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Natural Communities
Content of Natural Community Descriptions Natural Community Descriptions
The intention of the SuAsCo Biodiversity Plan is to include good examples of all the natural community types found in the SuAsCo Watershed within Biodiversity Sites. In this way the whole range of biodiversity including micro-organisms, lichens, fungi, plants, and animals is protected in functioning ecosystems. This section describes the natural communities and lists some of the sites with the best representative samples. The intention of this section is to help people know what lives in the different communities and to encourage additional surveys.
Natural communities include both plants and animals which live together in a particular environment. “It is the characteristic combination of species which make up the identity of a given community.” (Chris Leahy, The Nature of Massachusetts). A natural community is a result of several influences:
Bedrock geology determines the type of underlying rock and, therefore, whether the soils are acidic or sweet. Limestone veins and associated subacid or alkaline soils provide patches of unusual plants in the SuAsCo Watershed. The hardness of the rock also affects the topography. Hard rocks withstood the erosive forces of the glaciers. Differences in the structure of the underlying bedrock also has an influence on the hydrology. Fractured rocks may be sources of springs, unusual landscape features which may harbor rare plants and animals. Glaciers affected the topography, hydrology, and soils that are key environmental factors. Glacial till on drumlins has poorly drained soils and perched water tables. Glacial outwash plains and kame terraces have very well drained soils. Land use history, such as row cropping, grazing, or timbering, can affect plant associations, particularly the herbaceous species. The development of the forest type may be altered forever by how a farmer used his land 200 years ago. Chance events, such as hurricanes, floods, and insect outbreaks, affect the plant life depending on the intensity, frequency, and duration of the event. For instance, floodplain forests have species, such as silver maples, that are tolerant of deep waters and scouring. Small chance events also can affect populations. Small populations of a plant species may be eliminated from a site by browsing deer or off-road vehicle use. What may colonize an abandoned field depends in part on what seed sources are available. A prolific year of pine seed will result in a pine stand, while a good acorn year may result in an oak forest gaining a root hold in a given area. The intrinsic adaptability of plants and animals to various conditions over time determines what communities are present today. Plants in particular are the “expression” of the place. Aquatic microinvertebrates populations are also very site specific.
Natural communities are usually described based on the underlying environmental setting (topography, soils, and hydrology) and the composition and structure of plants, i.e., what are the most common plants and how they are arranged. Plants are used because they are easy to inventory compared to animals and all animals rely on plants for their support. Some natural communities are quite clearly delineated, as in the case of kettlehole level bogs, which have distinct geomorphologic settings--kettleholes formed by blocks of ice left by the glaciers--and very specific plants, such as pitcher plants. Other communities are much less distinct, such as the forest types found in eastern Massachusetts. Mixed oak/white pine forests grow in a variety of conditions with different species of trees in different proportions. It is not surprising, therefore, that classification of community types is more of an art than a strict science and that finding examples of them is not easy. Content of Natural Community Descriptions
Community descriptions are included here to: 1. Increase understanding of what lives in the SuAsCo Watershed. 2. Facilitate inventories of known sites. 3. Prioritize conservation targets. 4. Encourage searches for new sites for community types. 5. Stimulate additional research of natural communities in the SuAsCo Watershed.
The following descriptions are based on the Massachusetts Natural Heritage and Endangered Species Program’s (NHESP) recent draft publication Classification of Natural Communities of Massachusetts. This publication describes in detail most upland and wetland community types, but does not include aquatic communities. The community descriptions have often been shortened, merged, or otherwise adapted to serve the purposes of this report. For complete information, see the Natural Heritage Program publication.
The descriptions include the following information: 1. General description lists the typical species of trees, shrubs, and herbs. This species list is organized by layers: canopy, subcanopy, tall shrub/shrub, herbaceous/groundcover, and by the relative abundance: dominant, common, frequent, occasional, and rare. Underlying geology and soils are mentioned as geomorphology determines what can grow in a particular place. The vegetation description can aid in finding and inventorying representative community types. 2. Associated species includes common and rare animals which regularly use the community type. Some of these are Focal Species. Animals are an integral part of the community and knowing what animals live in a place encourages public support and guides stewardship goals. 3. What to look for highlights what features should be inventoried and protected within a site. These points also can be used to prioritize protection of similar communities. 4. Threats indicate what might harm the quality of a particular community. 5. Stewardship suggests some ways to protect the values of a community. More information will be provided in the stewardship section. 6. Examples list Biodiversity Sites where the community may be found. Not all the possible or even likely community types were found in the SuAsCo Watershed during this project for several reasons. Many of the NHESP descriptions are based on surveys in other parts of the state and may not apply precisely here. This is especially true of the floodplain communities that are such an important feature of the Sudbury and Concord Rivers. Furthermore, many of our communities have been degraded and have lost key defining components. For instance, our bogs no longer contain orchids and several of the ericaceous plants described in old floras. In addition, there was time only for limited inventory work. Color infra-red aerial photographs that can help target searches were available only for certain parts of the watershed and site visits were limited to only a couple of hours. Finally, plant communities are rarely distinct entities. There are many variations on the theme and the boundaries often blend to form a mosaic of community types. Even so, the proposed Biodiversity Sites encompass 21 natural communities in the SuAsCo Watershed.
