Ephemeral ponds, also called vernal ponds, aren’t what many people think of when they think of wetlands. But these wetlands are some of the most important wetlands for a variety of wildlife, including frogs and toads. If you own or care for property that has vernal ponds, there are a number of things you can do to keep these wetlands healthy. Thanks to Amanda B. Yeager, former wildlife extension assistant, and Margaret C. Brittingham, professor of Wildlife Resources at PennState for allowing us to reprint their article.
Have you ever walked through the woods in spring and found an immense puddle that wasn’t there over the winter? You may have discovered one of the most ecologically important habitats to be found among woodlands. Vernal ponds are temporary wetlands that fill after the snowfall each spring. They become the seasonal breeding and feeding grounds for many intriguing amphibians and insects, as well as the reptiles, birds, and mammals that depend on them for food. You may have been led to this pond by the unmistakable sounds of spring peepers and wood frogs calling for a mate.
If you crouch by the water’s edge, you’ll find an entire community of creatures. You might witness the bustling activity of salamanders, frogs, toads, and newts that have come to breed, as well as all kinds of aquatic insects and their eggs that will develop over the spring months. Jellylike masses and strings of eggs will be visible in the water and on the pond vegetation where salamanders and frogs have left them behind.
Vernal ponds are extraordinary wetlands, fascinating to observe, and essential to the lives of many woodland species. With the rapid population declines of so many amphibian species, it’s crucial that these often unnoticed habitats be recognized and protected.
What to look for
It’s easy to recognize vernal ponds in the late winter and early spring. Named from vernalis, the Latin word for spring, vernal ponds form seasonally in shallow ground depressions from spring snowmelt, precipitation, and rising water tables. Generally drying up in late summer, these ponds are only temporary woodland reservoirs. They are slightly harder to identify during the summer and fall months; however, there are several clues to look for. Blackened, compressed leaf litter; gray soil; watermarks on surrounding tree trunks; and the presence of moisture-tolerant vegetation all suggest an area that collects water part of the year.
Vernal ponds themselves are generally less than 40 yards in diameter and no more than 4 feet deep, although they receive water from a larger surrounding landscape. Look for:
Wet, gray soils
Water-stained tree trunks
Plants that prefer wet soils (like smartweed)
If a vernal pond’s physical features don’t tip you off, the wildlife living there will certainly give away its location. Vernal ponds are home for a diversity of animals that count on them for the spring breeding season.
The seasonal nature of vernal ponds means that they are uninhabited by fish. This makes them the perfect habitat for a variety of amphibians and invertebrates to breed and develop with less chance of predation. Species like mole salamanders, wood frogs, and fairy shrimp depend exclusively on vernal ponds for this part of their life cycles. Often a pond is the ancestral home of an amphibian community that resides nearby in the forest each winter, then migrates to the same pond each spring to lay its eggs.
During the early spring, wood frogs make their trek to the ponds. Finding this species in its breeding season is a guarantee that you have found a vernal pond—and wood frogs noisily make their presence known. Male wood frogs attract females with a loud, distinctive call that sounds like the quacking of ducks. Often an entire chorus of this species can be heard from afar, and you can easily follow the sound until you find the pond.
Many other species use vernal ponds in spring. The spring peeper has one of the animal kingdom’s loudest voices for its size. Choruses of its high-pitched, birdlike peeps can sound like sleigh bells from a distance. American toads, gray tree frogs, and green frogs are among the many other creatures that may come to breed. By the end of the breeding season, ponds are filled with egg clusters that appear as jellylike masses containing small, round eggs.
Species to look for:
As young amphibian larvae hatch and develop, they feed on invertebrate species that have emerged from their eggs at the same time. Fairy shrimp, dragonflies, damselflies, caddisflies, mosquitoes, daphnia, and other invertebrates drop egg cases in vernal ponds each year.
The egg cases lie dormant over winter and hatch the following spring. While amphibian larvae feast on these delights, insect predators like fishflies, diving beetles, and backswimmers also look for amphibian larvae to feed upon.
