San Diego Management & Monitoring Program


Appendix A - Assessment of Wildlife Crossing Sites for the Interstate 15 and Highway 101 Freeways in Southern California

Type: report

Article abstract: Roads can cause significant mortality for wildlife, but large roads like freeways can also form major barriers to wildlife movement and gene flow. Freeways are ubiquitous in southern California, and two freeways, Interstate 15 and U.S. 101, have been found to be barriers to wildlife passage and gene exchange, especially for mountain lions, between the Santa Ana Mountains and the Palomar Mountains and other mountains to the east (separated by Interstate 15), and between the Santa Monica Mountains and the Simi Hills, Santa Susana Mountains, and others to the north (separated by the 101 Freeway). We used two sources of information with the goal of bridging the gap between connectivity science and conservation practice. In early 2015 we engaged an independent panel of connectivity experts to evaluate possible locations and concepts for wildlife crossings along stretches of both freeways. We also developed and implemented an evaluation tool based on landscape characteristics and wildlife data to help prioritize locations for wildlife crossing infrastructure. The experts were asked to evaluate stretches of each freeway where wildlife studies have indicated that some connectivity potential remains due to the presence of natural habitat on both sides of the road, but where new or enhanced structures are likely required to restore lost connectivity. Multiple specific sites were examined along these stretches of each freeway. For I-15, both the Landscape and Expert scoring indicated that retention and enhancement of function under the Temecula Creek Bridge, and construction of a new under or overpass south of the bridge, were both likely needed for long term connectivity. For the 101 Freeway, the Landscape and Expert scoring both strongly concluded that West Liberty Canyon is the best location for a new wildlife crossing structure, with several other locations being sites where enhancements or new construction could serve the role of providing secondary crossings. The experts indicated that an overpass, over both 101 and the parallel Agoura Rd, was the best option here to provide connectivity for a range of species. The experts agreed that accompanying measures, such as effective wildlife fencing to funnel animals to crossing points and appropriate vegetative cover on and near structures were also important. They also recommended that, over the long term, more than one crossing structure should be enhanced or created for each linkage to assure sufficient movement of

Number of pages: 78

Month: March

Year: 2018

Prepared by: Riley, Seth; Smith, Trish; Vickers, Winston;

Keywords: connectivity corridors; corridors; mountain lion; wildlife and infrastructure;

Species: Mountain lion

Projects: