Bird Habitats

Disturbed Areas Life Zone
Eastern Forests Life Zone
Wetlands Life Zone


Disturbed Areas Life Zone

New York City Central Park
Cities, suburbs, towns (incl. gardens, parks, lawns)
Dumps

Though not truly a life zone in the biological sense, disturbed areas are so much a part of today’s environment that they can readily be treated as such. From a practical standpoint, a disturbed area can be described as any habitat that has been altered by humans.

In many cases, disturbed areas are populated by a variety of plant and animal species at least as great as those found in more pure habitat associations. Because many disturbed areas often contain edge habitat (where two habitats merge), such areas often bring together assemblages of organisms that otherwise tend to remain isolated in more extensive and more unfragmented habitats. On the face of it, this increased species diversity might seem positive, yet for many species, habitat disturbance has not generally been favorable. The very act of disturbing a habitat invariably affects the organisms that live there in an adverse way. Furthermore, in the aftermath of habitat disturbance inevitably come population changes, often involving the arrival of new predators or competitors, or a decline in the population of a prey or food species.

A more positive way of viewing disturbed areas is to realize that habitat disturbances can be the vehicle for range expansion. The clearing of the eastern forests, for example, clearly provided a window of opportunity for grassland birds to colonize the once heavily forested eastern states. Likewise the creation of artificial islands from dredge spoil has aided colonial waterbirds that are able to use such disturbed sites for nesting. Similarly, as more and more once open landfills are closed and capped, the possibilities for managing the caps for grassland species are considerable.

In more benign ways, disturbed areas that have been abandoned, especially in urban areas, often provide suitable habitat for birds during migration, especially those that feed on weed seeds. Waste areas and community gardens are often overgrown with seed- bearing and other seed-eating birds. In the same way, disturbed areas often harbor an abundance of small rodents, thus making them attractive to raptors, particularly during the winter months. The edges of dumps and landfills are especially good in this regard.

Regardless of how disturbed areas are defined, both animals and nature enthusiasts often find them to be valuable habitats to investigate. The fact that they usually comprise a mix of native and introduced plant species means that an equally surprising mix animal life may also be found in such artificial associations.

Cities, suburbs, towns (incl. gardens, parks, lawns)

As human populations in North America have increased over the years, suburban sprawl has settled across a large part of the land. Much wildlife has retreated in the face of skyscrapers, strip malls, and housing complexes, but development has also created new ecological niches. One need not live in the countryside to enjoy nature and note its pleasantries and vagaries. Backyards and city parks are fine natural laboratories that attract mammals, birds, reptiles, insects, and arachnids, and harbor grasses, trees, vines, and wildflowers. Even in the biggest cities Black-capped Chickadees visit third-story window feeders and Common Nighthawks and Killdeers transform flat-topped gravel roofs into nesting territories. The palm trees in southern California cities provide nesting sites for the Hooded Oriole. A backyard swimming pool can recreate the pond-like habitat of the Black Phoebe. The Virginia Opossum and an occasional Common Raccoon make nighttime visits to trash cans or pet food dishes left outdoors. Coyotes can be seen and often heard in the evenings on golf courses. Homeowners may complain about Woodchucks and squirrels and even flocks of boisterous Common Grackles, but each year sales of garden seedlings and wild bird feed set new records and help ensure that the not-so-wild suburbs will continue to attract their share of adaptable wildlife.

Gardens

Perennial gardens of wildflowers and cultivated plants are wonderful places to enjoy birds, butterflies and other insects, and, of course, flowers and shrubs throughout the season. Flowering shrubs provide nest sites, shelter, and food for birds while wildflowers attract butterflies and hummingbirds. Planting flora appropriate for the caterpillars as well as the adult butterflies makes a garden more welcoming to a wide spectrum of swallowtails, sulphurs, azures, fritillaries, admirals, and skippers. Community gardens are great birding areas in the fall, as harvesting gardeners tend to leave behind lots of extra fruits, vegetables, and flowers.

Urban Parks

City planners have saved a bit of nature for city dwellers, with parks, arboretums, and even garden cemeteries integrated into the urban landscape. One of the most notable landscape designers was Frederick Law Olmsted who laid out Boston’s "Emerald Necklace" of green spaces and designed New York’s Central and Prospect Parks. Birders come to these urban oases in spring and fall to see the migrant songbirds that flock to sizable green spaces as well as to other, smaller parks and arboretums. In the western United States, some cities have developed extensive parks, such as Tucson Mountain Park in Arizona, that preserve large wild areas close to their borders. They offer outstanding recreational opportunities and valuable wildlife habitat, even for such usually retiring animals as Mountain Lions and Bobcats.

Suburbs

Suburbs around larger cities sustain a substantial variety of flora and fauna, especially where ravines and hillsides are too steep to be developed. Through the use of native and ornamental plantings, man-made pools, and feeding stations, suburban properties attract a surprising range of wildlife. Backyard wildlife spotting is a popular hobby, and wildlife agencies have taken advantage of this, gathering valuable data through surveys of backyard mammals, birds, and insects. Nest boxes, including special designs for bats and small owls, and special plantings can help make a suburban plot more of a wildlife sanctuary.

Buildings and Bridges

Many introduced bird species, such as the cacophonous European Starling and the ubiquitous Rock Dove, find nesting and roosting sites among urban structures large and small. Chimney Swifts, after spending the winter feeding over South American forests and savannas, depend on city and suburban chimneys for nest sites. In recent years, wildlife biologists have coaxed Peregrines into nesting successfully on bridges and tall buildings, after DDT poisoning had completely obliterated them as a breeding bird in the East. Many, usually unwelcome, animals, such as the House Mouse, various insects and spiders, and bats, which often roost in attics, set up residence inside homes and other buildings. In certain parts of the South, Mediterranean Geckos can be seen darting along walls and ceilings feeding on insects attracted to lights.

Roadsides

The construction of roads has disrupted many habitats and dislodged countless animals from their homes. However, many plants and animals reside along roadsides or visit them in search of food. Butterflies and other insects, crows and other birds, and myriad wildflowers, such as Chicory, Purple Loosestrife, and milkweed, can all be observed while driving down the road. During warm evenings, reptiles sometimes appear in car headlights as they rest on country roads, soaking up warmth from the blacktop. White-tailed Deer, Woodchucks, foxes, and raccoons often venture into the road looking for food or while travelling from area to another. Unfortunately many of the animals that take advantage of roadsides end up being hit by automobiles.

Dumps

Dumps, landfills, and waste areas tend to be filled with vegetation discarded by home owners, landscapers, and municipalities. Many of these plant species are hardy enough to take hold readily and flourish in the outskirts of dump areas. A number of these exotic weeds and shrubs produce seeds or fruit that can be highly attractive to species with these food preferences. In addition to weeds and low-growing shrubs, the actual contents of an open landfill can provide nutrition for quite an assortment of creatures, including vultures, gulls, crows, rats, skunks, raccoons, and even bears (including Polar Bears in the Arctic). Dumps provide feeding opportunities for species whose other sources have become unavailable, especially in winter, when the borders of many dumps sometimes literally throng with sparrows that are attracted by the abundance of weed seeds.

Eastern Forests Life Zone
White Mountains National Forest in New HampshireForests & Woodlands

North America’s forests, much like great forests anywhere in the world, represent a complex of plant species occurring in specific regions and influenced by a variety of factors, including latitude, elevation, slope, soil type, rainfall, and temperature. In addition, events such as fire and human disturbance play an important part in determining the composition and structure of plant communities in this life zone.

The forests and woodlands of North America can be divided into two zones: the eastern forest zone and the western forest zone. The eastern forest zone is a vast swath that begins in the north with the enormous boreal coniferous forests of Canada and extends southward, incorporating the transition forests of New England and the Great Lakes states, the mixed deciduous forests of the middle states, and the pine forests of the Southeast, finally reaching the subtropical hardwood hammocks of extreme southern Florida.

In broad terms, eastern forests reflect the pattern described above; however, within those forest types are numerous subtypes--the pine barrens of New Jersey, the oak-hickory forests of the Ozarks, and the magnificent forest complexity of the southern Appalachians, to name but a few. All of these forest types are characterized by dominant tree species, and with each dominant tree are other plants, along with bird and animal life, to match.

Over the last 300 years eastern forests have seen many ecological changes: fragmentation brought about by human disturbance and development, changes wrought by forest products industries, ravages by insect pests and tree diseases, acid precipitation, fire damage, and extensive clearing for farming.

Western forests are considerably more complex than the forests of eastern North America. Subtypes include magnificent old-growth rain forests in the Pacific Northwest; diverse conifer associations in the Sierran mountain forests of California and Oregon; vast mid-elevation Lodgepole and Ponderosa Pine/Douglas Fir forests in the Rocky Mountains; upper-elevation subalpine forests in nearly all western mountains; and corresponding woodland habitats on their lower slopes.

The growing conditions in western forests are often highly variable. Because of the severity of western winters, many conifers have adaptations to give them greater survivability than is found in the less hardy deciduous trees of eastern forests. In the coastal redwood forests of California and in the old growth forests of Washington and southeastern Alaska, trees of immense proportions thrive under the influence of heavy rainfall and a mild coastal climate. In the Rocky Mountains, unbroken stands of Lodgepole Pine flourish wherever forest fires periodically ravage the mountain slopes, thereby releasing seeds from cones that will quickly germinate and renew the process of forest regeneration.

Forests & Woodlands

Eastern Forsests
The great and varied North American forests spread from the Pacific to the Atlantic and from the subtropics to the Arctic. From the pinyon-oak woodlands of the Great Basin to the boreal forests of eastern Canada, they achieve richness and grandeur in every corner of the continent. Temperature and moisture are the two elemental forces that shape the make-up and distribution of North American forests. Hemlocks in cool, shady glens, redwoods in mist-shrouded valleys, and spruces along the southern rim of Hudson Bay are growing where they want to be, in the conditions that suit them best.

Although the major forests in North America differ from one another in many aspects, they are also alike in some ways. Trees, of course, are the single most important element of forests, but they are not the only element. A forest is made up of communities, from the soil, which is alive with microscopic, life-giving organisms, to the forest floor, where decaying leaves provide nourishment for wildflowers and ferns, to the understory, with its array of shrubs and small trees, to the canopy, where the tallest trees form the upper layers of the forest. Each community of each forest type has a more-or-less distinct group of plants and animals. Together, they make North America’s forests enduringly inspiring natural wonders.


Eastern Forests

Over their north-south range of 2,000 miles, the forests of eastern North America extend from the southern shores of Hudson Bay to Florida. They range from near-Arctic to near-tropical, and are part of every landscape, from seashore to mountaintop. Eastern forests, often in unbroken swaths that stretch for hundreds of miles, support thousands of species of trees, shrubs, and wildflowers, including mighty trees of enormous dimensions, as well as a wide variety of wildlife ranging from microorganisms to the imposing Black Bear--all coexisting with human settlements in one of the most heavily populated regions of the globe.

Boreal Forest

The boreal forest extends from Alaska to the Atlantic Ocean and from Hudson Bay to the northernmost United States. It is the coldest and slowest-growing forest, and the conifer species that dominate--Balsam Fir, Tamarack, and Red, White, and Black Spruces--are adapted to withstand below-zero temperatures for long periods of time. These trees are equipped to reproduce quickly in a short summer growing season, and are also able to come back, albeit slowly, from the ravages of fire.

