Habitat description
Vernal pools are relatively small, shallow, freshwater wetland basins (or, sometimes, sub-basins within broader wetlands) that hold water during parts of the year in response to precipitation and/or rising groundwater. They are unique wildlife habitats, perhaps known best for the amphibians and invertebrate animals that use them to breed and reproduce. In Massachusetts, most vernal pools fill with water during fall, winter, or spring and then remain ponded through spring and into summer. As ambient air temperatures rise and the growing season advances during spring, vernal pools lose water to evaporation, transpiration, or falling water tables, eventually becoming completely dry by the middle or end of summer each year. This wet-dry cycle, described as the vernal pool’s hydroperiod, precludes the establishment of fish populations in the basin and is critical to the reproductive success of many amphibian and invertebrate species that rely on breeding habitats free of fish predators.
Depending on context, setting, hydrological regime, and even personal preference, “vernal pool” may go by alternative names, including but not limited to ephemeral pool, seasonal pool, autumnal pool, temporary pond, or woodland pond. Some pools have a “flashy” hydroperiod, filling with water for only several weeks at a time in response to heavy rain and surface runoff, while others may hold water most of the year or dry out in only some years due to proximity of the water table. Pools may occur in forest, shrubland, grassland, or even coastal dune settings. Vernal pools may be “perched” above bedrock, or they may be groundwater-fed. They may contain very low to very high densities of shrubs, sedges, grasses, or mosses. They have varying amounts of coarse woody debris, leaf litter, and detritus. Surface area may be less than 9 m2 (100 sq ft) or exceed 1 ha (2.5 ac). Maximum depth can be under 15 cm (6 in) or exceed 1.5 m (5 ft).
In a regulatory context, the meaning of “vernal pool” depends on the state or municipal entity defining it. For example, some types of vernal pools are regulated as “vernal pool habitat” under the Massachusetts Wetlands Protection Act (MWPA) regulations (310 CMR 10.00), provided they meet certain physical and biological thresholds for wildlife habitat function. Some municipal bylaws, on the other hand, might rely strictly on physical characteristics of a wetland basin to define it as a vernal pool.
For purposes of the Massachusetts State Wildlife Action Plan (SWAP), vernal pools are generally defined as wetland basins that (a) exhibit temporary or non-permanent inundation, (b) are free of fish populations, (c) meet critical life history requirements of native vertebrate and invertebrate Species of Greatest Conservation Need (SGCN), and (d) provide important habitat for other native animal and plant species.
Vernal pools are relatively common in Massachusetts, except in highly urbanized areas. In 2000, MassWildlife’s Natural Heritage & Endangered Species Program (NHESP) undertook a major project to identify locations of possible vernal pools throughout Massachusetts, conducting a visual evaluation of aerial photographs for evidence of small water bodies that might be expected to support pool-dependent wildlife. Approximately 30,000 such features were identified statewide and dubbed “Potential Vernal Pools” (PVPs). Indeed, most PVPs that are field-checked are confirmed to be functioning as vernal pool habitat as defined in the MWPA regulations. Although some PVPs do not function as such, the PVP data set does ultimately underestimate the true number of vernal pools occurring across the Massachusetts landscape. Reliance on aerial photo interpretation alone cannot identify all pools that are very small, occur beneath a conifer canopy, and/or occur within wooded swamps. Locations of the PVPs can be obtained via a Geographic Information System (GIS) datalayer (“NHESP Potential Vernal Pools”) made available on the MassGIS website.
Vernal pool habitats can be “certified” voluntarily by the Massachusetts public for legal protections afforded by the MWPA, several other state and local laws, and – in limited circumstances – the Department of the Army General Permits for Massachusetts (2023). The certification process, which is administered by the NHESP, involves documentation of minimum physical and biological criteria presumed to be strong indicators of vernal pool habitat (e.g., presence of a confined basin depression holding water during the spring and supporting breeding activity of obligate vernal pool species). Anyone can survey a vernal pool, document its physical and biological characteristics, and submit a completed report to the NHESP for possible certification of the pool as vernal pool habitat. Vernal pool observation reports (also called “certification applications”) are reviewed for possible approval in accordance with certification guidelines established by the NHESP. Additional details about vernal pool certification, including the NHESP Guidelines for the Certification of Vernal Pool Habitat, are available on the NHESP website. Over 8,200 vernal pools are designated Certified Vernal Pools (CVPs) in Massachusetts, and the number continues to grow annually as more biological surveys are completed. Since the certification of vernal pool habitat is a voluntary process and relies heavily on efforts of the general public, the overall distribution of CVPs may differ substantially from that of PVPs. However, there is considerable overlap in some areas, as many PVPs ultimately become CVPs.
Characteristic natural communities
Vernal pools are generally considered discrete, small-scale habitats embedded within larger communities. They occur within a variety of forested uplands, open lands, land-water interfaces, and broader palustrine habitats. Their occurrences in Massachusetts are characteristic not so much of any particular group or subset of natural communities but, rather, of localized circumstances of post-glacial geology and physical depressions on the landscape. The assemblages of plant species in vernal pools vary widely by the broader habitat types in which they occur and by hydrological regime.
Characteristic plants and animals
Some taxa are considered vernal pool “obligates”, meaning they require vernal pools (or at least fishless portions of wetlands) to complete critical stages of their life cycles (e.g., reproduction). Examples of some common vernal pool obligates in Massachusetts include wood frog (Lithobates sylvaticus), spotted salamander (Ambystoma maculatum), and eastern fairy shrimp (Eubranchipus vernalis). Some Massachusetts SGCN considered to be vernal pool obligates include Jefferson salamander (Ambystoma jeffersonianum), blue-spotted salamander (Ambystoma laterale), marbled salamander (Ambystoma opacum), eastern spadefoot (Scaphiopus holbrookii), intricate fairy shrimp (Eubranchipus intricatus), Agassiz’s clam shrimp (Eulimnadia agassizii), and American clam shrimp (Limnadia lenticularis). In fact, eastern spadefoot and the aforementioned clam shrimp species tend to utilize pools that are so ephemeral that they do not always hold water long enough to meet the regulatory definition of “vernal pool habitat” under the MWPA regulations, thus highlighting the potential vulnerability of certain types of vernal pools in Massachusetts.
Many other taxa, although not strictly dependent on vernal pools, heavily utilize them as a resource for certain needs (e.g., feeding, breeding, over-wintering, aestivating, hydrating) when other wetland types are less available or are near their biological carrying capacities. In those respects, vernal pools may function as habitat links between distant wetlands or as supporting habitats when resources in other wetlands become limited. Examples of Massachusetts biota that frequently utilize vernal pools to help meet their life-history requirements include four-toed salamander (Hemidactylium scutatum), eastern newt (Notophthalmus viridescens), Fowler’s toad (Anaxyrus fowleri), American toad (Anaxyrus americanus), spring peeper (Pseudacris crucifer), gray treefrog (Hyla versicolor), green frog (Lithobates clamitans), pickerel frog (Lithobates palustris), northern leopard frog (Lithobates pipiens), Blanding’s turtle (Emydoidea blandingii), spotted turtle (Clemmys guttata), eastern box turtle (Terrapene carolina), wood turtle (Glyptemys insculpta), painted turtle (Chrysemys picta), snapping turtle (Chelydra serpentina), water shrew (Sorex palustris), spatterdock darner (Rhionaeschna mutata), emerald spreadwing (Lestes dryas), lyre-tipped spreadwing (Lestes unguiculatus), fingernail clams, amphibious air-breathing snails, leeches, diving beetles, water scorpions, dobsonflies, whirligig beetles, and caddisflies. Common shrubs of vernal pools in Massachusetts include highbush blueberry (Vaccinium corymbosum), winterberry (Ilex verticillata), buttonbush (Cephalanthus occidentalis), coastal sweet-pepperbush (Clethra alnifolia), and meadowsweets (Spiraea spp.). Some plant SGCN in Massachusetts include false hop sedge (Carex lupuliformis), Tuckerman's sedge (Carex tuckermanii), and swamp cottonwood (Populus heterophylla).
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).
Associated habitats
Vernal pools may occur in isolation within uplands or as sub-basins within other wetlands, such as forest swamps and seeps, riparian and floodplains, shrub swamps, marshes and wet meadows, calcareous wetlands, and acidic peatlands. The association of “vernal pool habitat” (as defined in the MWPA regulations) with other wetlands is dependent on the presence of standing water with an appropriate inundation period (and isolation from predatory fish) to support reproduction by certain amphibian species. In general, vernal pools are most commonly associated with forests and woodlands, though some do occur in open habitats (e.g., shrublands, grasslands, dune systems).
Ecological processes
Vernal pools occur in a variety of situations, but their original formation is most strongly tied to post-glacial processes involving scouring of bedrock, movement and subsequent deposition of soils, and/or melting of buried ice deposits to form basin depressions on the landscape. Some pools formed where soil deposits of low permeability settled within depressions, others formed where depressions intercepted seasonally high water tables. Over time, vernal pools also formed in riparian meander scars and in depressions scoured by floodwaters. Some vernal pools have formed from human activities (e.g., sand and gravel extraction, ditching, deliberate pool creation).
Besides direct precipitation, vernal pools receive water via surface runoff, groundwater inputs, or stream overflow, and the vegetation community is influenced mainly by the underlying geology, soils, hydrological regime, and sunlight. Depending on setting, vernal pools may also receive inputs of sediment and organic debris. Like forest succession, vernal pools may transform over time when there is a lack of disturbance. Long-term accumulation of organic material and/or sediment can facilitate conditions for increasingly dense plant growth, such that depth and surface area of standing water gradually decreases. In some cases, vernal pools may eventually succeed to a different type of wetland and cease to provide critical habitat functions for pool-dependent taxa. Conversely, where succession occurs in larger wetlands, vernal pools may form as a result of the wetland basin becoming shallower or fragmented and fish being extirpated.
Natural disturbance regimes of the Northeast that influence the physical structure and hydroperiod of vernal pools consist mainly of wind and wildlife. Windstorms uproot trees, creating new depressions within a wetland (e.g., forested swamp) or expanding the margin of an existing pool, while simultaneously reducing leaf-litter inputs and increasing direct sunlight. In some areas (especially at lower elevations), beavers (Castor canadensis) may significantly alter pool hydrology by damming intermittent outflows, removing shrubs, and excavating pool substrates (mud, leaves, and detritus) to deepen the basin profile. In extreme cases, damming of a nearby stream or wetland outlet can cause standing water to rise and overtake a vernal pool, whereby the pool is converted to a permanently inundated sub-basin of the dammed wetland. However, when beavers abandon a site, the process of pool or wetland succession resumes. Hence, ecological processes of vernal pools are dynamic and, in some situations, may occur in cycles over periods of decades and centuries.