Natural Community Descriptions White pine/oak forest: This is the predominant forest of the SuAsCo watershed. It grades into oak/hemlock/white pine forest, oak forest, and transitional forest communities described by NHESP. The typical SuAsCo forest is dominated by white pine, mostly red and white oaks, with red maple, black birch, and black cherry in various proportions. White ash, American beech, pignut hickory, and hemlock also are present. Shrubs include typically lowbush and highbush blueberries, black huckleberry, maple-leaved and witherod viburnums, witch-hazel, and hazelnuts. American chestnut sprouts can be frequent. Herbs vary but usually include Canada mayflower, wild sarsaparilla, star flower, and occasionally spring ephemerals such as rue anemone, trout lily, and wild oats. Acid loving plants such as wintergreen, partridgeberry, pipsissewa, pink lady’s-slipper, and cow-wheat are typical in small patches. Clubmosses and various ferns, such as hayscented, New York, and wood fern, are scattered through the understory. These forests are frequently found on glacial till soils of drumlins and moraines in the eastern part of the watershed. Associated species: No species are restricted to this forest type. Small mammals include white-footed mice, short-tailed shrews, red-backed voles, chipmunks, and gray and red squirrels. Southern flying squirrels are present but due to their nocturnal nature are usually not observed. Small rodents in particular are excellent prey species for larger mammals and birds. Birds that nest in larger forests include eastern wood-peewees, great crested fly-catchers, red-eyed vireos, blue-headed (formerly solitary) vireos, brown creepers, ovenbirds, veerys, and wood thrushes. More unusual nesting species are scarlet tanagers, black-throated green warblers, and hermit thrushes (see Focal Species). Several hawks (Cooper’s, red-tailed, and goshawk) and owls (barred and screech) nest and hunt in these forests. Woodpeckers are keystone species in that they create the holes for many of the small birds and animals to nest and rest in. Pileated woodpeckers are particularly attracted to large trees. Red-backed salamanders and red-spotted newts (red efts) live in the humus and logs on the forest floor. Box turtles are denizens of forests along with northern red-belly snakes, northern ring-neck snakes, and northern black racers. What to look for: A good quality forest has several elements: a diversity of characteristic species; lack of or low amounts of exotics such as buckthorn or cowbirds; presence of well developed shrub and herbaceous layers which provide a variety of habitats, particularly for birds; and large trees with trunks greater than 18-24” diameter at breast height (DBH) that serve as denning sites for mammals and nesting sites for owls and hawks. Dead standing trees (snags) and downed logs and limbs provide habitat for a variety of moss, fungi, rodent, and amphibian species. Patches of light from canopy trees that have fallen add structural and species variety. Large tracts of forest--at least 500 acres, preferably over 1000 acres--can support a combination of interior birds (see Focal Species). Rock outcrops, stands of hemlocks, seeps, and water sources all provide habitat for different species. Areas with different land-use histories such as farming, grazing, or woodlot management affect the degree of soil disturbance and the presence of different plants over the long term. Rich pockets with mostly ash, sugar maple, basswood, trilliums, snakeroot, baneberry, bloodroot, silvery spleenwort, and maidenhair fern are rare and should be protected. Limestone outcrop areas support an usual mix of wildflowers and ferns as well. Examples of these richer sites are found within the Estabrook Woods Site in Concord and at the Rattlesnake Hill Site in Bolton. Threats: Residential, commercial, industrial, and transportation development is decreasing the total acerage of the forests in the SuAsCo Watershed. This development eliminates large forested tracts, fragments the remaining forest, reduces stands of large trees, damages shrub and herbaceous vegetation, and creates sites for invasive exotics. Improper or ill-advised forest harvesting practices, in anticipation of development or as a source of short-term revenue, also impacts these components of biodiversity. An over abundance of white-tail deer reduce recruitment of seedlings through browsing, change the herb layer, and affect the density and diversity of birds. Recreational activity can reduce the sanctuary of the forest for wildlife, particularly for ground-nesting birds and small mammals. Stewardship: Protect large tracts, allow trees to grow old, manage trail access and usage with consideration of wildlife values, allow natural litter and debris to accumulate on forest floor, and control exotics. Forest stewardship plans foresters who understand biodiversity goals and careful loggers can be beneficial to biodiversity. All plans should be designed in context of the overall region so that sufficient core areas of “old growth” are allowed to develop. Example: Estabrook Woods Site in Concord and Carlisle; Greater Walden Site in Lincoln and Concord; Long Pond Site in Littleton. [back to List of Natural Communities] Mixed oak forest: This forest is dominated by red, white, black, and red oaks that form a somewhat sparse canopy. Pitch pine and white oak is occasional. Lowbush