These dark, fragrant coniferous forests are almost devoid of ground cover vegetation, as little light penetrates the thick evergreen groves. The attractive Bunchberry is one wildflower that thrives in the highly acidic soil in these low-light surroundings. Spruce Grouse survive in the dark groves by eating conifer needles, while wood warblers and various insects abound in summer.

Transition Forests

Between the pure coniferous woodlands of the boreal forest and the mixed deciduous woodlands of temperate North America lies a transition zone of forest that combines both types. Conifers mingle with deciduous trees as far south, and deciduous trees mix with conifers as far north, as their evolutionary adaptations enable them. As a result, there is a curving band of mixed forest types, ranging from 100 to 500 miles wide, from Minnesota to New England and the Canadian Maritime Provinces.

The transition forest differs from the boreal forest in a number of ways. It is warmer, with a longer growing season. The forest canopy is patchier, and the woods are therefore more open and more filled with sunlight, enabling a richer understory and herbaceous layer to grow. Moisture evaporates at a faster rate in the transition forest, and the woods are less damp and the soils less saturated.

Spring wildflowers, summer birdsong, and the finest fall foliage in the world are outstanding features of transition forests. The Sugar Maple reigns supreme wherever it can crowd out spruce, pine, and hemlock. Violets of bewildering number and variety, trilliums, geraniums, and any number of carpeting wildflowers greet springtime visitors. Woodland butterflies such as the White Admiral and Northern Pearly Eye can be common in summer. Resident White-tailed Deer, American Beavers, Common Porcupines, and Moose occupy various tracts of this wide-ranging forest. The songs of Black-throated Green and Black-throated Blue Warblers, and Blue-headed, Red-eyed, and Yellow-throated Vireos, which glean arboreal insects and their larvae, may be heard throughout these woods from May to August.

Mixed Deciduous Forest

From the Great Lakes to New England and south to the beginnings of the Deep South, the mixed deciduous forest spreads like a green blanket. There is an explosion in the number of tree species, with well over a hundred. The Sugar Maple no longer dominates but rather joins with dozens of other species, among them Yellow Poplar, American Sycamore, Sweetgum, Yellow Birch, maples, oaks, hickories, and magnolias. In the north-central portion of the mixed deciduous forest, Sugar Maple and American Beech are abundant. In the northwestern portion, Sugar Maple associates primarily with American Basswood. And while oaks and hickories occur over most of the deciduous forest, the dominant concentration of these trees is found in the Ozark Highlands west of the Mississippi River.

From Virginia to Tennessee, along the Blue Ridge Mountains and the southern Appalachians, the deciduous forest achieves its peak in age, maturity, number of species, size of individuals, and area preserved in a virgin state. The cove hardwood forests of mountain ravines are the most impressive; remote and undisturbed, they express the destiny of a deciduous forest after millions of years of evolutionary development.

Acorn-loving and hickory-loving Eastern Gray Squirrels, Eastern Chipmunks, and Wild Turkeys are often seen in mixed broadleaf forests. Eastern Screech-Owls find Deer Mice, Southern Flying Squirrels, woodland moths, and earthworms aplenty for feeding their broods. Virginia Opossums--active, like owls, mainly at night--may sometimes be glimpsed padding along woodland paths.

Eastern Pinewoods

Pines are everywhere in eastern North America. They exist in every eastern forest habitat from the subarctic to the subtropical, from lowlands to highlands and wetlands to uplands. Pines are among the most tenacious of trees, flexible in response to wind, salt spray, and other environmental stresses and celebrated for their ability to recover and reproduce after forest fires. Pines grow extremely well in relatively infertile sandy soil. Because huge areas of eastern North America are underlain by sand, there are immense concentrations of pines covering thousands of square miles.

The pinelands of eastern North America are not one kind of forest, but many: pure groves of Longleaf Pine; groves of Loblolly Pine mixed with oaks and hickories or with White and Post Oaks; Shortleaf Pine with oak and hickory; Slash Pine groves in the southernmost regions; Sand Pine on sterile sites; Pitch Pine and Bear Oak on Cape Cod and in the New Jersey Pine Barrens; and dozens more. Situated primarily on the coastal plains of the Atlantic Ocean and the Gulf of Mexico, pinewoods extend from Cape Cod south to Florida, west to the Big Thicket of Texas, and south intermittently to the mouth of the Rio Grande.

Animal life abounds in pine woodlands. Woodpeckers of all sorts, from the abundant Red-bellied to the very local and endangered Red-cockaded, reside in various pinelands. Carolina and Black-capped Chickadees are constant companions in southern and northern pinewoods, respectively, and Eastern Bluebirds and Pine Warblers occur throughout the East. Southern pineland reptiles include the rare Gopher Tortoise and Indigo Snake and the much-maligned Pygmy and Diamondback Rattlesnakes.


Eastern Forests

Boreal Forests
Transition Forests
Mixed Deciduous Forests
Pine Barrens

Image: Baxter State Park, Maine
Photographer: Stephen G. Maka

Eastern forests, much like great forests anywhere in the world, represent a complex of plant species occurring in specific regions and influenced by a variety of factors, including latitude, elevation, slope, soil type, rainfall, and temperature. In addition, events such as fire and human disturbance play an important part in determining the composition and structure of plant communities in this life zone. The way to best appreciate the Eastern Forest Life Zone is to travel south from the vast boreal coniferous forests of Canada into the transition forests of New England and the Great Lakes states, then on through the mixed deciduous forests of the middle states to the pine forests of the Southeast, and then finally reaching the subtropical hardwood hammocks of extreme southern Florida.

In broad terms, eastern forests reflect the pattern described above; however, such a description fails to highlight the numerous subsets that comprise the entire eastern forest region--the pine barrens of New Jersey, the oak-hickory forests of the Ozarks, and the magnificent forest complexity of the southern Appalachians, to name but a few. In all of these ecosystems, there are dominant tree species that characterize the forests, and where these dominant trees occur, there are other plants, along with bird and animal life to match.

While some Eastern forest bird species such as the Blue Jay are common and widespread, others like the Kirtland’s Warbler are rare and local. Some bird species are specifically confined to one forest type or another and in some bird groups, replacement species are found, such as Boreal, Black-capped, and Carolina chickadees as one moves from north the south from one forest type to another.

The Eastern Forest life Zone represents one of the most important ecosystems in North America for a number of Neotropical migrant species that are increasingly being demonstrated to have declining populations. While the reasons for these declines are complex, ecological changes in eastern forests are clearly a factor. Forest fragmentation brought about by human disturbance and development, changes wrought by forest products industries, ravages by forest insect pests and tree diseases, acid precipitation, and forest fire damage are among the more immediate events affecting birds in eastern forest ecosystems. Additionally, in the aftermath of extensive forest clearing since the arrival of the colonists in the 1700’s, bird populations in the Eastern Forest Life Zone have witnessed a variety of changes through the years, including the increase of pernicious species such as the brood-parasitic Brown-headed Cowbird. Combined with changes in land use and a general overall increase of bird predators, there is justifiable reason for concern over the ultimate welfare of many bird species in eastern forests.

Boreal Forests
Image: Mountain National Park, Manitoba
Photographer: Rick Cech

The northernmost forest in North America--and the largest forest by far--is known as the boreal forest. The boreal forest can be divided roughly into three bands: 1) a pine and hemlock zone in the south; 2) a central belt of spruce-fir climax forest in the center; and 3) a northern zone of taiga, where the spruces and firs become increasingly dwarfed in more northerly latitudes, until they are replaced by tundra. The boreal forest forms a continent-wide band that extends northwestward in a wide arc from Newfoundland to Alaska. Over most of the area between the Cordillera and the Atlantic Ocean the landscape is uninterrupted by mountains, and the forest virtually unbroken. Within this area is one of the world's most extensive systems of rivers and lakes.

The great ice sheets that sprawled across this region from 500,000 to 10,000 years ago left a random series of channels and basins. Some of the lakes seem somewhat aligned in a northeast-southeast trend, but whatever drainage patterns existed in preglacial times have been distorted and otherwise deranged into a system that seems to make little sense. The glaciers picked up giant boulders and transported them, then melted to deposit random hills of till (glacial drift) and to fill up valleys on a less than systematic basis.

A typical summer day in the boreal forest begins calmly, the ponds placid, the waters overhung with mist. By midmorning, wind blows the fog away, clouds race over the tips of the spruces, and the rain squalls blot out the forest. The rest of the day is likely to be cool and cloudy, with light breezes. There are few roads, trails, or settlements over most of the boreal forest, and the principal means of access is by canoe. A canoeist gliding along placid water's surface, stepping out on a point of land, or entering the forest experiences a feeling of water everywhere. In roving through this wilderness during summer, the traveler encounters water continuously.

Conifers

The woods are broken by light brown outcrops of granite and other ancient rocks that underlie the forest, or by huge boulders, called erratics, that were dropped as the glaciers melted. Nearly every geological feature is obscured by forest, which is dominated by Balsam Fir, Black and White spruces, and Red, White, and Jack pines.

The Red Pine is a handsome species that grows as high as one hundred feet. The Jack Pine presents a ragged, stunted appearance and seldom exceeds sixty feet in height, but it covers thousands of square miles; pioneering mostly on relatively sterile soils that few other trees inhabit, it shelters the seedlings of Red Pines for a time, yielding to their dominance as the trees mature.

As for the White Pine, no other tree in northern North America was as important to early settlers. It has been called the most generally useful wood our country has ever possessed. Soft and lightweight yet strong, it was ideal for the masts of ships, among other uses, and was therefore so widely and extensively employed that the tree was nearly removed from the greater part of its range. No other tree grew so large in eastern forests; many specimens in primeval forests are thought to have been more than 250 feet tall (although some experts question this). It was also one of the most widespread species in northern woods. By 1900, however, the virgin White Pines had nearly all been eliminated from the North, and less useful trees such as spruce and fir took over much of their range.

Today White Spruce, more common on drier soils, is a taller and more shapely tree than the Black Spruce, which is well adapted to moist and poorly drained soils. Because of their disparate habitat requirements, these two species are among the most abundant and widely distributed of North American conifers. The Balsam Fir also reproduces and spreads vigorously because of its plentiful winged seeds, adaptability, and speed of growth.

The boreal forest is not made up entirely of coniferous trees. Stands of white-barked Quaking Aspen mingle with the conifers, and in wetter places the Paper Birch sinks its roots into shallow, sandy loam. Balsam Poplar and Big-toothed Aspen also occur.

Bogs

Occasionally the canoe glides over a mucklike "soup," which contrasts sharply with the pure clean lakes and crystal-clear rivers of the region. This means that the traveler has entered a bog. A bog can be virtually any size, shape, or depth, but its existence usually signifies that the area is in some stage of transition from lake to meadow to forest. The presence of aquatic plants--Common Spatterdock, water lilies, pondweed, sedges, and the like--indicates that vegetation and soil are moving in and taking over.

Farther on, there are bogs in which the aquatic species are crowded out by sphagnum moss, ferns, Wild Rice, Labrador Tea, and shrubs such as blueberry, Mountain Maple, and Showy Mountain-ash. Where sunlight reaches the water's edge, there is likely to be an abundance of willows, Northern White-cedar, and Tamarack. It is only a matter of time until spruce and fir become established on the developing meadow and eventually dominate, as they do across the granite uplands. Uphill, away from the bogs, the soil is well drained and Bur and Northern Red oaks have become established, at least tentatively.

