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On the Lookout for Vernal Pools

It's 10 pm on an April evening and chilly rain has been pouring down for hours. This might not seem like the time to go for a walk, but for those who do, the sight of hordes of salamanders creeping steadily towards a shallow pond could make it a magical night. The yellow spotted salamander (figure 1) is one animal that uses vernal pools, small temporary wetlands often found in forested areas, as a place to lay eggs every spring.

This year is the first spring after the implementation of the new rules recently adopted by the Maine Department of Environmental Protection (DEP) to protect vernal pools that provide significant wildlife habitat, and similar rules are undergoing review in New Hampshire. This spring as the snow melts and April showers arrive, the narrow window of time when it's possible to definitively identify a vernal pool will begin, and the time is ripe to search for amphibians.

Figure 1. The yellow spotted salamander, Ambystoma maculatum, hides under logs or stones, except during the spring breeding period, when it travels to vernal pools or other shallow ponds to lay eggs. Photo courtesy of Maine Department of Inland Fisheries and Wildlife.

If drainage is poor or the water table is high, spring rains accumulate at the ground surface and a pool forms. Herons and wood ducks, garter snakes and skunks pass through to feed, and reptiles like the Spotted turtle (figure 2), a species classified as threatened, can be found lurking. Since the pool is free of fish, amphibian larvae are relatively safe from predators. Delicate fairy shrimp are found only in vernal pools. Vernal pool habitats are small but important.

Figure 2. Spotted turtle, Clemmys guttata, Photo courtesy of Maine Department of Inland Fisheries and Wildlife.

Like other wetlands, vernal pools provide services like stormwater retention and water filtration, but their special distinguishing value is as wildlife habitat. Centers of biodiversity, they provide food for forest-dwelling species. Amphibians like the yellow spotted salamander rely on vernal pools for reproduction; without vernal pools, these species would be in trouble. Due to their sensitivity to pollution, amphibians are useful indicators of overall ecosystem state or health.

Vernal pools are often described as wetland islands in a forest or field (figure 3), but they are connected indirectly to rivers, ponds, streams, and even the ocean. Animals move between bodies of water, and the water itself moves also, through the soil and bedrock and through the air as vapor, rain, and snow. Vernal pools bring the forest floor's connection to the water cycle to the surface --  literally -- for a brief time. Vernal pools are difficult to spot out of season. As the season shifts and water leaves, the pool may dry up to the extent that it is no longer visible, and soon it may looks like any patch of the forest floor.

Figure 3. Vernal pools are indentations in the ground where water collects with no permanent inlet or outlet. The vernal pool pictured here is in a deciduous forest, where it provides wildlife habitat, boosting biodiversity.

Being aware of vernal pool habitat on your property can not only help you catch a glimpse of elusive amphibians but also help you to follow the newly established regulations that protect their habitat.  If you are planning a construction project, it's important to know that Maine and New Hampshire establish rules to protect all wetlands, and you will need to follow them in order to get a permit.

The new Maine DEP rules also protect a buffer zone surrounding significant vernal pools, acknowledging that it is the forest and the pool together that provide critical habitat.  The rules specify a 250 foot buffer around the pool, protecting a larger area than in many other states. Species that depend on vernal pools live in the forest for the rest of the year and must be able to travel to breeding pools from those upland habitats. Roads and other barriers increase amphibian mortality during these journeys. Tree cover and a deep layer of leaf litter (figure 4) provide the shade and protection that make vernal pools in forested areas so valuable to amphibians.

Significant vernal pools are defined by the presence of endangered species or by sufficient numbers of the following indicator species: wood frog, blue- and yellow-spotted salamanders, and fairy shrimp. If a licensed field biologist or experienced naturalist is the person evaluating the habitat, he or she should use a form available from the Maine DEP (see contact information below).  If the pool qualifies, the Maine DEP will catalog its location.  The vernal pool depression itself and a 250 foot-wide area surrounding it on all sides will be protected as significant wildlife habitat: construction within that 250 foot envelope will be restricted.  Vernal pools are assumed to be significant unless proven otherwise.

If you are planning a construction project, you should now make sure your project meets the requirements established by the new vernal pool rules. Exact requirements are available from the Maine DEP and include disturbing no more than 25 percent of a significant pool's 250 foot buffer zone.  For more information from the Maine DEP, consult the following resources:

Figure 4. A forest vernal pool with adjacent leaf litter and tree cover. This pool is visible to springtime visitors  from the Muskie Trail at the Wells Reserve.

In New Hampshire, changes in the Army Corps of Engineers wetlands regulations have been the driving force behind proposed vernal pool rules, which are currently in development. Vernal pools are listed as critical habitats under New Hampshire’s Wildlife Action Plan, approved in 2006.  The plan includes a data clearinghouse for wildlife sightings, which is maintained by UNH. You can read the plan here. The book Identification and Documentation of Vernal Pools in New Hampshire is available from the Nongame Program for $6.95.

For further information on vernal pools and amphibians, consult the following manuals and books. Those marked with a star (*) are available in the Wells Reserve Coastal Resource Library as of Spring 2008.

  • *Maine Citizen's Guide to Locating and Documenting Vernal Pools. Maine Audubon Society, August, 1999. See http://www.maineaudubon.org/conserve/citsci/vip.shtml for a digital copy.
  • *Calhoun, AJK, Klemens, MW, 2002. Best development practices: Conserving pool-breeding amphibians in residential and commercial developments in the northeastern United States. MCA Technical Paper No. 5, Metropolitan Conservation Alliance, Wildlife Conservation Society, Bronx, New York.
  • Calhoun, AJK, DeMaynadier, PG, 2004. Forestry Habitat Management Guidelines for Vernal Pool Wildlife. MCA Technical Paper No. 6, Metropolitan Conservation Alliance, Wildlife Conservation Society, Bronx, New York.
  • *Colburn, EA. 2004. Vernal Pools: Natural History and Conservation. McDonald and Woodward, Blacksburg, VA.
  • Calhoun, AJK, DeMaynadier, PG, 2008. Science and Conservation of Vernal Pools in Northeastern North America. CRC Press, Boca Raton.

Also, the following spring 2007 power point presentations are archived on SWIM:
You can take action to protect vernal pools by getting involved with citizen groups have been collecting data on amphibian populations for many years. The Maine Amphibian and Reptile Atlas Project (MARAP) and Maine Audubon's Very Important Pools (VIP) project are examples. 

For New Hampsire residents, an easy way to get involved with this effort is to fill out a form documenting reptiles and amphibians you have seen, and (if possible) photographed and sending it to the Reptile and Amphibian Reporting Program (RAARP).

Additional options for those wishing to become volunteer monitors are to join Frogwatch USA or the Maine Amphibian Monitoring Program  to help collect data on frog populations by listening to their calls as you walk in the woods.

Also, simply searching for vernal pools and their associated wildlife in your neighborhood is a great way to raise awareness, but make sure to get permission to go on private property.  Grassroots groups acting as salamander crossing guards take action in many parts of the northeast and beyond. This is a fun way to observe wildlife and protect salamanders. Just one example of a crossing guard group can be found at the Hilltown Families Blog.

Forest vernal pools are unique habitats and not only a valuable part of the landscape we live in because they are beautiful and intriguing, but also because they provide act as indicators of overall ecosystem state or health that we can use to understand how well the landscape can support human populations.  Your interest and effort in protecting vernal pools can help salamanders, but it can help people as well.

The Wells National Estuarine Research Reserve at Laudholm Farm, Wells, Maine Copyright 2006 All rights reserved. Collaboration with NOAA CSC, Charleston SC