Threats
Limited public knowledge and education about the importance of vernal pools, combined with deficiencies in regulatory protections and oversight, contribute to the vulnerability of this habitat to a variety of threats in Massachusetts. In general, the relatively small sizes of vernal pools and their periods without water often make them inconspicuous on the landscape, only exacerbating their vulnerabilities. Following is a description of known and potential threats to vernal pools in Massachusetts.
IUCN-CMP Threat 1: Residential, Commercial & Recreation Areas
Land development that involves clearing, grading, filling, and/or building-construction and associated landscaping may result in the direct filling and permanent physical loss of vernal pools. Blasting activities near a perched pool can fracture the underlying bedrock or impervious layer, thereby draining the basin and permanently impairing or destroying its hydrologic function. Increased impervious surface in the watershed, particularly in areas adjacent to a pool, may result in altered hydrologic function, reduced water quality, increased nutrient loading and sedimentation, increased salinization, and/or changes in surface water temperatures. Many vernal pool obligates also require the terrestrial habitats surrounding vernal pools to complete their life cycles; vernal pool function can be indirectly disrupted when residential and commercial developments destroy those terrestrial habitats. When development occurs in the immediate vicinity of pools and/or creates physical barriers between pools, the ability of organisms to access and populate those pools is impaired, thus affecting the habitat function of the pools and the metapopulation dynamics of associated SGCN. Development and associated traffic can also lead to direct mortality of amphibians and reptiles, which is especially concerning for SGCN whose reproductive strategies are based on high annual adult survivorship (e.g., Blanding’s Turtle, Spotted Turtle).
CVPs receive substantial, state-level regulatory protection from direct loss to residential and commercial development in Massachusetts. However, only a small percentage (likely <30%) of vernal pools in the state are currently recognized as CVPs. Some of the remaining vernal pools are protected from direct loss by local bylaws, but not all municipalities have established such regulations, and those that have vary in their level of oversight and enforcement. Terrestrial habitats surrounding vernal pools are highly vulnerable to residential and commercial development, as there are few legal protections for those areas besides threatened and endangered species legislation.
Development pressure in Massachusetts is high. Despite relatively strong environmental regulations in the state, residential and commercial development is considered a significant threat to its vernal pool habitats.
IUCN-CMP Threat 2: Agriculture & Aquaculture
Agricultural development involving clearing, grading, and/or filling may result in direct physical loss of vernal pools. Agricultural dumping may physically and/or chemically alter vernal pools. Runoff from agricultural fields may negatively alter vernal pool chemistry and harm associated amphibians via introduction of fertilizers, pesticides, and/or herbicides.
Agricultural development pressure in most parts of Massachusetts is relatively low, and demand for “green” (e.g., organic) products from existing operations is relatively high. Agricultural abandonments continue to occur and, in some situations, may result in creation of new vernal pool habitats, as abandoned farm ponds and watering holes naturally accumulate organic matter over time, naturalize, and become suitable for use by obligate pool-breeding species. All of these factors help to lessen the aforementioned threats of agriculture to vernal pool habitat. However, certain types of agricultural activities are exempt from most environmental regulations in Massachusetts, including the MWPA. Furthermore, the limited exemptions are sometimes perceived by landowners as unlimited, blanket exemptions, and so unlawful loss of vernal pools to agricultural development does occur occasionally.
IUCN-CMP Threat 3: Energy Production & Mining
Energy-production and/or mining activities that involve clearing, grading, and/or filling may result in the direct removal, filling, and permanent physical loss of vernal pools. Blasting activities near a perched pool can fracture the underlying bedrock or impervious layer, thereby draining the basin and permanently impairing or destroying its hydrologic function. Many vernal pool obligates also require the terrestrial habitats surrounding vernal pools to complete their life cycles; vernal pool function can be indirectly disrupted when energy-production and/or mining activities alter or destroy those terrestrial habitats. When such activities occur in the immediate vicinity of pools and/or create physical barriers between pools, the ability of organisms to access and populate those pools is impaired, thus affecting the habitat function of the pools and the metapopulation dynamics of associated SGCN. In some cases, vernal pool obligates may actually colonize mining sedimentation pools. Those pools are often considered population sinks, as they are unprotected, are reconfigured regularly to fit the needs of the mining operation, and may ultimately be filled, thereby leaving the newly dependent animals without a breeding site.
CVPs receive substantial state-level regulatory protection from direct loss to energy-production and/or mining activities in Massachusetts. However, only a small percentage (likely <30%) of vernal pools in the state are currently recognized as CVPs. Some of the remaining vernal pools are protected from direct loss by local bylaws, but not all municipalities have established such regulations, and those that have vary in their level of oversight and enforcement. Terrestrial habitats surrounding vernal pools are highly vulnerable to energy-production and/or mining activities, as there are few legal protections for those areas besides threatened and endangered species legislation.
Energy-production pressure in Massachusetts has increased substantially over the past decade (e.g., from construction of solar farms) and is likely to continue increasing over the next decade or more. Mining pressure (e.g., for sand and gravel extraction) is probably considered moderate. Despite relatively strong environmental regulations in the state, energy-production is a high-ranking public need, and some long-established mining operations are not always subject to more recently established regulations and/or permitting requirements. Energy-production and mining tend to be relatively localized threats, but their geographic footprints are expanding and are significant to vernal pool ecology where they occur. For example, both activities often involve the removal of forest near or between pools, disrupting pool ecology indirectly by altering their wildlife populations. Hydrology and water quality may also be disrupted by altered forest canopy, runoff and erosion, and altered drainage patterns.
