Natural Habitats of Nantucket
Nantucket is fortunate to have a great variety of plant communities on a relatively small island. These assemblages of species are at different stages of succession, influenced by land management practices and many different ecological factors such as soil type, water availability, slope, and exposure to salt spray. Several are rare to this region, and even the world. This publication provides descriptions of Nantucket’s most commonly-encountered natural habitats and their associated species.
Sandplain Grasslands and Coastal Heathlands
Nantucket's sandplain grasslands and coastal heathlands are upland plant communities that are unique to this region of North America. Once common along the northeastern seaboard, residential and commercial development and succession to shrublands has all but eliminated these habitats from coastal areas such as Cape Cod and Long Island, New York. It is currently estimated that over 80 percent of the worldwide acreage of sandplain grasslands occur on Nantucket, Tuckernuck, and Martha's Vineyard.
Sandplain grasslands are relatively flat, open habitats similar to the prairies found in the Midwest. They are generally found on the southern portion of the island, geologically known as the outwash plain, where fine sand and debris were deposited by glacial meltwaters. As the name implies, this habitat is dominated by grasses, interspersed with annual and perennial wild flowers such as false indigo, bluets, field pussytoes, pearly everlasting, trailing arbutus, yarrow, and many species of asters and goldenrods. Patches of low-growing shrubs occur among the grasses and wild flowers.
Coastal heathlands, or "moors," as they are locally called, contain many of the same plants as sandplain grasslands. However, heathlands contain larger patches of shrubs, including black huckleberry, lowbush blueberry, bayberry, and pasture rose, with grasses interspersed. They are located primarily in the central and northern portions of the island, where the glacier reached its southern-most extent and deposited large quantities of course sand and rock. Low ground cover plants such as bearberry, alpine reindeer moss, and false heather are adapted to growing on these nutrient-poor, gravelly soils.
Both of these habitats are the product of extensive human use. It is believed that the early Native American settlers burned plots of land to clear them for agricultural use and to stimulate the production of native berries. Later, European immigrants, who arrived in 1659, brought large numbers of grazing animals with them. By 1845, there were approximately 15,000 sheep grazing on Nantucket. The sheep overgrazed the trees and shrubs, allowing low-growing heathland and grassland plants to develop without competition for sunlight and nutrients. Grasslands and heathlands that occur in close proximity to the coast were, and still are, somewhat maintained by the constant impact of salt spray.
The grasslands and heathlands created by fire, grazing and other human activities now support high concentrations of rare and endangered animals and plants. Low, grassy vegetation provides the endangered short-eared owl and the rare northern harrier (formerly called marsh hawk) with ideal conditions for hunting their primary prey species, the meadow vole. However, populations of both these birds are declining as large, contiguous areas of nesting and hunting habitat are permanently lost to development.
Bushy rockrose, lion's foot, eastern silvery aster, sandplain blue-eyed grass, Nantucket shadbush, broom crowberry, and sandplain flax are examples of some of the rare and endangered plant species that are found in Nantucket's grasslands and heathlands. These wild flowers, grasses and shrubs thrive on the nutrient-poor soils that are common on Nantucket.
The change in plant species composition over time in a natural community is known as vegetative succession. This natural process has resulted in the loss of many of Nantucket's grasslands and heathlands. Whaling sharply declined in the late 1860's, causing many residents to leave the island in search of work. Sheep grazing became less common and eventually nonexistent. Over the last century, the lack of grazing pressure and a decline in the amount of natural and human-induced fires has allowed shrub species to grow and out-compete rare grassland and heathland plants. If left unchecked, Nantucket's rare plant communities will eventually be replaced by scrub oak and pitch pine, and its' endangered species will eventually disappear due to lack of suitable habitat.
Because these two habitats are largely the products of human land use practices, active management is needed to prevent them from disappearing. The Foundation has been involved in cooperative research programs with the Massachusetts Audubon Society, The Nature Conservancy, the Partnership for Harrier Habitat Preservation, and the University of Massachusetts aimed at developing methods to control the invasion of shrubs and restoring grassland and heathland habitats. Prescribed burning and mechanical brush cutting have been used as management techniques to achieve these goals. While these efforts may initially seem to be destructive, research has shown that they are effective in maintaining rare grasslands and heathland plant communities and providing habitat for their associated wildlife.
