USDA Forest Service

Pacific Southwest Research Station
Pacific Southwest
Research Station

800 Buchanan Street
Albany, CA 94710-0011
(510) 883-8830
United States Department of Agriculture Forest Service. USDA logo which links to the department's national site. Forest Service logo which links to the agency's national site.

Research Topics Ecosystem Processes

Sierra Nevada Ecosystems

Effects of Off-Highway Vehicles (OHV) on Vertebrate Communities

Research Project Summary

The Research

Direct effects of OHV use include noise, compaction, collision, trampling, and simple physical presence of plant and wildlife species, and they can affect a wide array of trophic levels, ranging from primary producers to top predators. OHV use in California is growing along with the burgeoning population of the State. Managing this growth in a manner that is consistent with multiple land management objectives poses a mounting challenge to land managers and the OHV user community. Basic information on how various aspects of OHV use (e.g., presence, sound, physical effects) affect populations and habitat elements of interest and concern have thus far presented a barrier to informed OHV use management. This is particularly true in California, where the number of species of concern in the State is the second highest in the United States, following Hawaii. OHV use -- if not managed properly -- has the potential to jeopardize the long-term persistence of some species.

The purpose of this research is to assess the effects of Off Highway Vehicles (OHV) on forest-associated vertebrate species and the condition of their habitats. The study will determine how spatio-temporal factors related to OHV use affect vertebrate species, with particular emphasis on shifts in species assemblages, impacts to understory-associated species, the presence of top carnivores (e.g., marten, northern goshawk, and spotted owl), and the abundance and distribution of their primary prey.


blue arrrow To determine the effects of summer OHV use on the composition and structure of vertebrate assemblages, with emphasis on understory associates, top predators, and their prey

blue arrrow To determine the differential effects of fragmentation, vehicle presence, and noise on vertebrate assemblages

blue arrrow To evaluate the effects of proximity and intensity of use on nest site selection for understory bird species, movement of small mammal species, and daily activity patterns of carnivore species

Methods and Design

photo of bobcatThe study is being conducted in the central Sierra Nevada between 6000 and 9000 ft in elevation. Sites have snow in the winter, so they experience winter use by snowmobiles and skiers, as well as summer use. Study sites are paired use and non-use 9 km 2 areas that are further subdivided into nine, 1 km 2 sample units. Each sample unit is sampled for plants and animals, and use is sampled along roads and trails in use areas, and along established transects in non-use areas. Sampling occurs from May through September.

Animal sampling consists of point counts for small birds, small mammal live-trapping for small mammals, baited trackplate and camera stations for larger mammals, and broadcast calling for raptors. In addition, nests of eight focal bird species are located and characteristics of nest sites are recorded, along with the characteristics of a randomly located site in close proximity. Vegetation structure and composition are sampled using a wide range of plot and transect methods.

Recreational use is characterized in multiple ways for each sample unit. The density of roads and trails is quantified based on map and ground reconnaissance. The intensity of use is calculated based on a combination of walking surveys, trailmaster counters, and sound recordings. Sound exposure is calculated based on sound recordings.

As of the close of 2006, five pairs of sample sites have been sampled. If field data collection continues in 2007, two additional pairs of sites will be sampled. The study is scheduled to conclude in 2008.

Application of Research Results

The results of the study will be applied to route designation and the management of OHV use at designated sites. It has already been used to inform the design of wildlife monitoring at OHV use areas.

photo of a map of the Sierra Nevada Ecoregion

The study area is located in the central Sierra Nevada on three National Forests: Lake Tahoe Basin Management Unit, Eldorado NF, and Humboldt-Toiyabe NF.

Lead Scientists/Collaborators

1) Manley, Patricia N.; 2) Campbell, Lori A.

USDA Forest Service
Sierra Nevada Research Center
2121 Second St., Suite A-101
Davis, CA 95616

Publications and Reports

Manley, P.N. and L.A. Campbell. In prep. Interim report: implementation of the Vertebrate Assemblage OHV study.

Manley, P. N., Stumpf, Joshua P., and Davis, Wesley B. 2004. Pilot test of programmatic approach to monitoring winter conditions and trends of wildlife populations and habitats in Off-Highway Vehicle use areas. Unpublished report submitted to U.S. Forest Service, Pacific Southwest Region, 1323 Club Drive, Vallejo, CA .

Last Modified: Aug 29, 2016 10:56:30 AM