IUCN-CMP Threat 4: Transportation, Service & Security Corridors
Existing transportation/service infrastructure may indirectly impact vernal pool habitat by limiting or reducing local biodiversity. Roads, highways, and railways often act as physical barriers to movement and/or sources of adult mortality for organisms (e.g., salamanders, turtles) that use vernal pools and must traverse terrestrial habitat to access them. Roads/highways with high traffic volume also create noise pollution, which may alter breeding behavior (e.g., frog calling) in nearby pools in ways that either impair breeding activity or result in certain tradeoffs that could conceivably reduce reproductive fitness. In addition, transportation corridors are sources of chemical pollution for many vernal pools in Massachusetts, as storm runoff from roads and highways introduces metals, salts, oils, and other compounds to vernal pools, thus altering pool chemistry and, in some cases, impairing or destroying the biological function of the habitat. Maintenance of service corridors (e.g., gas and electric utility rights-of-way) can alter vegetation composition and structure in vernal pools occurring within the corridors or modify light conditions at pools bordering corridors; those types of impacts are generally considered relatively minor, however.
Development of new transportation and service corridors (or widening of existing corridors) involves clearing, grading, and/or filling, which can result in direct filling and permanent physical loss of vernal pools. Blasting activities near a perched pool can fracture the underlying bedrock or impervious layer, thereby draining the basin and permanently impairing or destroying its hydrologic function. Construction of roads and railroads near any wetland systems, including vernal pools, changes the natural flow and/or hydrology of local surface water and groundwater. Once established, transportation and service corridors threaten vernal pool habitats as described in the preceding paragraph.
CVPs receive substantial state-level regulatory protection from direct loss to development of new transportation and service corridors in Massachusetts. However, only a small percentage (likely <30%) of vernal pools in the state are currently recognized as CVPs. Some of the remaining vernal pools are protected from direct loss by local bylaws, but not all municipalities have established such regulations, and those that have vary in their level of oversight and enforcement. Terrestrial habitats surrounding vernal pools are vulnerable to development of new transportation and service corridors, as there are few legal protections for those areas besides threatened and endangered species legislation. There are few to no regulatory protections for vernal pools with respect to pollution from road/highway runoff, or with respect to the alteration of pool ecology caused by road-related animal mortality and habitat fragmentation.
Density of transportation and service corridors in Massachusetts is relatively high, and so the threat of development of new corridors is relatively low in most parts of the state. One notable new service project is the South Coast Rail; if executed, it will impact vernal pools and pool-dependent SGCN in a highly important ecological area known as the Hockomock Swamp. Although such large-scale projects are rare, many existing transportation corridors continue to widen, and some vernal pools may ultimately be lost or impaired as a result. Pollution associated with road/highway/railway runoff is a continuing concern for many vernal pools, and mortality of pool-dependent organisms attempting to cross over roads is considered a major threat to pool ecology throughout much of the state. Massachusetts is also experiencing a significant increase in pressure to upgrade electric utility infrastructure and associated access roads. Vernal pools in and near utility rights of way are expected to incur direct or indirect impacts from these activities as a result of heavy-equipment operation, pool sedimentation, corridor widening (i.e., loss of canopy cover), increased off-road vehicle use by the public (see IUCN-CMP Threat 6), and introduction of non-native, invasive plant species (see IUCN-CMP Threat 8).
IUCN-CMP Threat 5: Biological Resource Use & Control
Some SGCN (e.g., Blanding’s Turtle, Spotted Turtle) that utilize vernal pools are poached or otherwise collected. However, the magnitude of the problem and the degree to which vernal pools act as collection sites are unknown.
Timber harvesting (logging) is a common land use in parts of Massachusetts (except for Cape Cod). Logging can impact vernal pool ecology in a number of ways, not all of which are well understood. Logging removes portions of the forest canopy and, therefore, alters light conditions, water temperature, organic inputs, and nutrient cycling in and around vernal pools. Logging also compacts soils and may introduce non-native invasive plants to the terrestrial habitat immediately surrounding vernal pools. Establishment of logging roads/trails adjacent to or through vernal pools can create problems with erosion and runoff, thus impacting water quality in pools (e.g., by increasing turbidity). Overall, logging is considered a relatively minor threat to vernal pools in Massachusetts; other than the problem of non-native invasive plants, logging-associated impacts to vernal pools are typically minor, temporary, and/or minimized by regulatory protections (e.g., the Forest Cutting Practices Act regulations [304 CMR 11.00]).
IUCN-CMP Threat 6: Human Intrusions & Disturbances
An unknown percentage of vernal pools in Massachusetts are impacted by human intrusions and disturbance. The most commonly observed disturbances are dumping, intentional filling, mosquito control, operation of off-road vehicles (ORVs), and biological surveys (both recreational and professional).
Dumping activity, as evidenced by the types of old cars and household appliances found in vernal pools, appears to be less substantial now than in decades past. However, dumping of trash, tires, brush, and lawn clippings is an ongoing threat to vernal pools located near roadside pull-offs, trailheads, and suburban yards. Intentional filling of vernal pools with tree limbs, leaves, and other yard waste by landowners attempting to manage surface water on or adjacent to their properties is an occasional problem. The degree to which dumping and filling impact vernal pools varies by locality, but smaller vernal pools in areas of greater human population density tend to be most at risk. While a small percentage of vernal pools are classified as CVPs and, therefore, are legally protected from dumping/filling, detection of violations and/or identification of violators can be difficult. An understudied and probably underappreciated threat to vernal pools in Massachusetts is mosquito control, whether conducted unofficially by residential landowners (e.g., via “Bti mosquito dunks”) or formally by state-agency control programs (e.g., via systematic wetlands survey and treatment, aerial insecticide spraying). Reduction of mosquito larvae in vernal pools removes an important food source for amphibian larvae and other natural predators, thereby diminishing habitat quality and biological function.
