Scott D. Jackson

Calibrating abundance indices with population size estimators of red back salamanders (Plethodon cinereus) in a New England forest

Herpetologists and conservation biologists frequently use convenient and cost-effective, but less accurate, abundance indices (e.g., number of individuals collected under artificial cover boards or during natural objects surveys) in lieu of more accurate, but costly and destructive, population size estimators to detect and monitor size, state, and trends of amphibian populations. Although there are advantages and disadvantages to each approach, reliable use of abundance indices requires that they be calibrated with accurate population estimators. Such calibrations, however, are rare. The red back salamander, Plethodon cinereus, is an ecologically useful indicator species of forest dynamics, and accurate calibration of indices of salamander abundance could increase the reliability of abundance indices used in monitoring programs. We calibrated abundance indices derived from surveys of P. cinereus under artificial cover boards or natural objects with a more accurate estimator of their population size in a New England forest. Average densities/m2 and capture probabilities of P. cinereus under natural objects or cover boards in independent, replicate sites at the Harvard Forest (Petersham, Massachusetts, USA) were similar in stands dominated by Tsuga canadensis (eastern hemlock) and deciduous hardwood species (predominantly Quercus rubra [red oak] and Acer rubrum [red maple]). The abundance index based on salamanders surveyed under natural objects was significantly associated with density estimates of P. cinereus derived from depletion (removal) surveys, but underestimated true density by 50%. In contrast, the abundance index based on cover-board surveys overestimated true density by a factor of 8 and the association between the cover-board index and the density estimates was not statistically significant. We conclude that when calibrated and used appropriately, some abundance indices may provide cost-effective and reliable measures of P. cinereus abundance that could be used in conservation assessments and long-term monitoring at Harvard Forest and other northeastern USA forests.

Issues and Methods for Transdisciplinary Planning of Combined Wildlife and Pedestrian Highway Crossings

Highways are increasingly understood as barriers to wildlife and pedestrian movement and as significant causes of landscape fragmentation–-especially in suburban and periurban areas. FHWAs Transportation, Community, and System Preservation (TCSP) Program encourages innovative solutions to reduce the impact of highways on the communities they link and traverse. This paper is based on research and public participation as part of an FHWA–TCSP sponsored feasibility study for a combined wildlife and pedestrian crossing to mitigate highway impacts on wildlife and recreation, and on the communities of Concord and Lincoln, Massachusetts. The interdisciplinary study team included representatives from landscape architecture, urban planning, wildlife biology, civil engineering, and landscape history. The study included diverse public participation and collaboration throughout the project. The paper defines significant planning issues likely to pertain to similar projects and offers a transdisciplinary method for conducting planning or feasibility studies for combined wildlife–pedestrian crossings. The method is innovative for its interdisciplinary integration and its inclusion of public officials, nongovernmental representatives, citizens, and other stakeholders. The study is being considered for further research and possible implementation by FHWA with support from the host communities and a private conservation organization.