Fires do occur in the boreal forest, but they are less frequent than in drier forests such as the southern pinelands. Although precipitation falls rather uniformly throughout the year, there are times in summer and autumn when the woods dry out and are ignited by lightning. Wide areas of the vast boreal forest may be burned, but the lakes and streams act as firebreaks.

Sunlight

Within the forest, sunlight is reduced to a minimum by the year-round canopy of interlaced evergreen branches, so wild flowers are scarce and hard to find. Harebells often grow next to waterfalls, where sunlight can reach them. In places where conifers are removed by fire and temporarily displaced by aspen, birch, and blueberry, the canopy is more open, and there are more extensive displays of flowers on the forest floor, including the magenta Fireweed and yellow Spotted Touch-me-not. Late in summer, more color is added to the forest in areas where the showy red fruits of Red Baneberry, Bunchberry, Thimbleberry, and Elderberry are produced. In autumn, the pockets of broad-leaved woods become patches of brilliant colors. For most of the year, however, these deciduous stands are leafless and gray. The boreal forest is dark and cold, its constituent species of plants and animals adapted to survive long months of winter when lands and lakes are frozen and the sun appears above the horizon for only a few hours each day.

Range

The boreal forest extends 4,000 miles between Newfoundland and Alaska, and ranges from the boundary of the United States north through southern Canada to the shores of Hudson Bay. Extensions of this forest type occur in suitably cool environments along the high ridges of the Appalachian Mountains as far south as Georgia. The largest expanse of boreal forest in the lower forty-eight states is found around the shores of Lake Superior in northern Minnesota, stretching from Lake Itasca State Park to the Boundary Waters Canoe Area. There are also a few boreal stands in the Upper Peninsula of Michigan, the northern tip of lower Michigan, and in a few localities in Wisconsin.

Physical Features

The boreal forest is locked in ice and buried in snow for perhaps eight months of each year. The elevation of the forest is never greater than 2,500 feet. Consequently, the forest does not ordinarily receive the very heavy accumulations of snow--more than fifteen feet a year--that characterize mountain forests. In eastern North America, precipitation throughout the boreal forest ranges from twenty to fifty inches annually, with higher amounts falling near the Great Lakes and the Atlantic Ocean. The average temperature in January is 0° to -20° F, with extremes of -60° F. The average July temperature is 50° to 70° F, but may reach as high as 100° F. Evaporation is normally slow in cool humid environments, and more precipitation falls than can be removed by sluggish streams in random drainage patterns. These factors help account for the exceptionally moist environment of the boreal forest.

The rocks underlying parts of the boreal forest are Precambrian, some of them among the oldest on earth. They form a complex collection of granite and metamorphic rocks that in the billions of years since their formation have been contorted and deeply eroded. In many places, little or no soil has accumulated above the bedrock, and the granite and granite-gneiss are exposed at the surface.

For more than 500,000 years, as glaciers advanced and retreated, these rocky surfaces were scraped clean, chiseled, and channeled. Evidence indicates that with each melting of the glaciers, ancient forests that had retreated to the south advanced and covered the northern landscapes again. These forests were inhabited by mammals such as mastodons, Beavers, and wolves. The last glacial retreat occurred roughly 10,000 years ago; at this time, the ancestors of our modern forests began to grow back, and it is likely that the ancestors of present-day mammals also moved north at that time.

After the last ice age, the wide distribution of lakes in the boreal forest helped to keep the climate cool and the atmosphere humid. Any soils that formed as a thin veneer on the barren rock remained largely sterile. Consequently, the boreal forest is young in terms of the development of its soils and life forms.

Considering the adverse conditions under which it grows, it may seem surprising that so dense a forest can grow successfully and spread for thousands of miles from coast to coast. One explanation is that there has been much less human intervention in this forest than in others. European settlers tried to introduce agriculture in the more southerly parts of the forest, but they succeeded only marginally. Increased commercial trade had a strong impact on forest ecosystems. Rivers were used as avenues of transport by fur trappers, and railroads made wood products accessible. The boreal forest was extensively exploited in the nineteenth century; White Pine was particularly in demand. The consequences of these activities on slow-growing forests were, in places, significant, but the intense fires that swept over the area had the most devastating effect on White Pines forests. The current impact of human intervention appears to be from sulphur dioxide in the air and the consequent effects of acid rain.

Plant Life

Despite the limitations imposed by climate, the boreal forest harbors a rich variety of life. At first glance, it appears to be composed of Black Spruce, White Spruce, and Balsam Fir for as far as the eye can see, but there are other types of vegetative associations in addition to the dominant conifers. These include glades, meadows, sedge marshes, swamps, bogs, deciduous woods, and communities along the shores of lakes and streams. The variety of plant communities creates diverse environments for animals. However, because of environmental limitations, particularly climatic ones, there is less diversity than in other forests. In fact, only the tundra to the north has a less varied flora and fauna.

The acidic soil offers some limits, too. Spruce and fir grow in moisture areas; Jack Pine inhabits drier areas, becoming established after fires. The cones of Jack Pine are serontinous, opening when heated; hence the seeds are most likely to be scattered at opportune times--when competing vegetation has been burned away, the shade removed, and needed mineral soil exposed.

The three principal broad-leaved trees in the boreal forest occupy not only sites opened by fire but also other types of clearings or disturbed soil. The Quaking Aspen is especially widespread throughout North America, partly because it can be blown great distances by the wind. The Paper Birch does well in northern latitudes because it has a corklike bark that protects it, at least to some degree, from the extreme cold of winter. The Balsam Poplar--our northernmost hardwood--grows to be the tallest broad-leaved tree in the boreal forest, reaching a height of eighty feet and a diameter of three feet. The perennial shrubs and herbs of the boreal forest are nearly all low-lying, weighted down much of the year by winter snows. But the protective blanket of snow enables them to survive the harsh winters and the drying effects of cold air. There is a considerable understory of blueberries, Bearberry, rhododendrons, and cassiope, together with a carpet of sphagnum moss, mushrooms, and lichens. Also common are Nodding Trillium, One-sided Pyrola, Northern White Violet, Twinflower, Bunchberry, Starflower, and the Bluebead Lily. It is curious that the forest floor of the cold coniferous is in places more heavily vegetated than parts of the oak-hickory forest a few hundred miles to the south.

Ecology

The key to such seeming anomalies is the presence of nutrients--chiefly carbon, oxygen, hydrogen, and nitrogen--in the soil. Nitrogen is especially important because it is a chief constituent of proteins. Cold slows the rate of decay, and often little nitrogen is released.

In the boreal forest, however, there is some fixation of nitrogen in the soil, especially by alders (which are nonetheless scarce in comparison to conifers). Nitrogen fixation is a process whereby certain bacteria in the soil convert atmospheric nitrogen into nitrogen compounds that plants can use. The spruce and fir succeed because they seem able to make more efficient use of nutrients. Being evergreen, they do not have to use energy to sprout new growth as systematically as deciduous trees. Moreover, they have a longer time to transfer valuable minerals from old leaves to new before shedding the old leaves, thus keeping the minerals at work within the plant. All conifers except the Tamarack keep their needles year-round and continue to grow even when the temperature is low.

Perhaps this is one reason that so much other vegetation in the boreal forest is also evergreen: Evolutionary processes have favored those plants that are thrifty with what they have and can make efficient use of it.

In addition to the recycling process, plants get nutrients from other sources, such as mosses. Sphagnum mosses abound where sufficient moisture exists--on tree trunks, tipped-over trees, rocks, and litter. If their roots don't penetrate deep in order to draw up water, the mosses have to depend to a considerable extent on water that falls through branches of trees above. Fallout from occasional showers, on passing down through the limbs from the canopy overhead, becomes a dilute solution of minerals by the time it reaches the forest floor. Even with that, nitrogen is still scarce and must be obtained from every possible source.

Scarcity of nutrients makes organic growth tenuous, and competition is vigorous. There is evidence that the germination, growth, and development of Jack Pine seedlings is inhibited by several things, among them the goldenrods that share the vicinity. It is believed that there may be a transfer of chemicals in the soil that limits the growth of plants that would compete with one another.

Among the deciduous trees found in the boreal forest, supple branches are the norm. Aspen and birch branches can bend almost double without breaking under the weight of snow. This suppleness has a distinct advantage for forest animals: It brings tree buds within their reach as food. The birch also has tough waterproof bark that can withstand cold, desiccating winds. All life here is adapted to survive the cold. These adaptations include a heavy coat of fur for mammals and feathers for birds that insulate them from the cold and permit them to remain more or less active all winter. Less hardy animals hibernate or remain within the relative warmth of burrows under the snow or in the ground.

Although extremes of temperature do limit the range and habits of animal life, they are not the most crucial factors governing northern forest ecology. More important to forest life is the length of the growing season, which averages three or four months in the boreal forest. The brevity of the summer is somewhat balanced by long midsummer days of close to twenty-two hours with uninterruptedly warm temperatures. So despite the severity of winter, the boreal forest in summer becomes an enormous engine of productivity.

The moist forest floor furnishes an ideal habitat for mushrooms and other fungi. Generally, only the larger, more colorful kinds are seen, but hundreds of species grow here in all sizes, shapes, and colors. The Clustered Blue Chanterelle and the bright orange Hemlock Varnish Shelf form bright spots in the shade. Some species, like the Clustered Coral, may resemble undersea corals, whereas the russulas and boletes have the more common stalked mushroom shape. All serve important functions in the forest. Many fungi provide food for various animals, and those that grow on dead or dying wood aid in the process of decomposition and thus help return nutrients to the soil.

Birdlife

The insect populations provide an important base in the boreal food chain for the next echelon of consumers, the insectivores, which includes millions of migratory birds that arrive in summer to find plentiful food supplies. Some of the most common birds in the boreal forest are the Yellow-bellied and Olive-sided flycatchers, Tree Swallows, and warblers such as the Northern Parula. Warblers, which are abundant and breed in the boreal forest, form an extensive consumer population.

Several species of nesting warblers have worked out a way to share the food resources in the tall spruces and firs of the boreal forest: They have specialized through evolution. Cape May Warblers nest and hunt insects in the treetops. Just below them are Blackburnian Warblers, while Black-throated Green Warblers are found as low as fifteen feet above the ground. At the lowest level of trees and shrubs live Magnolia Warblers. Sometimes this layering of animal life is completed when an Ovenbird nests on the forest floor.

Many species of birds make their summer homes in the boreal forest. Herring Gulls, Broad-winged Hawks, and Bald Eagles are commonly observed overhead; Three-tied Woodpeckers, Ruby-crowned and Golden-crowned kinglets, and Black-capped and Boreal chickadees inhabit the coniferous trees. Lincoln's Sparrows and American Redstarts live in alders by the bogs; and Common Loons and the Common, Hooded, and Red-breasted mergansers keep to the water. Some birds are easily but seldom seen: Ovenbirds and Solitary Vireos sing from the trees, and the distant song of the Hermit and Swainson's thrushes are heard in the early morning or evening. The Gray Jay is nearly everywhere. The voices of White-throated Sparrows and Song Sparrows are mixed with the hammering of various woodpeckers and the chatter of chickadees. Pine Siskins slip through the shrubbery. Cedar Waxwings move in flocks higher up in the trees. As the afternoon wanes, the evening is heralded by Common Nighthawks, which dive and buzz the water in their quest for insects. Sunset is characterized by the calls and answers of loons across the lakes.

