EVIDENCE OF UNAUTHORIZED OFF-HIGHWAY VEHICLE ACTIVITY IN THE RAND MOUNTAINS AND FREMONT VALLEY, KERN COUNTY CALIFORNIA
At the request of the Desert Tortoise Preserve Committee, EnviroPlus Consulting undertook a project to analyze unauthorized off-highway vehicle (OHV) activity in the Rand Mountains and Fremont Valley of eastern Kern County, California. The area is adjacent to the northeastern part of the Desert Tortoise Natural Area (DTNA) and Area of Critical Environmental Concern (ACEC), contains the western Rand Mountain Area of Critical Environmental Concern (ACEC), and has significant habitat for the desert tortoise (U.S. Bureau of Land Management 1980; Sievers et al. 1988).
Specific objectives of the study included the following:
- Investigate the degree of OHV impact on desert tortoise habitat in the study area with specific emphasis on those impacts that have occurred since the area was reopened to public use on November 21, 1990.
- Determine the degree to which public use of the land, most of which is OHV activity, conforms with the publicly announced BLM policies.
- If significant vehicle activity is occurring and if the vehicle use does not conform to BLM policies, identify the area of use.
- Determine if relationships exist between open routes and unauthorized activity.
The desert tortoise (Gopherus [Xerobates] agassizii) was listed by the State of California in June 1989 as a threatened species. A few months later, the U.S. Fish and Wildlife Service listed the species as endangered under an emergency rule, then followed with a permanent listing as threatened on April 4, 1990. The tortoise was listed because of rapidly declining populations, habitat loss and fragmentation. The sources for population losses include vandalism, vehicle kills, collections, disease, and excessive raven predation. For habitat damage and loss, the causes are multifold.
Declines in tortoise populations are well-documented for the western Mojave desert (Berry, 1990). Vandalism, damage to habitat from sheep grazing and off-highway vehicles (OHV), upper respiratory tract disease (URTD), and ravens are particularly critical issues in the Rand Mountains and Fremont Valley.
In 1989 the U.S. Bureau of Land Management (BLM) placed a significant portion of public land in the Rand Mountains and Fremont Valley under a temporary emergency quarantine and road closure to provide increased protection for the desert tortoise and its habitat (U.S. Bureau of Land Management, 1989). The area under quarantine included the Desert Tortoise Research Natural Area (DTNA) and Area of Critical Environmental Concern (ACEC) and West Rand Mountains ACEC. All human activities, except those administratively authorized, were excluded from the DTNA and West Rand Mountains ACEC.
The protective action was lifted on November 21, 1990 (U.S. Bureau of Land Management, 1990). According to a BLM media release, “Approximately 150 miles of roads will be opened in the area to provide access. Open routes will be signed with a brown post indicating their open status. Unmarked routes and trails and those marked with a red ‘closed’ post may not be used by motorized vehicles.” This is a “…75 percent reduction in the existing routes.” Further, “… camping will be allowed within 100 feet of a road in previously disturbed areas only.”
SUMMARY OF FINDINGS
Field surveys were conducted December 13-15, 1990 and January 20, 1991. Methods used to evaluate OHV impacts included: driving 46.2 miles of open routes and recording the unauthorized tracks and trails which crossed the open routes; walking 37 transacts, each of which was 500-feet long, perpendicular to open routes and recording OHV impacts; raking closed routes and rechecking them 34 days later for unauthorized vehicle use; and incidental observations.
A total of 287 unauthorized (unmarked or closed) trails with at least five tracks per trail were observed to cross 46.2 miles of surveyed open routes. Of these, 93% of trails were unmarked, and the remaining 7% were marked closed. The signed, closed routes represent a small fraction of the total number of trails being used by OHV enthusiasts.
On each of the 37 transacts, a mean of 27 unauthorized tracks were found, an average of one track every 20 feet. Impacts were found to vary in an inverse proportion to its distance from an open route. Near the edge of an open route (0-20 feet), an average of 2.70 OHV impacts (tracks and trails) per 20 linear feet were found. Further from the trail impacts tapered off to an average of 0.87 per 20 linear feet.
Twenty-one signed, closed routes were raked on December 15, 1991. Five of the signs marking these trails had been vandalized. When 16 of the trails were rechecked 34 days later, 206 new OHV tracks were found with a mean of 13 tracks per closed route.
Unauthorized OHV activity was observed during both survey periods. In one instance, group of about eight OHV riders were observed riding on unmarked trails. In another instance truck and motorcycle were observed riding on a signed, closed route.
Bureau of Land Management (BLM) policies limiting vehicle use to signed, open routes are ineffective. Intensive, negative impacts to desert tortoise habitat are occurring as a result. Only a small fraction of unauthorized trails (7%) are marked as closed. Even on the trails marked as closed, unauthorized use is continuing. Results from 37 transacts suggest that unauthorized OHV impacts are related to open routes with these impacts decreasing as the distance from the open route increased.
LEVELS OF UNAUTHORIZED VEHICLE USE
BLM instructions governing OHV activities are not being heeded. As a result, significant degradation of tortoise habitat is occurring. Unauthorized use is astoundingly high. From trail and track mapping, an average of 47 unauthorized tracks per linear mile was found. This estimate is low since single tracks not associated with a trail and trails with fewer than 5 tracks were not recorded. A more accurate estimate of unauthorized tracks is derived from the data set of 37 transacts. On the average, one unauthorized track was encountered every 20 linear feet. This represents an intensive, negative impact to the habitat of a federally listed species.
Transect data also reveal a relationship between open routes and unauthorized OHV impacts. Impacts are highest close to the open route, suggesting that the presence of an open route may induce negative impacts for substantial distances from the route edge. Even at 500 feet from an open route, unauthorized tracks were observed at a rate of almost one per 20 linear feet. These impacts are apparently difficult to control.
Marking routes as “closed” is an ineffective measure against trespassing. The contrary seems to be the case. Five of twenty-one signs on closed routes were vandalized. The degree of trespassing is intensive. An average of 11 tracks were found per closed route.
Berry, K. H. 1990. The Status of the Desert Tortoise in California. Draft Report from the U.S. Bureau of Land Management, Riverside, California, to the U.S. Fish and Wildlife Service, Portland, Oregon.
Sievers, A., J. B. Aardahl, K. H. Berry, B. L. Burge, L. D. Foreman, G. E. Moncsko, and J. St. Amant. 1988. Recommendations for Management of the Desert Tortoise in the California Desert. California Desert District, Riverside, California, 55 pp. with Appendices.
U.S. Bureau of Land Management. 1980. The California Desert Conservation Area Plan. U.S. Bureau of Land Management, Riverside, California. 173 pp.
U.S. Bureau of Land Management. 1989. U.S. Bureau of Land Management. Temporary emergency quarantine in the Desert Tortoise Natural Area and western Rand Mountain Area of Critical Environmental Concern. Federal Register 54(181).
U.S. Bureau of Land Management. 1990. Temporary emergency quarantine in the Desert Tortoise Natural Area and West Rand Mountains Area of the Critical Environmental Concern (ACEC); Ridgecrest Resource Area, Kern County, California. Federal Register 55(197): 41392-41393.