Operation of dirt bikes, all-terrain vehicles, and other vehicles (collectively “off-road vehicles”, or “ORVs”) in or near vernal pool basins is a common occurrence along electric transmission line rights-of-way and in woodlands near human habitation. Most such ORV use is illegal, and there is little enforcement. However, some public lands are open to ORV use and attract both resident and non-resident users. Hence, chronic physical disturbance, rutting, turbidity, and animal mortality from ORV operation is a threat to vernal pools in many parts of Massachusetts.
Vernal pools located on public lands are also threatened by human disturbance via excessive biological surveying. There is high demand for public open space in Massachusetts, and some pools are surveyed multiple times per year for various recreational, educational, and/or scientific endeavors. Some types of surveys (e.g., log/rock-rolling, dip-netting) are disruptive to microhabitats within pools, while others (e.g., funnel-trapping) are disruptive to breeding activity of organisms using the pools. Repeated disturbance of vernal pool basins at short intervals appears most problematic on lands near large population centers (e.g., Boston, Springfield) and in areas where public land is in relatively low supply. The magnitude of the impacts to vernal pool organisms has not been studied in Massachusetts, but physical alterations to pool microhabitats are apparent and could presumably harm their biological function. Human-caused spread of pathogens and disease among vernal pools is an additional threat to vernal pool ecology (see IUCN-CMP Threat 8).
IUCN-CMP Threat 7: Natural System Management & Modifications
Abstraction of ground water and surface water for residential, commercial, and agricultural use could potentially threaten vernal pools in Massachusetts. Substantial abstractions during droughty conditions (e.g., for residential and agricultural irrigation, commercial snow-production) could contribute to low water tables and, therefore, shorten vernal pool hydroperiods. This threat is under-investigated in Massachusetts, and so its magnitude is unknown.
IUCN-CMP Threat 8: Invasive/Other Problematic Species, Genes & Pathogens
Introduction and proliferation of non-native, invasive plant species are a threat to plant SGCN (i.e., False Hop Sedge, Tuckerman’s Sedge, Swamp Cottonwood) in some vernal pools, as is competition from other tree and shrub species. Dominance of non-native vegetation at and around vernal pools is also likely to impact leaf litter and soil stability, as thickets of some species – e.g., Multiflora Rose (Rosa multiflora) and Tatarian Honeysuckle (Lonicera tatarica) – often harbor bare-ground conditions beneath their canopies, thereby facilitating soil erosion and pool turbidity during rain events.
Isolated vernal pools are vulnerable to flooding by beaver activity when they are located near streams and larger wetlands. As beaver dams are created and grow in size, substantial impoundments of water are created, and they may encroach upon and ultimately engulf nearby vernal pools. Such flooding establishes a permanent hydroperiod and allows regular access by fish, rendering the former vernal pool area uninhabitable for smaller vernal pool organisms (e.g., fairy shrimp). Some vernal pool species (e.g., Spotted Salamander) can still utilize a beaver impoundment for the same purposes a former isolated vernal pool had been used, but others (e.g., Jefferson Salamander, fairy shrimp) are far less flexible in their habitat requirements and may either disappear from the local system or suffer population declines. After beavers abandon an impoundment and dams are breached, vernal pool basins may reappear. However, the cycle of beaver occupation, abandonment, draining, forest regrowth, and pool recolonization by vernal pool organisms can be lengthy, playing out over many decades. In habitat patches isolated by roads and development, such temporary loss of vernal pool habitat can have permanent impacts on local populations of pool-dependent organisms. Beaver activity is common and widespread in Massachusetts, but the magnitude of its threat to vernal pool habitat is under-investigated.
Emerging infectious disease is currently considered one of the greatest threats to global biodiversity, and amphibians are an especially vulnerable group. The primary pathogens known to be impacting Massachusetts vernal pools – and their amphibian species, in particular – include the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) and a group of viruses known as ranaviruses (family Iridoviridae). Although vernal pool amphibians in the New England region appear to be relatively resistant to Bd compared to amphibians elsewhere in the world, it is prevalent in Massachusetts and presumed to be having some level of impact. Ranavirus may be more impactful and is often the first suspect when mass mortality of larval amphibians is observed.
Of grave concern is the potential (and seemingly inevitable) introduction of the salamander chytrid fungus Batrachochytrium salamandrivorans (Bsal), known best for its devastating impacts on amphibians in Europe. This fungus of Asian origin is believed to have spread via the pet trade but has yet to be detected in the wild in North America. Some vernal pool amphibians (e.g., mole salamanders [Ambystoma spp.]) appear to be resistant to Bsal infection, though some species in the genus have been shown to be capable carriers. Eastern Newts are common to vernal pools in western Massachusetts and would likely be devastated by Bsal.
The potential spread of pathogens among vernal pools may be facilitated by animal commerce, illegal animal translocations, use of contaminated field gear during biological surveys, and natural dispersal of native fauna. Infection rates and long-term impacts to vernal pools and their associated organisms are understudied in Massachusetts. However, ranavirus is known to affect or be carried by a wide variety of taxa (e.g., frogs, salamanders, turtles, fish), and research findings in other parts of the country suggest that it can have severe, acute impacts on vernal pool amphibians. Bd is known to infect crayfish, and there is evidence that Bd causes reduced growth and increased mortality in certain species. Bd could conceivably pose a threat to other vernal pool crustaceans, including SGCN (e.g., Intricate Fairy Shrimp). Given great difficulty in controlling the spread of pathogens, and the lack of knowledge about persistence and long-term consequences of local outbreaks, emerging infectious disease must be considered a major threat to vernal pool ecology in Massachusetts.
