by Bruce Wenning
There are many types of wetlands in our environment, but all of them are declining. Learn more about the special nature of vernal pools, our smallest wetlands, and the habitat requirements of the species that inhabit them. Then find out how the built environment affects vernal pools and what you can do to minimize disruption and damage.
Section 1. Introduction to Wetlands and Vernal Pools
There are many types of wetlands in our environment. Their decline in rural and urban landscapes over the decades has raised concern, awareness and appreciation for their conservation value by people of all ages and walks of life. They are important natural habitats in many of our communities, and all wetlands, whether large or small, are part of our natural heritage.
Raising wetland conservation awareness through education is paramount for understanding the link between the ecological networks and biological processes of wetland plants and animals and the very important need for their continued protection. These important and diverse aquatic and semi-aquatic life forms depend directly on the local and regional hydrology (the movement of water in relation to land) where wetlands occur.
Changing Attitudes and Wetland Decline
Most of us working in the landscape have come across mixed attitudes concerning wetlands. And in general, we know little about what distinguishes one wetland type from another. Years ago, I heard home builders and land developers disparage wetlands as a “mosquito nuisance” or “wasteland” or “cheap land that could be developed.” Now, more people view wetlands as components of the local and regional ecosystem with the general consensus being that wetlands are important and “should not be disturbed.” Attitudes are changing, but the United States is still losing valuable wetlands at an alarming rate!
Freshwater wetlands are generally defined as areas of transitional ecosystems between upland (terrestrial) and bottomland (aquatic) where water is present for all or part of the growing season (Hobson, Barclay and Broderick, 1993). Whether a wetland is a wet meadow, marsh, swamp, forested wetland, bog, lake, pond, river, stream, or vernal pool, these and other more defined wetland types provide habitat for a diversity of plant and animal species: some site specific, some not (Hobson et al, 1993; Colburn, 2004).
Hobson et al (1993) reported that the total estimated wetland acreage in the U.S. was 127 million acres. By the late 1940s, wetland acreage dropped to 45 million acres and by the 1980s an annual loss of 300,000 acres was reported (Hobson et al, 1993). Wetland conservationists and land developers have had a history of land values disagreement for too long, particularly regarding our smallest and most cryptic wetlands, vernal pools.
All wetland types or classifications need better protection under the current federal, state, and local environmental laws, rules and regulations. Legislation needs to be more aggressive at embracing and instituting specific science based reasons for strengthening wetland protection laws beyond what currently exists in most states, particularly for vernal pools which are largely overlooked by the general population (Colburn, 2004).
What are vernal pools?
Vernal pools are small bodies of shallow water that contain no fish. They are termed temporary bodies of water because they fill up land depressions in the spring and dry down by summer, limiting the timeframe of use by specific water dependent animals. Their temporary nature precludes supporting fish. The hydrology of vernal pools distinguishes them from permanent water bodies like lakes and ponds since the water flow into vernal pools is due mostly to the movement of the spring time groundwater table, overland runoff from precipitation and flooding from overflow of nearby water bodies; by summer the water is gone – or almost gone (Colburn, 2004). These biologically unique, fishless water bodies are found in many types of woodlands and forests throughout the glaciated northeast (Colburn, 2004). They are considered the “smaller wetlands” in our landscapes.
Why are vernal pools important?
Vernal pools serve as critical environments for an assortment of biologically specialized aquatic and semi-aquatic life forms which include vertebrates, invertebrates, and plants. They serve as important habitat in the life cycles of several obligate and facultative vernal pool species.
Facultative vernal pool species may or may not use the vernal pool for the completion of their life cycles. If a stream, bog, pond or lake is nearby, they will use those water bodies instead, or in addition to, a vernal pool. They are not dependent on vernal pools to complete their life cycles. Some examples of facultative vernal pool species include the Red-spotted Newt (Notophthalmus viridescens), American Toad (Bufo species), Spring Peeper (Hyla crucifer), Fingernail Clams (Sphaerium species), etc. Snapping Turtle (Chelydra serpentina), and several insect caddisfly species are also included in this group.
