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Natural Heritage Elements - Community level


Vernal Pools 

Definition  

                 Vernal pools are small wetlands characterized by a lack of vegetation (though they may support some herbaceous wetland species) resulting from the persistence of standing water for a portion of the year. Vernal pools typically occur in small depressions in upland forests over a relatively impermeable substrate layer, but they also may be found in the depressions of some forested swamps. Although pools often lack woody vegetation, they are typically well shaded by the surrounding forest canopy. In the Northeast, many vernal pools start filling with the fall rains, retain water, ice, and snow through the winter, and collect more water with spring rains and snowmelt. They may also be influenced by rising groundwater in the fall and spring. The pools typically lack inlets and outlets, with the possible exception of outflow following heavy spring rains. A pool may be dry by mid-summer or may retain its water throughout the year in some wet years. 

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Importance 

                 Vernal, or temporary, pools are perhaps best known as important breeding habitat for amphibians. Typical Vermont species that rely on vernal pools for reproduction include the mole salamanders (Spotted salamander, Blue-spotted salamander, and Jefferson salamander), Eastern four-toed salamander, and wood frog. All of these species may breed in other wetlands, including artificial pools and ponds, but rely heavily on vernal pools to maintain their populations. For vernal pools to be effective breeding habitats for amphibian populations, they must retain water for at least two months during the spring and summer breeding season in most years so that amphibians can complete their larval stage. The periodic drying of a vernal pool excludes populations of predatory fish and diving beetles that prey on amphibian larvae. Other animals use pools as well, such as fairy shrimp, fingernail clams, snails, eastern newts, green frogs, American toads, spring peepers, and a diversity of aquatic insects. Fairy shrimp are thought to be restricted to these temporary pools. The amphibians and invertebrates found in vernal pools constitute a rich source of food for various species of birds, mammals, and reptiles that may be attracted to the pools. Wood ducks, mallards, black ducks, and great blue herons are occasionally known to feed at these pools. Despite their small size and temporary nature, vernal pools are highly productive ecosystems. 

                Vernal pools and the organisms that depend on them are threatened by activities that alter pool hydrology and substrate, as well as by significant alteration of the surrounding forest. Construction of roads and other development in the upland forests around vernal pools can result in negatively affecting salamander migration and in mortality (Forman, et al., 2003). Timber harvesting can have significant effects on vernal pools, including alteration of the vernal pool depression, changes in the amount of sunlight, leaf fall, and coarse woody debris in the pool, and disruption of amphibian migration routes by the creation of deep ruts. Even when the pool is dry, alteration of the depression substrate may affect its ability to hold water and may disrupt the eggs and other drought-resistant stages of invertebrate life that form the base of the vernal pool food chain.   

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Conservation Goals

                 A town or other planning group might adopt goals like the ones below for the conservation of vernal pools. 

1.        Provide for the long-term stewardship and/or protection of vernal pools and associated amphibian populations. 

2.        Provide for the long-term stewardship and/or protection or restoration of forested habitat between pools to provide dispersal corridors for dependent species, particularly amphibians. 

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Obtaining and Interpreting Information

Information Sources  

        See Resources for information on how to contact or visit the websites of the agencies and organizations mentioned below.

  • The Vermont Fish and Wildlife Department's Wildlife Diversity Program: This program has limited information on vernal pools and rare amphibian occurrences. Call NHIP for information on known vernal pool occurrences.

  • Citizens: People who work in the woods or who spend recreational time there often have a wealth of information on a variety of natural resources. Hang posters around town soliciting information. Host a public meeting to solicit local knowledge about this resource or set up a display in the local library asking residents to share information.  

Gathering New Information on Vernal Pools

Information regarding the distribution of vernal pools in Vermont is limited and further study is needed to better understand this natural resource. Use of large-scale, color infrared aerial photography is currently the most accurate, efficient, and widely accepted method of predicting vernal pool presence on a landscape scale (Burne, 2001). Amphibian surveys may be useful in locating some pools. In early spring, frogs and salamanders can often be found crossing roads in search of vernal pools and wood frogs can be heard calling from a breeding pool.

State agencies or conservation organizations in Massachusetts , Maine , and New Hampshire have launched citizen-based vernal pool inventories and produced valuable handbooks on the techniques. The Vermont Institute of Natural Science (VINS) promotes citizen science including vernal pool inventories and 'calling frog' surveys. We recommend studying some or all of these before embarking on your own inventory.

