Ecological function of created seasonal wetlands

Background/Question/Methods

Wetland creation was listed as a priority campaign in the Illinois Wildlife Action Plan in 2005. Since then, more than 250 seasonal wetlands have been created on state managed properties in east-central Illinois. In order to evaluate ecological function of these created wetlands, we sampled 80 seasonal wetlands including 20 references wetlands, 20 created wetlands 2–3 years of age, 20 created wetlands 4–5 years of age, and 20 wetlands 6–7 years of age (as of 2011). We examined wetland ecological function by assessing amphibian and plant diversity, both critical components of wetland ecosystems. Repeated amphibian surveys allowed us to estimate occupancy and detectability rates using program PRESENCE 3.1. Conservation coefficients were assigned to each amphibian species based upon species sensitivity to disturbance, species rarity in Illinois, and species range size in Illinois. Wetlands were then scored as the sum of conservation coefficient values of amphibians using the ponds. A stratified random plot design was utilized to sample the vegetation at each wetland. These components were incorporated into an index of biological integrity (IBI) to determine how well the created wetland is functioning within the ecosystem.

Results/Conclusions

Terrestrial vegetation tracts did not differ between pond categories in either native or invasive species composition. Pond embankment and canopy cover proved significant in determining amphibian occupancy rates. Spring Peepers (Pseudacris crucifer) were more likely to occupy less embanked ponds, whereas American Toads (Bufo americanus) preferred more embanked slopes. Canopy cover decreased occupancy estimates for Cricket Frogs (Acris crepitans), but increased the likelihood of occupancy for Spotted Salamanders (Ambystoma maculatum), Silvery Salamanders (A. platineum), Jefferson Salamanders (A. jeffersonianum), Bullfrogs (Rana catesbeiana), Green Frogs (R. clamitans), and Wood Frogs (R. sylvatica). There was no correlation between pond age and any of the measured values; however there were structural differences between ponds in canopy cover, size, and slope embankment. Further, reference ponds had conservation coefficient values 31% higher than the created ponds (p < 0.001), indicating that created ponds across the three age classes are not yet functioning like a reference pond when using amphibians as a monitoring tool.