Road Ecology Center
Mitigating potential impacts of herpetile habitat loss and fragmentation from new roadway construction in Southern New York state
- Author(s): Samanns, Ed
- Zacharias, Sebastian
- et al.
Construction of a 6.5-kilometer (4-mile) two-lane access roadway has been proposed to provide airport patrons with improved access to Stewart International Airport in Orange County, New York. The project design, environmental review and permitting process were a joint effort between the New York State Department of Transportation (NYSDOT) and the New York State Thruway Authority (NYTA). While the majority of the new access roadway will utilize an existing road network, an approximately one-mile portion will pass through extensive secondary growth forest on the southwest side of the airport. This area is in close proximity to the 6,000-acre Stewart State Forest. A 1.12-kilometer (0.7-mile) length of this alignment passes through a valley containing a complex of emergent and forested wetlands and a headwater stream. In order to minimize potential impacts to two New York State Species of Special Concern, the spotted turtle (Clemmys guttata) and the Jefferson salamander (Ambystoma jeffersonianum), as well as other wildlife species, a mitigation plan was devised to replace wetland habitat utilized by these species. The mitigation plan also includes four underpasses to maintain a connection between upland forest and wetland habitats on either side of the roadway. The mitigation plan was developed in a collaborative effort with the New York State Department of Environmental Conservation (NYSDEC), NYSDOT, NYTA and The Louis Berger Group, Inc. (Berger). Berger developed a design plan for the construction of 12 vernal pools in close proximity to the impacted wetlands to provide supplemental breeding habitat for several herpetile species. The 12 pools range in size from 0.01 to 0.13 hectares (0.04 to 0.33 acre), with a combined total area of 0.55 hectares (1.37 acres). The site selection, vernal pool design, water budget analysis, and plan and specifi cation preparation was a collaborative effort between biologists and engineers. Several criteria were used to select the best possible sites for pool construction. These criteria took multiple factors into consideration including proximity to existing wetlands, upslope drainage areas, forest quality, site topography, soil characteristics, and availability of adjacent upland buffer habitat. The design places major emphasis on site hydrology since this would be the determining factor for target species use of these habitats. The intended inundation hydroperiod (March through July) was based on the target species breeding requirements and was the basis of determining if an individual vernal pool site could be successful. Water budgets were developed for each proposed site to determine the necessary design elements required to establish naturally functioning vernal pool hydrology. Controlling infl uences such as pool watershed, subsoil infi ltration rates, precipitation rates, and substratum composition were all accounted for in the water budget analysis. Other elements such as maintaining a closed tree canopy and incorporating leaf litter to provide an appropriate substrate were addressed in the design. The mitigation plan also calls for the minimization of habitat fragmentation through the incorporation of wildlife passages. The roadway design incorporates the use of amphibian barriers at three locations to prevent herpetiles from entering the travel lanes of the new road and to direct them to pairs of culverts designed to provide passage through the roadway embankment. Two larger 12-ft by 8-ft con-spans were also incorporated into the design to provide deer, coyote and other mammals a safe point to cross beneath the roadway. The underpasses are openbottom box culverts with an openness ratio of 0.85. Upon construction, a fi ve-year monitoring program will be implemented by NYSDOT that will include monitoring both the herpetile colonization and use of the vernal pools, wildlife utilization of the wildlife underpasses, and road kills along the road segment. Information gathered from this mitigation plan would be adapted to other projects undertaken by NYSDOT and NYTA as appropriate.