Keywords: Ambystoma maculatum - Amphibians - Habitat management - Hydroperiod - Rana sylvatica - Rhode Island - Seasonal ponds - Vernal pools - Wetland hydrology - Wetlands
Estimating hydroperiod suitability for breeding amphibians in southern Rhode Island seasonal forest ponds
In New England, seasonal forest ponds provide primary breeding habitat for several amphibian species, including Rana sylvatica (LeConte) and Ambystoma maculatum (Shaw). Because each species requires a minimum duration of inundation to complete its breeding cycle, one of the most important factors determining habitat suitability is a pond’s hydroperiod. The objective of this research was to develop a method for estimating pond hydroperiod from site characteristics such as pond morphology, geology, chemistry, and vegetation structure, and to use the estimates to assess the suitability of individual ponds for breeding amphibians. We monitored the duration of surface inundation in 65 ponds in the Pawcatuck River watershed of southern Rhode Island during 2001 and 2002. Pond hydroperiods, measured from 1 March, ranged from 19 to 44 weeks in 2001 and from 2 to 44 weeks in 2002; mean values were 30 and 21 weeks, respectively. Akaike’s Information Criterion was used to select a multivariate hydroperiod estimation model (R2 = 0.59, p < 0.0001) that permitted identification of ponds with hydroperiods suitable for breeding by R. sylvatica (95.4% correct classification rate [CCR]) and A. maculatum (75.4% CCR). Canopy cover, open basin depth, and specific conductance of surface water were among the most useful site characteristics for estimating hydroperiod, while surficial geology and the texture of soil parent material made smaller contributions. The CCR using open basin depth alone was 95.4 and 73.8%, respectively. These findings indicate that it is possible to estimate the hydroperiod of seasonal ponds – and to assess their suitability for individual species of breeding amphibians – without prolonged periods of hydrologic monitoring. Such techniques could have considerable value to wetland regulatory agencies and for planning amphibian habitat management and acquisition at the landscape scale.