blueberries and black huckleberry are common in the understory. Scrub oak is found in openings. Pennsylvania sedge, wild sarsaparilla, and bracken fern are frequent. More rarely hickory is a main component (20-30% total cover of the canopy layer). Soils are often shallow Charlton-Hollis outcrop substrates found along the Shrewsbury Ridge in the western part of watershed. Associated species: Large tracts of oak forest provide habitat for wide ranging species such as fisher and deer (see forest above). Wild turkey, ruffed grouse, and deer thrive on acorns. What to look for: Signs of fire, south facing rocky ledges that may harbor snakes; south facing slopes which may have flowering dogwood, and a variety of unusual sedges, goldenrods, or tick-trefoils. Threats/Stewardship: Protect large tracts, allow trees to grow old, manage trail access and usage with consideration of wildlife values, allow natural litter and debris to accumulate on forest floor, control exotics. A forest stewardship plan by a forester who understands biodiversity goals and a careful logger can be beneficial to biodiversity. All plans should be designed in context of the overall region so that sufficient core areas of “old growth” are allowed to develop. Examples: Mt. Pisgah in Berlin and Northborough; Rattlesnake Hill in Berlin and Boylston. [back to List of Natural Communities] Successional white pine forest: This is an easily recognized community. White pine dominates areas of old fields, usually with very little diversity due to the shade and to the acidity of the needles. Some of these areas were planted as plantations. Poison ivy is a common associate. Other successional species will grow into light areas, such as blackberries, cherries, and gray birch. Associated species: White pine groves provide habitat for great horned owls and wintering birds. Blue-spotted salamanders often attain high densities in white pine dominated woods. Threats: Cutting of white pines can often allow exotic species to invade. Large trees are often cut as a source of revenue, often before land is divided into house lots. Stewardship: Allow trees to stand. A careful cutting of some of the pines, leaving any oaks that are coming in, would increase diversity. Example: Gardner Hill Site in Stow; Delaney Wetlands Area in Harvard, Desert Area in Marlboro. [back to List of Natural Communities] Pitch pine/scrub oak: Pitch pine is dominant along with a variety of oaks including scarlet and rarely chestnut oak. Trees often grow only to 30-40’ tall and form an open canopy. Scrub oak is common in understory and openings. Lowbush blueberry and black huckleberry are usually dense and intermingled with bracken fern and rarely wild indigo. This community is found on glacial outwash soils often near railroads that once sparked frequent fires or on areas that have otherwise been disturbed, such as by army maneuvers. Fire is key to their long-term viability. Without fire, oaks will eventually dominate. Pitch pine/scrub oak communities blend into grassland and scrub oak communities which are earlier successional states of the pitch pine forest. Associated species: Wild turkeys, ruffed grouse, eastern towhees, and pine warblers are common. Whip-poor-wills and nighthawks are rare birds. Hognose snakes may be in the more open, sandy areas. What to look for: Predominance of pitch pine with patches of scrub oak indicating recent burns. Areas which are isolated from development so that prescribed burns are feasible. Threats: These forests are particularly threatened by development because of the well-drained, sandy soils. Lack of fire and invasive plants are the two other threats. Stewardship: Prescribed burns to sustain pitch-pine oak communities over the long term. Examples: Desert Area Site, in Sudbury and Marlborough. [back to List of Natural Communities] Hemlock: Hemlock groves are dominated by hemlock with a component of black birch, red oak, yellow birch, or other forest species. They are often found on north-facing slopes, along streamsides, or in seepage areas where it is relatively cool. The understory is usually extremely sparse due to shade and acidity. Hemlock groves are extremely valuable components of deciduous forests as they provide cover for many birds including chickadees, golden-crowned kinglets, and owls in the winter and black-throated green warblers in summer. They also serve as shelters for deer in winter. Hemlocks are the preferred food of porcupines. Hemlock forests are threatened by the woolly adelgid insect which is decimating the trees. No control for the adelgid is known yet for wild situations. [back to List of Natural Communities]