IUCN-CMP Threat 9: Pollution
Vernal pools are vulnerable to nutrient loading and/or chemical contamination when they are adjacent to lawns, golf courses, crop fields, parking lots, roads, gas stations, and other areas where accidental spills or deliberate applications of chemicals occur. Surface runoff from those areas can introduce contaminants to vernal pools, thus altering water chemistry and impairing biological function. High nutrient pollution washing into vernal pools from anthropogenic landscapes can lead to high growth of plant species, and may also encourage exotic invasive species to grow, outcompeting the native SGCN. CVPs and PVPs are sometimes afforded 100-ft terrestrial buffers (via the MWPA and/or municipal bylaws) to mitigate the threat of contamination by runoff, but those regulatory protections do not apply to land uses that are in place prior to identification of a vernal pool and may not guard against infiltration of contaminated groundwater. Given the high human population density in Massachusetts, many vernal pools are impacted by contamination via surface runoff.
The threat of road deicing salts to amphibian reproduction is of especially strong concern in New England. Between 1990 and 2011, average concentrations of chloride in northern U.S. streams was believed to have doubled, exceeding the rate of urbanization. Chloride levels in groundwater appear to be increasing, thus feeding higher chloride-level water into adjacent wetland systems. Many vernal pools are groundwater-fed, and so vernal pool organisms would be vulnerable if chloride concentrations reach toxic levels.
Acidification of vernal pools is a concern for pool-dependent SGCN, especially amphibians (e.g., Jefferson Salamander). Low pH (e.g., <4.5) can inhibit embryonic and larval development and survival, thereby reducing reproduction and recruitment. Increases in acid precipitation may alter water chemistry in vernal pools slowly over time, or particularly heavy precipitation events may trigger sudden spikes in aluminum, which is toxic to larval amphibians. Anecdotal accounts of recent mass mortalities of larval amphibians in New England vernal pools seem to have some association with heavy rain events, though necropsies have not been performed. Plant SGCN associated with vernal pools in Massachusetts appear to inhabit pools with relatively higher pH; whether acidification of the pools would have a detrimental impact on those plant populations is not well understood.
Additional pollution-related threats to vernal pools in Massachusetts are described in IUCN Threat subsections 2, 4, and 6.
IUCN-CMP Threat 10: Natural Disasters
No perceived threats from geological events or most types of severe storms (but see IUCN-CMP Threat 11 for discussion of heavy precipitation events).
IUCN-CMP Threat 11: Climate Change and Severe Weather
A 2024 synthesis of climate data, climate modeling, and climate-related research indicates that temperature, total annual precipitation, and frequency of heavy precipitation events are trending upward in the northeastern United States and are expected to continue to do so into the future. A wetting trend might intuitively suggest potential benefits to vernal pool wildlife by extending the hydroperiod of the average pool, but the timing, frequency, and intensity of precipitation events are important considerations in evaluating the potential impacts of climate change to vernal pool function.
Climate data indicate that the Northeast is experiencing wetter summers and falls and drier winters and springs. Such a shift in precipitation patterns threatens how vernal pools will be able to function as productive amphibian breeding habitat, as some pools may begin the breeding period in early spring with lower water volumes and – with continued seasonal drought – dry prematurely. Reduced water volumes tend to increase larval density and competition, thereby reducing growth rates. Early pool drying results in substantial or complete reproductive failure, as amphibian larvae die before they can complete metamorphosis. Paradoxically, an increasing frequency of heavy precipitation events during early summer also threatens amphibian larvae, as sudden and large inputs of rainwater may cause spikes in pool acidification and leaching of metals (e.g., aluminum), potentially leading to mass mortality just prior to metamorphosis, when larvae are typically most stressed. Such occurrences would be expected to impact productivity of SGCN amphibians such as Jefferson Salamander and Blue-spotted Salamander. In the case of Marbled Salamander – a SGCN amphibian that requires dried portions of pool basins to deposit its eggs in late summer – wetter summers and increased frequency of storms may result in an increased frequency of vernal pools flooding prior to the breeding season, which would reduce annual breeding opportunities. Conversely, the same climate trends might provide greater breeding opportunities for another SGCN amphibian, Eastern Spadefoot, which is an opportunistic summer breeder and does not require an extended hydroperiod.
Larger or deeper vernal pools with greater water volumes are likely to be more resistant to climate change and function as climate “refugia” for most pool-dependent amphibians, but shifts in precipitation patterns do threaten the short- and long-term productivity of smaller pools. Climate change could act as a form of habitat degradation by impacting pool functions and consequently reducing the stability of smaller amphibian populations, weakening metapopulations, and facilitating declines.
Conservation actions
Direct Management of Natural Resources
Restore native vegetation communities in and around vernal pools. Vernal pools with infestations of non-native vegetation should be identified and prioritized for treatment, based on factors such as perceived conservation value to SGCN, protected status, vulnerability to reinfestation, and logistical and financial feasibility of treatment. Treatments can consist of a combination of herbicide application and hand removal, depending on the degree of infestation, plant species involved, and other considerations. During 2017-2020, the NHESP completed treatments of non-native, invasive plant infestations at two vernal pools used for breeding by local populations of Eastern Spadefoot. Monitoring and follow-up control efforts are ongoing.
