Vernal pools – more than woodland puddles?

Jamie Simpson

Nothing says spring is coming like a chorus of frogs looking for love.   Mating calls of frogs – the ringing of spring peepers and the guttural bass of wood frogs – echo through each spring that I can remember, their first calls before the last of the snow, before the first leaves, before the first fiddleheads.  It’s a promise of a shift in the seasons emanating from woodland pools and wetlands everywhere.

Few might realize that these springtime puddles – or vernal pools as they’re known – are among the richest wildlife habitats in our eastern forests, and may in fact be integral to the health of our forest ecosystems. Come summertime, however, these pools that teem with life in the spring shrink in the summer heat, sometimes drying up altogether, making these valuable habitats rather easy to overlook. While many landowners wouldn’t think of cutting down an ecologically valuable habitat tree, these same landowners might inadvertently destroy a vernal pool by cutting the forest around it just for lack of seeing it. The easiest way to find a vernal pool is to locate it in the spring or early summer, with the tell-tale frog calls, masses of eggs deposited in the pools or swimming tadpoles. In summer, identifying pools can the tricky if they’re dried up, but the presence of darker-than-normal, water-stained leaf mats in low depressions can be a good indicator.

The fact that vernal pools are generally not connected to other watercourses, and may dry out in the heat of summer, ensures that they are free of fish predators that would otherwise devour amphibian eggs and young.  Wood frogs, yellow- and blue-spotted salamanders and numerous other species hatch out in these pools, and live the first part of their lives there as tadpoles in these food-rich pools, before morphing to a life on land.

Unlikely as it may seem, these woodland puddles are so productive that in some eastern forests, the mass of amphibian life nurtured in vernal pools, largely unseen, outweighs the combined weight of all the mammals and birds in these forests.  These frogs and salamanders, in eating and being eaten in such abundance, are far more fundamental to the forest ecosystem than scientists had realized.  As well, vernal pools are used by numerous other species for finding food or as temporary habitat, including species-at-risk such as Blanding’s turtles and ribbon snakes, and common wildlife such as turtles, ducks, snakes, herons and many more.  Some 500 species of invertebrates have been found in vernal pools of eastern forests.

Despite their importance to wildlife, only one jurisdiction in the eastern forest region, the State of Maine, has rules to mitigate the loss of vernal pool habitat.  With an impressive effort, Maine has identified vernal pools with high wildlife significance, which is roughly a quarter or fifth of all vernal pools documented in the State.  These are pools that host an abundance of amphibian life, or species of special conservation concern.  Developers are not permitted to build within the immediate area of the vernal pool depression itself, and are required to maintain at least 75% of surrounding forest intact, within 750 feet of the pool.

Maine’s rules are based on research showing that the forest surrounding vernal pools is just as critical to vernal pool life as the pool itself.  For example, one researcher documented the effects of a development that protected a vernal pool, but which destroyed 90% of the upland forest near the pool. The wood frog population plummeted by 94% in the first year following the development, and within three years there was no evidence of a breeding population left. When reassessed after six years, the researchers still found no evidence of frogs returning to the pool.   Protecting the pools themselves, without protecting some of the upland forest, was woefully inadequate in this case.

Maine’s vernal pool regulations, however, do not apply to forestry operations.  While cutting that maintains deadwood and tree cover can be compatible with amphibian life, researchers find that clearcutting and especially whole-tree cutting for biomass tends to kill frogs and salamanders and fragments and degrades the habitat they need to survive.  While the bodies of amphibians born in water change to allow them to live on land, it is, in a way, only a partial transition to terrestrial life.  Although they migrate out of the pools and live their adult lives on land, their bodies still require moisture to breath, and only a damp forest enables them to move about to feed and migrate to their upland forest habitat and new vernal pools.  Scientists have found that without the cool, moist climate that a forest and deadwood provide, many amphibian species simply die from exposure.