On the other hand, obligate vernal pool species are dependent on using the pool. These species have evolved accelerated reproductive strategies that allow them to use vernal pools more effectively than permanent water bodies for mating and egg laying activities. In the glaciated northeast, four mole salamanders, one wood frog, and one fairy shrimp group use vernal pools for reproduction (Colburn, 2004). There are many fewer vernal pool obligate species than facultative species. The ecology and biology of the obligate species is what drives vernal pool conservation laws and protection strategies; they are vernal pool indicator species.
Section 1 – Vernal Pool Surroundings and Inhabitants
Vernal Pool Uplands
What most people don’t know or understand is that many existing vernal pools have lost much of their important surrounding woodland or upland areas, often referred to as life zones, which are essential for pool amphibian life cycle completion. Colburn borrows the term, “life zone” from University of Missouri herpetologist, Raymond Semlitsch. In this case, the life zone includes the minimum area necessary for protection and maturation of obligate vernal pool amphibian juveniles and adults (Colburn, 2004) and includes the vernal pool. All of the life zone includes habitat critical to obligate species (Colburn, 2004).
Table 1, illustrates some of the major ecological or life history needs determined to be essential for the aquatic reproductive phase and associated land-dwelling phase for obligate vernal pool species. Though the fairy shrimp spends its entire life time in the pool, wet and dry, the woodland area surrounding the pool is just as important as the pool for amphibians. The salamanders listed are all mole salamanders so named for their tendency to hide in upland leaf litter, rock crevices, stump holes, moss, and small abandoned rodent holes for protection from predators and for conservation of body moisture during the day (Colburn, 2004).
Table 1. An abbreviated summary of the life cycle requirements for obligate vernal pool species (data compiled from Colburn, 2004).
|Obligate vernal pool species||Uses vernal pool for||Site fidelity: uses the same pool year after year||Life zone distances of juveniles and adults from natal pool to uplands||A long adult life span ( a reproductive strategy for breeding more than one season)||Hybridizes with closely related species|
|Spotted Salamander Ambystoma maculatum||Courtship / breeding / egg-laying and larval development||Yes, (>95% of the time)||Up to 650+ feet; distances vary||18+ years||No|
|Jefferson’s Salamander A. jeffersonianum||Same as above||Yes, (> 90% of the time)||Varies greatly; close to pool but up to 1 mile for some||10+ years||Yes, with A. laterale|
|Blue-spotted salamander A. laterale||Same as above||Same as above||Same as above||Same as above||Yes, with A. jeffersonianum|
|Marbled Salamander A. opacum||Same as above, but breed in late summer or early fall||Same as above||Up to 1475 feet||9 to 10 years||No|
|Wood Frog Rana sylvatica||Courtship / breeding / egg-laying and larval development||Yes, (100% of the time after the first year)||Up to 2,625 feet||3 to 5 years||No|
|Fairy Shrimp Eubranchipus species||Entire life cycle||Yes. Never leaves the pool||Not applicable||?||No|
The Limits of Buffer Zone Protection
In Massachusetts, vernal pools are legally recognized only if they have been certified by the Massachusetts Natural Heritage and Endangered Species Vernal Pool Program. Certified: A Citizen’s Step-by-Step Guide To Protecting Vernal Pools” is a Mass Audubon publication that guides citizens through the certification process.
Protections offered by certification vary:
- Any pool shown to meet the hydrologic requirements to provide vernal pool habitat can be certified.
- Under the wetlands protection act regulations, the 100 foot buffer zone around a vernal pool is the legal protection zone as long as the pool is surrounded by or is part of a wetland resource area that extends at least 100 feet from the edge of the pool. If the vernal pool is surrounded by floodplain or a wetland resource area that extends less than 100 feet beyond the pool, the buffer zone extends only as far as the wetland resource area.
- If the vernal pool is not lying in a protected floodplain or wetland resource area, but is in an isolated upland area and meets the regulatory definition of Isolated Land Subject to Flooding, the pool is not eligible for 100 foot buffer zone protection because of its isolation. Only the pool water body is protected. (Colburn, 2004).
