New science exhibits need for wildlife crossing structures in Southwest Washington

Research reveals wildlife habitat connectivity hot spots along Interstate 5

By Brian Stewart, Cascades to Olympics Program Manager and and James Blacklaw, Cascades to Olympics Program Intern

Since 2010, Conservation Northwest (CNW) has been a dedicated partner and champion of the Washington Wildlife Habitat Connectivity Working Group (WWHCWG). The working group is composed of leading experts in the field of habitat connectivity and modeling in the Pacific Northwest (PNW). Their latest modeling effort, focused on the Southwest and Coastal areas in Washington state, has identified hot spots along Interstate 5, US 101, US 6, and SR 8. Maps they have produced will be used by planners and practitioners to identify and improve key wildlife corridors and landscape permeability along these and many more roadways across the region.

Southwest Washington is a unique and treasured Pacific Northwest landscape. It boasts the state’s second largest river system, multiple mountain ranges, and national parks and forests. It is considered one of the most bio-diverse regions in Washington State, as well as the wettest. The region is also home to many endangered and threatened species as well as some of the area’s most iconic species (i.e., salmon, elk, and cougar). In addition, southwest Washington is the ancestral homeland of many diverse indigenous communities and provides ecosystem services that sustains local Tribes, families, businesses, and livelihoods.

While, historically, this landscape has been resilient to natural stressors, today the region is unfortunately facing unprecedented threats heavily influenced by human activities such as climate change, ever-increasing development and urban sprawl, and land use changes. These threats  continue to diminish many of the thriving systems that keep this land and those that live in it thriving. To mitigate these challenges, resource managers need to have the best available science to create a future-aimed adaptive management strategy that is relevant under today’s conditions while being flexible enough to account for future conditions. This is why the WWHCWG has focused its modeling efforts on creating, restoring, and protecting resilient landscapes and ecosystems through the lens of habitat connectivity, conservation, and environmentally minded infrastructure development. We believe that using this framework is the best way to mitigate developmental stressors, provide wildlife an opportunity to safely move so they can adapt to climate change, and protect corridors and key habitat patches that also sequester carbon. Our goal is to ultimately install wildlife-specific crossing structures on highways and roads that we have identified with our models.

In all, the WWHCWG developed models that represent the 6 distinct habitats of the region using expert opinion, on the ground data, and scientific literature. To accomplish this, the group decided to select unique terrestrial species that could be used as proxies for other species associated with the same habitat type. For example, we selected cougar as a proxy for generalist species, beaver for semi riparian habitat, mt. beaver for mid-elevation and mid-seral stage habitat, fisher for old growth, and western gray squirrel for oak woodland prairie. In addition, we utilized a landscape integrity model (naturalness) to take advantage of the “intactness” of the landscape in this region. Finally, these models were overlaid to create a composite model. This then shows where most of the species’ connectivity needs overlapped with our other species’ connectivity needs.

This data can be used to identify and prioritize locations for feasibility studies and the final implementation of wildlife connectivity projects. Including restoration, wildlife crossing structures on roads, habitat conservation, protection and more. These types of landscape-level considerations offer multiple benefits to people and wildlife: making the roads safer, the landscape permeable, and people safer, all while saving money. It’s the mythical win, win, win, win, win.

The biggest takeaways from this report center on Washington’s major state highways. First, Interstate 5 (I-5) is a major barrier to wildlife. However, our models have identified 3 priority areas on I-5 where further research is needed and where crossing structures would potentially be most effective. CNW’s Cascades to Olympics program manager identified the exact same locations on I-5 using different methods in his 2019 graduate thesis, validating both bodies of work. Unfortunately, the Northern, Southern, and middle linkages on I-5 are the last remaining bastions of potential along the corridor in the state. With development moving at a breakneck pace, time is running out and it is imperative that action is taken to make use of our findings. Second, highways 8, 10 and 12 are significant barriers for species moving between the Chehalis Basin and the Olympic peninsula; a handful of potential linkages have been identified along these highways as well.

Read more about the Washington Cascades to Coast Habitat Connectivity Analysis report!

Overall, we are thrilled and elated to present and be a part of such a herculean group effort. CNW is proud to have been able to offer the knowledge and experience of our Cascades to Olympics manager, who has been studying I-5 for nearly 6 years now and was the first researcher to assess the permeability of I-5 for wildlife. CNW will leverage this connection as we look to validate and implement the science that has been developed for this region. We are enthusiastic about carrying on this exciting and important work.

The next big thing in west coast habitat connectivity projects, planning, and implementation will be finding ways to get wildlife over and under I-5 safely in SW Washington.

Learn more about the Cascades to Olympics program on our website.