Transition Forests

Image: Bear Notch Road, New Hampshire
Photographer: Don Johnson

Between the pure coniferous woodlands of the boreal forest and the mixed deciduous woodlands of temperate North America lies a transition zone of forests that combines both types. Conifers mingle with deciduous trees as far south, and deciduous trees mix with conifers as far north, as their evolutionary adaptations enable them. As a result, there is a curving band of mixed forest types, ranging from 100 to 500 miles wide, in which this transition occurs, from Minnesota to New England and the Canadian Maritime Province. The transition forest differs from the boreal forest in a number of ways. It is warmer, with a longer growing season. In winter, the snowfall may be heavy, but it does not remain on the ground as long. The forest canopy is patchier, and the woods are therefore more open, more filled with sunlight, with a richer understory and herbaceous layer. In the transition forest, moisture evaporates at a faster rate; consequently the woods are less damp and the soils less saturated.

In some ways, however, the transition forest resembles the boreal forest. For example, it has numerous lakes, especially in northern Wisconsin and northern Minnesota, and bogs are common across the northern tier of states. Where temperatures are cooler and the ground is moist, as on the northern sides and summits of mountain ranges, there are forests that are actually southern extensions of the boreal forest.

If that sounds complex enough, be assured that the transition region is regarded, in the eyes of ecologists, as having many more individual forest types and associations. The best way to study in depth the numerous forest communities in this region--or in any other, for that matter--is to visit state and national parks or forests where the details of forest populations and ecology are provided in signs, folders, and booklets. In this habitat guide, the emphasis is on describing how the transition forest appears generally to a person entering portions of it from the east or west. Included are areas of mountaintop boreal forests and of pine forests that are often encountered by visitors exploring the transition forest, although these areas technically do not form part of the transition forest.

The transition forest has recovered so well that parts of it resemble a Gothic cathedral, with massive pillars of Yellow Birch and Sugar Maple rising up to a canopy of leaves that permits sprinklings of sunlight to illuminate the exalis leaves, ferns, and beds of maple saplings on the forest floor. The moisture is sufficient to support rich growths of mosses and lichen over the trunks and gnarled roots of giant beeches. The woods are redolent with the scent of Balsam Fir and Balsam Poplar. The forests are frequently spotted with Eastern Hemlock, and evergreen that appears in deciduous forests from the northern tier of states to the southern. The forest floor is padded with the needles and cones of this hemlock.

Mushrooms are usually mixed with the debris, and shelf fungi cling to fallen trunks. As in virtually every forest of North America, there is some member of the heath family present--most often small blueberries--especially where the soil is acidic. Waterleaf is also common.

Because the transition forest occurs mostly on relatively low land, its general character is maintained over thousands of square miles. But within the broad outlines of mixed conifers and deciduous trees, the constituent species tend to collect in specific communities, according to such factors as soil composition, temperature, gradients, moisture, and the stage of contemporary distribution patterns.

Dominant Tree Types in the Midwest

For example, the Eastern Hemlock is lacking in most of Minnesota. Yellow Birch and Eastern White Pine are also diminished there, whereas Red, White, and Bur oaks are more abundant than in other parts of the transition forest. The most common species is White Pine, sometimes growing in pure stands or with scattered Sugar Maple and American Basswood. But to the south, as environmental conditions moderate, Sugar maple and Basswood become more dominant.

In northern Wisconsin the picture is similar, except that Eastern Hemlock is more apparent, though it is at the western edge of its range. Sugar maple continues to be prominent, though American Basswood dominates from place to place. White Pine, Red Spruce, and Balsam Fir mingle with the hardwoods, and among the bogs and lades are communities of various pines and Quaking Aspen. The aspen springs up thickly wherever conditions are just right: open places recently burned or cultivated, scattered sunny sports within the woods, around the edges of lakes and bogs, or along streambanks. Quaking Aspen is not a sturdy tree, will not tolerate much crowding, and is merely a temporary growth that eventually gives way to climax conifers or more hardy deciduous trees. But it is a major factor in forests at these latitudes from the Atlantic ocean to Alaska. The Bigtooth Aspen is less widespread, but its role in transition forests is similar to that of the Quaking Aspen.

In the northern parts of Michigan, there is much more Eastern Hemlock, with maple, American Beech, and Eastern Hornbeam in the understory. The western part of the transition forest has a considerable understory, although some places may support little shrubby or herbaceous growth except saplings of maples and beeches. The small tree layer is usually made up of young individuals of dominant species, especially beeches and maple. But there are also other small trees, such as American Mountain-ash and Mountain Maple. The shrubs include Elderberry, Thimbleberry, Beaked Hazel, and Bush Honeysuckle. Numerous ferns grow in transition woods; some, like the Maidenhair, occupy very moist sites.

Dominant Tree Types in the East

From Pennsylvania northward to eastern Canada is a region of moderate relief with occasional glacial features and low mountain complexes. The forests vary from mixed deciduous in the Allegheny Mountains to boreal in eastern Canada. Red Spruce and Gray Birch assume important roles. The character of the transition forest changes with rises in elevation. The higher Catskill Mountains are covered with spruce and fir, beneath which are transition areas, and finally deciduous forests of Sugar Maple, Beech, and Yellow Birch mixed with spruce and fir, while the lower elevations support Eastern hemlock mixed with oak and hickory.

New York State lies squarely in the midst of the transition zone. Southern species--intrusions from the more southerly mixed deciduous woodlands as well as of pinelands or pine barrens--are found around New York City and on Long Island. Up the Hudson River valley, oaks, hickories, and Yellow-poplars ("Tuliptrees") grow. Over the greater part of the state are communities of Sugar Maple, Beech, Yellow Birch, White Pine, and Eastern hemlock. On the uplands and in the northern part of the state are coniferous forests with paper Birch. The Adirondacks, with their pronounced relief and peaks of over a mile high, support a mixture of forests: swamp, hardwood, spruce, and stunted communities--mostly of Balsam Fir--at tree line.

In New England, where most of the virgin forests were removed, the recovering species are primarily birch, and a few remnants--largely Beech, Sugar Maple, and American Basswood--mix with hemlock, as do White Birch and aspens. Toward the coasts are white-cedar and Pitch Pine. To the far north, the transition forest meets the boreal on the Gaspe Peninsula, in southeastern Quebec.

New England forests are exceptional for their autumn color, especially that of the Sugar Maple. There is, of course, a fair amount of fall color throughout the transition forest; on high ground in New York and New England, it is possible to view wide panoramas painted with nearly every shade of red, orange, and yellow. At such times, the mosaic nature of the transition forest is clearly revealed, because the patches of red, yellow, or orange contrast with the dark green pockets of coniferous forests.

The autumn mixture of colors demonstrates that the shift from boreal to deciduous forest is gradual. No sudden line delineates the change; it is instead marked by a gentle transition between two large forests of markedly different characteristics.

The spruces and firs extend all the way through the transition forest and down the Appalachian Mountains to Georgia as spruce-fir "islands" in a sea of deciduous trees. In a sense, they are outliers of the boreal forest and follow the climate to which they have adapted. Red Spruce is distributed uninterruptedly between Nova Scotia and northern New York, but only in isolated ridgetop localities from there south Fraser Fir replaces Balsam Fir, but the overall appearance of the forest is the same. On the low points and saddles, where spruce and fir fail to grow, pure stands of American Beech are often found, because Beech has a wide tolerance and can inhabit near-boreal climatic conditions.

Range

The transition forest stretches across the northern portions of the Great Lakes states and nearly all of New England, southern Ontario, part of Quebec, and the lower portions of the Canadian maritime Provinces, where the deciduous forest associates with spruce, fir, and hemlock. Included are most of Minnesota, Wisconsin, Michigan, and New York, and all of Vermont, New Hampshire, and Maine. Outliers of boreal and transition forests occur southward along ridges of the Appalachian Mountains, where the elevation is high enough and cool enough to sustain a mixture of northern conifers and middle-latitude hardwoods.

Climate

South of the boreal forest, the growing season becomes longer and solar radiation more intense. The amount of rainfall increases along with the rate of evaporation, and the ground has a chance to dry out now and then. When drenched in fog, the transition forest can be soaking wet with dew; moisture of that sort supports a luxuriant vegetation.

Across the transition forest, precipitation is a fairly uniform thirty to forty inches a year, reaching greater amounts only in northern Mine and parts of the Canadian maritime Province, where the influence of atmospheric moisture from the sea is greater. The precipitation decreases to around twenty-two inches in the western part of the transition forest, a relative aridity that favors growth of grasslands more than woodlands.

The transition forest endures severe temperature extremes, from -60 degres F to more than 110 degres F. The average temperature in winter months is below 32 degrees F, and the snowfall is heavy. The transition forest generally has good weather and a growing season of four or five months; as a result, a considerable number of temperate deciduous trees, such as hickories, most oaks, and the American Beech, reach the northern limit of their range here. But this forest is also vulnerable to severe storms, which generally move from west to east, with freezing polar air masses occasionally descending southward from the northern interior of the continent. Around the Great Lakes it is not uncommon for shores and islands to be shrouded in fog, awash with drizzle, or battered by gales. It is also colder in such localities, which makes the growing season a little shorter. The mountains experience rough storms as well. From time to time the weather is exceptionally violent. In 1977, a squall line advanced across Wisconsin and leveled or severely damaged 850,000 acres of forest, and a 1939 hurricane felled a million Sugar Maples in Vermont. High winds prune the trees and thin the woods, opening up patches of the forest and affecting the whole community of life.

Geology and Soils

The Canadian shield, which underlies much of the boreal forest, also underlies the western third of the transition forest as far east as the upper Peninsula of Michigan. This extremely old Precambrian bedrock of granite, gneiss, schist, and basalt is exposed in some of the uplands and shore features around Lake Superior. Younger sandstones and dolomite protrude on cliffs on the edge of Lake Superior, whereas sandy soils occur locally around parts of the lakes.

Most soils have developed on bedrock or on glacial deposits, and their fertility depends on the nature of the underlying rock, the richness of transported materials, and the length of time humus has accumulated since glacial retreat. Generally, soils that develop on granites and metamorphic rocks are less fertile than those formed on sedimentary formations; soils on limestone tend to be richest because of the high carbonate content of the limestones. Where mixed deciduous forests have reached a climax, the soils are likely to be deep and fertile. The Great Lakes themselves are a product of the scouring and gouging effects of glaciers. Some of the bedrock polished by these continental ice sheets has not yet been covered by rich soil. But as the ice melted, it also deposited a considerable load of sediment, or till, that had been scooped up in its advance. The huge blocks of ice continued on and the glacial debris melted, creating small lakes. Some of these lakes still exist as far east as Cape Cod; others filled in to become bogs, marshes, or swamps.

In the eastern part of the transition forest lies a concentration of high mountains that carry a tundra flora on their summits. The northern peaks of the Appalachian Mountains wind through Quebec and New England, between the Atlantic Coast and the Adirondacks.

Westward to the Great Lakes the landscape is less mountainous, composed of basalt ridges, sand hills, and valleys filled with rich alluvial soil. The mountains and ridges, persistent eroding forces of running water and freezing ice over thousands of years. The legacy is a base of rock and soil on which primitive forests began to develop perhaps as long ago as 60 million years.

The transition forest has little of the disordered maze of lakes and ponds characteristic of the drainage system of the boreal forest. Northern Minnesota and Wisconsin do have large numbers of lakes, but most other localities in the transition region are drained by streams arranged in the more common patterns of trunks and branches, in a process called dendritic drainage. In the center of the transition forest, the Great Lakes drain northeastward into the Saint Lawrence River and thence to the Atlantic Ocean.

Competition

Because the transition forest is a geographic region where plants from one type of forest environment meet and compete with plants from another type, there inevitably are conflicts. This is true at the outer fringes of nearly every community. Changes in water, soil, and weather guarantee to each community a limit of its expansion. Boundary changes are usually gradual, not only in the transition zone but also where the boreal forest turns into taiga and tundra in the far North, and where the transition forest dwindles on the western prairies. Competition is a limiting factor, and many trees compete for space.

In New England's mountains, for example, one can observe what happens to trees that try to grow in climates or regions that are outside their normal range. The weather is windy, cold, or snowy for extended periods. Ridges of nearly barren rock possess low amounts of soil and nutrients to nourish organisms of any size. But herbaceous plants and trees cling to life with notable tenacity and for surprisingly long times. How this happens is not fully understood, though certain adaptations are obvious: reduced size of leaves cuts down exposure and helps prevent excessive loss of moisture; a thickened epidermis protects against weather extremes; large subterranean parts and smaller aerial parts make a plant less vulnerable to its environment; and the rooting of branches lying prostrate against the slope facilitates the spread of the trees. The climate near the ground can be markedly milder than that a few feet above it. The three principal trees that reach high altitudes in New England are Balsam Fir, Black Spruce, and Paper Birch.

Trees

With well-distributed rainfall in summer, and weather extremes less severe than in the boreal forest, the productivity of the transition forest is remarkable. Left undisturbed, the trees reach immense proportions. But they do so only under tension, a constant competition among trees for available sunlight, minerals, and moisture. Usually the Sugar Maple and Yellow Birch dominate the forest; any fir, spruce, or other plant that manages to get started in the understory must compete with thousands of maple seedlings and saplings. The Yellow Birch is not always successful when competing with Sugar Maple, but in places the Beech holds its own quite well. There are pure stands in which Sugar Maple shares it dominance with no other tree. Usually, though, the giants of the forest join in dominance (maple-beech, maple-birch, maple-basswood) with an understory of those species in association with Red Maple, Red Spruce, White Ash, and Black Cherry.

In the transition forest, the Paper Birch grows at considerable distance south of its boreal forest home, but it more commonly grows on cooler north-facing slopes than on slopes with warm southern exposures. This habitat selection may be partly due to the preeminence of Bronze Birch Borers on southern slopes.

In any forest, the tree with the greatest ability to withstand a wide variety of conditions is the one most likely to dominate. Sugar Maple, the most abundant tree in New York State, has a wide tolerance for many kinds of weather; it can also tolerate vigorously growing neighbors and shaded conditions, under which it grows to maturity. It is flexible, able to share dominance from place to place, and long-lived (up to 400 years). White Pines thrive in areas disturbed by fire, although aspens are likely to spring up and cast some growth-inhibiting shade. In the transition forest, White Pines do better than other conifers because they grow faster and root deeper.

One conifer that competes most successfully with hardwoods is the Easter Hemlock. It ranges into the boreal forest, but it is better adapted to environments that are cool rather than cold. Because it tolerates shade, it can grow well in dense forests that would choke out pines and larches. Eastern Hemlock thrives on the moisture and high humidity prevalent in lake country and along river bottoms. It does well individually and in shady groves on ridge tops farther south, in Virginia, North Carolina, and Tennessee, where it reaches near-record proportions. It can even germinate on decaying logs. This ubiquitous species, easily recognized by its drooping tip and soft, dark-green foliage, has exceptional environmental tolerance and tenacity.

The Red Spruce has similar characteristics; it tolerates cold a bit better than hemlock, and so has become that master species in the Adirondack Mountains and along the summits of the Appalachians. Within the past decade, however, its growth has stopped in certain localities, and the trees are dying. Forest experts are trying to find out why this is happening, focusing on the possibility of long-range damage by pollutants in the air.

The softwoods compete vigorously, although they are limited by climatic conditions. Both Quaking and Bigtooth aspens, which range widely in the boreal forest, come down into the transition forest but are found no farther south. Where fire or wind levels an old forest, aspen springs up vigorously. Eventually, though, it commits a kind of suicide: Maturing trees shade the seedling, and shade is something that an aspen cannot tolerate.

When aspen invades fire-racked terrain, it often competes with Paper Birch, which outdoes it is places. The Yellow Birch can also compete aggressively in transition forest, and it tolerates harsher conditions than either aspen or Paper Birch. Yellow Birch mingles with conifers and hardwoods alike, from New England to the southern Appalachians. Nevertheless, it remains sensitive to change, and it withers and dies when disturbed by fire, logging, and the like.

One tough and durable tree from the South has managed to compete well with northern species and to extend its range into colder climates. Northern Red Oak is the only widespread oak in the transition forest; it usually grows along rivers in association with basswood and elm.

Basswoods, commonly known as lindens, are popular, well-known, and widely planted. American Basswood thrives in the wild, especially in the rich moist soil of lowlands, and trees reach large dimensions--100 feet tall and 3 feet in diameter. Its flowers are markedly fragrant and highly attractive to bees. The American Basswood of transition forests differs from the White Basswood of mixed deciduous forests in being larger and more northerly in range.

American Elms thrive from subtropical to boreal habitats. But they are vulnerable to Dutch elm disease, which, in the last half century, has much reduced their populations. The Slippery Elm occupies the same moist environment but is a bit less widespread.

For the most part, the floor of the transition forest is a veritable botanical garden of hundreds of species of herbaceous plants. Among the most common are Wild Sarsaparilla, Starflower, milkworts, Pipsissewa, Rose Twisted-stalk, Round-leaved Orchis, Hepatica, Wood Lily, Twinflower, and various species of baneberry, violet, trillium, and clematis. The herbaceous layer on the forest floor endures overwhelming competition from the massive trees above, especially the deciduous woods whose canopy fills with leaves each spring and cuts out much of the sunlight. The evolutionary trick here is that these plants bloom before the leaves of trees appear. Hence they accomplish the bulk of their reproduction by the time they are shaded. As a consequence, early spring in transition deciduous forests is characterized by thick carpets of wild flowers on the forest floor. In the Great Lakes region, the progression includes Wood Anemones first, followed by Canada Mayflower, trillium, lilies, and others.

Wildlife and The Food Chain

The most active stream of life in the transition forest is that of the billions of microorganisms in the soil. They digest fallen plant debris and convert it into nutrients required for forest growth. These microscopic consumers are preyed upon by tiny predators, and so on up the scale of size in a complex web of food production and consumption.

Above the forest floor, the staple of life is vegetation and the principle food products are seeds and leaves, often gathered before they have a chance to fall. Grosbeaks, finches, buntings, towhees, siskins, juncos, and sparrows consume large quantities of seeds. Cedar Waxwings flock to sources of fruits. Ruffed Grouse browse on fruits, catkins, and tree buds. Herbivores occupy all levels of the forest, from ground to treetop, because their food is found at all levels. Carnivores, too penetrate every level of the forest. Insects, for example, are found from the ground to the canopy, and they become a food source for a wide variety of animal life. The most abundant insectivores are birds, from the tiny Ruby-crowned and Golden-crowned kinglets to multiple species of warblers, Black-capped and boreal chickadees, White-breasted and Red-breasted nuthatches, Northern Orioles, Scarlet Tanagers, and Brown Creepers, most of which get their principal sustenance from insects associated with trees. The same is true of flickers and other woodpeckers. Insects in the open air are captured by aerial feeders such as bats and flycatchers. On the forest floor the invertebrate fauna is consumed by robins, thrushes, thrashers, and woodcocks, as well as by snakes and frogs. Dominating these animals--hunted and hunter alike--are the large carnivores. Hovering over all in the transition forest are two dozen species of raptors, including eagles, owls, and hawks. These birds trim the populations of fish, snakes, birds, and small mammals.

Many of these food chains continue southward into the mixed deciduous forest, though the farther south one goes the less evidence there is of boreal forest elements, except on ridgetops. Eventually the climate becomes so warm that most boreal species give way to competitive species better adapted to warm weather and a long growing season. But where the elements of both boreal and deciduous forests mingle, one finds interesting competition, adaptation, and food chains with characteristics of both. Clearly the transition forest is a busy middle ground between two worlds, where the life of the North meets the life of the South.

Mixed Deciduous Forests
Image: New England
Photographer: Thomas A. Schneider

From the Potomac to the Mississippi, down the Ohio River valley, across the mountains and plateaus of West Virginia, Kentucky, and Tennessee, and to the fringes of the Old South, the deciduous forest reigns supreme. Every spring, the warm sun and abundant rain convert the heartland of eastern North America from a gray landscape of barren trunks and leafless branches to a rich and productive green forest. Every autumn, uncounted millions of trees shed their leaves in an unparalleled, almost unbroken display of color, heralding another six months of dormancy. The mixed deciduous forest of North America is an immense nursery, food-storage center, water-catchment complex, and engine of productivity.

Unlike the boreal and transition forests, the mixed deciduous woods have a preponderance of broad-leaved trees; pines, hemlocks, and magnolias represent the minority evergreens. And unlike the spruce-fir forests, in which only a few major trees stand out, three dozen species are prominent here, all competing for light and space, nutrients and water. The trees are diverse and crowded; so are the understory trees and shrubs and the organisms on the forest floor and in the soil.

On a typical walk through a rocky patch of deciduous woodland in early morning, much of the wildlife is visible and vociferous. Patches of moss drape the gray limestones and carpet the forest floor. Old stumps, eaten and rotted almost to the ground, sport speckles of lichen. Across the forest floor, new grounds burst from the dank, fragrant litter: clumps of mushrooms, quadruplet leaves of oak, triples of hickory, clumps of burgeoning dogwood, tiny Eastern Redbuds with heart-shaped leaves, and fountains of tiny locust leaves reaching tall above the rest. The maples have fresh new leaves of the brightest green and stems of a vivid red.

Springs emerge from black mossy banks; their waters tumble over carpeted boulders and fall from pool to pool. Watercress grows in the ripples or gathers on flats beside eddies.

There is continuous movement here. Some animals are silent, such as the six-foot-long black Racer that moves along logs, then into the water, and across streams as it explores crevices, shrubs, and the layer of leaves on the forest floor.

Silver-spotted Skippers land on moss beside miniature waterfalls and fly back and forth above the creeks. Bees visit the flowers of Queen Anne’s Lace. Cardinals flip from shrub to shrub. Whippoorwills and thrushes call from within the woods, wood-pewees and vireos from up on the higher branches.

Seldom is the growth in the mixed deciduous forest as dense as that in the boreal forest. There are fewer large animals here than in boreal or transition forests--deer and bear are the principal ones--but small life abounds: snakes, birds, butterflies, and the lesser mammals such as Raccoons, foxes and skunks.

From summit balds, the traveler can have unobstructed views of a tumble of rolling hills and plunging valleys for as far as the eye can see. In spring and summer, the mixed deciduous forest is a uniform and mist-covered mass of green, but it appears most spectacular in October. Millions of splotches of color convert the solid green of spring and summer into the multiple hues of autumn. The air is sharper then, and colder. At no other time is the mixture of trees so apparent. Each type of tree assumes its own distinctive color. The giant Yellow-poplar, which bears such large yellow flowers in spring that it earns the nickname--Tuliptree--has leaves of the brightest yellow in the forest, and it is possible from one vantage point to discern dozens or hundreds of these trees scattered along lower slopes and valley bottoms. The scarlet leaves of oaks, the maroon of dogwoods, the purple of Sweetgum, the cinnamon-orange of sassafras, the ivory of Beech--all contribute to what has been called the most magnificent display of color in the kingdom of plants.

