Habitat description
Vernal pools, also known as ephemeral pools, autumnal pools, and temporary woodland ponds, typically fill with water in the autumn or winter due to rainfall and rising groundwater and remain ponded through the spring and into summer. Vernal pools dry completely by the middle or end of summer each year, or at least every few years. Occasional drying prevents fish from establishing permanent populations, which is critical to the reproductive success of many amphibian and invertebrate species that rely on breeding habitats free of fish predators.
Associated habitat types
Meadow can also function as vernal pool habitat. Vernal pool habitat can also occur within Major-river Floodplain Forest, Interdunal Marsh/Swale, or Kettlehole Wet Meadow habitats.
- Wet Meadow
- Shallow Emergent Marsh
- Deep Emergent Marsh
- Shrub swamp
- Major-river Floodplain Forest
- Interdunal Marsh/Swale
- Kettlehole Wet Meadow
Characteristic communities and species
Several species are considered vernal pool obligates, meaning they require vernal pools to complete critical stages of their life cycles (typically reproduction) and, therefore, maintain viable populations. Examples of some common vernal pool obligates in Massachusetts include Wood Frog (Lithobates sylvaticus), Spotted Salamander (Ambystoma maculatum), and Eastern Fairy Shrimp (Eubranchipus vernalis). Massachusetts Species of Greatest Conservation Need that are vernal-pool obligates include Jefferson Salamander (Ambystoma jeffersonianum), Blue-spotted Salamander (Ambystoma laterale), Marbled Salamander (Ambystoma opacum), Eastern Spadefoot (Scaphiopus holbrookii), and Intricate Fairy Shrimp (Eubranchipus intricatus).
Ecological processes
Vernal Pools typically fill with water in the autumn or winter months due to rainfall and rising groundwater and remain ponded through the spring and into summer. As ambient air temperatures rise and the growing season advances during spring, vernal pools lose water to evaporation, transpiration, and falling water tables, eventually becoming completely dry by the middle or end of summer each year (or at least every few years). This wet-dry cycle, described as the vernal pool’s hydroperiod, precludes the establishment of permanent fish populations in the basin, which is critical to the reproductive success of many amphibian and invertebrate species that rely on breeding habitats free of fish predators. Breeding success shifts among pools with changing environmental conditions and clusters of vernal pools and the surrounding habitat allow for successful breeding, dispersal, overwintering, foraging, and migration.
The persistence of populations of vernal pool breeding species relies not only on the presence of the vernal pool itself but also on adjacent upland forest habitat where species spend most of their annual life cycle foraging and overwintering. These upland areas are also important for successful migration among pools. Because Vernal Pool habitats are dynamic, populations of Vernal Pool species have a greater likelihood of persistence over time in settings that allow individuals to move among multiple breeding pools.
Threats
- Climate Change: Analyses project varying scenarios for the northeastern United States. Although total precipitation is expected to increase, other common predictions include warmer temperatures, longer and more severe summer droughts, shorter but more intense winter/spring floods, and reduced extent and duration of winter snow cover. Taken together, such changes could dramatically alter the hydroperiods of many vernal pools in the region, thereby posing significant threats to their dependent organisms.
Due to changing environmental conditions and the resulting shifts in breeding success among pools, clusters of vernal pools and intact upland habitat surrounding them allows for successful breeding, dispersal, overwintering, foraging, and migration. Clusters of vernal pools will maximize the resistance and resilience of vernal pool habitats and their resident species in the context of climate change. Therefore, the quality and connectivity of upland habitats within the surrounding landscape will contribute to the resilience of this habitat type. - Habitat loss and fragmentation of the terrestrial habitats surrounding vernal pools and vernal pool complexes is the primary threat. This can result from residential and commercial, road building, and land clearing for other purposes. In addition to the outright loss of forest habitat that many vernal pool species need to survive, increased road mortality of amphibians and reptiles, physical barriers to migration, and adverse changes to water quality and quantity (hydrology) can be associated with roads and development. This includes increased nutrient-loading and sedimentation, increased salinity, and/or changes in surface-water temperatures. Development occurring within the immediate vicinity of several pools it creates physical barriers between pools, negatively impacting the ability of organisms to access and populate those pools thus affecting the habitat function of them and the metapopulation dynamics of associated species.
