Amphibian monitoring in hardwood forests: optimizing methods for contaminant-based compensatory restorations

Abstract/Summary

Amphibians such as frogs, toads, and salamanders provide important services in aquatic and terrestrial ecosystems and have been proposed as useful indicators of progress and success for ecological restoration projects. Limited guidance is available, however, on the costs and benefits of different amphibian monitoring techniques that might be applied to sites restored in compensation for contaminant injury. We used a variety of methods to document the amphibian communities present at four restored bottomland hardwood sites in Indiana, and to compare the information return and cost of each method. For one method—automated recording units—we also modeled the effect of varying levels of sampling effort on the number of species detected, using sample-based rarefaction and Bayesian nonlinear (Michaelis-Menten) mixed effects models. We detected 13 amphibian species across the restored sites, including two species of conservation concern in Indiana—northern leopard frogs (Lithobates pipiens) and northern cricket frogs (Acris crepitans). Sites across a range of restoration ages demonstrated encouraging returns of amphibian communities. While more mature sites showed greater species richness, recently restored sites still provided important habitat for amphibians, including species of conservation concern. Among the four methods compared, amphibian rapid assessment yielded the highest number of species detected and the greatest catch per unit effort, with the lowest per-site cost. Our analysis of rarefied acoustic data found that number of nights sampled was a better predictor of observed species richness than the number of hours sampled within a night or minutes sampled within an hour. These data will assist restoration practitioners in selecting amphibian monitoring methods appropriate for their site characteristics and budget.