Scrub Oak and Pitch Pine Barrens
Many of Nantucket's grasslands and heathlands have become overgrown by taller shrubs and trees to the extent that few, if any, of the plant species characteristic of these habitats remain. The most common species to invade and take over these sites are scrub oak and pitch pine, with pitch pine being more common in areas that were once plowed for agriculture and scrub oak being more dominant at sites where the soil has not been disturbed.
These overgrown heathland communities are collectively referred to as barrens. Examples of this type of habitat occur on many of the Foundation's properties, including the Middle Moors and along the south shore of the island between Nantucket Memorial Airport and the former Tom Nevers Naval Facility.
At many of these sites, scrub oak forms dense, impenetrable thickets that shade and out-compete most of the grasses and herbaceous plants in the understory. Plant diversity in barrens communities is further limited by the drought-prone, acidic, nutrient poor nature of the soils. Other species that are well-adapted to these conditions and can occur amidst the scrub oaks include northern arrowwood, bayberry, huckleberry, dwarf chestnut oak, sweet fern, blueberry, and eastern red cedar.
Scrub oak is an extremely tough and resilient shrub. The plant has a large root collar that lies just below the surface of the soil and bears hundreds of dormant buds. If the above ground branches are destroyed by fire, brushcutting, or some other type of disturbance, the plant quickly sends up numerous resprouts that grow up to 3-4 feet per year. Acorn production begins when the resprouts are 3 years old, reaches its maximum between years 5-7, and slowly declines thereafter. Therefore, this species benefits from periodic disturbance such as fire, which stimulates the production of acorns and thereby promotes the establishment of new seedlings.
Pitch pine is another barrens species that is well adapted to periodic fires, with dormant buds that are protected under thick layers of bark. This tree is native to the eastern United States, but it was either very uncommon or nonexistent on Nantucket prior to 1847. At this time, Josiah Sturgis planted pitch pine seedlings along the Milestone Road to serve as a windbreak. The trees thrived in the sandy, disturbed soil along the road edge. This species has since become one of the most common trees on the island, where it has overgrown and outshaded many acres that formerly supported grasslands, heathlands, and scrub oak barrens.
Barrens communities are dependent on periodic disturbance to prevent them from becoming overgrown by taller hardwoods such as black oak, white oak, black cherry, and shadbush. Conservation partners on the island, with the assistance of other off-island organizations and agencies involved with prescribed burning, have conducted burns aimed at maintaining scrub oak barren communities. However, these burns are difficult in nature and need to be undertaken with great care and planning because scrub oak and huckleberry are tall, extremely flammable shrubs.
Frost bottoms are interesting landscape features that often occur within scrub oak and pitch pine barrens communities. They are depressions that pool cold air at their lowest elevation, resulting in more frequent frosts that can occur at almost any time of the year, and a much shorter growing season than the surrounding upland. Most shrubs, with the exception of scrub oak, cannot tolerate these conditions. Therefore, recurrent frosts maintain the vegetative composition of these sites without the need for fire or other disturbances. Scrub oak and pitch pine barrens and their associated frost bottoms provide habitat for several species of rare moths, including the barren's buckmoth, Melsheimer's sack-bearer moth, and pine barrens lycia moth.
On Cape Cod, many former barrens communities have already reverted to upland forests because of the lack of periodic fire or other disturbances. Because of Nantucket's recent history of sheep grazing, mature forests are still relatively rare on the island. However, given time and the absence of fire, many of the scrub oak barren communities here will eventually become similar to the forests on Cape Cod today.
Found all along the eastern coast of North America from Newfoundland to Florida, salt marshes occupy the constantly fluctuating border between land and sea, being exposed and flooded twice daily by the tide. They are usually found on the less exposed side of barrier beaches and harbor shorelines, where the wave energy is not as great as on the ocean beach. On Nantucket, salt marshes are relatively rare because most of the island's shoreline is exposed to the Atlantic Ocean and Nantucket Sound. Well-developed salt marshes can be found in the sheltered waters of Nantucket Harbor at First Point, Second Point, Third Point, Five-fingered Point, Coskata, The Haulover, Quaise, Pimney's Point, the Creeks, and within Polpis Harbor. Additionally, the west end of the island supports salt marshes at Eel Point, Jackson's Point, and Hither Creek.
