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Out & About: Vernal Pools Q&A with Liza Morse

  • Liza Morse, of the Vermont Center for Ecostudies.

  • Vernal pools are breeding grounds for a variety of amphibians during the spring. (Courtesy photograph)



Valley News Correspondent
Monday, March 19, 2018

The winter-weary among us can take heart: the recent snowfall will disappear sooner, rather than later. As it melts, it will create the temporary puddles and ponds throughout the woods known as vernal pools. These springtime wetlands are critical to the survival of many species, in part because they provide a breeding habitat protected from fish, which would otherwise be significant predators.

And yet in spite of their ecological importance, vernal pools haven’t been extensively studied. Many are threatened by climate change, pollution and development. In 2009, the Vermont Center for Ecostudies in White River Junction, in cooperation with Arrowwood Environmental, an environmental consulting group in Huntington, Vt., began a project to map the state’s more than 5,000 vernal pools and collect data about each one.

Using satellite photos, researchers identified the locations of potential pools. Now volunteers — landowners, hikers and other outdoor enthusiasts — are helping to field-verify and monitor these pools and report other pools they come across that haven’t yet been mapped.

Vernal pool monitoring project coordinator Liza Morse, from the Vermont Center for Ecostudies, will explain how to get involved at the Norman Williams Public Library in Woodstock this Tuesday, at 6 p.m. In a recent email Q&A, Morse, a Woodstock resident, discussed what makes vernal pools so special. The exchange has been edited for length and clarity.

Question: Which species commonly found in Vermont and the Upper Valley depend on vernal pools during their life cycles?

Answer: Spotted salamanders, blue-spotted salamanders, Jefferson salamanders and wood frogs are largely dependent on vernal pools for breeding. While vernal pools may not be the only places these amphibians breed, without vernal pools many local populations would be lost. Several species of insects, snails, fingernail clams, fairy shrimp and other invertebrates use vernal pools for their entire lives.

The pools are also important to other amphibian species, such as spring peepers, eastern newts and green frogs, because they provide habitat connectivity. As one of the more numerous wetland types on the landscape, vernal pools provide hospitable habitat for a variety of amphibian species to move across an otherwise terrestrial environment.

Q: What conditions are necessary for vernal pools to appear?

Vernal pools are sometimes referred to colloquially as woodland pools or frog ponds. And those terms aren’t wrong, in that vernal pools are usually found in forested areas and are important for amphibian species.

But what distinguishes a vernal pool from a pond is that they are ephemeral, meaning they contain water for only part of the year. Vernal pools are filled primarily through rainfall and snow melt in the spring and are usually dry during the summer months. They also tend not to have a permanent inlet or outlet. The combined lack of outlet and the temporary nature of the pools makes life challenging for fish. That’s bad news for the fish, but great for amphibians, which now have a place to lay their eggs free from the threat of their predation.

The word “vernal” refers to the springtime, and while vernal pools can contain water in the fall, amphibians that rely on vernal pools as breeding sites use them in the springtime and spend the rest of their lives in the surrounding forest. So the majority of activity that occurs in vernal pools occurs in the springtime. In order to be productive for amphibian breeding, vernal pools must hold water for at least three months after ice-out.

Q: What are some of the current threats to these wetlands?

A: Vernal pools are under threat from airborne pollutants, climate change, and of course, human activity. The Vermont Center for Ecostudies has been looking at mercury as an airborne pollutant that threatens both terrestrial and aquatic wildlife. Mercury is a neurotoxin that alters the function and development of the central nervous system. It’s released by coal-burning power plants and other industrial sources, and studies have shown that New England is a hot-spot for atmospheric mercury arriving from power plants and incinerators in the Midwest. 

Climate change can affect vernal pools because of the effects weather patterns have on pool hydrology. Based on predictions that climate change will lead to more irregular precipitation events — both in frequency and intensity — vernal pools may experience longer periods of dryness or faster cycles of drying and refilling. Climate change may also change the timing of snow melt, which will affect species that migrate and lay their eggs around that time.

As far as human activity goes, clearly the most urgent threat comes from development that results in the direct loss of a pool. But other activity that disturbs the pool itself or the surrounding habitat can have negative effects on the pool and the species that call it home. Forestry practices or development can isolate pools and cut off migration corridors for pool-breeding amphibians, causing genetic isolation and direct mortality to amphibians crossing roadways.

Disturbance of the pool by hikers or people on recreational vehicles can destroy amphibian eggs, larvae and invertebrate species in the pool and negatively affect the soil structure of the pool. Because so many vernal pool amphibians spend the majority of their lives in the upland forest surrounding the pool, activity in the surrounding forest can directly affect those species. But it can disturb the pool as well. If canopy trees surrounding the pool are removed, more sunlight can reach the pool and this can cause it to dry faster than it would otherwise. In turn, this affects invertebrates and amphibians that need to spend a minimum length of time in water to go through all their life stages.

Q: What do scientists need to learn about vernal pools in order to protect them?

A: Unlike permanent wetlands, vernal pools don’t tend to be mapped, so even in places where there are regulations protecting vernal pools, it’s very difficult to protect them when we don’t know where they’re located. The problem is by no means solved yet, but the mapping project has taken a significant step toward addressing it.

Another gap in knowledge that we are now looking to address is the lack of baseline data on vernal pools. Ongoing monitoring, which gives us data over time, is what allows us to evaluate change. If we see a change is occurring, we can direct future research toward looking into why. Understanding how and where the pools are changing (e.g., Is water quality declining? Are pools flooded for shorter periods each year? Are amphibian populations decreasing?), can help us direct conservation efforts.

There is far more beyond baseline monitoring and mapping that we need to understand about the ecology of vernal pools and the organisms that rely on them, but that’s an important start.

Q: How can volunteers help with the effort? What’s required of participants?

A: Landowners or interested citizens can get involved as “citizen scientists” with either the vernal pool mapping project or the vernal pool monitoring project.

Mapping requires a one-time visit to a pool that has not been identified on the map or is a potential pool that has not yet been verified. Volunteers should check the map online (visit https://vtecostudies.org/projects/forests/vernal-pool-conservation/vermont-vernal-pool-mapping-project/), and if there is a pool that you want to verify, the map will tell you if access by the landowner has been previously permitted, if access is not allowed or if access has yet to be solicited.

Obviously, if you are the landowner, problem solved. But if access has not been solicited, the volunteer must first reach out to the landowner to get permission. For potential pools where access has been granted, the landowner may still ask that volunteers notify them before visiting.

The monitoring project is looking for volunteers interested in monitoring a pool annually, as the goal is to gain long-term data. These volunteers will need to be trained before starting. We’ll be having a variety of trainings, as well as other vernal pool-related events, this spring. Dates are available on our blog at https://vtecostudies.org/blog/ or on the Vermont Center for Ecostudies Facebook page.

Editor’s Note: Morse may be reached for more information at emorse@vtecostudies.org.