Acidic rocky summit/rocky outcrop community: Uncommon in the SuAsCo Watershed, this community type features low shrubs, scattered grasses, mosses, and lichens growing on rocky summits with exposed acidic bedrock. These outcrop communities are characteristically dry with little or no soil and can often be found as open patches within the ridge-top and dry, mixed oak communities. Low shrubs and scattered clumps of grass dominate. The exposed rocks often have extensive patches of lichen and moss. The canopy cover is largely absent, but trees commonly found near the margin of the bedrock areas may include pignut hickory, scarlet oak, and white pine. The dominant shrubs include scrub oak, black huckleberry, lowbush blueberries, dwarf serviceberry, and rarely bearberry. Chestnut oak and dwarf chestnut oak are uncommon. Herbaceous species include little bluestem , poverty grass, common hairgrass, Pennsylvania sedge, rock harlequin, cow-wheat, and dwarf dandelion. Non-native weedy species, such as crabgrass and field sorrel, also colonize disturbed sites. Associated species: Exposed rock outcrops support an unusual array of plants. Snakes would be those of dry areas, such as black racer, ringneck, and redbelly snake. Gray tree frogs are often common on ledges and American toads are often found at their bases. Ravens may be possible along the Shrewsbury Ridge especially near cliffs where they might nest. Coyotes, red fox, and gray fox den in among outcrops and talus. Bobcats also use outcrops for denning and loafing. Threats: The largest threat at this time is the construction of microwave (cell phone) towers. Another major threat is the use of the areas as viewpoints. Trampling can destroy the vegetation. The larger and steeper areas where the community occurs are probably stable and not likely to be overgrown by trees. Stewardship: Work on careful siting of towers in other less sensitive places. Design trails to avoid these areas and/or educate the public so they understand how fragile the community is. Controlled burns may be useful in keeping areas open. Examples: Mt. Pisgah in Northborough; Nobscot Hill in Sudbury. Many ridge lines along the Shrewsbury Ridge have outcrops that are shaded and therefore do not include the range of herbaceous species typical of an acidic outcrop. More exploration is needed. [back to List of Natural Communities]
Shrub-scrub: Hedgerows, field edges, early successional fields, and utility right-of-ways often support shrub habitat. A mixture of young trees, shrubs, grasses, and wildflowers provide dense cover for a variety of mice, rabbits, and snakes, such as black racers. Many bird species thrive on these communities, including indigo buntings, brown thrashers, and blue-winged warblers, along with more common species, such as catbirds, mockingbirds, and American robins. Threats: Succession to forest, exotics invasive plants. Stewardship: Control of exotics, periodic cutting back to sustain different successional stages. There are opportunities in the state parks that already have significant edge habitat to develop shrub-scrub management plans. Examples: Baiting Brook Site in Framingham; Great Brook Farm and Environs Site in Carlisle. The Massachusetts Division of Fisheries and Wildlife has reclaimed a successional habitat overgrown by exotic invasives and plans to manage it for successional habitat at the Westborough Wildlife Management Area in Westborough. This is part of the Crane Swamp to Westborough WMA Site. [back to List of Natural Communities]
Little bluestem grasslands: Dry, native grasslands are dominated by a native bunch grasses, such as little bluestem, oat grass, and love grass. They are usually found on glacial outwash soils in small patches in the SuAsCo Watershed. They are not the same as the sandplain grasslands described by NHESP for the southeast or islands which contain many rare species. Stiff aster, downy golden rod, Green’s rush, wild lupine, wild indigo, frostweed, bird’s-foot violet, and goat’s rue are indicative of this community type. These communities are maintained by fire. Associated species: Open, sandy soils are critical nesting sites for spotted, wood, eastern box, painted, Blanding’s, and snapping turtles. Also, they are prime habitat for tiger beetles and support high diversity of bees and wasps. Little bluestem is host plant to three butterflies: Leonard’s skipper, cobweb skipper, and dusted skipper. Whip-poor-wills and prairie warblers are found in dry areas mixed with shrubs. What to look for: Little bluestem fields with a minimum of non-native species. These are often in small patches associated with pitch pine habitats. Buffers should be great enough to allow for prescribed burning. These native grasslands should be given protection priority. Stewardship: Prescribed burning of pitch pine/scrub oak communities and associated bluestem grasslands will help preserve this plant community. Mowing is a less satisfactory but perhaps more practical alternative. The proper timing of these measures is important. Examples: Desert Area Site in Marlborough and Sudbury; Assabet River NWR Site in Stow, Maynard, Sudbury, and Hudson. [back to List of Natural Communities] Successional grasslands: Successional grasslands are frequently found along power lines and gas pipelines. They may have many of the same species as the little bluestem grasslands but also include many non-native species. Additional species include fescue grasses, red-top, milkweed, spreading dogbanes, small white asters, dewberries, meadowsweets, common juniper, and various goldenrods. Usually these areas are mowed every few years or may be dry, old fields succeeding into forest. Associated species: These more or less wild grasslands can have a rich assortment of butterflies and other insects. Powerline corridors can have many edge species, both native and exotic, and can serve as travel corridors for some animals, depending on the amount of cover. Raptors, including American kestrels and red-tailed hawks, are common. What to look for: A mixture of herbs and shrubs with minimal invasive exotics. A good range of butterflies. Signs of use as a wildlife corridor. Threats: Grasslands along utility rights-of-way are cut or herbicided every five years or so. Herbicide applications kill not only the plants but also the many associated species which thrive on them, such as butterflies. Off-road vehicles damage plants and runover or harass animals and birds. Exotic invasives are often a major component of these grasslands because of the frequent disturbance, abundant edge, and many sources of seeds, from birds to off-road vehicles. These areas serve as sources of entry of exotics that spread into adjacent forests and wetlands. Stewardship: Cooperative efforts with utility companies could enhance the wildlife value of these wild grasslands and make sure they are a continuing source of wildlife instead of a “sink” where more individuals are lost than gained. Example: Westborough Wildlife Management Area in Westborough. [back to List of Natural Communities] Cultivated fields: Hay fields or pastures are part of the rural landscape but are not a natural community. Mostly they are dominated by European forage grasses such as Kentucky blue grass, orchard grass, fescues, and sweet vernal grass. Non-native flowering plants include colorful cow vetch, alfalfa, black-eyed susans, and ox-eye daisies. Native flowers are fleabanes, milkweed, asters, and goldenrods. Usually these fields are mowed once a year to prevent woody plants from invading. Hayfields are often mowed 2-3 times a year. Associated species: These fields are most significant for birds, small mammals, and invertebrates. Bluebirds, field sparrows, white-footed mice, voles, and butterflies all utilize the habitat. Butterfly species will depend on what plants are available for both larval food and nectaring. Grassland birds such as bobolinks, savannah sparrows, and eastern meadowlarks require large areas of unbroken fields of at least 5 acres and preferably 20-30 acres. American kestrels, a declining species, will forage where there are large insects such as grasshoppers. Fields of any size provide cover for many small rodents and snakes, such as the milk and green snakes, which in turn, are prey to red-tailed hawks and other raptors. Green snakes are a Focal Species for fields. Fallow crop fields in winter provide resting areas for snow buntings, water pipets, and horned larks. What to look for: Large hay fields greater than 15 acres or clusters of hayfields each greater than 5 acres that can be managed for grassland birds, particularly for late mowings. Proximity to moist field areas is preferable for bobolinks. Older fields with a mixture of grasses and wildflowers support an array of butterfly species. Threats: Development of farm land is rapidly eliminating these sites. Some agricultural practices, particularly mowing before mid to late July, reduce value for nesting birds and butterflies. Recreational activities and dog walking reduce habitat suitability for nesting grassland birds and resting wintering birds. Stewardship: Protect large fields and clusters of fields and manage for grassland birds. Ownership by entities with conservation interests is essential to maintaining the presence of grassland birds in the SuAsCo Watershed. Owners can form leases with farmers to maintain mowing regimes conducive to bird productivity. Public use also needs to be appropriate to biodiversity objectives. A range of field types will provide the most potential for including a variety of organisms. Examples: Heard Farm in Wayland; Baiting Brook in Framingham; Wataquadock Fields in Bolton. Minute Man National Historical Park is creating fields that will be managed for grassland birds. [back to List of Natural Communities] Red maple swamp: Red maple swamps are the most common wetland type in the SuAsCo Watershed. Red maple swamps form in a variety of settings. Red maple is the dominant tree, providing an almost total canopy cover to sparse cover. White pine and white ash and more rarely hemlock and yellow birch are present. Black ash is rare. Highbush blueberries, swamp azalea, sweet pepperbush, male berry, and winterberry are a few of the common shrubs. Skunk cabbage, cinnamon fern, royal fern, and tussock sedge form the herb layer. Soils are usually Freetown or Swansea mucks. Associated species: Few species depend exclusively on red maple swamps, but over a third of the bird species in the state, many mammals, and most amphibians and reptiles use these wetlands. Beaver are a keystone species which alters the habitat to increase natural diversity. Otters, spotted turtles, herons, bluebirds, wood ducks, frogs, and snakes are just a few of the species which are flourishing in the SuAsCo Watershed due to beaver activity. Beaver disturbance is one of the few natural, large-scale dynamics currently in effect in the SuAsCo Watershed. Barred owls and red shouldered hawks also are found in red maple swamps. What to look For: Protection of a variety of red maple swamps in different settings will assure a good representation of this community type and the full range of biological diversity. Hillside seeps and perched wetlands are often poorly represented. Basin swamps with varied micro-topography, sphagnum moss, and impounding of water provide particular habitat values for amphibians as they can serve as vernal pool habitat. Alluvial red maple swamps form important riparian habitat. Areas lacking purple loosestrife and other exotics are rare and should be given extra protection. Wetlands