Most of the salt marshes in New England were formed after the retreat of the last glacier approximately 12,000 years ago. As this ice sheet melted, large amounts of fine silt, clay, sand, and other organic sediments were picked up, carried, and deposited in sheltered locations. The seeds of marsh grasses that are adapted to being periodically inundated by the tide germinated and colonized the surface of this rich, organic soil.
The roots of salt marsh plants bind the sediments together to form a firm, peat-like substrate that traps organic debris brought in by each tide. As the marsh develops, dead blades of grass that are replaced each year by new growth accumulate on the surface of the peat and decompose, slowly increasing the elevation of the surface. For thousands of years, this process of peat formation has kept pace with the slow rise in sea level that has been occurring since the retreat of the glacier. This substrate forms the foundation for the plants and animals that inhabit the salt marsh.
There are two distinct zones in this habitat that can be readily distinguished by the plants that grow there: the low marsh and the high marsh. The low marsh is the area closest to the water and along tidal creeks that is regularly flooded at high tide. The dominant plant in this zone is salt marsh cordgrass (Spartina alterniflora). This species, which can grow to four feet in height, is adapted to being submerged in salt water about half the time, based on the tide cycle. Despite its long length, only the tips of the blades are usually visible during the peak of high tide.
As the name implies, the high marsh is further back from the shoreline and is at a higher elevation than the low marsh. This zone is only flooded during the extremely high tides associated with the full and new moons. Here, salt marsh cordgrass is replaced by several other plant species. The most common is high water grass, or salt meadow grass (Spartina patens), which grows to a maximum of 15 inches in height. This species can be recognized at a distance by its tousled appearance, due to new growth arising from the flat, matted stems of the previous year's growth. It grows in pure, continuous stands that give the surface of the high marsh a textured appearance. Also found in this zone are spike grass (Distichlis spicata) and black grass (Juncus gerardi). The former species is light green and prefers the wettest portions of the high marsh. The latter species, which occurs in drier areas, is dark green and derives its name from its blackish fruits, which ripen in June and persist into the autumn.
There are many other species of plants that grow on the marsh. Sea lavender, or marsh rosemary, grows in the high marsh near the upland border. Its leaves form a small rosette that grows close to the ground, sending up a flower stalk with many small, lavender flowers in late summer. This species has become quite rare in recent years because it has been over-collected. Salt marsh aster, seaside goldenrod, and seabeach knotweed are examples of other flowering plants that are associated with salt marshes.
Another species that can be found along the upper edge of the marsh is Phragmites, or common reed. This perennial grass can reach 15 feet in height and forms purplish, plume-like seed heads in late summer. Phragmites grows in wetlands around the world, spreading rapidly by underground rhizomes that out-compete cattails and other marsh plants. The resulting thick, impenetrable stands of reeds provide minimal value for wildlife.
Phragmites is especially prolific in salt marshes and other wetland areas that have been disturbed by construction that has altered the daily ebb and flow of the tide. Ditching and filling, two common management practices that continue to be undertaken to control mosquito populations (with limited success) also disturb marsh soil and make these sites more prone to colonization by this species.
Although Phragmites is native to North America, it has become very invasive across its range within the last fifty years. Research has demonstrated that highly invasive populations are genetically different from natural populations, leading scientists to speculate that an "aggressive" strain of this species has recently evolved and is responsible for degrading wetlands. Once established, Phragmites is extremely difficult to eradicate without the use of mechanical alterations and herbicides.
The high marsh also provides habitat for several species of shrubs that are adapted to being occasionally flooded by salt water during storms and the most extreme high tides. Groundsel tree is a sizable shrub with thick, coarsely toothed leaves. It produces whitish bristly flowers in late summer. Marsh elder often grows in thickets along the marsh edge. It has dark green, sharply toothed leaves and produces plain, green flowers in late summer. Both of these species are also called high tide bush, because they grow along the border between the upland and where the highest tides reach their peak.
