Efficacy of created wetlands for amphibian conservation in Illinois
Within Illinois, wetland conversion and drainage has been especially extensive where an estimated 90% of original wetland area has been lost. As such, wetland creation was listed as a priority campaign in the Illinois Wildlife Action Plan in 2005 with a primary goal of increasing suitable breeding sites for amphibians across the state. To date, more than 300 seasonal wetlands have been created on state-managed properties in east-central Illinois. In order to assess the effectiveness of these created wetlands for amphibians, we sampled 78 total wetlands across four categories: 1) 16 reference (natural) wetlands; 2) 20 created wetlands, 2-3 years of age; 3) 20 created wetlands, 4-5 years of age; and 4) 22 created wetlands, 6-7 years of age. All wetlands were repeatedly sampled from February to July in both 2011 and 2012 to account for imperfect detection. Species richness and wetland conservation coefficients were calculated to determine how well each created wetland was performing. 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.
In wetlands that were unoccupied by predatory fish, we found no significant difference in species richness (p = 0.087) between the reference and created wetland categories; however wetland conservation coefficients were significantly different (p = 0.001) between the reference and created wetlands. Wetland conservation coefficients provided an adjustment for a species’ tolerance of disturbance, its rarity, and its distribution. There were significant differences in wetland structure including greater canopy cover, greater wetland area, and less slope embankment in reference wetlands. Overall, reference wetlands had conservation coefficient values 22.3% higher than created wetlands (range 14.6-30.1%) indicating that created wetlands are not yet functioning like a reference wetland. Further, a metric such as species richness may not be the best measure of a wetland’s amphibian assemblage because it treats all species equally (i.e. a generalist is scored with equal weight as a specialist).