Effects of off-road vehicles on vertebrates and habitat quality in the Mojave Desert

The use of off-road vehicles (ORVs) in the California desert has become increasingly popular during the past 15 years. This study was designed to assess the impact of this activity on habitat quality and the small vertebrate fauna in the creosote bush community of the Mojave Desert. Two ORV-frequented sites in each of two localities and four control areas (one for each experimental site) were compared. Vegetation, small mammals and reptiles were sampled during late spring. Density and diversity of mammalian and reptilian vertebrates were significantly lower in all ORV-used areas, as was habitat quality. Moderately used areas contained 49% as much perennial plant cover, supporting 81% as many individuals and 76% as many species of vertebrates as the control areas. Where vehicular activity is concentrated, areas become denuded, supporting little or no animal life or vegetation. These "pit areas" averaged 5.3% as much plant cover as controls, while the number of individuals and species was 12.4% and 34.5% of the controls, respectively. These results indicate that ORVs have a detrimental effect on the desert habitat proportional to the degree of usage.