with small streams are ideal beaver habitat and should be protected with large buffers so that the beaver dynamic can continue without control. Sensitive wildlife areas should have buffers of at least 100-300’. Threats: Incremental disturbance of buffer zones due to development and changes in hydrology affect wildlife values and water quality. Invasive plant species, particularly European buckthorn, phragmites, honeysuckle, and Japanese barberry, invade from edges into disturbed zones. Aggressive control of beaver can eliminate the benefits of beaver activity on these communities. Stewardship: Strictly enforce the Wetlands Protection Act. Monitor upgrading of roads to prevent invasive exotics and changes in hydrology. Remove incipient colonies of invasive species. Examples: Crane Swamp and Little Crane Swamp Site in Westborough; Great Swamp Site in Stow and Acton. [back to List of Natural Communities] Small river floodplain forest: This wetland forest community is found along the mainstems of the Assabet, Sudbury, and Concord Rivers and intermingles with marshes and shrub swamps. Silver maple dominates and can be very large and multi-trunked. Swamp white oak is a common associate in more persistently flooded zones, and red maple is found in more upland edges. River birch and green ash are occasional components. The understory can be sparse where flooding is severe with much debris caught in the backwaters. Herbs can be very sparse with just a few scattered annuals, such as false nettle and beggar’s ticks, filling in late in the season, or relatively dense with ferns, such as sensitive and royal. In other locations, shrubs, such as silky dogwood, arrowwood, sweet pepperbush, and buttonbush, may form a relatively thick shrub layer with cat-brier and grapes scrambling over them. Purple loosestrife grows on the perimeter along with the native cardinal flower. More work is necessary to describe this community in the SuAsCo Watershed. Associated Species: Numerous species use the floodplain forest, including otters, wood ducks, star-nosed moles, mink, and wood turtles. Yellow-throated vireo and warbling vireo also nest here. Threats: Alteration of the flooding cycles by upstream detention and water withdrawals. Exotic species, such as Japanese knotweed. Stewardship: The River Protection Act contained in the Wetlands Protection Act adds extra protection to these unusual floodplain communities. The Wild and Scenic River designation also offers some protection. Examples: Great Meadows Site in Wayland, Sudbury, and Concord; Egg Rock Site in Concord; River Pines Site in Billerica. [back to List of Natural Communities] Shrub swamp: Shrub-dominated wetlands are often found in the transition zone between emergent marshes and swamp forests where mucky soils are permanently saturated only seasonally or are temporarily inundated. They are common in the SuAsCo Watershed, especially along streams. Shrub swamps are highly variable communities but typically have a mixture of wetland shrubs species, such as highbush blueberry, winterberry, sweet gale, swamp azalea, silky dogwood, northern arrow-wood , and maleberry. Non-native European buckthorn may be a frequent, unwanted component in drier areas. Alders, meadowsweets, buttonbush, and willows are found in different situations. Scattered red maple saplings also occur. Dense buttonbush and occasional willow is a common combination along the Sudbury and Concord Rivers. Where shrubs form dense thickets, the herbaceous layer is often sparse. A mixture of the following species is typical: skunk cabbage; cinnamon, royal, and sensitive ferns; sedges; and sphagnum moss. Associated species. Shrub swamps often function as vernal pool habitat in sections that have extended periods of ponding (2-3 months) and lack fish. They also provide important amphibian breeding habitat. Blue spotted salamanders, spotted turtles, wood turtles, Blanding’s turtles, and four-toed salamanders may be present. Wood turtles may be found along deep flowing streams with a dense shrub community along the banks. Willow fly-catchers, and rarely alder fly-catchers are found in shrub swamps with a good portion of willows and alders. What to look for: Shrub swamps interspersed with marsh and forested wetland habitats. Isolated, well buffered shrub swamps which have hummock and hollow microtopography, open water for part of the year, and sphagnum moss. Areas with a good suite of focal species. Threats: Invasion by purple loosestrife and European buckthorn threatens the diversity of the shrub swamps. Where this habitat lies along streams, alteration of road culverts can affect hydrology and cause invasion of exotic plant species. Stewardship: As with other more common wetland types, provide buffers, control exotic invasives, and maintain hydrology. Examples: Assabet Marsh Site in Stow and Hudson; Cold Harbor Brook Impoundment Site in Northborough; Great Meadows Site in Sudbury and Wayland. [back to List of Natural Communities] Emergent marshes: Deep emergent marsh is the deepest of the three marsh communities described here. Water inundates areas from 6 inches to 3 feet. Saturated mucky mineral soils are seasonally inundated and permanently saturated. Deep emergent marshes cover broad, flat, low-energy rivers and streams. Cattails are dominant plants along with river bulrush (in Sudbury and Concord Rivers). Other graminoids (grass-like plants) include