|Natural vernal pool - photo from WarwickMA.org|
|These tadpoles will probably run out of water and |
die before having the chance to metamorph
into adult toads - photo from Owlsland.com
Top Five Reasons that Vernal Pool Projects Fail
5. Failed long term maintenance of project site
4. Incoherent or impossible project goals
3. Habitat has poor structure
2. Improper soil
1. Improper hydrology
What does it take to make vernal pools really work?
1. Sufficient hydrology - For a vernal pool to be functional as amphibian habitat, it needs to provide habitat for the entire larval period of amphibians, plus provide habitat for prey items of the amphibian larvae. The single biggest error in vernal pool design and construction is to build pools that are not sufficiently deep (or are too well drained) to stay flooded into late June, when the last amphibian larvae, notably toad and tree frog tadpoles, transform and move into drier habitats.
During typical east coast winters and early springs, many areas appear to amphibians (and humans) to be wet enough to serve as wetland habitat. The problem is that these pools often dry up before the majority of larvae can survive on land. Even before the pool has dried up, smaller volumes of water mean high densities of amphibian larvae - which mean great hunting for raccoons and birds.
While this is a natural phenomenon in existing low-lying areas and seasonal wetlands, it is unacceptable to "not be sure" if a project you're designing will be too shallow or evaporate/drain too quickly to perform many of the critical functions of vernal pools. Successfully designed vernal pools have deeper areas called "refugia" that will remain flooded (and free of fish) into the summer.
|A successful vernal pool may look like this in July. A failed (built) or false (natural) vernal pool may look like this in May. The difference between the two is site selection, good design, and proper construction method.|
|False vernal pool in winter, courtesy of www.HikingwithChuck.com|
|Nice vernal pool, photo courtesy of www.field-notebook.com|
|Created vernal pool with significant habitat structure. Photo: Tom Biebighauser, USFS|
|Sediment entering a restored wetland from this |
pipe may eventually convert the wetland to an
upland if the sediment is not periodically
removed by volunteers or maintenance crews
(photo: Cacapon Institute)
Hint: It's not true. The wetland you've designed and created is an ecological snapshot. If you'd like it to remain the same, that "snapshot" will have to be maintained. The physical components of the wetland - soil, hydrology, and vegetation - will have to be managed by someone.
Otherwise, nature will take its course.....remember - wetlands come and go over time. Is a long term conversion of your wetland to an upland a positive outcome for your project? If not, consider long term maintenance. Here's two ways to do that:
1. Engaging volunteers throughout the project
As the designer or ecologist, you won't want to do this. You don't even have to tell me. It's complicated. And it's difficult. But maximizing the number of people involved in the project is one of the best ways to make sure it gets taken care of (and not totally forgotten) over the long run. Reality: the average job in the environmental field is between 2.9 and 5.2 years, depending on which study you believe. You will move on, and when you do, you will probably leave your vernal pool projects behind. Volunteers will remember it and occasionally check on it, though. And they may just hold somebody accountable!
2. Engaging the maintenance staff of the property throughout the project.
Gosh, this is a big one too. It's great that a refuge manager or a school principal tells you, "Sure, we'll take care of those vernal pools you're building!" But you need to talk to the men and ladies with the lawnmowers, backpack sprayers, and weedeaters. Will they leave the project in place? Watch over it? Your project will be well-served if you take the time to educate maintenance staff about how the vernal pool is supposed to look, and what they (staff) are supposed to do to take care of it (or leave it alone).
|Yes, O Mighty Wetland Designer, these guys will be in charge of your project|
after you kill the budget and wrap up the project.
Better be nice to them and tell them how to take care of it!
|Creating a small vernal pool in Maryland. Photo: Wayne Davis, EPA|