Anuran assemblages associated with roadside ditches in a managed pine landscape

Managed forests support a diverse assemblage of herpetofauna. However, less is known about how aquatic features embedded in intensively managed landscapes, particularly modified aquatic habitat types, influence biodiversity. Further, whether additional anthropogenic disturbances to modified aquatic habitats affect occupancy of amphibians has not been studied, but has important ramifications for ongoing policy debates regarding water quality regulations in the United States. We examined species diversity and occupancy of anuran assemblages in an intensively managed forest landscape with a history of ditching, draining, and periodic maintenance of ditches. During 2012-2013, we conducted repeated aural surveys for calling male frogs and toads across 16 roadside ditch segments that were maintained from 3 to 17 years earlier. Across 12 survey events, we detected 15 species of frogs and toads 555 times. We used a community occupancy model to estimate occupancy for multiple anurans and to examine associations between species occupancy for roadside ditches and the time since drainage ditch maintenance, amount of nearby mature forest cover, and metrics describing adjacent depressional wetlands. We predicted a quadratic relationship between both species richness and probability of occupancy for individual species with time since ditch maintenance because we hypothesized anurans would respond positively to intermediate vegetation structure and canopy cover when selecting calling and oviposition sites. Based on previous studies, we also predicted positive relationships between anuran occupancy and diversity with proportion of the surrounding landscape in mature forest or in depressional wetlands, and negative relationship with increasing distance to nearest wetland. Contrary to our prediction, we did not find evidence of a positive response (95% credible intervals included 0) by the community or individual species to time since ditch maintenance or the forest or wetland covariates, but we did observe a diverse assemblage of frogs and toads associated with roadside ditches in managed pine forest. Estimated richness ranged from 5.5 to 11.5 species/site and probabilities of occurrence ranged from 0.01 to 1.00 by species and site. Detection probabilities by species within a season ranged from 0 to 0.93 and were positively influenced by rainfall for several species and differed across months for many species. Our results indicate that reconfigured aquatic habitat types embedded in managed forests can support local and regional occupancy of anurans, but the current anuran community likely differs from what occurred historically.