blue joint grass, reed canary grass, soft-stemmed rush, and wool grass. A variety of smaller, showy forbs (wildflowers) intermingle, such as water hemlock and swamp candles. Along stream edges, pickerel-weed, burreed, arrowheads, and water arum emerge out of the water. In scoured pockets of pooled water or along sluggish streams there are floating-leaved plants, such as water-lilies and pond lilies, pondweeds, and duckweed. Shallow emergent marshes are similar to deep emergent marshes, but the water depth averages less than 6 inches deep during times of inundation. Shorter grasses, sedges, and rushes dominate. Tussock sedge and Canada bluejoint are typical along with reed canary grass. Often they can be found in abandoned beaver flowages. Associated Species: Emergent marshes are excellent waterfowl habitat and provide important habitat for frogs--especially leopard, pickerel, green, and bull frogs--and red-spotted newts. Several state-listed rare bird species require areas greater than 40 acres of emergent marsh: American and least bitterns, pied-billed grebes, king rails, and common moorhens. Red-winged black-birds, marsh wrens, and swamp sparrows are common species in our area. Spotted turtles, wood turtles, and Blanding’s turtles all benefit from protected marshes. Water shrews are small and obscure and therefore often overlooked. More common is the use of marshes by muskrats which serve as keystone species by creating burrows, cutting cattails, creating mounds, and changing the structure and nutrient cycle of the marsh for the benefit of other species. Migrating northern harriers need these open areas for hunting. What to look for: A mosaic of marsh and shrub swamp types with minimal purple loosestrife or phragmites and with a range of Focal Species and common amphibians and birds. Large expanses of emergent marsh greater than 40 acres with good buffers provide habitat for many of the marsh Focal Species of birds. Diversity of structure including ice scours. Threats: Purple loosestrife and phragmites are dramatically changing the quality of our marshes. Intense public use of canoes, motorboats, and particularly jet-skis can reduce habitat where marshes are found along a river such as the Sudbury and Concord. Hydrology changes by water withdrawals or diversion upset the natural flow and flooding reqimes. Stewardship: Control of recreational use is important to maximize marsh habitat. Biological control of purple loosestrife may help in reducing the dominance of this pest species. Incipient colonies of phragmites should be immediately eliminated. Maintain natural water levels. Examples: Delaney Wetlands Site in Harvard and Stow; Allowance Brook Site in Sudbury; Pod Meadow Site in Framingham. [back to List of Natural Communities] Wet meadows: Wet meadows are only temporarily rather than seasonally flooded. The soil is saturated during the growing season but is generally not inundated. Repeated disturbance, usually from grazing or mowing, keeps these communities open. Some wet meadows may be dominated by a single species, such as tussock sedge, bluejoint, or reed canary grass. In drier areas that are mowed more frequently, wet meadows support a variety of showy plants such as jewelweed, Joe pye-weeds, ironweeds, blue vervains, and cow parsnips, as well as an unusual array of sedges, beak-sedges, and spikerushes. Associated Species: Mole salamanders, American toads, wood frogs, and spring peepers may breed in vernal pools that become wet meadows in late summer. American bitterns, green snakes, and Elderberry borer beetles are all denizens of wet meadows. Various butterflies nectar on showy flowers such as silver-bordered fritillary on violets and Baltimore fritillary on turtleheads. Swamp milkweed is a particularly attractive nectar plan. Threats: Mowed wet meadows are often overlooked and, therefore, may be developed without application of the Wetlands Protection Act. In other instances, interpretation of the Wetlands Protection Act often does not allow management of these successional wetland areas as mowing is considered “alteration” of the vegetation. If left alone, wet meadows will succeed into red maple swamps, our most common wetland type. Purple loosestrife frequently overwhelms these communities. Stewardship: Education as to the appearance and values of wet meadows so that they will be protected. Management of these sites by mowing and exotic plant removal in conjunction with the Wetlands Protection Act. Examples: Great Meadows Site in Concord; Sunk Meadow Site in Bolton. [back to List of Natural Communities] Fens: Two fen community types are described by the Natural Heritage Program. Both are acidic peatlands that experience some groundwater and/or surface water flow, which provides some nutrients to the system. Both can have scattered Atlantic white cedar and red maple. Acidic graminoid fens are dominated by sedges and sphagnum. Inlets and outlets are usually present and standing water is present throughout much of the growing season. Peat mats are quaking. Sedges dominate. White beak-sedge, twig sedge, and a pondshore-rush are good indicators. Broad-leaved herbs include arrow-arum and rarely the rose pogonia orchid. Large cranberry is often abundant. Trees and shrubs are patchy. The other type of fen, acidic shrub fens, are similar in their setting, but typically have many shrubs instead of sedges: leatherleaf, water-willow, and