Determining Thresholds for Conservation of Vernal Pools

Abstract

Vernal pools—small seasonal wetlands—provide critical breeding habitat for many species but are under-protected in environmental regulation. Because vernal pools are not rare in the northeastern United States, regulatory emphasis is typically placed on protecting “significant” vernal pools yet scientific criteria for determining thresholds for conservation significance remain poorly developed. We used an evidence-based approach to identify thresholds of pool significance based on populations of breeding amphibians in five ecoregions and across urbanization gradients of New York State, where a recent revision to wetland law allows regulation based on amphibian productivity. We combined existing population survey data with new surveys to yield a dataset of 587 pools for estimating statistical distributions of productivity of two indicator species: spotted salamanders (Ambystoma maculatum) and wood frogs (Lithobates sylvaticus). Spotted salamander egg mass counts were significantly lower in highly developed landscapes. Larger pools were generally more productive for both species yet no single habitat feature reliably predicted high egg mass counts. Pool incidence and productivity also varied regionally: the Hudson-Mohawk region hosted the most known vernal pools and highest egg mass counts and the Lake Plain region the fewest known pools. Our dataset yielded threshold options for guiding pool protection that varied by the proportion of pools targeted. We suggest a lower standard for protecting pools in high-development areas and that presence of other pool-breeding indicator species could also qualify pools for significance. These recommendations can guide regulators in affording protection critical to small wetland habitats specific to regional and landscape contexts.