The buffer zones awarded by certification are not big enough to accommodate migratory obligate pool amphibian life cycles. In fact, because of the limited size of the law mandated buffer zone, a vernal pool’s ecological habitat or life zone could occupy private and public land not suitable for amphibian life, including parking lots, athletic fields, chemically treated lawns and gardens, or new construction. Refer to Figure 1.
Obligate vernal pool species evolved over time to take advantage of fish-devoid, temporary waters and undisturbed uplands that were much more numerous in the landscape when the Pilgrims landed than they are now. It’s unreasonable to expect that their innate aquatic phase, including their unique reproductive physiology and behaviors coupled with their upland juvenile and adult phase requirements, will change to accommodate current wetland law. Instead, we need to recognize that the Massachusetts 100 foot buffer zone law does not provide adequate protection for vernal pool conservation habitat, and that, in fact, its limited size is actually contributing to the decline of obligate salamander species and wood frog in many areas. For life cycle completion, these amphibians need life zones that include protected (shaded), productive, and undisturbed wooded uplands much larger than the current 100 foot buffer zone provides (Colburn, 2004).
Biological Determination of Vernal Pool Inhabitants
Unfortunately, the life zones of mole salamanders and wood frogs are biologically determined by their innate migratory behavior patterns and not by wetland protection law. An adequate life zone is critical for obligate vernal pool species to feed, mature into reproductive adults, and return to their natal (birth) pool for breeding over several years. All three salamanders found in vernal pools spend the shortest part of their life cycle (months) in the pool as eggs and larvae and the longest (years) dwelling on land as juveniles and adults. Expanding buffer zones to a minimum of 750 feet as suggested by Morgan and Calhoun (2012) would aid migratory travel and keep life zone habitat undisturbed.
Colburn (2004, p. 174) describes an amphibian’s return to the natal (birth) pool as a behavior that shows a “high degree of site fidelity.” Petranka (1998), discussing the Spotted salamander’s breeding behavior states that the natal pool odors (an olfaction characteristic) directs that salamander back to its natal pool for breeding. There is a high possibility that natal pool odor detection is responsible for mostly directing these obligates back to their natal pools. This is why upland life, which is measured in years, is as important to life cycle completion for these obligate animals as the breeding (natal) pool. Without maturing into long-lived reproducing adults in their uplands or life zones, they cannot return to their natal pools for reproduction activity and without their natal pools to reproduce they will become eliminated from that area. Taking away or degrading valuable uplands from these obligate species is like taking away oak trees from squirrels or milkweed plants from monarch butterflies.
Salamanders, toads, and frogs are amphibians
Amphibians are excellent biological indicators of environmental stress and their declining populations can be partially attributed to various land use changes affecting their survival ecology. Stresses include the destruction and fragmentation of critical habitat due mostly to the vast expansion of housing and commercial land development with associated road networks, and various agriculture and forestry logging practices. These human induced land use changes have destroyed vital wetland habitats including the filling in and siltation of vernal pool water bodies (Colburn, 2004).
Reader’s note: for a more in depth description of vernal pool organisms, their biology, interrelationships, natural threats and threats caused by humans the reader is referred to Colburn (2004).
Section 2 – Where Vernal Pool and Built Environment Meet
Conflicts Between Vernal Pool Life Zones and the Built Environment
Built environment land use and maintenance activities contribute greatly to vernal pool life zone threats like soil erosion, runoff, and pool sedimentation. Compacted soils, parking lots, roads and cleared land all alter vernal pool hydrology and threaten amphibians as all life cycle states Introducing water impervious surfaces and removing vegetation within several hundred feet of a pool contributes to runoff events through the life zone to the pool. More frequent and larger runoff water may also carry sediments, pollution, and seeds of common exotic invasive plants into the pool with every big rain storm. Additionally, the pool risks becoming deeper and wider resulting in a longer than expected dry down phase which affects the sequence and timing of vernal pool fauna and associated predator-prey relationships (Colburn, 2004). The portion of vernal pool uplands affected by or lost to development determines the survival of the vernal pool and the life dependent on it.
