Vernal Pools

 

Vernal pools or "spring pools" are shallow depressions that usually contain water for only part of the year. In the Northeast, vernal pools may fill during the fall and winter as the water table rises. Rain and melting snow also contribute water during the spring. Vernal pools typically dry out by mid to late summer. Although vernal pools may only contain water for a relatively short period of time, they serve as essential breeding habitat for certain species of wildlife, including salamanders and frogs. Since vernal pools dry out on a regular basis, they cannot support permanent populations of fish. The absence of fish provides an important ecological advantage for species that have adapted to vernal pools, because their eggs and young are safe from predation.Species that must have access to vernal pools in order to survive and reproduce are known as "obligate" vernal pool species. In Maine, obligate vernal pool species include wood frogs, spotted and blue-spotted salamanders (two types of mole salamanders) and fairy shrimp. While wood frogs and mole salamanders live most of their lives in uplands, they must return to vernal pools to mate and lay their eggs. The eggs and young of these amphibians develop in the pools until they are mature enough to migrate to adjacent uplands. Fairy shrimp are small crustaceans which spend their entire life cycle in vernal pools, and have adapted to constantly changing environmental conditions. Fairy shrimp egg cases remain on the pool bottom even after all water has disappeared. The eggs can survive long periods of drying and freezing, but will hatch in late winter or early spring when water returns to the pool.

 

Forest management activities are exempt from vernal pool regulations.  The Maine Forest Service promotes the use of voluntary habitat management guidelines for the protection of important vernal pools during timber harvest operations.

 

Vernal Pool Fact Sheet:  A Significant Wildlife Habitat 

 

Vernal pools provide important habitat for many common and specialized forest-dwelling species. Timber harvesting activities should avoid disturbing high-value vernal pools and limit impacts to the immediate surrounding forest.

 

What is a vernal pool?

 

A vernal pool is a natural, temporary to semi permanent body of water occurring in a shallow depression that typically fills during the spring or fall and may dry during the summer. Vernal pools are small (usually less than an acre), have no permanentinlet and no viable populations of predatory fish. In Maine, vernal pools are also defined by the animals that use them for breeding, including the following indicator species:

 

Spotted salamander.

Blue spotted salamander.

Wood frog.

Fairy shrimp.

 

How do I identify a vernal pool?

 

When planning a timber harvest look for potential vernal pools on:  National Wetland Inventory Maps—look for isolated depressions designated as:

 

PUB/POW (open water).

PSS (shrub swamp).

PFO (forested wetland).

PEM (marsh).

Aerial photographs (large scale, color infrared taken with leaves off the trees are best).

USGS topographical maps (look for depressions, indications of wetlands).

 

In early spring vernal pools can be identified by looking for:

 

Small, isolated wetlands that are at least 12” deep and likely to hold water for more than 2 ½ months.

Evidence of one or more indicator species (mating adults, egg masses, spermatophores, or larvae).

In drier periods look for depressions in the forest with:  Compacted leaves and objects with water stains or a film of sediment.

Wetland plants (mosses, sedges, some ferns and shrubs) and soils.

Fingernail clams, snails and/or caddisfly cases.

 

What do I do once I identify a vernal pool?

 

Document the pool’s existence. Identify it on your management plan maps and/or include it in a planning GIS layer. Plan your harvesting activities using the vernal pool Habitat Management Guidelines described below.

 

Vernal pools that have been mapped as Significant Wildlife Habitat by the Department of Inland Fisheries and Wildlife have statutory protection (38 MRSA § 480-Q) and may require a permit by rule for activities within 250 ft of the pool perimeter (DEP rules Chapter 335).

 

What are Habitat Management Guidelines?

 

Habitat Management Guidelines have been developed to help forest managers, harvesters and landowners protect elements of critical habitat for vernal pool - dependent wildlife. They are meant to be applied within a working forest where trees are regenerated and grown in the vicinity of important vernal pools. It may not be possible to protect all vernal pools during forest management activities.  Priority should be placed on protecting high-value pools that show significant breeding activity (more than one indicator species, and/or more than 20 egg masses of one indicator species).

The habitat guidelines, outlined below, are broken into three zones. Full descriptions and justifications can be found in Forestry Habitat Management Guidelines for Vernal Pool Wildlife. 

 

The habitat management zones include the pool itself, the area within 100 ft of the pool perimeter (Protection Zone), and the area between 100 ft and 400 ft of the pool perimeter (Life Zone).  When planning management activities:

Scout for potential vernal pools using wetland maps, aerial photographs and topographic maps. Document vernal pools found in the field.  Map vernal pools and surrounding habitat management zones. Avoid vernal pools and associated management zones when planning roads and log landings.  Avoid clearcuts and pesticide applications near vernal pools.  Limit roads, landings and heavy cuttings between valuable pools separated by less than ¼ mile. Within the pool depression (delimited by spring high water level):  Flag the pool perimeter during harvest layout and prior to cutting (can be done during spring breakup when harvesting activities are curtailed).  Avoid disturbing the basin and surrounding vegetation.  Prevent slash and sediment from entering the pool.  Between March and June leave debris that falls in accidentally to avoid disturbing breeding activity and development of young.  Within 100’ of the pool perimeter (Protection Zone):  Flag the boundaries of the protection zone.  Maintain a uniformly distributed stand of trees, at least 20-30 feet tall, with at least 75% canopy cover.  Minimize soil disturbance and limit harvest to periods when soil is dry or frozen.  Avoid use of heavy machinery.  Avoid construction of new roads or landings; use BMP’s to protect water quality on old ones.  Avoid disturbing fallen logs.  Leave some older or dying trees as sources of future coarse woody debris.  Leave tops and limbs from harvested trees.  Avoid chemical use.  Outside 100’ of pool perimeter but within 400’ (Life Zone):  Maintain a uniformly distributed stand of trees, at least 20-30 feet tall, with at least 50% canopy cover.  Avoid plantations and large-scale changes in forest cover type.  Limit canopy openings to less than 1 acre.  Leave older or dying trees (2 per acre or more).  Minimize soil compaction by harvesting when soil is frozen or dry.  Avoid constructing new roads or landings; apply BMP’s to existing ones.  Minimize the use of chemicals, especially during  early spring and late summer/early fall, when amphibians are migrating.  Summarized from:  Calhoun, A.J.K. and P. deMaynadier. 2004. (Forestry habitat management guidelines for vernal pool wildlife).

 

To review, vernal pools are:

 

Fishless.

Seasonal (usually).

Naturally occurring water bodies.

 

Vernal pool-dependent organisms rely on the pool itself as well as an intact forest immediately surrounding the pool to complete their lifecycle. Some important habitat elements that should be maintained within 750 ft of the pool are:

 

Water quality.

Forest cover.

Uncompacted soil.

Woody debris.

 

 

Vernal Pool in Wallagrass, Maine (This vernal pool was flagged and protected during a logging operation).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Maine Forest Service DEPARTMENT OF CONSERVATION 22 State House Station Augusta, ME04333-0022 (207) 287-2791