Peat sometimes accumulates faster in some portions of the marsh than in others, creating slight differences in topography. As the high tide recedes, water will often become trapped where the elevation is slightly lower than the surrounding peat. None of the marsh grasses can survive with their roots continuously soaked in salt water, so the vegetation at such sites gradually dies off and decomposes, leaving small salt ponds on the marsh surface. These locations often contain pools of standing, concentrated salt water even when the tide is low, and contain a variety of interesting microscopic organisms that have adapted to living under these extremely saline conditions.
The daily ebb and flow of the tide not only nourishes the salt marsh, but also provides a constant source of microscopic algae, plankton (larval forms of marine life), small crustaceans, and other nutrients that feed the larger animals that live in this unique environment. Salt marshes are important feeding sites for a variety of nesting and migrating shorebirds and colonial waterbirds, including egrets, herons, plovers, yellowlegs, sandpipers, dowitchers, and whimbrels. Additionally, many marine organisms that spend their adult lives in the open waters of the harbor, sound, and ocean use salt marshes as nursery areas when they are young and more vulnerable to predators associated with deeper waters. Examples include mollusks, crustaceans, and saltwater fish such as striped bass and flounder.
The water, plants, animals, and peaty soils associated with salt marshes are all parts of an intricate biological ecosystem that stores huge amounts of energy in the form of organic matter, or biomass. In fact, salt marshes are considered to be one of the most productive ecosystems on the planet. It has been estimated that these habitats generate approximately ten tons of organic matter per acre per year. By comparison, the average cultivated wheat field produces only one and a half tons per acre per year, including stems and leaves.
The productivity of salt marshes and the important role they play in the life cycles of many marine organisms has only been recently recognized. As little as thirty years ago, these habitats were considered to be worthless real estate infested with mosquitoes, greenhead flies, and other biting insects. Ever since Europeans began arriving in North America, salt marshes and other wetlands have been filled in, dredged, and otherwise altered and destroyed. Fortunately, these unique habitats are now protected by local, state, and federal laws that place restrictions on what, if any, types of development activities can occur in and around them.
Ponds and Bogs
Nantucket's ponds and bogs were formed by the retreat of the last glacier that covered the New England area, which began melting approximately 12,000 years ago in response to a gradual warming in the earth's climate. Meltwaters from the glacier formed river valleys that ran from the glacier to the ocean, which was more than 45 miles south of Nantucket at the time. As the ice melted, sea level rose and flooded all but the highest elevations surrounding Nantucket, isolating it from the mainland. Ocean currents deposited sand into the areas where these valleys met the shore, blocking their southern ends and causing them to fill up with freshwater. Thus, a system of long, narrow ponds running perpendicular to Nantucket's south shore was formed. The larger of these include Long Pond, Hummock Pond, Mioxes Pond, Miacomet Pond, and Weweeder Pond.
The glacier also left behind large chunks of ice scattered across the northern portion of the island, where it reached its southernmost advance. Their massive weight formed depressions in the ground that intersected the water table. Ponds formed in such a manner are called kettle holes, and are characterized by having no inflowing or outflowing streams. Instead, the pond water level fluctuates with the groundwater level. Examples of such ponds include the Pout Ponds, Maxcy Pond, and Almanac Pond.
Nantucket's ponds provide habitat for many species of wildlife. White-tailed deer use them as a source of fresh drinking water and often browse on the nearby vegetation. Many also support diverse populations of fish, amphibians, and reptiles, including yellow perch, pickerel, snapping turtles, painted turtles, spring peepers, green frogs, and northern water snakes. Aquatic animals and submerged pond vegetation are important sources of food for black-crowned night herons, ospreys, hooded mergansers, buffleheads, Canada geese, mallards, and many other species of birds, who use these areas for nesting, feeding, and as temporary stop-over sites along their migration routes.
Immediately after a pond is formed, nature begins to reclaim the land at its shallow edges. Emergent wetland plants that colonize this area form a thick mat of root stalks and vegetation just below the water's surface. This becomes covered with plant debris that settles and decays, gradually replacing the shallow water with damp, organic soil. Wetland shrubs such as sweet pepperbush and highbush blueberry are then able to colonize these areas, crowding out aquatic plants and thereby reducing the size of the pond.