As ecological landscaping professionals, we always try to reduce the magnitude of native soil and vegetation destruction. Nevertheless, construction of new homes and commercial buildings that encroach into vernal pool wetlands result in lost native vegetation, compacted soils, newly installed garden beds and lawns that require maintenance (often with inorganic fertilizers and non-organic pest control chemicals).
Effects of Construction Activities on the Life Zone
The problems posed by urban/suburban development to life zone soils are several: an altered and unnatural soil texture and structure; decreased water drainage, aeration, and water holding capacity; an increase in soil pH, and soil compaction of the subsoil with accompanying importation of soil around newly constructed buildings, parking lots, roads and recreation areas (Craul, 1994; Hammitt and Cole, 1987). The removal of organic matter and shade-casting trees is also problematic (Harris, Clark and Matheny, 2004). These soil and vegetation problems contribute to poor growth of existing landscape plants and increase the potential for siltation runoff toward vernal pool areas from lawn and garden irrigation and rain events. Soils on building and road construction sites are highly compacted to strengthen the soil for providing a stable building and road site base and are not designed for growing landscape plants (Harris et al, 2004: Craul, 1994; Randrup, 1998; Coder, 1998).
During construction, heavy equipment crushes the soil, pushing soil oxygen out of soil macropores. With macropore collapse or reduction the resulting soil eventually gets filled with water, depleting available soil oxygen which limits plant root growth. Macropore space collapse reduces the water holding capacity of soil, decreasing soil water drainage and also creates a hardened barrier to root penetration. As a result, root growth is severely limited due to the fact that plant root tips can only grow into macropores of the same or larger diameter with adequate soil oxygen (Craul, 1994).
Because soil compaction restricts the water and air spaces needed for proper plant root growth and expansion and because alleviating construction site soil compaction is difficult (Randrup, 1998), it is best to determine plan and design specifications that limit soil compaction prior to planting trees, and lawns, thus encouraging long-term success (Randrup, 1998). You want plant installation to be successful the first time to reduce the need for plant replacement and additional soil disruption and compaction that could negatively impact the life zone land where vernal pool obligate amphibians hide, roam, and feed.
Once construction site soil compaction has occurred, the condition can be regarded as permanent (Randrup, 1998). The natural soil structure has been damaged and little correction of this problem will be alleviated by natural freeze-thaw cycles of late winter and early spring (Randrup, 1998). All soil compaction contributes to water running over the hardened soil and washing away adjacent non-compacted soils. You especially want to minimize compaction in or near vernal pool life zones because it destroys amphibian hiding places and increases the threat of direct siltation of the pool over time.
Organic Material Removal
During construction activities, leaf litter that normally occurs in life zone areas is often partially or completely eliminated for aesthetic appeal and/or weed geotextile barriers are installed in perennial beds to control weed growth. Removing leaf litter disrupts the natural organic matter breakdown that supplies nutrients to the soil (Craul, 1994). As a result, the soil decomposer populations decrease their activity and the natural generation of soil nutrients for plant growth and soil water infiltration is greatly hindered. The variety of microarthropod populations decreases as well. Microarthropods are part of the decomposer community and serve as food for vernal pool amphibians in the life zone. If an inorganic fertility program is also introduced, then the natural decomposer organisms and newly installed landscape plants may be subjected to an increase in susceptibility to soil pH reactions, over fertility issues, an increase in plant pest incidents, and soil water runoff events.
Natural Debris removal
Obligate vernal pool amphibians need naturally occurring rocks, stones, soil crevices, abandoned rodent tunnels and holes, and leaf litter (including fallen branches and sticks) to serve as hiding and resting places for juveniles and adults in their life zone habitats (Colburn, 2004; Petranka, 1998). Amphibians need moist environments, and when residing in their uplands or life zones, they frequently hide under natural objects during the daylight hours to conserve moisture (Colburn, 2004). Heavy construction equipment, land clearing operations, and activity associated with the removal of soil organic matter collapse the crevices and the abandoned rodent tunnels and holes. Likewise, removal of stumps, rotting logs, and low growing vegetation that amphibians use for cover, destroys habitat for future generations and possibly kills them in the process. Any type of life zone habitat destruction will threaten the existence of these secretive creatures.