 The Department's NHIP is administering a two-town pilot program for developing the best inventory protocol; check on the status of this pilot program before starting your own inventory. We encourage those undertaking vernal pool inventories or amphibian surveys to contribute records to the Vermont Reptile and Amphibian Atlas, a repository of documentation of reptile and amphibian sightings throughout Vermont , as well as a source of information and inspiration to those interested in herptile conservation. For information about these organizations and agencies, see Resources.

 Mapping vernal pools allows you to analyze their distribution in relation to the surrounding natural and human environments and visualize conservation opportunities and limitations. We recommend using GIS for mapping, but manual maps can be used as well.

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Interpreting the Information 

                Management planning that protects populations of pool-specialist amphibians must recognize the importance of their terrestrial habitat as well as the breeding pool. The area used by a population year round can be represented by three management zones: the breeding pool, a 100-foot zone around the pool, and a third zone that extends an additional 500 feet (600 feet from the pool edge). 

Breeding Pool — This area includes the pool depression measured at spring high water. It is important to note that the pool may not be entirely full or may even be completely dry during part of the year. At such times, the high water mark must be determined using such evidence as water marks on trees within the depression, water-stained or silted leaves, or an obvious change in topography at the pool edge. Management recommendations: No disturbance should be introduced to the breeding pool.  

100-foot Zone — Within this zone, pool-breeding adults and juveniles emerging from the pool can occur at high densities at critical times of the year. This zone also protects water quality and habitat by providing shade to the forest floor and pool, filtering runoff, providing root tunnels, and supplying leaf litter and woody debris to the pool. Management recommendations: Avoid clearing of land or permanent development including roads and driveways, changes in water quality or hydrology (including no use of pesticides), and barriers to amphibian movement. Some studies recommend maintaining or establishing a forested condition with at least 80% canopy cover.  

600-foot Zone — This zone represents the majority of the important terrestrial habitat needed by these species during most of the year (Semlitsch, 1998; Faccio, 2001). Recent studies indicate that at least this much area around the pool is needed to protect 95% of adults in mole salamander populations. Faccio found that females move farther than males and other studies indicate that average distances of movement for mole salamanders and juvenile wood frogs can go well beyond 600 feet from the pool.  Management recommendations: Attempt to retain this area in a forested condition on greater than 75% of the area with at least 60% canopy cover (composed of trees at least 25 feet tall), maintaining a moist forest floor with deep litter and abundant coarse woody debris. Avoid establishing new roads and driveways that will carry more than very light traffic (5-10 vehicles per hour) within this area of habitat . Where existing roads are known to bisect amphibian habitat and cause mortality, it may be advisable to explore methods that can help reduce this result (for example, wildlife passage structures). Avoid creating ruts and other artificial depressions that hold water, as these may attract breeding amphibians but do not provide suitable habitat for developing larvae. Avoid clearing steep slopes that contribute runoff into breeding habitat. Employ erosion control methods to prevent sediment and pollutants from entering breeding habitat during and after clearing and construction, but minimize use of silt fencing within 600 feet of a breeding pool, as these can interfere with amphibian migration to and from breeding habitat. Avoid using pesticides within 600 feet of a breeding pool. Avoid any activities that direct water away from a breeding pool, as this reduces the amount of water held in the depression and increases the chance that the pool will dry before amphibian larvae complete their development. Do not direct additional runoff into a breeding pool from outside its natural basin. This can change the hydrology of the pool and introduce pollutants and sediments, both of which can kill eggs and developing larvae.    

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Vernal Pools

Vernal Pools with Buffers

When all of the existing information about known pools has been assembled and new locations identified, the distribution map of vernal pools in your town may look like this. (Note: These are not actual known locations of vernal pools, but a fictional scenario developed expressly for demonstration purposes.)

This map shows 100' and 600' zones around a vernal pool, which are critical to pool-breeding amphibian habitat. The section of road shown here serves three single-family homes and poses limited mortality risk to migrating and dispersing amphibians. With very light traffic (5-10 vehicles per hour) and ,25% of the 600' zone developed, this configuration of houses, road and driveways meets recommendations for conserving pool-breeding amphibians found in the literature. 

Conservation Strategies

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1. Goal: Provide long-term stewardship of and/or protect all significant vernal pools and maintain associated amphibian populations.  