The trees shut down for the season by growing a corky layer of cells, the abscission layer, between leaf stems and twigs. Because water and minerals to the leaf are cut off, chlorophyll production increases, and the green fades to reveal orange, yellow, and red pigments, as well as purples and browns. The first leaves of the next spring have already been manufactured; they wait at the edges of twigs as buds, tightly wrapped and protectively encased to withstand the extremes of winter. In spring the new leaves surge to life, and the cycle of seasons begins anew.

The composition of the mixed deciduous forest varies as a result of selective climatic, soil, and topographical factors, together with the history of fire and civilization. Generally, the richness of soil and the favorable climate produce conditions for a diversity of plant life. This is most evident in the understory trees. Whereas the transition forest has few understory trees, and the boreal forest even fewer, the mixed deciduous understory is thickly populated with dogwoods, Redbud, American Holly, Striped Maple, Hornbeam, and various members of the magnolia family. Beneath those are shrubs of Spicebush, Witch Hazel, Papaw, Wild Hydrangea, Mountain Pepperbush, and Hercules' Club. The forest floor, celebrated for its surpassing variety of wild flowers, supports hundreds of species, many with showy blossoms: Trout Lily, Yellow Lady's Slipper, Bloodroot, Wood Poppy, larkspur, Phacelia, Spring Beauty, trillium, and various violets and mints.

In an overall sense, a deciduous forest exists wherever there are broad-leaved trees that lose their leaves more or less in unison every fall. But the mixed deciduous forest lies in the heart of eastern North America: along the foothills of the Blue Ridge and southern Appalachians in Virginia and North Carolina, across the Cumberland Mountains of Kentucky and Tennessee, in the ridge and valley country from New York and Pennsylvania southwestward, across much of Ohio and Indiana, and into Illinois. The mixed deciduous forest may seem homogeneous, but there are many variations, outlets, and intrusions. These woods reach up the sides of mountains, mingle with pines on the coastal plains, and extend their range westward and southwestward. They reach their optimum development in the central uplands, plateaus, ridges and valleys, and across unplowed flatlands.

Pollen evidence shows that following the retreat of the last glaciers 10,000 years ago, much of the northern part of the mixed deciduous area was spruce-fir forest. Undoubtedly the freshly exposed land remained cold and moist for centuries, suitable only for the establishment of boreal forest. But as the continent warmed, the hardwoods slowly spread northward and finally established climax communities that replaced the conifers. The speed of this transformation depended on how rapidly a suitable soil horizon was built up. In geological terms, 10,000 years is only a short time; the process of soil building and climax adjustment has not yet finished, at least not to the degree of maturity found in forests of the southern Appalachians that were never glaciated.

Hence, the northern tier of the mixed deciduous forest is ecologically young, characterized by two dominant species of trees, the Beech and the Sugar Maple. It is located on what is left of the young glacial deposits of the Wisconsin ice sheet, except in places where the moraines and other ridges are too sandy, gravelly, or dry, in which case oaks and hickories are dominant. Generally, maples and Beeches form a nearly pure community around the southern portion of the Great Lakes, in southern Ontario, and in northern Ohio and Indiana and western Pennsylvania.

Although the two climax trees form an almost exclusive canopy, other trees, chiefly White Oak and Yellow-poplar, do associate. The understory is mostly composed of young maples and Beeches, and the forest floor is covered with ferns, Canada Mayapple, and Wild Sarsaparilla.

In the northwestern part of the mixed deciduous forest, mainly in southern Minnesota, southwestern Wisconsin, and northwestern Illinois, another shared dominance has evolved, that of Sugar Maple with American Basswood. This dominance is persistent; if birches and aspens grow in open or burned areas, they are soon crowded out by maples and basswoods. The chief shrub is Elderberry. In the rich soil of the forest floor are Maidenhair, Rattlesnake, Interrupted, and Silvery Spleenwort ferns; Jack-in-the-pulpit, Wild Ginger, Rue Anemone, Hepatica, Bloodroot, violets, Lopseed, Spikenard, and Large-flowered Trillium.

The rest of the mixed deciduous forest occupies landscapes from the Mississippi River to the Blue Ridge, an east-west distance of more than 600 miles. The northern limits of this part of the forest, which was never covered by glaciers, are along the latitude of southern Pennsylvania; in the south, the deciduous woods merge with the southern pinelands at the northern edge of the Gulf coastal plain, a north-south distance of about 400 miles. This is the heart of the eastern forests, a landlocked interior with no direct coastal influence, no frigid winters, no extensive pinelands of spruce-fir forests, no arid prairies, no high-mountain forests.

However, there are modest uplands at the center of the mixed deciduous forest in the Cumberland Mountains and parts of the Allegheny and Cumberland plateaus. The principal characteristics of these uplands, except for the northern fringes, is that there is not a single dominant tree, as in a pure maple grove, or two dominant trees, as in the maple-beech community, but many. The climax is undifferentiated, formed from three dozen species of trees, among them Beech, White Basswood, Sugar Maple, Yellow-poplar, Sweet Buckeye, Red and White oak, hemlock, magnolia, birch, White Ash, and Black Cherry--a roll call of the most notable and abundant deciduous trees in North America. The principal exception is the hickories, and although these occur sparsely in mixed deciduous forests, they are more dominant to the west, beyond the Mississippi River; they are discussed in the essay on the oak-hickory forest.

The mixed deciduous forest has four seasons, all more or less the same length. Winter usually arrives on schedule in the middle of December, and the next three months of uninterrupted cold winds from the north bring snow, ice storms, glaze, sleet, and sometimes weeks of temperatures below freezing. The season is usually relatively mild, but occasionally there are days of bitter cold and heavy snow. When spring arrives, cold air masses from the Arctic collide with warm and moist air from the Gulf of Mexico. This collision usually produces unsettled weather, including electrical storms, fast-moving squalls, heavy downpours, and tornadoes. Nonetheless, April can be dry, which may lead to desiccated woods and wildfires.

Sunshine and precipitation are usually adequate and uniformly distributed throughout the seasons, despite rare dry spells in August; the average precipitation is approximately thirty-seven inches. Average summer temperatures in the Ohio Valley are around 79 degrees F; in January, the average temperature ranges between 22 degrees F and 46 degrees F. If the air masses that provide precipitation slow down, stop, and become stagnant, then the humidity builds up, the temperature rises, and a hot, muggy spell sets in. At such times, the sky becomes hazy and the concentration of atmosphere pollutants increases. Even the forest itself contributes water vapor; each day in summer, evaporation is estimated to return as much as 2,500 gallons of water to the air from each acre of forest.

The mixed deciduous forest comprises numerous microhabitats--cool shady ravines and north-facing slopes for organisms requiring lower temperatures, and open areas, ridgetops, and south-facing slopes for the sun-loving species. It is complex because it is old geologically and biologically, and evolution has been at work, relatively uninterrupted, for millions of years. The trees compete vigorously for space in which to raise their leaves to the sunlight.

This growth translates into an abundance of food for herbivores, and although the animal life in the woods is not nearly as conspicuous as the showy wild flowers, it is there in great numbers. Bees make direct use of the nectar of the flowers and in so doing transfer pollen from plant to plant. Bears eat the honey produced by bees. Other insects are attracted to flowers, and so there are flycatchers in the deciduous forests, including wood-pewees, phoebes, and kingbirds. Hummingbirds fly from flower to flower, as do butterflies and moths. Flowers are clearly hubs of activity in the deciduous forest but of course are just one aspect of the food chain.

The deciduous forest is rich in species not only because of the cycling of nutrients but also because of numerous organisms that can coexist in virtually the same space. All trees and understory plants need sunlight. The herbaceous layer blossoms in early spring and completes a large portion of its reproductive process before the leaves of canopy trees shade the forest floor. Such adaptation allows a host of species, including Bloodroot and various trilliums and violets, to share the same ground as the trees.

Such adaptations are not necessary in the case of phlox, which spreads over exposed and rocky slopes and hence is seldom shaded as spring progresses. Sumac and blackberries are also pioneers on open and distributed ground, often at the edge of the forest. Other plants, such as goldenrods and asters, bloom later and tend to do best on meadows or at the forest edge, where more sunlight is available. Some understory plants, including wild grape, Virginia creeper, and clematis, are adapted to climb up away from the forest floor and secure more sunlight while clinging to tree trunks and rock faces. Every leaf is a source of nutrients, and the search for food is universal, as indicated by the work of leaf-chewing insects, twig borers, cambium eaters, wood eaters, sapsucking insects, seed eaters, and gall makers. All of this action, including both production and consumption, requires energy. One scientist has estimated that the total energy used by plants and animals on an acre of beech-maple forest every year is equal to that needed to supply an average home with electricity for nearly half a century.

Because the climate varies from cold in winter to hot in summer, and because the mixed deciduous forest is well supplied with food and shelter, this region is a biological crossroads. Many species of birds that nest in transition or boreal forests migrate through these woods in spring, just as insects and larvae emerge, and then pass through again on the return trip in autumn. Other species, such as the Kentucky Warbler, fly only as far north as the deciduous forest to breed. Some species, such as the Tree Sparrow, breed in the North and winter in the deciduous forest. And dozens of species, such as juncos, are resident year-round. If they migrate at all, it is only to the top of the nearest ridge to reproduce in summer, returning to the valley for the winter.

The migratory flights of autumn are characterized by large numbers of birds, especially warblers, passing through the forest canopy or high above it. The most spectacular migratory flights are those of hawks, notably the Broad-winged, which make use of strong updrafts above Appalachian ridges. In contrast with the long-range movements of most birds, other animals of the mixed deciduous woods are short-range travelers. Their peregrinations cover only short distances from their places of birth. Their ranges overlap without conflict if feeding habits differ, or if the animals are "layered"--that is, if they occupy the same territory but at different levels in the forest. For example, the Gray Squirrel gathers most of its seeds from the forest canopy and seldom competes with the Ruffed Grouse, which feeds on the forest floor.

The Ruffed Grouse has a unique adaptation to winter. Each autumn, special cuticular appendages, called pectinations, grow on the outer edges of each toe. These serve as "snowshoes," holding the bird up in all but the softest snow. Animals without such adaptations must be prepared to withstand temperature extremes or avoid them altogether.

Pine Barrens

Image: New Jersey
Photographer: John Gerlach / Dembinsky Photo Associates

Pines exist in every eastern forest habitat from the sub-Arctic to the subtropical, from lowlands to highlands, and wetlands to dry lands. Pines are so flexible in response to wind, salt spray, and other environmental stresses that they are among the most tenacious of trees, and are especially celebrated for their ability to recover and reproduce after forest fires.

Pines can also grow extremely well in relatively infertile sandy soil. Because huge areas of eastern North America are underlain by sand, there are immense concentrations of pines covering thousands of square miles.

There are fascinating coastal pine forests on Cape Cod in Massachusetts. The pine forests of Wisconsin, Kentucky, and those on the sand plains between Schenectady and Albany, New York, deserve mention, and ecologists feel that the dwarf pine plains of New Jersey are also extremely interesting.

The reader should avoid a mental picture of pineland habitats composed of pines and no other types of trees. While there are forests that are almost entirely pine, it is much more common to encounter pine-dominated forests in which deciduous trees are also present. In such places, although deciduous trees may constitute the bulk of the population, the forest may still be considered "pineland," because such deciduous intruders are apt to be only transient. After the next forest fire, the more vulnerable deciduous trees will be much less in evidence, while the pines, recovering quickly, reestablish their dominance.