As activity inside the pond increases each spring, it attracts other animals to the vernal community. Some turtle species visit the ponds to feed on egg masses, while snakes and raccoons may feed on tadpoles and frogs. Birds like the green heron and red-shouldered hawk also visit ponds to feed.
By late spring or early summer, tens of thousands of young salamanders and frogs that have undergone metamorphosis leave the pond for the forest to continue their life cycles. The huge number of organisms using vernal ponds each year shows how essential they are to the life cycles of forest species both in and out of the ponds. In fact, the amphibian species developing in ponds alone generally amount to more vertebrate biomass than the mass of all the birds and mammals in a forest. The ability of vernal ponds to continue supporting this biodiversity remains dependent on the activities occurring around them.
Protecting your vernal pond
If you think your property contains a vernal pond, you can do a lot to protect it from potentially harmful effects of land use. The key is to protect both the stability of the forest and the hydrology of the pond. For instance, amphibian species depend on forests for their adult lives and on ponds for breeding and the development of young. Surrounding land that may be used for recreation, timber harvesting, or residential structures can be managed in ways that keep the impact on vernal ponds to a minimum.
Avoid using chemicals and fertilizers: Vernal ponds accumulate runoff water from surrounding upland areas. Even a minimal amount of pesticide, herbicide, or fertilizer can upset the food chain and cause deadly results in a water body as small as a vernal pond.
Maintain forest canopy: The forest canopy provides essential shade for regulating pond temperatures, and slows the loss of water from the pond by evapotranspiration. In addition, the forest canopy helps to maintain a cool, moist environment in the surrounding forest, a necessity for many amphibians.
Do not add or remove plant debris: Amphibians use small to medium-sized twigs on which to attach their eggs, so no woody material needs to be added to the pond. Although tree tops and debris should be kept out of the pond depression during forest maintenance, if some material does fall in, it should be left there. Removal could disturb amphibian eggs or young.
Do not drain ponds or alter the surrounding watershed: A vernal pond’s location, dimensions, and surrounding topography are the product of thousands of years of geologic evolution. Diverting or draining the area’s water or depleting the underground water table would cause irreversible changes to the ecosystem.
Protect water quality: Be aware of water flow patterns and the amount of area that drains into your property’s vernal pond. This way, it is possible to prevent the flow of materials like chemicals, fertilizers, and silt from reaching ponds. All earth-moving activities must be carefully managed to prevent silt from flowing into the pond. A minimum 100-foot buffer is recommended between ponds and any activities that can alter water quality or produce sediment. This material is hazardous because it fills in pond floors, suffocates egg masses, and can harm developing larvae. Nearby roads with water diversion structures should be positioned in a way that keeps sediment from entering the buffer area and pond.
Protect ponds from off-road vehicles and machinery: Consider fencing off vernal ponds; also be sure to prevent disturbance from recreational and industrial off-road vehicles in the surrounding area year-round. It is essential that pond beds and walls remain undisturbed even during the dry season. Compaction of the soil can change water flow and damage dormant eggs and larvae buried in the pond leaf litter. Tire ruts in the pond can also promote early drainage at a time when amphibian eggs have not yet hatched. Ruts in the surrounding forested area can cause amphibians to lay eggs in locations too shallow to sustain their young. Ruts can also trap young salamanders and turtles on their way into the forest, leaving them to be eaten by predators or die of dehydration. Existing ruts can be filled in with soil.
Do not add fish or other animals: Making a fish pond out of a vernal wetland quickly defeats its ecological purpose. The animals in a vernal pond’s food chain rely on the absence of fish or other animals that would feed on amphibian young or compete with them for insects.
Do not allow collection of plants or animals: Be sure that plants and animals are not removed from the pond. Even small changes in a vernal pond’s ecosystem can upset the balance of predator-prey relationships and could include the removal of endangered plants and animals.
Adapted from a Vernal Ponds Factsheet, written by Amanda B. Yeager, former wildlife extension assistant, and Margaret C. Brittingham, professor of Wildlife Resources at PennState. This story was originally published by the Pennsylvania State Extension, © The Pennsylvania State University 2016.
Photos by Heidi Kennedy, Josh Mayer, Kate Redmond, Ken Tapp, Pat Trochlell, and Tim Wilder