Guidelines for forestry work around vernal pools have been created in Maine, and are a good resource for anyone who wishes to carry out forestry in a way that is minimally damaging to vernal pools and the wildlife they support.  The guidelines recommend first identifying any vernal pools on the property, especially those with an abundance of wildlife, and then ensuring that the forest canopy is maintained to provide a cool and shaded habitat.  The pool area itself should be left undisturbed completely, and at least 75% forest canopy, plus an undisturbed forest floor and abundant deadwood, should be maintained within 100 feet of the pool.  The zone from 100-400 feet from the pool should be kept with at least 50% canopy cover, with ground disturbance minimized and deadwood left undisturbed.  Search the internet for Forestry Habitat Management Guidelines for Vernal Pool Wildlife to read the complete Guidelines. Those interested in learning more can also visit Maine’s website on vernal pools, which includes a video about vernal pool life: http://www.umaine.edu/vernalpools/index.htm.

While there are no measures to protect vernal pools in the Maritimes, Nova Scotia Environment (NSE) recently launched a Vernal Pool Mapping and Monitoring Project to document Nova Scotia’s vernal pool habitat. Dr. John Brazner, Wetland Program Coordinator with NSE, is asking landowners to check their properties for vernal pools, and asking those who find pools to record basic information about them and to pass this on to the Department. The NSE website has information about vernal pools, photos of various species found living in vernal pools, and a data sheet that can be used to record information about vernal pools found on landowners’ properties. (http://www.gov.ns.ca/nse/wetland/vernal.pool.mapping.project.asp).

Dr. Ron Russell, a professor at Saint Mary’s University in Halifax, is also working to understand life in Nova Scotia’s vernal pools. He and some of his students have been monitoring some 200 wetlands for more than a decade. “Our work with these wetlands shows that vernal pools enable certain species of salamanders and frogs to move across the land,” explains Dr. Russell. “So when vernal pools are lost,” Dr. Russell continues, “we likely lose many populations of these species, even if larger wetlands are protected, because it disrupts their ability to migrate to find food and new breeding habitats.” Loss of wetland habitat is not an abstract concern for Dr. Russell; he and his students have seen the loss of nearly a third of their research wetlands to development and road construction during the last decade. Even when roads don’t entirely destroy a wetland, Dr. Russell has found that road de-icing chemicals can kill amphibian eggs in some sites they’ve studied.

With the efforts of Dr. Russell and his students, and Dr. Brazner and Nova Scotia Environment, we should soon begin to have, at least, a sense of Nova Scotia’s vernal pool resource. As more people come to understand the critical role vernal pools play in our forest ecosystem, hopefully we’ll be less likely to bulldoze over them, fill them in, or clearcut around them, and the spring-time chorus of frogs will continue to delight winter-weary Maritimers.

Nova Scotia’s Wetland Policy and Vernal Pools:

Nova Scotia’s Wetland Policy does not apply to wetlands less than 100 square metres. As vernal pools are often smaller than 100 square metres, wetland alteration permits are usually not required for developments that destroy vernal pools. Furthermore, the Wetland Policy does not apply to forest cutting or to roads that are less than 10 metres wide or less than 600 square metres total (such as forestry access roads), so there is no protection for the upland component of vernal pool habitat .   A wetland alteration permit is required for a development (for example, a subdivision or an industrial park) that would impact a vernal pool (that is, fill it, drain it, excavate it, etc) if the pool is greater than 100 square metres. According to Dr. Russell of St. Mary’s University, this policy falls short because it lacks enforcement measures, and because it does not address wetlands less than 100 square metres, which includes most vernal pools.

Landowners who wish to protect amphibians and their habitat can identify vernal pools on their property in the spring or early summer, and ensure that any forest cutting maintains a forest canopy, deadwood and minimal disturbance to the forest floor within a few hundred metres of the pool. The key to protecting amphibian habitat is to protect both their vernal pools, as well as the forest around the pools so that they can move across the land to find food and new breeding habitats.

Originally published in Atlantic Forestry Review

2 comments
  1. aaron schneider said:

    Very informative Jamie, I didn’t know that they were so much more than mosquito breeding sumps.

    Aaron

    • Thanks so much Aaron! Ha, yup, more than just mosquitoes. 🙂

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