This ongoing process causes the pond to become smaller and shallower, creating optimum conditions for Sphagnum, a genus of mosses that can hold up to twenty-five times their weight in water. As the top portions of these plants grow, the underlying layers become deprived of sunlight and die. Thick mats of dead Sphagnum gradually accumulate and become compressed by the weight of the waterlogged plants above them. Highly acidic conditions prevent this material from completely decaying, and it builds up and forms extensive layers of organic material called peat. At this point, natural succession has transformed the pond into a bog, and most of the visible areas of open water are gone. Other plants, such as cotton grass and swamp azalea, are then able to colonize the bog's peaty surface.
In the early stages of this process, mats of Sphagnum, often with the roots of other bog plants entangled in them, float on the surface of the open water. Such bogs are called quaking bogs because their surfaces are unstable. In later stages, the bog depression becomes completely filled with layers of peat. Bogs that are located in hilly terrain are often entirely surrounded by a moat, where surface water from the adjacent upland collects after it runs downhill.
Peat was historically excavated from many of Nantucket's bogs during times when firewood was unavailable. When Nantucket was blockaded during the Revolutionary War, peat was mined, dried and burned as a heating fuel. However, bogs and other such wetland systems are now protected from such activities by state and federal wetlands protection legislation.
As Sphagnum accumulates in a bog, acids that are produced during the process of plant decay build up. The thick layers of peat further serve to isolate the surface of the bog from the groundwater and its minerals and nutrients. Most plants cannot tolerate these acidic, nutrient-poor conditions, with the exception of a few species that have developed special survival adaptations.
A group of carnivorous bog plants obtain scarce nutrients from insects and other organic material that they capture. The brightly-covered leaves of the pitcher plant form a water-holding vessel with nectar glands that lure insects into this cavity, where they fall in and are "digested" by special enzymes produced by the plant. Similarly, sundews bear a rosette of leaves with sticky, glandular hairs that entrap insects that land on them.
Leatherleaf, sheep laurel, and bog rosemary are woody shrubs that belong to the heath family, a group of plants that are often found in bogs. These species conserve nutrients by having evergreen leaves, thus eliminating the need to invest energy in producing them annually. They also form extensive root systems that efficiently absorb oxygen and nutrients with the assistance of beneficial fungi associated with their root hairs.
Several rare and endangered species occur in bogs and shallow ponds with peaty, sandy soils. Spotted turtles, named for their yellow polka-dot spotted shells, are listed as a "Species of Special Concern" in Massachusetts. These small turtles, which feed on insects and aquatic vegetation, lay their eggs in shallow nests excavated in sandy upland areas adjacent to ponds, bogs and other wetlands.
Arethusa is a showy, perennial orchid that produces magenta to dark pink flowers in late May to mid-June. This species is listed as "Threatened" and is believed to occur at only eleven sites in the Commonwealth, one of which is Nantucket. Torrey's beak-rush and two-flowered rush are grass-like plants that also occur in these habitats. Both of these species are listed as "Endangered" in Massachusetts.
One of North America's native bog plants is the cranberry. Although cranberry vines occur naturally in many smaller bogs in the northern portion of the island, they were not actively cultivated here until 1857. The 234-acre Milestone Cranberry Bog, located on the Milestone Road near Siasconset, was established around 1865. The Windswept Cranberry Bog, located on the Polpis Road, is a 40-acre man-made bog that was constructed at the turn of the century. Both of these bogs are owned by the Foundation.
Barrier Beaches and Dunes
Nantucket's barrier beaches occur at the interface between the island and the surrounding sea. Coatue, Great Point, Coskata, and the Haulover collectively comprise an ever-changing fragile strip of sand that shelters Nantucket Harbor from the open waters of Nantucket Sound and the Atlantic Ocean. These beaches have been deposited and reshaped over the last 6,000 years by ocean currents moving sand northward in a process called littoral drift, forming Nantucket's northernmost place - Great Point. An east-west current called long shore drift transported and deposited sand in a similar process to form the adjoining barrier beach known as Coatue. Smaller barrier beaches also occur at Smith Point and Eel Point, on the southwest and northwest corners of the island.