Pine barrens occur mostly on sand, shale, and serpentine soil types in eastern North America. We will concentrate on the most expensive, which are found in central and southern New Jersey. Located thirty miles east of Philadelphia and sixty miles south of New York City, they cover nearly one and one-half million acres. This tract is bordered on the east by the Atlantic Coast and on the west by deciduous forest and urban and agricultural land.

Despite their many assets, the New Jersey Pine Barrens have not been densely settled and today are a comparative wilderness in the heavily populated stretch from New York to Washington. Throughout recent history, people have made some use of the area; for example, early Indians hunted deer here, setting the woods afire to claim their quarry as it fled. There was some farming and pasturing by European settlers, but better soils existed elsewhere. Lumbering and the commercial collection of fuel wood proved short-lived industries, and for a time, cranberry cultivation centered in the bogs.

In more recent years, entrepreneurs subdivided parts of the land into homesites and small farms. Forest fires continued to be set for various purposes--by charcoal makers, for example, to render the trees unfit for other use, and by agriculturists to clear the way for the growth of blueberries. But even though hundreds of thousands of acres were disturbed by human intervention, the forests have recovered, and much of the Pine Barrens is relatively wild today. There is no denying, however, that one of the reasons for this is that the Pine Barrens are out of the way. It is reasonable to assume that had they been located in a direct line between New York and Philadelphia, most of their natural ecological processes would not now exist.

The general appearance is one of open flatlands dominated nearly everywhere by Pitch Pine. But in fact, the Pine Barrens are a mosaic of forest types, and instead of growing on a uniformly flat terrain, the forests occupy both uplands and lowlands. The difference in elevation between the two areas is not significant, but in the lowlands the underground water is much closer to the surface--hence to the roots of plants--than it is in the uplands. This availability of water has an important influence on plant distribution.

Ecologists have identified six major vegetation types in the Pine Barrens: pine-oak forest; Atlantic White-cedar-Red Maple swamp; bog; marsh; stream-pond; and old field.

In the lowlands, the ground is often thoroughly saturated for most of the year. The swamplike forest that results is dominated by Red Maple, Sweetbay (Swamp Magnolia), and Black Tupelo; Pitch Pine is also present, sometimes in abundance. In other wet places grow dense stands of Atlantic White-cedar, also with pines. These communities are localized to a considerable degree, because they have developed along marshes or stream courses or near ponds. The shrubby understory consists of Highbush Blueberry, azaleas, bayberry, Fetterbush, and the ground cover of Chain Fern, sphagnum moss, Partridgeberry, bladderworts, pitcher plants, and older species characteristic of soils that are continuously damp or periodically inundated.

At subtly higher elevations the forest is almost continuously dominated by Pitch Pine, with occasional Shortleaf and Virginia pines. Oaks are much more prominent in the drier uplands; the most commonly encountered species are Black, Blackjack, White, Chestnut, and Post oaks. The shrubby understory also differs from the vegetation of the swampy lowlands; the major species here are Lowbush Blueberry, Black Huckleberry, and Bear Oak, which form a dominant and continuous thicket under the pines. The herbaceous layer includes goldenrods, asters, lobelias, Wild Indigo, False Foxglove, and Turkey Beard.

The pines, however, are not universally dominant; nor does the percentage of oaks per acre follow any precise pattern. The presence of certain trees in certain areas is most likely the result of the repeated action of fire over the centuries. Severe forest fires have a profound capacity to thin out forests, and the Pine Barrens are a good place to observe how different vegetative associations develop in response to natural burning. A large portion of the Pine Barrens is currently composed of Pitch Pines averaging twenty-five feet in height; these associate with Blackjack Oaks less than twenty feet high. Small patches of Pitch Pine grow with Post Oak, and at other sites there are Pitch Pines with a Sprinkling of Black, Scarlet and Red oaks.

There are also patches of woods that demonstrate how oaks have managed to gain some dominance. In these, the Black, Chestnut, White, and Scarlet oaks are slightly more abundant than pines, and in a few places, the oaks form ninety percent or more of the canopy. In others, Pitch Pine becomes a minor component of the community, and Shortleaf Pine becomes more abundant.

Because there are many ecological variables in the coastal plain environment, the tree mosaics in these two floristic complexes of the Pine Barrens--wet lowlands and dry uplands--are much less stable than in such forests as those of the southern Appalachians, which are characterized by ecological repose. There is no lack of animal life, as abundant footprints in the sands of old roads suggest: For herbivores, the Pine Barrens are a gourmet's paradise. In places the undergrowth is so thick that a human traveler must plow through densely interlocked shrubs and headhigh Bracken Fern, both of which provide good shelter for birds and small mammals. On the forest floor animal life is sustained in an environment of Club Moss, large clumps of Reindeer Lichen, Trailing Arbutus, and mats of pine needles through which grasses grow. The water-loving plants found in ponds, bogs, and swamps--such as alders, cranberries, rushes, and sedges--attract wild herbivores, which in turn bring carnivores.

Nine different kinds of salamanders live in the Pine Barrens, along with three kinds of lizards, eighteen kinds of snakes, ten kinds of turtles, and thirteen kinds of frogs and toads. Scores of species of birds live or pass through these woods, and seventy species breed here.

Human observers need to watch for Timber Rattlesnakes, and sometimes the presence of skunks is strongly indicated. The sounds of flickers and woodpeckers drilling in trees, the songs of doves and wrens, and the music of warblers can all be heard in season. Among the most common birds are the Rufous-sided Towhee, Turkey Vulture, American Kestrel, Common Crow, Fish Crow, Mourning Dove, Carolina Chickadee, Blue Jay, Carolina Wren, Northern Mockingbird, Common Nighthawk, and Whip-poor-will. The Pine Barrens possess a unique invertebrate fauna, including abundant populations of moths, gall wasps, tiger beetles, velvet ants, and ant lions. Wood ticks are common, as are Daddy-long-legs. But earthworms are rare, probably owing to the acid nature of the soils.

Climate and Geology

Based on available evidence from ancient pollens in coastal plain sediments, the pines, cedars, oaks, heaths, magnolias, and other genera that dominate the Pine Barrens today have occupied this region intermittently since upper Cretaceous times, 100 million years ago. There are extensive interruptions in the record, owing to long climatic changes and inundations by the sea. During glacial ages, this area was almost certainly covered by tundra and arctic forests of spruce and fir. The habitat as now constituted appears to have developed about 10,000 years ago, and today survives under the influence of climate, soils, fire, and humans.

Every form of life in the Pine Barrens must be adaptable to extremes of weather. There are no protective mountain ranges to keep out storms or to moderate very extreme temperatures, although the area's proximity to the Atlantic Ocean does have a moderating effect on the weather patterns. Cold air masses repeatedly surge southeastward from the interior of the continent, bringing snow, ice, freezing rain, and subfreezing temperatures. Ordinarily such cold causes few problems in the Pine Barrens, where vegetation and animal life have adapted to withstand it. Occasional long winters, however, with low temperatures that coincide with the beginning of the growing season, may wreak havoc just at the time of year when new growth is exposed and delicate.

In summer, warm air masses from the Gulf of Mexico or the Caribbean bring high humidity, afternoon and evening thundershowers, and temperatures that exceed 100 degrees F. Most weather patterns are fairly uniform from one year to the next. The average annual precipitation ranges around forty-four inches, but prolonged droughts now and then may persist for years. At the other extreme are the tropical storms that occasionally advance northward along the Pine Barrens, with winds reaching hurricane intensity and carrying with them torrential rains. Although such excesses are rare, they loom as limiting factors; only those life forms that can withstand occasional deep snow, high winds, and floods have a chance to survive here.

During the ice ages, the southern terminus of the continental ice sheet came very near to the Pine Barrens, stopping less than a dozen miles to the north. The icy north winds that blew from the nearby glaciers profoundly influenced the vegetation.

For millions of years the ocean rose and fell in response to the melting and refreezing of glacial ice; on several occasions it covered the coastal plain of eastern North America. Since the last retreat of the Atlantic, the present vegetation has developed. Sea-level fluctuations during the glacial and interglacial periods left the coastal plain geologically a product of the sea and the land, a place where incoming streams from the continental side mixed their muddy sediments with the sands at the shore. The result is sedimentation typical of deltas, beaches, and floodplains. The gravels, sands, silts, and clay that make up the soil of the Pine Barrens form a substrate of loose and unconsolidated particles with little water-retaining capacity. The frequent thundershowers that come in spring and summer--when plants need moisture most--make it possible for roots to find enough moisture to survive. The water flows rapidly away, however, leaching nutrients from the soil. The remaining substrate is effectively described in one word: impoverished. It is sterile and acidic, largely poor in nutrients. How any vegetation can sustain itself seems at first a remarkable puzzle. But soils like these typify the coastal plain from Massachusetts to Mexico, and a great deal of vegetation does grow.

An exceptional characteristic of the New Jersey Pine Barrens is the extent of groundwater. Some precipitation is intercepted by vegetation and some runs off, but the rest drains into an underground reservoir so vast that it could furnish a billion gallons of water daily to New Jersey cities without endangering the supply.

Ecology

Forest ecology is dictated by a number of circumstances. Climate determines patterns of forest distribution, and the abundance of water influences forest growth. Soils determine what grows where, and human and wildlife settlement can have significant impact. Yet there is one factor that overrides all others. In the Pine Barrens, as much as anywhere in North America, fire has been the dominant force in determining the makeup of the vegetation. In most places in the Pine Barrens, fires have seared the forest every dozen years or so. During the last few years, there has been an average of nearly 2,000 fires annually.

How the forest recovers each time and grows anew attests to the resilience and tenacity of the vegetation. For one thing, not all fires are alike. Some burn quickly, sweeping rapidly and lightly through the woods; others are extremely hot and burn slowly, destroying vegetation down to the ground. When the woods are wet or humid, fires make little headway and do little more than smolder. If there is copious dry undergrowth, a fire can be intense, long-lasting, and destructive; flames fanned by wind can devastate thousands of acres. Controlled fires, deliberately set by land-managing agencies, are used to manage the ecosystem.

After a fire occurs, the natural processes of recovery and succession begin. Grasses and sedges appear first, then seedlings of pine, which must begin to grow in open places with ample sunlight; they soon tower above everything else. In their shade other plants grow slowly and new generations of pines hardly at all. The oaks, however, which can do quite well in shade, grow slowly but steadily among the pines. Under ordinary circumstances, the oaks would likely join with hickories to form a climax forest. But fire, wind, disease, or human action fells the trees before the oaks can reach maturity and choke the pines in shade. Oaks are more susceptible than pines to fire, especially in the seedling and sapling stages, and cannot recover as rapidly; in a fire-prone forest such as this, the pines retain mastery. It is only a matter of a few years until the pines, germinating from seeds or sprouting from stumps, have covered the old burn site.

There are variations in this process. Some pines with especially thick bark may not be killed by fire. Winter fires may also prove less destructive than summer ones, because the prevailing temperature is lower. Such factors help determine whether a tree is killed outright or merely wounded. The degree of destruction of a forest depends on whether a burn is a ground fire or a crown fire, how fast the fire moves, and how intense it is. There is always something left behind to be decomposed.