Strategies: 

        a. Use information gathering, mapping, and inventory work to learn the location of all the vernal pools in your town. Solicit the help of a qualified wildlife biologist or herpetologist to assess amphibian populations at the pools, which may help you prioritize pools for further stewardship, protection, and/or restoration strategies. Keep in mind, however, that the absence of amphibians in any single year does not necessarily indicate that a pool is not valuable. For an accurate assessment of amphibian use of the habitat, surveys should be conducted over several years. Vernal pools lacking amphibian populations may still support other organisms such as fairy shrimp and fingernail clams, and may be worthy of conservation as well. Secure proper landower permission before initiating any surveys. 

        b. Inform landowners of the locations of vernal pools on their property, the habitat needs of the associated amphibians, and how they can protect these pools and the amphibians using them. Develop a stewardship program to help landowners manage pools. Secure proper landower permission before initiating any surveys. 

        c. Include a vernal pool map in your town plan and emphasize the importance of conserving them. Sample Language: Vernal pools will be protected from encroaching development, including roads and driveways, by retaining and/or establishing adequate forested habitat around all vernal pools in town.  

        d. Establish an overlay district that identifies vernal pools and their surrounding terrestrial amphibian habitat. To be most effective, this district should provide a large buffer surrounding the pool in which no development is allowed and other ground disturbing activities are limited. Even though current literature indicates some amphibians need a large area (e.g., 600 feet) around high quality vernal pools, it is advisable to determine habitat protection on a case-by-case basis. Development projects in this zone should be sensitive to the vegetation in this area. Other strategies, such as reducing the road width standards or prohibiting vertical curbing, could be employed in the overlay district to lessen the effect on amphibians. Although conditional use and site plan review can be used within the overlay district to regulate activity around vernal pools, these are less effective strategies than restricting development around vernal pools altogether. For recommendations on protecting pool-breeding amphibian habitat, refer to Calhoun and Klemens (2002) or contact the Vermont Fish and Wildlife Department. 

        e. Target vernal pools in open space planning and land acquisition programs. Pools associated with other natural heritage elements and pools of particularly high quality should be given higher priority. 

        f. Allow for PUDs in the town zoning and/or subdivision regulations as an alternative to conventional subdivisions and require, or provide incentives (such as density bonuses) for PUD designs that cluster development away from vernal pools and their surrounding terrestrial amphibian habitat. Note: A 600-foot zone around even the smallest vernal pool will cover about 26 acres. 

        g. Plan to locate new roads (both public and private) and driveways such that adequate terrestrial habitat is maintained between roads and vernal pools. Incorporate into subdivision or zoning regulations minimum setbacks from vernal pools of 600 feet or greater for new roads and driveways created through subdivisions. All road designs should avoid increasing runoff to, or changing the hydrology of, vernal pools and other wetlands. 

        h. Seek to reclassify highly significant pools as Class II wetlands so that they are protected by the Vermont Wetland Rules. More information on wetlands reclassification is available by contacting the Vermont Wetlands Office (Department of Environmental Conservation) or the Water Resources Board. See Resources for contact information. 

        i. Write land management plans for town-owned lands designed to protect the ecological functions of vernal pools (and other natural heritage elements). 

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2. Goal: Provide for the long-term stewardship of, protect, and/or restore forested habitat between pools to provide dispersal corridors for amphibians.  

Strategies: 

        a. Use vernal pool distribution map(s), tax maps, and aerial or ortho photos to visualize opportunities for maintaining or creating connections between pools. These connections are vital to sustaining healthy populations of pool-breeding amphibians by allowing for dispersal of individuals and genetic exchange. Existing forested connections between pools should be considered high priority for protection. 

        b. Include a vernal pool map in your town plan showing possible dispersal corridors between pools and emphasize the importance of conserving them. Sample Language: Vernal pools and pool-breeding amphibian populations will be protected from encroaching development, including roads and driveways, by maintaining and/or establishing adequate forested habitat around all vernal pools in town. Dispersal corridors connecting adjacent pools will be protected to ensure long-term viability of amphibian populations.  

        c. Target high priority corridors through open space planning and land and easement acquisition programs to ensure long-term conservation of dispersal corridors. 

        d. Develop stewardship programs for private landowners and use certification programs for foresters to encourage management of forested lands in a manner compatible with pool-breeding amphibian conservation. 

        e. Write management plans for town forests that incorporate these practices as policy.  

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