by Elizabeth Ahearn, Conservation Staff
Vernal pools, also also known as vernal ponds or ephemeral pools, are seasonal wetlands that fill with shallow water in the spring, before eventually drying up in the summer. The word "vernal" means relating to or occurring in the spring. At first glance, you might think a vernal pool is just a large puddle in the middle of woods. But upon closer inspection you’ll see an incredibly unique habitat teeming with life. While they may not be very big or look overly impressive, vernal pools play a crucial role in many forest ecosystems. Their unique environment provides habitat for rare plants and animals that are able to survive and thrive in harsh conditions, and they are essential breeding grounds for amphibians like frogs and salamanders and macroinvertebrates (invertebrates visible without a microscope or magnifying glass) such as fairy shrimp. As temporary wetlands, vernal pools lack fish that cannot survive in water bodies that dry out for part of the year. This characteristic allows amphibians and aquatic invertebrates to grow and reproduce safely without the kind of predation that typically exists in permanent water bodies. Wood frogs, spotted salamanders, four-toed salamanders, and fairy shrimp all experience higher rates of breeding success in vernal pools than in permanent waters.
Source: New York Natural Heritage Program. 2024. Online Conservation Guide for Vernal Pool. https://guides.nynhp.org/vernal-pool/
Despite their ephemeral nature, vernal pools are ecologically significant and provide many of the same essential “ecosystem services” as larger and more permanent bodies of water, including erosion control, groundwater recharge, carbon sequestration, and water purification. A decline in the presence of vernal pools and the terrestrial habitat surrounding them in turn results in the decline of unique and rare species, biodiversity, and the availability of food for many animals. As climate change accelerates the extinction crisis, these breeding grounds for rare species are becoming more valuable, and as such should be more treasured and protected. Avoiding impacts to vernal pools and their surrounding habitat is important because many amphibian species are “pool specific,” meaning they must return to the pond in which they were born to breed. An estimated 85% of vernal pool amphibians return each year to breed in the pond where they were born, and they will even bypass other pools with suitable habitat and cross obstacles in order to return to the pool of their birth (1). This strong demonstration of “site fidelity” to their natal pool means that when a specific pool is lost, the amphibians that return there to breed may be lost also. Wood frogs and fairy shrimp are examples of vernal pool “obligates,” species that rely on vernal pools for all or part of their life cycle and can't complete their life cycle without them.
The most prominent threat to vernal pool habitats and their wildlife is human development. The construction of buildings, roads, ditches, and drainage ponds destroys vernal pools and causes an immediate loss of habitat, and for some particularly vulnerable species, can even lead to permanent loss of populations. As vernal pools are often overlooked as valuable habitat areas due to their small size and isolated nature, they often get filled in during construction or become receptacles for polluted run-off and sedimentation. An alarming number of vernal pools have already been dredged, drained, or built over. And to date, the ephemeral nature of vernal pools has made them ineligible for permitting protection under the freshwater wetlands program, which has endangered countless invertebrates and amphibians.
The proposed wetland regulatory changes to Part 664 include first-time protections for New York State’s vernal pools, which is exciting news. Before 2022, the DEC had no tools to protect these rare habitats, unless there was a critically endangered species present. The new draft regulations identify jurisdictional vernal pools by using egg mass counts for specific amphibians according to geographic region. (Example: DEC will protect a vernal pool in the Hudson Valley if agency staff observes, during breeding season, at least 10 wood frog egg masses or 25 spotted salamander egg masses within a pool complex). While we understand DEC needs to create criteria that allows them to discern valuable breeding pools from lifeless mud puddles, this method may not accurately reflect a vernal pool’s true value. Some species exhibit interannual variation in egg mass counts, and others can reproduce with great variability from year to year. Interannual variation in egg mass counts for wood frogs, for instance, is so high that it takes nine years of monitoring data to detect small changes in population size for declining populations and a staggering two decades for populations that are stable. (2)
Source: Vermont Center for Ecostudies. 2024. Wood Frog. https://vtecostudies.org/wildlife/amphibians/wood-frog/.
Widening variability in temperature and precipitation as the result of climate change will in turn lead to an increase in the interannual variation observed in egg mass counts. A particular vernal pool may be critical for the long term success of local amphibian species, but if one specific year is drier and warmer than usual, there may not be enough water in the pool to support breeding populations. As such, any use of a vernal pool for breeding by a listed amphibian species should be considered when evaluating wetlands of unusual importance, regardless of the number of egg masses. Documentation of individual criteria for an amphibian species, whether through the presence of eggs, larvae, or adults, should be sufficient enough to warrant permitting protection. Several U.S. states simply require evidence that vernal pools facilitate active breeding of amphibians in order to be mapped and protected, regardless of egg mass counts, allowing for greater flexibility in determining jurisdictional vernal pools. The DEC should follow suit and adopt an inclusive standard to certify and protect vernal pools, because their intermittent nature already inherently makes them difficult enough to identify without requiring specific egg mass counts.
Buffers are critical to help maintain the vitality of vernal pool communities and the important role they play in the surrounding ecosystem. Since 1975 when the Freshwater Wetlands Act was first passed, the DEC has regulated activities that occur within a 100 foot area adjacent to the wetland boundary. Though it is rarely done, the DEC does have the discretion to extend the buffer from a minimum of 100 feet to a distance deemed necessary to protect rare or especially vulnerable wetlands. To protect vernal pools in a meaningful way, the DEC must regulate activities beyond 100 feet of the boundary, as it is insufficient to maintain viable amphibian populations where roadways and development can facilitate high species mortality. The draft regulations expand the adjacent area to 800 feet for vernal pools known to be productive for amphibian breeding. While it is excellent that vernal pools in New York will have expanded buffer protections, it might not be a sufficient buffer size for all species. Studies have shown that some “indicator species” amphibians used to identify productive vernal pools within the regulations travel further from breeding pools than 800 feet. Four-toed salamanders have been found to move a maximum of 650 feet, while juvenile wood frogs have been observed to migrate, on average, 1550 feet between upland and breeding pool habitats.(3) An 800 feet buffer may be adequate enough protection for a four-toed salamander that travels only 650 feet, but might not be sufficient for a wood frog with a larger range of movement.
Vernal pools are undeniably important in maintaining the health and balance of many forest ecosystems. They are woven into the life cycles of amphibians, and their absence leads to fewer frogs, toads, and salamanders in an area. Amphibians are critical to the food web, as healthy amphibian populations keep insect populations in check, and larger animals rely on amphibians as their food sources. A balanced food chain is necessary for the survival and success of life within an ecosystem, and vernal pools are incredible hotspots of biodiversity and life. As anthropogenic climate change intensifies, the ecosystem services provided by vernal pools will become even more invaluable, and it is imperative that we protect these unique habitats now.
Notes:
(1): Colburn, Elizabeth A. Vernal Pools: Natural History and Conservation. McDonald & Woodward Pub. Co, 2004.
(2): Scherer, R.D. and J.A. Tracy. 2011. A power analysis for the use of counts of egg masses to monitor wood frog (Lithobates sylvaticus) populations. Herpetological Conservation and Biology 6(1): 81-90.
(3) Calhoun, A.J.K. and M. W. Klemens, 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.