Road Ecology Center

The purpose of this project was to develop methods to analyze impacts from and find solutions for habitat fragmentation resulting from the construction of a new highway across two military bases (McChord Air Force Base and Fort Lewis Army Base). The bases contain large blocks of rare terrestrial habitats. The need to maintain the security of the bases limits the ability to use on-site methods, such as underpasses and crossing structures. In 2003, the Crossbase highway project, which had been a Pierce County-sponsored project, was identified as a new state highway, and thus became the Washington State Department of Transportation’s (WSDOT) responsibility. The six-mile-long highway cuts through two adjoining military bases to connect a heavily developed urban/industrial area with Interstate 5. Both military bases have core areas containing airfields, housing, operational, and commercial areas that are surrounded by largely undeveloped natural habitats consisting of large wetlands, coniferous forests, rare oak woodlands, and rare native prairie areas. These natural areas are bisected by an extensive network of gravel and paved roads and are used for military training activities. These rare habitats support four federal candidate species, and one state-listed endangered species. Development activities surrounding the military bases have fragmented and eliminated much of the habitats outside of the bases. The new highway is expected to result in three main ecological impacts: direct loss of rare habitat types, decreased use of surrounding habitat due to impacts associated with the operation of the highway (e.g., noise), and habitat fragmentation or isolation of habitats. While mitigation ratios exist to address the elimination of habitats such as wetlands, no ratios or methods exist to quantify impacts associated with operation impacts or habitat fragmentation. Working in conjunction with Washington State Department of Fish and Wildlife (WDFW), WSDOT developed a method to assess these impacts based on the level of function that would be lost. This method was used to determine what the total habitat enhancement and restoration package for the Crossbase highway should be. The resulting habitat enhancement and restoration package that was developed consists of three parts: acquisition of a large parcel of rare habitat, restoration and enhancement of the acquired site, and providing funding for additional restoration, acquisition, and enhancement activities. While construction of the highway has not begun, WSDOT is proceeding with acquiring the restoration and enhancement site and has provided funding for the additional acquisition, restoration, and enhancement activities. The developed method will be used on other new highway projects in the future.