The Carlisle Mosquito Online

Friday, March 28, 2008


Vernal pools, spring’s breeding habitats, are ready to reappear

Are there vernal pools on your property?

The maple sap is rising and migratory birds are flying north. Another sure sign of spring in Carlisle is the sound of spring peepers calling from wetlands, and the breeding chorus of wood frogs from vernal pools. Carlisle’s smallest wetlands are an important habitat, the only

Vernal pool

Ice remained earlier this week in a vernal pool surrounded by trees in Great Brook Farm State Park. (Photo by Sally Zielinski)

place where some Massachusetts amphibians can breed successfully, and home to a number of state-listed rare species. Now is the best time of year to find vernal pools and observe the wildlife.

Vernal pools are temporary shallow depressions in the landscape that capture water from rain or snowmelt, or are located where groundwater comes to the surface. They are found in wooded swamps, along the edges of ponds, or in the flood zones of rivers and streams, but can also be low pockets in upland areas. They range in size from a few yards across to several acres, though few are wider than 150 feet. Vernal pools are seldom more than three feet deep, and may be as shallow as six inches.


Mole salamanders of the genus Ambystoma, the wood frog (Rana sylvatica), the eastern spadefoot toad (Scaphiopus holbrooki) and fairy shrimp (Eubranchipus species) can breed successfully only in ponds without adult fish, which prey on their eggs and larvae. To provide a vernal pool habitat, an area must hold water for more than two months from early spring to early summer and dry up in the summer of most years (so fish cannot mature). Vernal pool amphibians lay their eggs in water in the spring and the young develop in the aquatic environment. This process takes a few weeks to two months depending on the species.

The spadefoot toad and three of the mole salamanders are state-listed rare species by the Massachusetts Natural Heritage and Endangered Species Program (NHESP). The salamanders are the blue-spotted (Ambystoma laterale), Jefferson (A. jeffersonianum), and marbled (A. opacum). Only the blue-spotted salamander has been recorded to date in Carlisle.

Limited protection

The reasons for a worldwide decline in amphibians are not well understood but clearly habitat loss is a factor. Conservation commissions frequently receive permit requests for projects that will alter or destroy vernal pools, which means entire breeding populations can be lost. A pool and the 100-foot buffer zone around it receive protection under the Massachusetts Wetlands Protection Act only if they sit within another wetland resource area, like a wooded swamp or wet meadow, and then only if the pool is certified by NHESP or convincing evidence that it is a functioning vernal pool is presented at a public hearing. There is also limited protection under several other state laws, Title 5 and the federal Clean Water Act.

Certified vernal pools

There are an estimated 30,000 vernal pools in Massachusetts. NHESP certified about 4,350 as of January 2007. The agency’s web site ( has both a map and a table of certified vernal pools by town, which shows 34 in Carlisle. The Massachusetts Aerial Photo Survey of Potential Vernal Pools, published in 2001, identified 87 potential pools in town.

Certification process



Certification is a way of documenting the existence and location of a functioning vernal pool, and is one of the best ways to gain protection. Guidelines for the Certification of Vernal Pool Habitat and Vernal Pool Field Observation forms can be downloaded from the NHESP site. Obligate species are those species which require vernal pools to live and reproduce. Evidence that the obligate amphibians are breeding is among the best ways to meet the state’s Specific Certification Criteria. The evidence may include photos of mating adults or audio tapes of the breeding chorus of wood frogs, which can be heard from a considerable distance.

On the first warm rainy night of spring, mole salamanders migrate en masse from the upland areas where they have lived since the preceding summer, generally back to the pools where they were born. Since they may overwinter as far as 600 feet from the vernal pool, they may be seen crossing roads and trails.

If you would like to certify a vernal pool the first step is to locate a likely pool and determine whether it has already been certified. This can be done by contacting the Conservation Commission and/or checking the Aerial Photo Survey. It is also important to have permission before entering private property. Next, be clear about the criteria for certification. In most cases you will need to observe the water status of the pool over time and collect data on wildlife at the time of year when they are breeding.

Handy tools are a camera, notebook, fine net and bucket to scoop up water and small critters, a shallow container to dump water into for close observation, high boots or hip waders for at least one person to go in the water, and a recorder if you are documenting wood frog choruses. A good field guide is important to distinguish the egg masses, young and adults of different vernal pool species (see below). A person with some training in biology can help with identification. When all the information is organized, send it to NHESP.

Residents with vernal pools on their property should make certain that the pool and surrounding area are left in their natural condition. Communities can gain greater protection through wetlands bylaws. For example, wider buffer zones can be designated or pools located in upland areas defined as protectable. The Carlisle Conservation Commission is currently studying options for strengthening Carlisle’s wetlands bylaw.

Vernal pool walk

Herpetologist Chris Kavalauskas will lead a vernal pool walk on the Conant land on Sunday April 27 at 2 p.m. The walk is co-sponsored by the Trails Committee and the Conservation Commission.

A well-written, portable and easy-to-use publication on vernal pools and vernal pool wildlife is NHESP’s Field Guide to the Animals of Vernal Pools, written by Matthew Burne and Leo Kenney. The Conservation Commission and the library have copies. This and the Aerial Photo Survey are available through the NHESP web site, which also has fact sheets on individual rare species and information on reporting rare species sightings. ∆

© 2008 The Carlisle Mosquito