Travel Management Planning for Wildlife with a Case Study on the Mojave Desert Tortoise

Roads are important drivers of habitat loss, degradation, and fragmentation that affect global biodiversity. Detrimental effects of roads include direct mortality of individual animals, spread of habitat-altering invasive plants, and loss of demographic and genetic connectivity of wildlife populations. Various measures address the negative effects of roads on wildlife. However, most strategies for minimizing or mitigating the effects of roads are focused on the actual roads themselves rather than on the collective travel network across landscapes. We summarized a growing body of literature that has documented the effects of road density on wildlife populations and the benefits associated with lower densities. This literature supports the application of limits on road density as a viable tool for managing cumulative effects. Based on these examples, we recommend road densities, including all linear features used for travel, < 0.6 km/km2 as a general target for travel management in areas where wildlife conservation is a priority. Lower densities may be necessary in particularly sensitive areas, whereas higher densities may be appropriate in areas less important to landscape-level conservation and wildlife connectivity. Public policy and funding also are needed to address challenges of enforcing off-highway vehicle regulations. In applying this general overview to a case study of the Mojave desert tortoise Gopherus agassizii, we found that all management plans across the species’ range lack considerations of road density and that tortoise populations declined within all conservation areas with road densities > 0.75 km/km2. From this we provide several travel-management recommendations specific to Mojave desert tortoise conservation beginning with identifying the entire travel network within management areas. Specific actions for managing or setting limits for road density depend on the site-specific biological or management context, for instance relative to habitat quality or proximity to designated tortoise conservation areas. In addition, increasing law enforcement and public outreach will improve enforcement and compliance of travel regulations, and installing tortoise-exclusion fencing along highways will reduce road-kills and allow tortoise populations to reoccupy depleted areas adjacent to highways. Implementation of these recommendations would improve the prospects of reversing desert tortoise population declines.