sweet gale along with meadow sweet, sweet-pepperbush, and alders. Associated species: Spotted turtles and ringed boghaunters are rare species in fens. The tiny four-toed salamander lives in sphagnum moss. Bog lemming also can be found. Water-willow stem borer is possible but has not been recorded in the SuAsCo Watershed. What to look for: Note the hydrology, limited sources of nutrients, peat substrates, and suite of indicator species. The community should be well-buffered from development to prevent changes in the hydrology over the long term. They should have a good representation of fen species. Threat: Changes in hydrology, nutrient enrichment, invasive species, and trampling. Stewardship: Protect large buffer zones, control new colonies of invasives, and provide boardwalks if the site is to be open to the public. Examples: Grassy Pond Site and Will’s Hole Site in Acton; Whitehall Fens Site in Hopkinton; Greater Walden Site and Dugan Kames Site in Concord. [back to List of Natural Communities] Bogs: These peatlands receive little or no stream flow and are isolated from the water table and, therefore, are the most acidic and nutrient poor of the natural communities. Level bogs are the poorest of the peatlands with pH ranging from of 3-4. Level bogs form along pond margins, at the headwaters of streams, or in isolated valley bottoms without inlet or outlets. They are characterized by a mixture of tall and short shrubs that are primarily ericaceous. Leatherleaf is dominant. Rhodora, sheep laurel, and large cranberry are typical. Bog rosemary, Labrador tea, and small cranberry have historically been found in the SuAsCo Watershed. Scattered, stunted coniferous trees, mostly tamarack and black spruce, occur throughout. Pitcher plant and sundews grow in the sphagnum. Kettlehole level bogs have many similar species but their setting is different. These acidic peatlands form in kettle depressions in sandy glacial outwash. The vegetation is zoned in rings. Wetland shrubs such as blueberry and azalea grow outside a moat which surrounds a sphagnum mat. The mat is a mixture of tall and short shrubs similar to those found in the level bog. Associated species: Spotted and blue-spotted salamanders, four-toed salamanders, green frogs, northern red-bellied snakes, bog copper butterflies, pitcher plant borer moths, boghaunter dragonflies, and several plants such as northern yellow-eyed grass and pod grass might be found in level bogs in the SuAsCo Watershed. What to look for: Characteristic array of species without exotics in situations that have not been compromised by ditching, nutrient run-off, etc. Threats: Changes in hydrology, nutrient enrichment, invasive species, and trampling. Stewardship: Protect large buffer zones to protect the hydrology of the bog; control new colonies of invasives; and provide boardwalks if the site is to be open to the public. Examples: Assabet NWR Site in Stow; Greater Walden Site in Concord; Estabrook Woods Site in Concord. While we have many peatlands in the SuAsCo Watershed, additional inventory is needed to determine what type of peatlands are in fact represented in the Biodiversity Sites. [back to List of Natural Communities] Atlantic white cedar (AWC) communities: Cedar swamps have been variously categorized over the years. Currently, Natural Heritage describes four Atlantic white cedar communities. The most likely type to be found in the SuAsCo Watershed is the alluvial AWC swamp. This community is found along low-gradient rivers and streams that flood and along fringes of open marshy areas along ponds. This community receives annual or semi-annual overbank flooding making it more mineral rich than other AWC wetlands. Peat is about three feet thick and standing water remains for over half the year. These communities are highly variable with AWC and red maple dominating the tree layer and highbush blueberry and sweet pepperbush occurring in the shrub layer along with silky dogwood. The herb layer consists of several common wetland ferns: sensitive, royal, cinnamon, and marsh. AWC bogs are found in semi-forested level bogs with sphagnum mats. Black spruce is a typical component. These peatlands are more nutrient poor and support a nearly continuous layer of ericaceous shrubs such as leatherleaf, sheep laurel, huckleberry, fetterbush, and rhodora. Sundews and pitcher plants occur in the thick sphagnum mats. Associated species: spotted turtles, wood turtles, mystic valley amphipod, and four-toed salamander. Hessel’s hairstreak butterfly is an indicator species. What to look for: Indicator plants of Atlantic white cedar and black spruce, and Hessel’s hairstreak is an indicator insect. In bog habitats look for a full suite of ericaceous and carnivorous species. Seedlings of AWC would indicate potential recruitment. Lack of ditching, intact buffers, and lack of exotics are signs of intact hydrological systems. Several studies have been conducted on these communities for the state and in the SuAsCo Watershed. Threats: Changes in hydrology including nutrient inputs and water withdrawals; dumping and filling; invasive exotics; trampling by visitors. Stewardship: Vigilant enforcement of Wetlands Protection Act. Control of exotics. Provision of boardwalks. Examples: Assabet River NWR Site in Maynard; Whitehall Fens Site in Hopkinton. Cedar Swamp Site in Westborough is an Area of Critical Environmental Concern (ACEC). |