Restore the physical profile of altered and impaired vernal pool basins. Vernal pools that have been impaired by basin alterations such as filling or ditching should be identified and prioritized for potential restoration, depending on the feasibility of restoring adequate hydrological conditions for target SGCN. Restoration work can be achieved by mechanical means or by hand, depending on the scope of the project. In 2020, the NHESP partially restored the depth profile and surface area of an Eastern Spadefoot breeding pool that had been substantially filled by residential land use. Ongoing monitoring work will determine whether additional action is needed.
Improve reproductive opportunities for vernal pool SGCN by constructing vernal pool basins. In some situations, construction of vernal pool basins can be used as a management strategy to mitigate prior habitat loss or to improve breeding opportunities for local populations of SGCN that are threatened with other stressors. Several experimental pool-construction projects to benefit Eastern Spadefoot have been undertaken since 2011, with mixed results. Monitoring work to determine successes, identify challenges, and/or troubleshoot shortcomings is ongoing. Those projects have focused on sites with significant agricultural activity and a history of breeding pool loss, as well as population introduction sites. Construction of vernal pools for Jefferson Salamander could be a viable conservation strategy, given the species’ habit of colonizing abandoned farm ponds and other man-made impoundments. Creation of vernal pool basins for Blue-spotted Salamander and Marbled Salamander still requires development of proven engineering. Other vernal pool SGCN would be expected to benefit incidentally from pools designed for the aforementioned amphibians. Although vernal pool creation for salamanders in Massachusetts is not a high conservation priority, pool construction would be beneficial in areas where breeding habitat is a limiting resource, especially on protected lands. Sites and precise pool locations should be chosen very cautiously, however, to minimize risk of unintended consequences.
Data Collection and Analysis
Conduct targeted biological surveys of known and potential vernal pools for SGCN. Biological inventory and monitoring of vernal pools is necessary to identify and understand the distribution and abundance of vernal pool SGCN. Data generated by such surveys are critical to establishing and maintaining site-specific regulatory protections for SGCN and to developing effective, long-term conservation plans for the species. For example, all populations of False Hop Sedge likely occur in certifiable vernal pools, but not all have been certified. Prioritization of land protection efforts for vernal pool SGCN, as was done in the BioMap project by MassWildlife and The Nature Conservancy, was largely dependent on biological inventory and monitoring data.
Develop and implement a long-term, statewide vernal pool monitoring program. Long-term monitoring of vernal pool hydrology, chemistry, pathogen loads, and use by associated SGCN would be very helpful in detecting, understanding, and acting on SGCN population trends at local and state scales. Such a program would be especially beneficial in understanding and planning for impacts associated with climate change, emerging infectious disease, pollution, environmental acidification, and habitat loss/fragmentation.
Conduct species-specific research at vernal pools to fill data gaps associated with SGCN life history, habitat requirements, population ecology, sampling techniques, and other subjects. Vernal pools function as population centers for several SGCN and, therefore, are natural sites for studying fundamental aspects of species ecology and improving our knowledge about how to study or monitor populations more effectively. Investigations into population genetics, microhabitat preferences, metapopulation dynamics, and survey efficacy are examples of pool-based research that has helped inform conservation planning and associated actions over the past decade and will continue to do so into the future. For example, the NHESP conducted genetic studies of the Jefferson and Blue-spotted salamander complex at vernal pools during 2015–2018, which ultimately led to proper taxonomic identifications of local populations across the state, identification of and stronger regulatory protections for unique populations of Blue-spotted Salamander in southeastern Massachusetts, and an improved inventory program. Research on aquatic habitat use by Blue-spotted Salamander has improved our understanding of the role that vernal pools play in population dynamics and long-term population viability.
Education and Outreach
Promote vernal pool certification in Massachusetts. One of the most effective means of protecting vernal pool basins from direct loss is to have them certified as “vernal pool habitat” per the MWPA regulations. Promotion of the certification program is an effective way to involve the Massachusetts public in “hands-on” stewardship of the environment, and the certification process involves participants in ways that educate them about vernal pool habitats, their functions, and their value to SGCN and local biodiversity. Promotional tools may include website and/or social media development, listserv announcements, and workshops.
Produce and provide educational products, services, and opportunities to the Massachusetts public regarding vernal pool ecology and conservation. Keeping the public knowledgeable about vernal pool ecology and the importance of vernal pools to SGCN and biodiversity is prerequisite to raising awareness of conservation needs and support for action. Providing educational services and opportunities for hands-on experience are key methods to keeping the public interested and active in vernal pool conservation. Together, those actions should help foster public support for vernal pool research, regulatory protections, and conservation initiatives. Products, services, and opportunities may include vernal pool publications, website development, technical support for vernal pool certification, technical support for school studies/programs, coordination of citizen science projects, public presentations, and inclusion of individuals in the NHESP’s biological survey work.
Harvest and Trade Management
See “Law Enforcement” and “Law and Policy” below.
Land and Water Rights Acquisition and Protection
Develop and maintain a list of vernal pools that should be considered priorities in land protection for SGCN. The BioMap project by MassWildlife and The Nature Conservancy prioritized coarse areas statewide for potential land-protection efforts, and some of those areas were based more finely on occurrences of PVPs. In addition, occurrences of confirmed breeding pools of amphibian SGCN were ranked for relative conservation value and used to prioritize specific vernal pools and their associated uplands for land protection. However, additional work will always be needed to better understand local pool-breeding amphibian and invertebrate populations and, therefore, refine existing rankings of vernal pools for continued land acquisition and protection efforts. Some of the “Data Collection and Analysis” actions described above are designed in part to inform land-protection decisions.
