last update July 8, 2000
Based on percent cover, there appears to be a distinct difference between the desert pavement creosotebush scrub community and the more sandy swale creosotebush scrub community, with the swale communities consistently displaying 34 times more cover than the desert pavement communities. There also appears to be a common denominator between the creosotebush scrub swale communities and the other communities that have higher percent vegetation cover. The 8 communities with above 10% cover are all located on sandy soil sites, while those communities with below 10% vegetation cover appear to have a more rocky/clay substrate. It appears, overall, that the sandy wash and swale habitats have higher vegetation cover compared to the rocky soil of the desert pavement communities or the clay-dominated soil of the desert sunflower barrens. This is undoubtedly the result of the ability for rainwater to more easily penetrate through sandy soil than through the heavier rock or clay dominated soils.
No connection between OHV activity and any of the indicators used could befound. Evena comparison between percent cover and amount of OHV activity provedinconclusive. This is probably caused by the fact that there are manyfactors involved indetermining the level of OHV activity any one site experiences: factorssuch as locationwithin the park; topography; aspect; and nearness to established trails orpoints of interest.Only through studying the past history of an area and tracking suchindicators as percentcover over a period of time through a continuation of vegetation surveyssuch as this onewould it be possible to determine what values could serve as indicators ofOHV impact.
RECOMMENDATIONS
It is recommended that the park establish an on site voucher system, particularly for annual species. This would provide the basis for maintaining a complete listing of plant species found within the park's boundaries with annotations pertaining to specific species as they exist in the park, not in a generalized field guide or text. Specimens should be kept in a pest proof herbarium case, located on the park grounds, and maintained and used by the park's resource ecologists. This would entail some training in the proper management of herbarium specimens which could be obtained from one of the local universities such as the University of California at Riverside or San Diego State University.
The accuracy of future surveys by park personnel will be based on their knowledge of the plant species to be found within the park. Having specimens to view before, during and after such surveys are conducted will greatly benefit those individuals involved and allow for a more accurate identification program for the future. Due to the extreme climate of the Ocotillo Wells area and long periods of drought experienced by the park, many annual species may appear only a very rare occasions and not easily identified unless a voucher specimen is available for comparison. Personnel turnover, a normal occurrence for state and federal parks, can also lead to new individuals being responsible for conducting future surveys that are unfamiliar with the local flora. Thus a voucher program would be of ever increasing value as an accurate way of ensuring the park maintains its vegetation monitoring program.
A second recommendation is the establishment of fixed transect markers for all monitoring plots. Since these plots are to be monitored in the future and comparative analysis run, it is imperative that future surveys be conducted along the same exact transect lines to obtain statistically accurate data. Though interference with OHV activity is a legitimate concern, the use of fixed markers is a necessity for the conduct of accurate future surveys.
The use of benchmarks sunk in concrete is recommended as one way of establishing a fixed marker for each transect line. Because of shifting sand, these would need to be identified by some type of marker post, more permanent than a carsonite stake, to mark the benchmark's location even if it becomes buried over time. This post could be painted international orange or marked in some other manner to ensure its visibility to OHV drivers to prevent accidental collisions. Information as to the compass direction of the transect and actual transect length could also be stamped on the benchmark as an additional insurance toward the accuracy of future surveys.