Calhoun and colleagues just published a very nice review in Wetlands on creating vernal pools with emphasis pool-breeding amphibians. I’m not going to summarize the paper as it’s a review (not too long) and worth reading in full. However, one of the take home messages is that creating effective vernal pools is extremely difficult. The hardest part is getting the hydroperiod (timing and duration of wetland filling) right. Hydroperiod is one of the most critical characteristics of wetlands for species dependent on ephemeral wetland habitats (e.g. wood frogs, spotted salamanders, fairy shrimp).
To further complicate things, most mitigation permits only require monitoring for 2 years post-creation. Even “long” monitoring is usually only 5 years. This is generally insufficient to understand population dynamics of amphibians in stable systems, much less in newly created wetlands that are rapidly changing. Most vernal pools in the northeast US are embedded in forested landscapes and have trees growing on the margins and shading large portions of the pools. Most newly created pools do not have trees on the banks so even if the hydroperiod is suitable for amphibians in the first years, the regrowth of trees changes the throughfall and evapotransporation which can significantly alter the hydroperiod decades after the monitoring is completed.
Despite the challenges, these wetlands often have to be created to mitigate for loss during development and road expansions. As Calhoun and colleagues aptly point out, the priority should be protection of existing pools. However, when creation of new pools is needed to replace the loss of existing pools they provide nice guidelines for practitioners and suggestions for areas of future research.
I actually started studying amphibians because I was interested in wetland restoration and creation following a terrific course on the subject I took as an undergraduate at UNH. Through various twists and turns, I have yet to study wetland restoration and creation but still plan to in the future. This review was a nice way to keep abreast of some of the relevant literature.