One of the unique characteristics of Coatue is its scalloped harbor shoreline. The six points, or cuspate spits, have interested geologists for years. They were produced and are maintained by wind, wave and tidal action. Because of the harbor's orientation, the prevailing northeast winter winds and southwest summer winds hit Coatue at oblique angles. The resulting waves erode sand from the curves, or bends, and deposit it on the points. In contrast, tidal currents flowing in and out of the harbor erode sand from the points and deposit it back into the bends. These opposing forces have been in equilibrium for hundreds of years.
The processes that formed and maintain these barrier beaches are ongoing. Coatue's westward movement is slowed by man-made jetties and tidal flow in and out of the harbor. However, long shore drift continues to deposit sand on Coatue's north beach, causing it to slowly migrate to the northwest, into Nantucket Sound. The thin and elongated sand bridge that links Great Point to the rest of the island is known as The Galls, meaning "weak place." It is appropriately named because it is periodically washed over and broken through by ocean storms.
Although storm events are dramatic and destructive, they are a natural part of the dynamic processes that form and maintain barrier beaches. In the Northeast, ocean waves tend to be shallow and gentle during the summer, causing sand to build up and make the beach wide and gently sloped. The stronger, more destructive waves that hit the coast during winter erode the beach, making it narrow and very steep. Thus, Nantucket's beaches are constantly changing.
The landward side of a barrier beach is characteristically covered by a system of sand dunes that are deposited by wind and wave action. The primary dune is located closest to the ocean and is the most exposed to the elements. Several other distinct dune ridges behind the primary dune collectively form the more sheltered interdune habitat. A salt marsh is often located on the back side of the barrier beach dune system.
During major storms, large waves often break through and destroy a portion of the dune system, creating an overwash fan of sand. These low areas are important for dissipating wave energy, thus minimizing damage to adjacent dunes. Over time, beach grass and other pioneering vegetation will colonize the overwash fan, trapping sand and forming a new dune. In this way, the beach gradually heals from the damage done by destructive storm events.
In many parts of the United States, off-road vehicle use has become a popular means of accessing and exploring the beach. If not carefully managed, this activity can lead to the permanent destruction of this fragile ecosystem. Beaches and dunes are more susceptible to erosion if the vegetation that holds them in place has been previously damaged.
Nantucket's beaches provide important habitat for several species of rare and endangered shorebirds, including the least tern and piping plover. These species lay their highly-camouflaged eggs in nests that consist of slight depressions in the sand. While these birds are well-adapted to surviving temperature extremes and lack of shade, they can not tolerate the presence of humans and associated species such as dogs, cats, gulls, and crows in and around their nesting areas. Because of strict federal and state laws, beachfront property owners are required to protect tern and plover nesting areas. As a result of these efforts, their populations have steadily increased in recent years.
Many upland birds nest and feed in the interdune areas of barrier beaches, including the American crow, common yellowthroat, gray catbird, northern harrier, savannah sparrow, and song sparrow. On Coatue, this habitat also supports the largest colony of nesting herring and great black-backed gulls on Nantucket.
Plants that grow on the open beach are also well adapted to this harsh environment. They obtain fresh water by absorbing rain and by forming long, penetrating roots. American beach grass is the most common plant found growing on the beaches of the Northeast. It forms an extensive network of underground stems. These rhizomes send up new shoots that hold windblown sand in place and promote the formation of new dunes. In the more protected areas behind the dunes, low shrubs that are able to grow under nutrient-poor conditions serve to further anchor the sand.
Salt-spray rose, bayberry, and beach plum are salt-tolerant shrubs that shed their leaves annually, adding nutrients to the sand as they decay. As the soil becomes more stable and enriched, other species such as eastern red cedar, black huckleberry, and low-bush blueberry are able to colonize these areas, resulting in a diverse interdune plant community. Several rare and unusual plant species occur on the island's dunes, including the prickly pear cactus, oysterleaf, and pink lady's slipper.
As compared to the rest of New England, Nantucket has relatively few hardwood forests. However, it appears that this was not always the case. At the end of the last glacial period, the region's climate was considerably colder. During this time, it is believed that the island was covered with tree species typical of more northern climates, such as spruce and jack pine.
As the glacier melted and the climate warmed, the northern tree species were slowly replaced by trees that prefer warmer temperatures. Analysis of historic pollen excavated from ponds and bogs on the island has revealed that, just prior to European settlement, large areas were dominated by oak, with some beech, pine, maple, and hickory.