Law Enforcement
Continue to implement legal mandates of the Massachusetts Endangered Species Act (M.G.L. c. 131A) and regulations (321 CMR 10.00). The NHESP regulates environmental impacts to vernal pools where they are known to function as habitat for SGCN listed as Endangered, Threatened, or Special Concern pursuant to the Massachusetts Endangered Species Act (hereinafter “MESA-listed SGCN”). Published delineations of “Priority Habitat” for those species (e.g., Blue-spotted Salamander, Jefferson Salamander, Marbled Salamander, Eastern Spadefoot, Blanding’s Turtle, Intricate Fairy Shrimp, Agassiz’s Clam Shrimp, American Clam Shrimp, False Hop Sedge, Tuckerman’s Sedge, Swamp Cottonwood) define specific geographic areas where most types of proposed land, water, or vegetation alterations are required to be reviewed and approved in advance by the NHESP. The review process can involve adjustment of project plans to avoid or minimize impacts to vernal pools and their associated MESA-listed SGCN, or require mitigation of impacts that are deemed unavoidable. The Massachusetts Endangered Species Act also provides for criminal and civil penalties for any unauthorized “take” of MESA-listed SGCN.
Enforce other laws that protect SGCN associated with vernal pools. Hunting regulations (321 CMR 3.05) prohibit disturbance, harassment, or other taking of SGCN associated with vernal pools, such as Blue-spotted Salamander, Jefferson Salamander, Marbled Salamander, Eastern Spadefoot, Northern Leopard Frog, Blanding’s Turtle, and Spotted Turtle.
Continue to provide technical support for implementation of other laws protecting vernal pools and associated SGCN. The NHESP provides technical support to conservation commissions and the Massachusetts Department of Environmental Protection regarding their implementation of state-listed rare species and vernal pool protection provisions of the MWPA.
Law and Policy
Develop or update regulations and policies as necessary to address emerging threats. Needs to adopt new regulations and/or policies may arise as knowledge is gained about climate change, emerging infectious disease, animal trade, and other threats to vernal pool ecology and related SGCN. For example, stronger controls are needed to guard against the introduction and spread of amphibian pathogens and infectious disease, especially with respect to the potential introduction of Bsal to the wild in Massachusetts.
Planning
Develop and maintain lists of vernal pools that should be considered priorities in future biological surveys for SGCN. Discovery of undocumented populations of vernal pool SGCN is a conservation priority. Additional priorities include identification of all vernal pools currently used by a given population (e.g., in a metapopulation of Marbled Salamander) and an evaluation of the relative importance of each pool to the population. Biological survey continues to be a cornerstone of the conservation strategy for vernal pool SGCN, as the data generated are invaluable to informing other types of conservation actions. Identification and prioritization of prospective survey sites is an essential, annual planning activity to maximize survey efficacy.
Develop detailed conservation plans for SGCN associated with vernal pools. Conservation plans are essential blueprints for setting and achieving conservation objectives. Conservation plans should include detailed needs, actions, and schedules specific to each SGCN and include conservation measures for vernal pools that, among other considerations, account for expected impacts of climate change.
Species Reintroduction and Stocking
Conduct species introduction and/or reintroduction projects with vernal pools as release sites. Translocation of vernal pool SGCN to sites within geographic ranges of historic occurrence is a potential conservation strategy in Massachusetts that is still in an experimental phase. One project to reintroduce Eastern Spadefoot to a site on Cape Cod was initiated by conservation partners in 2011, and a replicate project to introduce Eastern Spadefoot to a site in the Connecticut Valley was initiated by MassWildlife in 2015. Both projects involved construction of vernal pools and subsequent introductions of tadpoles and metamorphs to the pool basins. Although both projects were successful in establishing adult populations of Eastern Spadefoot, reproduction and recruitment results have been mixed, and further monitoring work is needed to determine efficacy of the pool construction method for this species. Incidentally, one of the projects has established a new population of Agassiz’s Clam Shrimp, and so a viable pool-construction and stocking method appears to have been identified for that SGCN. A Marbled Salamander reintroduction project was initiated by conservation partners in 2015 and established an adult population after multiple years of releasing larvae to a natural vernal pool. Subsequently, at least one reproduction event was documented through 2024. These experimental projects ultimately aim to identify effective ways to reestablish extirpated populations of pool-breeding SGCN. Thus far, amphibian introduction or stocking seems to be a viable option for reestablishing populations where only the organisms have been lost, but the habitat remains (e.g., as might occur with episodic disease outbreaks). Introductions that rely on vernal pool creation, however, need further investigation.
Restoration & management recommendations
The “Direct Management of Natural Resources” subsection of the Conservation Actions section above provides some restoration and management actions to be undertaken or coordinated by MassWildlife and its partners. However, private landowners are also encouraged to be involved with vernal pool management.
Private landowners whose properties contain vernal pools are mainly encouraged to manage their pools passively. Some general measures include minimizing landscaping, avoiding use of fertilizers and pesticides, and leaving vernal pools undisturbed (i.e., keeping dogs out during the spring, not removing fallen branches or leaf litter, not dumping yard waste or refuse in the basin). However, landowners may also help to maintain the habitat quality of vernal pools and their bordering uplands by removing or controlling non-native trees, shrubs, and vines on the property. If a vernal pool is impaired by prior land use practices (e.g., filling or ditching), landowners may seek potential restoration recommendations from the NHESP.
Additional resources
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