The Effects of Recreational Activities in the Life Zone
Soil compaction and vegetation trampling are major issues caused by human recreational and landscape maintenance activities in vernal pool life zones. Hammitt and Cole (1987), cover the negative interrelationships of human foot traffic and overland recreational vehicle (ORV) use on soil and ground cover vegetation in wilderness recreation areas of the western U.S. Their findings can apply to the glaciated northeast where construction development occurs either near or in vernal pool life zones.
The action of unrestricted foot and vehicle traffic on unprotected woodland life zone ground cover and bare soil areas will undoubtedly lead to widespread soil compaction and plant damage including the collapse of abandoned rodent tunnels and burrows used as homes and hiding places for obligate pool amphibians during their juvenile and adult life cycle stages. Trampling causes plant cover deterioration, soil compaction and weed invasion which, over time, leads to a reduction in native plant cover composition (see Figure 2). Native plant germination, establishment, growth, and reproductive capacity are all greatly altered as a result of the effects of soil compaction and plant cover trampling (Hammitt and Cole, 1987).
For woodlands that are located in the vernal pool life zone area, recreational activates such as running, walking, and dog walking should be confined to a single trail. Trails should be wood chipped to curtail erosion. Multiple trail use or creation should be discouraged. Signage should be posted with rules for conservation of vernal pool habitat near private property and parking areas. For example, Figure 1 shows too many walking trails near housing. Signage is important to keep people on designated paths and discourage users from creating new paths (Hammitt and Cole, 1987). Signage could declare the area as a vernal pool sanctuary and list the amphibians living in the area with accompanying photographs so faces are put to the names; however, these amphibians are mostly nocturnal so they would rarely been seen during the day. As ecological landscaping professionals, it would be a positive volunteer conservation effort to consult with residents and the proper officials to do this.
Winter activity in the life zone also causes problems. Snowmobile use during winter should be banned in the life zone because these machines crush small mammal populations that tunnel under snow looking for food and snow compaction destroys their tunnels (Hammitt and Cole, 1987). Small mammals (rodents) are important associates to vernal pool life zones during the growing season because they create holes and tunnels the obligate amphibians use as hiding places.
Trampling damage can occur rapidly and, if allowed to continue, increases site susceptibility to widespread soil erosion which could lead to vernal pool siltation. This is especially true if new trails are created through the woodland life zone and around the shore line of the vernal pool. The more trails created, the more fragmentation occurs. The possible risk of siltation impact on vernal pool water depth and/or water quality can produce pronounced deviations in vernal pool hydrology, obligate species biology, and water chemistry (Colburn, 2004; Hammitt and Cole, 1987). If you are doing any landscaping project, whether it is a design or maintenance, in or near a vernal pool life zone, it will be up to you to introduce protective (conservation) measures to stop or slow down any type of life zone degradation. Figure 2 will help you develop strategies for reducing such degradation.
Section 3 – Minimizing Damage to Vernal Pools
Construction Site Planning in the Interface Between Life Zone and Built Environment
Effective vernal pool conservation practices in the life zone:built environment interface includes well-planned construction activities to alleviate soil compaction as well as the addition of amphibian-friendly post construction activities such as organic lawn and garden management. We need to create and maintain the life zone as being conducive to a healthy vernal pool amphibian habitat.
The following strategies can help with management of soil compaction on new construction sites.
