Forest land-use history affects outcomes of habitat augmentation for amphibian conservation

Abstract

Historical land use (especially agriculture) has seldom been considered in the development of conservation programs for amphibians, a group in global decline. Habitat augmentation (e.g., wetland creation) is a growing conservation strategy to stem population declines in regions affected by habitat loss, but such actions are often implemented indiscriminately of landscape contexts that may mediate conservation outcomes for species with complex life cycles (i.e., distinct larval, juvenile, and adult stages). We examined the contribution of variation in quantity of larval (aquatic) and quality of juvenile/adult (terrestrial) habitat to the distribution of two pool-breeding and forest-dependent amphibian species in upland forest patches with histories that ranged from former agricultural lands (secondary forests) to never having been deforested (legacy forests). Using area-constrained visual encounter surveys in two consecutive years with contrasting precipitation conditions (extreme drought and extreme rainfall), we estimated forest patch occupancy probabilities of wood frogs (Lithobates sylvaticus) and spotted salamanders (Ambystoma maculatum) at a study area in central New York State, USA, and characterized terrestrial microhabitats in 29 population “neighborhoods” (9.3 ha) that varied in larval habitat availability (0–10 constructed vernal pools) and extent of secondary versus legacy forest. Terrestrial amphibian habitat in secondary forests featured shallower leaf litter, denser understory vegetation, and fewer cover object refuges than in legacy forests. The presence of wood frogs was solely affected by breeding pool densities whereas that of the longer-lived and less dispersive spotted salamanders depended on both quantity of larval habitat and quality of terrestrial habitat, with higher levels of occurrence in legacy forests and, during the drought year, where pool densities were greater. These results suggest that larval habitat augmentation can boost populations of amphibians with complex life cycles, but climate variation and land-use legacies mediate conservation outcomes for long-lived habitat specialists.