- Tree clearing associated with harvesting of wood products can also have negative impacts by removing portions of the forest canopy and altering light conditions, water temperature, organic inputs, and nutrient cycling in and around vernal pools. Logging also compacts soils and may introduce nonnative invasive plants to the terrestrial habitat immediately surrounding vernal pools. The effects of tree harvesting can be minimized through the implementation of best practices and regulatory protections afforded vernal pools (e.g., the Massachusetts Forest Cutting Practices Act regulations [304 CMR 11.00]). In some cases, agricultural activities can either directly or indirectly impact vernal pools. Human disturbance associated with dumping, intentional filling, or off-road vehicle (ORV) use in dry basins can have detrimental effects on vernal pools. Finally, human-caused spread of pathogens and disease among vernal pools is an additional threat.
Restoration & management recommendations
While Vernal Pool habitats can be less than one acre and they are used by vernal pool breeding amphibians for two weeks or less during their annual life cycles, they are essential for reproduction. The upland habitat surrounding the vernal pool basin is used by vernal pool breeding amphibians for most of their annual cycles. Management and restoration of upland habitat that creates or maintains features preferred during the terrestrial phase of annual life cycles can enhance the overall vernal pool and upland habitat complex. In addition, it can maintain connectivity between vernal pools. Vernal Pool upland habitat can extend 1,000 feet beyond the vernal pool basin. Beneficial features in upland habitats surrounding Vernal Pools include predominantly closed-canopy deciduous or mixed deciduous-coniferous tree cover, thick leaf litter, abundant coarse woody debris, and loose soils as some vernal pool dependent species spend most their time underground or hidden beneath rocks, logs, leaf litter, or other debris. The following management activities can be implemented within 1,000 feet of Potential or Certified Vernal Pool habitat to enhance beneficial characteristics and minimize threats.
- Revegetation: Restoring forest habitat in the vicinity of vernal pools will increase the available terrestrial habitat for many pool-breeding species, increase connectivity between pools, and potentially improve pool water quality and quantity. Promote hardwood tree species if possible to provide preferred forest floor cover for many amphibians.
- Water quality and quantity restoration: A variety of techniques may be needed to minimize the effects of road runoff and other threats to water quality and pool hydrology. This may include the construction of swales, or other practices to maximize groundwater infiltration. Effective design of roads and developments, including minimizing development, impervious surface, and forest clearing near pools, and including vernal pool watershed analyses in stormwater design, will minimize the need to attempt mitigation later.
- Wildlife passages: In some cases, structures have been constructed to facilitate the passage of amphibians and other wildlife under roads. However, it is complicated to site these structures effectively, barriers are also necessary to funnel wildlife to the structures, and they are expensive. Therefore, the best approach is to consider vernal pool protection when designing developments, by maximizing protection of forested habitat around pools, and minimizing traffic in the vicinity.
Best practices should be implemented for tree harvesting in the vicinity of vernal pools. Mechanized equipment can compact soils and may introduce nonnative invasive plants to the terrestrial habitat immediately surrounding vernal pools. Establishment of logging roads or trails adjacent to or through vernal pools can create problems with erosion and runoff, thus impacting water quality in pools. The primary concern about the use of forest harvesting equipment is alteration of the upland forest around vernal pools and other potential wetland breeding sites, and the mortality of amphibians. The Department of Conservation and Recreation’s Massachusetts Forestry Best Management Practices Manual contains required and guideline practices for Certified Vernal Pools. These include applying required Certified Vernal Pool practices to Potential Vernal Pools functioning as vernal pool habitat or to those that are identified during the planning process.
Some Certified Vernal Pools occur in Priority Habitat for state listed species and inclusion of management practices contained in the Forestry Conservation Management Practices for Massachusetts Endangered Species Act Listed Mole Salamanders developed by the Massachusetts Division of Fisheries & Wildlife is applicable. In association with special approval procedures of the Forest Cutting Practices regulations (304 CMR 11.04(6)), MassWildlife’s Natural Heritage and Endangered Species Program reviews forestry projects to determine whether proposed activities will negatively impact state-listed rare species.
- Access Control: In the upland habitat surrounding Vernal Pools, prevent human and/or vehicle damage and stabilize access for management or recreation with the installation of gates, boulders, fences, or symbolic fencing, etc. Minimize road and trail densities used for recreation or other purposes and soil compaction in upland areas by relocating or designing and maintaining efficient trail systems along with limiting entry of heavy equipment to 20-30 year intervals.
- Invasive Plant Control: Treat invasive plants species currently present in uplands adjacent to vernal pools. In some cases, the treatment of invasives such as common reed in pools themselves may be warranted.
Examples
- Spadefoot Success at Southwick WMA: Six years ago, MassWildlife launched an effort to establish a secure population of the state-threatened eastern spadefoot at Southwick WMA. MassWildlife confirmed this population successfully bred for the first time in July 2021.
- Burrage Pond WMA
- Martin Burns WMA