Define Use Zones: For new construction projects, developing an inventory of equipment, worker, and materials storage needs, and any additional resources required before construction begins will help plan for better timing and sequencing of project developments prior to laying out roads, paths, storage areas for heavy equipment and building materials, dividing up building lots and positioning buildings (Perry, 1998). Randrup (1998) recommends that construction sites should plan and practice work site zoning. He describes using three zones on work sites with the goal of restricting building activities that cause soil compaction to specific areas:
- Zone 1 is strictly for heavy equipment operation and building construction
- Zone 2 allows for light work or work with little to no heavy equipment
- Zone 3 is off limits to all construction activities and associated traffic and is zoned to protect trees, shrubs, lawns, and gardens whether existing or to be installed on the site later
The use of appropriate signage and fencing helps with designating these zones.
Use Mulch: Lichter and Lindsey (1994) also recommend the use of fencing and applying soil protective mulches: six inches of woody mulch or four inches of gravel to reduce vehicle soil compaction in unfenced areas. Poor soil water infiltration as a result of soil compaction acts like rain on a house roof or asphalt parking lot in a heavy rainstorm. When soil compaction precautions are not deployed, soil erosion increases from the impervious areas towards or in vernal pool life zones. Site planners, architects, and engineers should all share information about managing soil compaction and water runoff from the construction site before major investments are made in determining road layout, parking lot designs, subdivision configurations, and proposed building site excavation (Perry, 1998).
Use Load-bearing Soil Mixes: To help alleviate construction site soil compaction and reduce potential erosion problems especially in vernal pool life zones, Stal and Rolf (1998) recommend that parking lots and planting sites in parking lots have a specially designed loadbearing soil that uses a combination of crushed rock mixed with soil. The surface should be compacted enough to carry light traffic while remaining permeable to air and water. This created soil type could help reduce soil erosion and polluted runoff towards vernal pools and associated life zones. Loadbearing soil mixes provide better drainage and more root zone oxygen for plant growth (post construction) than compacted soils. Test trials of loadbearing soils in Scandinavia, Holland and England have proven successful (Stal and Rolf, 1998).
Use Pervious Parking Lot and Foot Path Products: There are specialized water pervious paving compounds made of concrete or rubber that are designed to intercept precipitation into the ground and support vehicle and/or pedestrian foot traffic at the same time. Water pervious concrete pavers and mixes allow water to flow through interconnected voids that are present in these materials thus reducing precipitation runoff and preventing or reducing precipitation caused soil compaction (Garber, 2010). The eco-friendly concrete products allow rain and snow melt to enter the soil slowly, preventing pooling (puddles) and soil erosion adjacent to landscaped soils near driveways, parking lots, and pathways. The best candidates for water pervious concrete products are driveways and parking lots (Garber, 2010). Use of these products would be particularly beneficial for new housing developments and commercial complexes in vernal pool life zones.
Use Water or Rain Gardens: Water or rain gardens can be constructed in parking lot islands and edges to help catch runoff. Do not construct storm water detention ponds or biofiltration ponds for catching storm water runoff within the vernal pool life zone. Constructed gardens have an altered water chemistry, higher water temperatures, more pollutants, and a lack of effective tree cover to protect amphibians from the harshness of the sun. Breeding amphibians may also become confused by constructed ponds and use them for reproduction instead of their natal pools. (Calhoun and Klemons, 2002).
Encourage Vernal Pool Conservation as Part of Your Process
Follow these three easy steps to encourage conservation of vernal pools.
First, check for the presence of a vernal pool. Checking for this type of wetland, on your client’s property or other property adjacent to it, should be added to your landscaping practices checklist. Ask your client if a wetland exists. If you are working on a property that has adjacent woodlands, check that area in spring for vernal pool water bodies. In summer and fall look for muddy depressions in the landscape that could fill and hold water. These are signs of a vernal pool.. From a distance, vernal pool habitat is visually harder to detect than streams or ponds. Get in the woodland and walk around.
Second, find out about protecting the pool. If you find a vernal, check with your local conservation commission and/or the Massachusetts Natural Heritage and Endangered Species Vernal Pool Program to determine if the pool has been certified or, if not, how you and your client can certify it. Vernal pool certification is essential for protecting this type of wetland. Without proper certification, the vernal pool has little, if any, legal rights of protection from building development and other major land use changes.
