webb, R.H., Steiger, J.W., and Turner, R.M., 1987, Dynamics of Mojave Desert shrub vegetation in the Panamint Mountains: Ecology, v. 68, p. 478-490.

Periodic wet periods, which typically are associated with El Niño events in the Mojave Desert, may result in a large cohort in a good year with many years between cohorts. The combination of seed dispersal, consumption by animals, and favorable climatic conditions likely drives the initial establishment of perennial vegetation following disturbance, and quantitative knowledge of these processes is essential to modeling of the recovery process.

The objectives of this research are the following:

• Determine seed dispersal mechanisms for common Mojave Desert species through a combination of literature review and active research

• Conduct research on the dispersal and fate of seeds transported by rodent and arthropod populations

• Determine cohort age and age-stand distributions for common Mojave Desert assemblages (particularly blackbrush)

• Quantitatively define the probabilities and processes that lead to establishment of common dominant species

RVDE scientists studied seed dispersal mechanisms and establishment frequency of species involved in the recovery of burned blackbrush stands on the Nevada Test Site and in the northeastern Mojave Desert, primarily on the alluvial aprons surrounding the Spring Mountains near Las Vegas. This work included age-dating of blackbrush seedlings using newly developed stem-ring counts and measurements; use of radio-labeled seeds to determine dispersal mechanisms and seed fate; trapping of rodents to determine species compositions of individuals involved in the recovery process; literature reviews to determine past work; and remeasurement of perennial vegetation in selected plots recovering from historical fires.

Vegetation in the Mojave Desert responds to disturbance in ways that can be characterize temporally and spatially. Prediction of vegetation dynamics and recoverability requires maps of vegetation distribution of suitable resolution and accuracy. Vegetation maps exist for the east Mojave in California (the Central Mojave Vegetation Map) and for the Nevada Test Site (the Nevada Test Site Vegetation Map). These maps can be used for preliminary modeling of vegetation recoverability and dynamics, and these maps can be modified to be even more applicable to the spatial-temporal modeling of vegetation dynamics. Vegetation mapping for the remainder of the Mojave is still needed.

Rabbitbrush in bloom. Photo by David Miller, USGS.

The objectives for this research are the following:

• Develop quantitative models of vegetation recovery based on existing literature and measured dated disturbances

• Determine how the two existing vegetation maps can be modified for the best use for modeling vegetation dynamics and recovery

• Develop prototype maps of vegetation recovery for the Mojave National Preserve and the Nevada Test Site

• Develop plans to map vegetation for the remainder of the Mojave Desert that is adequate for ecosystem-wide modeling of vegetation dynamics and recovery

To create the prototype maps of vegetation recoverability for the Mojave National Preserve and the Nevada Test Site, the transfer functions developed from quantitative examination of measured dated disturbances will be applied to maps of vegetation assemblages for both areas. This requires reworking the plot data for both the Central Mojave Vegetation Map and the Nevada Test Site Vegetation Map to reflect vegetation assemblages suitable for modeling. Distribution of the assemblages will be correlated with available maps of environmental variables such as surficial geology, aridity indices, soil moisture, and derived satellite imagery (if available) and will be statistically analyzed. The assemblage distributions will be modified as appropriate. The results will determine techniques suitable for ecoregion-wide vegetation dynamics mapping.

Webb, R.H., Esque, T.C., Medica, P.A., DeFalco, L.A., and Murov, M.A., 2001, Monitoring of ecosystem dynamics in the Mojave Desert: the Beatley permanent data: U.S. Geological Survey Fact Sheet 040-01, 4 p.

Thomas, K.A., Franklin, J., Keeler-Wolf, T., and Stine, P., 2004, (ArcInfo), U.S. Geological Survey Technical Report.

The Central Mojave Vegetation Map displays vegetation and other land cover types in the eastern Mojave of California. Map labels represent alliances and groups of alliances as described by the National Vegetation Classification. The nominal minimum mapping unit is 5 hectares. A primary land cover type and a secondary type label each map unit where applicable. In addition, the source of data for labeling each map unit is also identified in the attribute table for each map unit. Data were developed using field visits, 1:32,000 aerial photography, SPOT satellite imagery, and predictive modeling. These data were developed as part of the Department of Defense Legacy funded Mojave Desert Ecosystem Program.

Thomas, K.A., Franklin, J., Keeler-Wolf, T., and Stine, P., 2005, Central Mojave vegetaion database: U.S. Geological Survey Fact Sheet 2005-3098, 4 p.