This situation changed when emigrants settled Nantucket in 1659 and began to cut trees for home construction, ship building, and firewood. Large areas were also cleared for growing crops and as pasture land. These activities quickly depleted the island of its forests. Several sources report that islanders began depending on firewood shipments from the mainland within several decades of settlement.
Visitors to Nantucket in the late 1700's and early 1800's described the island as virtually treeless. In 1854, the famous naturalist Henry David Thoreau wrote "There is not a tree to be seen, except such as are set out about houses...This Island must look exactly like a prairie, except that the view in clear weather is bounded by the sea..." Since the decline and eventual elimination of livestock grazing in the early 1900's, tall shrubs have gradually become reestablished in many areas of the island. However, hardwood forest communities are still relatively rare on Nantucket and limited to certain areas.
There are several distinctive types of hardwood forests on Nantucket. A maritime forest occurs at Coskata, just north of the Foundation's Haulover property. This unique area contains dry, upland soils but is surrounded by salt marsh, harbor, salt pond, sand dunes, and ocean. The predominant species here are mature black and white oak trees, with huckleberry, hazelnut, bracken, and wintergreen as understory plants. During the Revolutionary War and the War of 1812, there was a severe shortage of firewood on the island because shipping from the mainland was disrupted. It was reported that islanders had to cut down trees from Coskata Woods and transport them over the ice on Nantucket Harbor to town during these times.
The northeastern portion of Nantucket is currently the most forested area of the island because the retreating glacier left behind many poorly drained depressions that developed rich, peaty organic soil. Here, forest trees can grow to be 30 to 40 feet tall before they are impacted by high winds and salt. These wooded areas are locally referred to as hidden forests because they tend to occur in depressions that are surrounded by hills, which reduces salt exposure and makes them somewhat hidden when viewed from a distance.
Some forested areas, such as lower elevations of the Squam Swamp, have standing water in them year-round. The only trees that can grow here are those with adaptations that allow them to tolerate water-logged, oxygen depleted soils. Red maples are able to survive in these conditions by developing shallow, spreading root systems that maximize the absorption of what little oxygen is available. Shrub species such as swamp azalea and high bush blueberry can also thrive in damp soils.
Some of the higher elevations of the Squam Swamp, the Masquetuck Reservation in Quaise, and the forest surrounding Stump Pond (south of the Windswept Cranberry Bog) have wet soils during only a portion of the year. These areas contain trees and shrubs that are adapted to growing under such conditions, including tupelo or black gum, sassafras, shadbush, and sweet pepperbush. Small patches of dry upland soils within these forests contain some beautiful, old examples of American beech, black oak, white oak, and American holly - all trees that are relatively rare on Nantucket.
The vegetation patterns in the forest are influenced by a variety of other factors besides soil water content. Black tupelo, sassafras, and shadbush prefer high levels of sunlight, while American beech, flowering dogwood, red maple, and American holly are understory species that can tolerate shade. Growing below the tree canopy and forming another layer in the forest are shrubs such as highbush blueberry, arrowwood, American hazelnut, common winterberry, and inkberry. Below these is a third layer of flowering plants, ferns, mosses, and ground covers, including cinnamon fern, wintergreen, jack-in-the-pulpit, starflower, and swamp candles.
These arrangements of vegetation also influences the types of songbirds that nest and feed in the forest. Different species divide the same habitat by using different levels, thus allowing multiple species to co-exist in the same area. Birds known to nest in Nantucket's hardwood forests include the black-capped chickadee, yellow warbler, black and white warbler, red-eyed vireo, red-tailed hawk, and great-crested flycatcher.
Many of the trunks and branches of trees in these forests bear a colorful assortment of lichens. One particular species, old man's beard, is particularly common and is so named because of its stringy habit of growth. These plants, as well as algae and mosses, are epiphytes that live attached to the bark of shrubs and trees and manufacture their own food by photosynthesis using sunlight, moisture, and carbon dioxide. Lichens are extremely sensitive to pollution and are therefore rare in urban and suburban areas. However, they occur in abundance on Nantucket because of the island's relatively clean air and high humidity conditions.