Third, identify the pool perimeter. Mark or use wooden stakes to identify the pool perimeter. You may need to identify the perimeter for permanent signage that cautions people not to disturb vernal pool wildlife. A suggested list of disturbances to keep in mind to protect the vernal pool from include dumping green waste, soil, household trash, and garbage; collection of plant and vernal pool organisms; campfires and other camping activities, use of Overland Recreational Vehicles (ORV); dog walking; cutting down trees and brush; and removing rocks, leaf litter, and woody debris (MCCS, 2014; Hammitt and Cole, 1987; Colburn, 2004). Depending on the vernal pool life zone location and associated infrastructure you may think of other disturbances that could be added to this list.
Additional Management Practices in the Life Zone:Built Environment Interface
Your design goals and decisions, as well as the land management practices that you provide for your client can allow you to be a direct contributor to vernal pool conservation on that property and in that community. Vernal pool habitats are part of our natural heritage; talk about them.
If you are currently maintaining a property in a vernal pool upland area (life zone), you can perform the following ecological landscaping practices as an addition to your own personal, voluntary protection measures for these vital wetlands.
- Do not cut down trees, shrubs, or grassy meadow areas that do not directly compete with infrastructure safety issues, buildings, roads, and parking lot operations. Woody vegetation provides the needed shade and accompanying cool and moist microhabitat that trees and shrubs provide. Unprotected or bare soil heats up quicker and stays hot longer during exposure to direct rays of sunlight. Germinating life zone vegetation is at an increased risk of root dieback due to harsh sunlight and accompanying drought conditions of the exposed area (Graves, 1998). If you discover a vernal pool close by, do not alter or remove the shore line vegetation or any native vegetation in the surrounding area. Calhoun and Klemons (2002) suggest that 75% tree canopy cover should be maintained within the 100 foot buffer zone and at least 50% canopy tree cover be maintained in the 100 to 400 foot life zone.
- Do not remove leaf litter and coarse woody debris off of the life zone floor. This kind of non-living ground cover is part of the decomposer food web and also provides protection to the obligate pool amphibians as they feed, roam, and hide. Do not remove boulders and rocks either. They too, serve as hiding places for amphibians (Colburn, 2004; MCCS, 2014; Calhoun and Klemons, 2002).
- Do not fill the vernal pool basin with additional water from flooded cellars, clogged storm drains, flooded parking lots, and above ground or below ground swimming pools at any time of the year. These actions negatively affect pool water temperature, chemistry, natural hydrology cycles, and pool organism life cycle stages, and they increase pool siltation (Morgan and Calhoun, 2012; MCCS, 2014; Colburn, 2004; Calhoun and Klemons, 2002).
- Do not use the dry pool phase for human generated trash or green waste refuse disposal.
- Do not use the adjacent wooded portion of an existing life zone as an extension to your property for recreational activities, such as camping, ORV use, and individual or group athletic activities. These activities compact soil, degrade leaf litter and living ground cover, crush amphibian hiding places (abandoned rodent holes, rotten root channels, leaf and stick covered soil depressions, etc.) and displace surviving salamanders and wood frogs to more inhospitable habitat farther from their natal pools. You could actually run over or step on a hiding amphibian and not know it!
- Do not use inorganic lawn and garden fertilizers or insecticides, fungicides, and herbicides. Inorganic fertilizers may irritate the sensitive skin of the amphibians and they also reduce or repel soil arthropod populations that work in concert with beneficial soil microbes to break down organic matter as part of the decomposing process. Many soil arthropods are food for these amphibians. Practice only organic lawn and garden care in these life zone areas. Several trace insecticides and herbicides have been detected in vernal pools when such pest control compounds have been used close to vernal pool water bodies (Battaglin, Rice, Focazio, Salmon, and Barry, 2009).In fact, Battaglin et al (2009) states that several weed control compounds, including herbicides containing glyphosate and triclopyr, have been detected in various amounts in vernal pools located in selected parks and wildlife refuges in the U. S. According to Battaglin et al (2009), these herbicidal compounds were used to control common agricultural weeds and invasive plants and measurable trace amounts were transported to vernal pools by way of surface runoff and shallow groundwater flow. These detected herbicidal compounds pose a threat to disrupting amphibian development and other organism life cycle stages in vernal pools (Battaglin et al, 2009).For ecological landscaping professionals, this information highlights the need to use non-chemical weed control practices in life zones that are in the built environment. When it comes to vernal pool conservation, stick with organic pest controls.
- Use appropriate erosion control products as needed. Coir products used for erosion control are the best for wetland protection and can be applied to vernal pool protection strategies when and where applicable. According to Jonathan Gawrys, Restoration Manager, SumCo, Salem, MA, strategic placement/installation of site-specific coir log products in the threatened vernal pool uplands would curtail unnecessary runoff. Before such an action takes place, Gawrys suggests that all contractors consult with the proper wetland legal authorities and a vernal pool expert. John Engwer, ecological restorationist and developer of the FilterMittTM in Wrentham, MA, stresses that runoff from point sources of pollution like parking lots, roads, and chemically treated horticultural projects would benefit from erosion control products that filtered the runoff more efficiently, effectively purifying before it enters a specific wetland. He stresses that on site coir products that are designed for pollution filtering are superior to hay bales and silt fences.
- Use non-chemical means for invasive removal. When you are requested to remove exotic invasive woody plants from a life zone area, you should pull by hand or wrench plants out of the ground using a puller device. Alternatively, practice repeated cutting. Woody exotic invasive shrubs and vines are shade tolerant and can grow successfully with native plants in the shaded environment of vernal pool habitats. Exotic invasive woody shrubs could create a more competitive environment for vernal pool specific native vegetation. The best time for removal would be from November to February, and work on only a small area each year so as to not compact the site and risk crushing hiding amphibians.
- Increase shade within the life zone. For life zones that run into private property, particularly property with lawns and little to no tree cover, consider planting trees in selected areas in relation to the wooded portion of the life zone. Plant trees or shrubs in clusters or a zigzag row to create an extended shade corridor from the tree area of the life zone into the lawn area of the residential area. Extending the shaded area into the built environment or altered life zone replaces shade lost due to lawn installation.Shade-casting woodland corridors of undeveloped woodland parcels are useful between closely located vernal pools so that pool amphibians can mate with conspecifics (same species of a different pool), increasing genetic exchange, and help decrease predation pressure (Colburn, 2004).
- Consider making life zone enhancement to mitigate the effects of climate change. This involves unorthodox but safe techniques to replenish microhabitat cover and moisture and temperature regimes in an effort to conserve vernal pool amphibians and other woodland amphibians in their natural habitats that have been degraded (Parks, 2011). Consult a vernal pool expert about this kind of restoration. These ideas come from aquatic ecologists that work with amphibian conservation projects from all over the world. Deanna Olson, research ecologist at the Pacific Northwest Research Station, USDA Forest Service, Corvallis, OR, and colleagues published an article on this kind of research about conserving amphibians and their habitats from the damages of climate change. The following links may be helpful: www.parcplace.org, http://www.fs.fed.us/pnw/lwm/aem/docs/olson/2011_shoo_et_al_j_appl_ecol.pdf
Vernal Pool Websites:
Erosion control and Storm water management services and products:
Phase II Storm Water Products, Wrentham, Massachusetts. info@phaseIIstormwaterproducts.com, 508-384-1984
SumCo ECO-CONTRACTING, Salem, Mass. 978-744-1515
Filtrexx Northeast Systems, Goffstown, N.H. 603-621-9800
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About the Author
Bruce Wenning is a horticulturist at The Country Club, Brookline, MA. He was the grounds manager at Habitat, Mass Audubon’s sanctuary in Belmont, for 15 years. During that time Bruce occasionally worked for Betsy Colburn, Mass Audubon’s aquatic ecologist, assisting her and her staff with vernal pool insect identification and some field work. Betsy currently is the aquatic ecologist at the Harvard Forest, Petersham, MA. Her text book on vernal pool natural history and conservation is listed above in the Literature Cited.