The Pitch Pine may not be as tall and graceful as other pines or as commercially in demand, but few trees rival it in the ability to survive. Its greatest strength is its adaptability. Evolution has prepared it to grow successfully in sterile soils, to recover from fire, and to withstand attacks by sawflies, webworms, needle miners, beetles, moths, and loopers. Many individual trees are serotinous, opening their cones and casting out seeds when heated. When a fire has eliminated some or all of the competing vegetation, such as oaks, the seeds can sprout and grow in the clearings that have been created. However, seedlings can be eliminated by deer, drought, or competition from overshadowing hardwoods. But despite these inroads the Pitch Pine reproduces in sufficient numbers to assure survival. On the outer reaches of its range, the Pitch Pine even hybridizes with other pines to produce genetically improved trees.

Not every plant that gets a start in this environment succeeds, especially when the margin of survival is narrowed by human intervention. The Pine Barrens contain a large proportion of rare or endangered plants, including species of sedge, orchid, lily, lobelia, and bladderwort. More than seventy plant species are considered to be in jeopardy.

Bird Life

The abundance and variety of vegetation in the Pine Barrens guarantees an abundance and variety of bird life. On a summer morning, the American crow is heard first, loud and clear, before the sun has washed the trees with orange light. A White-breasted Nuthatch is vociferous as it zigzags up, around, and down the trunk of a tree, then over to another to repeat its exploration. Robins join in with their warning notes, followed by the Blue Jay with its explosive calls.

A Whip-poor-will sings its last notes of the night, flying up into the limbs or treetops. Towhees flit through the shrubbery and scratch in the leaves for acorns. A Ruffed Grouse swoops by with its tail fanned, moving to a quiet locality to peck among the leaves and shrubs for insects and buds. A Brown Thrasher slips unobtrusively among the bracken ferns, little more than a shadow as it chases insects or digs in the soft ground for larvae.

The streams, tinted with tannin from the decaying vegetation, are populated with enough fishes to support kingfishers, which perch on limbs overhanging the water. From that vantage point they either dive into the water with a dramatic splash or drop from the tree and glide above the surface of the stream. The moisture here and in wet spots throughout the woods provides a medium for the breeding of insects, and the activity of phoebes, flycatchers, kingbirds, bats, and other insect eaters indicates a plentiful food supply.

Despite the thickets of Bear and Blackjack oaks, much of the forest is relatively open pineland, thanks to the dominance of Pitch Pines. Sunlight usually falls into these woods with little obstruction. If there is no moderating sea breeze, the midday heat can be stifling. From midmorning to mid-afternoon, the animals quiet down to avoid the heat.

By evening the woods are noisy again. As darkness descends, the jays and crows subside, bats and nighthawks begin their nocturnal flights, and Whip-poor-wills resume their calls. A high-pitched hum of crickets rises, and the constant scratching cadence of katydids fills the woods. A night shower may silence these noisemakers, but only briefly.

There are complex ecological relations here, the most obvious of which have to do with food. As would be expected, pine seeds are a staple in the diet of numerous inhabitants, including Carolina Chickadees, Dark-eyed Juncos, Ruffed Grouse, and Bobwhites.

Wetlands Life Zone
Lakes and Ponds
Rivers and Streams
Freshwater Swamps, Marshes, and Bogs

Wetlands are areas with fresh water as a visible and dominant component, at least during some portion of the year. Comprising a myriad of habitat types ranging from large lakes to fragile quaking bogs and wooded swamps to open marshlands, wetlands represent one of the richest, if not most variable, life zones in North America.

Because of their diversity, wetland types are difficult to characterize in a few broad strokes. Changes in groundwater level, as well as fluctuations in rainfall, can significantly affect the amount of water present in certain wetlands from season to season and from year to year. Some wetlands, such as floodplains, contain water only after spring thaws. All wetlands, whether flowing or still, permanent or ephemeral, serve an important ecological role. They recharge water tables, absorb and hold floodwaters, carry nutrients and minerals, and provide shelter and food for an array of animals from tadpoles to Great Blue Herons. Standing-water wetlands such as marshes and swamps filter impurities from the water before it reenters the aquifer, helping to keep lakes and rivers clean.

Wetland vegetation is luxuriant and varied, ranging from lovely yellow pond lilies, rare and delicate orchids, and insect-eating plants to ten-foot-tall sawgrass and cattails to broad-based cypresses and towering riverside cottonwood trees. The vegetation of a wetland is determined by water depth, composition, and acidity, whether the water is moving or still, whether water levels fluctuate at different seasons, the underlying soil composition, and climate.

Different wetlands support different arrays of wildlife. Amphibians, fishes, and insects such as dragonflies are some of the most common inhabitants. These smaller animals make wetlands superb feeding grounds for many types of birds, including herons, egrets, cormorants, hawks, and kingfishers. Beavers and muskrats are among the most amphibious of mammals, while other more landlocked species come to wetlands for food and water. In the southeast, alligators are famous wetland inhabitants, patrolling the Everglades and other marshlands for just about anything that moves, from fishes and frogs to raccoons and waterbirds.

In shallow water, emergent aquatic plants help to support large numbers of breeding marsh birds including grebes, bitterns, waterfowl, rails, moorhens, Marsh Wrens, and Red-winged and Yellow-headed Blackbirds. In wooded swamps and along forested river edges a variety of forest birds, such as Red-shouldered Hawks, Barred Owls, Pileated Woodpeckers, Acadian Flycatchers, Northern Parulas, and Prothonotary Warblers often make their homes. Such forested wetland habitats are especially productive during bird migration seasons because they frequently produce an interesting blend of true wetland birds amidst a variety of more upland species.

Certain wetland habitats, such as those found along the Rio Grande in southern Texas or the San Pedro River in southeastern Arizona, are justifiably famous for their unusual bird and other wildlife. The spectacular waterbird concentrations in the Florida Everglades in winter, and the enormous flocks of Sandhill Cranes along Nebraska’s Platte River in spring are stunning examples of how wetland habitats support and concentrate huge numbers of birds at different times of the year. Indeed, without such habitats, a number of North America’s bird species would be in peril.

Regrettably, wetlands are perhaps in greater jeopardy than almost any other habitats in North America. Historically, wetland environments have been desecrated, either deliberately through filling and dumping, or incidentally through over-exploitation and pollution. Today, many wetland species are showing serious declines that are symptomatic of this wetland degradation.

Lakes and Ponds

Lakes and ponds are bodies of standing fresh water. They may be fed by streams, springs, precipitation, or groundwater. Plants of lakes and ponds may be submergent (entirely underwater), emergent (rooted but extending above the water, such as the Broad-leaved Cattail), or floating (rooted but floating on the surface, such as the Yellow Pond Lily). Lakes and ponds provide habitat for an abundance of wildlife. Mammals and birds use these habitats for watering, foraging, and resting, while in spring, amphibians seek out small lake edges and shallow ephemeral ponds to lay thousands of jelly-like eggs.

Many lakes and ponds were created by the glaciers that once clad much of North America. Kettle ponds are small round pools that formed when a chunk of glacial ice broke free from a retreating glacier, settled into a depression, and gradually melted. Hundreds of kettle ponds dot the New England landscape, including Walden Pond.

A pond is a body of water shallow enough for sunlight to reach the bottom, allowing rooted plants to grow anywhere across its area. Because of the luxuriant plant growth a wealth of animal forms is associated with ponds. Among the roots of Pickerelweed and Spatterdock may be the hungry naiads of damselflies and dragonflies. Bullfrogs and Green Frogs rest upon water-lily leaves. Red-winged Blackbirds and Marsh Wrens raise their families in nests built in reeds or other plants inches above the pond waters. Muskrats and beavers construct lodges on the edges of ponds.

It is depth rather than surface area that distinguishes a lake from a pond: a lake is a still body of water that is deep enough so that at least some part of it does not receive sunlight on the bottom, making plant growth impossible. Lakes are prime habitat for loons, waterfowl, and many game fishes. Bats of several species chase aerial insect prey over cattails on summer evenings. Bluegills, Largemouth Bass, and other fishes share the waters with several types of water snakes.

Rivers and Streams

Inland waterways range from trickling streams that dry out part of the year to roaring white-water channels to wide meandering rivers. Waterways and their surrounding bottomlands are tremendously important to the survival of wildlife. These immensely productive systems are critical to fishes, amphibians, certain mammals, such as beavers, muskrats, and otters, and legions of aquatic invertebrates. These watersides are often lined by diverse and nutrient-rich communities, among them floodplains, bottomland hardwood swamps, and marshes.

Rivers

Rivers and their valleys are natural transportation systems and in many regions of North America have been used by humans since the earliest Native Americans as well as by migrating birds, fishes, and other creatures. Rivers are dynamic forces in the natural landscape, creating islands, sloughs, marshes, and oxbows. Whether they lazily flow with black water or rush headlong in foaming white cascades, they engage the riverbanks and floodplain in a seasonal movement of water, topsoil, and fallen leaves. Fishes beneath the waters provide food for Belted Kingfishers, hawks, eagles, and other birds.

Undammed rivers are subject to seasonal flooding, which has numerous beneficial effects on streamside forests. The Yellowstone, one of North America’s longest and last major undammed rivers, is recharged each spring with mountain snowmelt. Cottonwoods, willows, and shrubs dispense seeds during the spring runoff, and the river’s pounding waters till the soils of islands and banks, leaving fresh deposits of silt that are ideal for new seedlings. Dams on rivers reduce seasonal flooding and affect the regenerative capacity of streamside forests and riparian zones.

Alluvial Rivers

The large alluvial rivers that flow through southeastern and central North America are sluggish muddy waterways rich in organic matter, with fishes and invertebrates living and breeding in and on the water. Bordering floodplain swamps, which can be twenty-five miles wide, are regularly flooded with silt-rich waters, creating ideal conditions for oaks, hickories, elms, and other wetland trees. The Mississippi is one of the continent’s largest alluvial rivers. Small alluvial rivers are often called bayous in the South.

Streams, Brooks, and Creeks

Streams are a vital element of the ecological landscape. From spring through fall they recycle and transport nutrients from fallen leaves and the soil that collects in them. Smaller and shallower than rivers, streams, brooks, and creeks provide living quarters for stonefly and mayfly larvae, trouts and other fishes, brook salamanders, crayfishes, and Minks. Streamside Speckled Alders may hide a family of Yellow Warblers or a Smooth Green Snake within their thick, sheltering branches. Jack-in-the-pulpits grow alongside many streams. The vast numbers of aquatic insects that thrive in these habitats provide food for animals further up the food chain, including snakes, turtles, frogs, fishes, birds, and mammals. In the swift stretches of streams called riffles, immature insects clinging to submerged branches and rocks must possess special streamlining and attachment mechanisms to keep from being carried away. Water striders and Water Boatmen prefer the quiet pools that are also part of a stream’s makeup.

Mountain Creeks

Mountain creeks race and tumble down steep slopes flanked with riparian swaths of firs and aspens and tangles of shrubs, ferns, and moss-covered boulders. Where gradients diminish, such as on meadows, they spread out and begin to cut deep meanders, creating ideal habitat for trout. The creeks nourish a diversity of grasses, wildflowers, and deciduous shrubs ideal for vireos, flycatchers, and Common Muskrats. American Beavers build dams along these waterways. Moose favor these wet meadows for browsing, especially with the shelter of a densely forested area close by.

Dams and Reservoirs

In the American West many of the rivers that once drained the region and provided migration routes for breeding salmon and other fish, have been modified by dams, reservoirs, and channels. Reservoirs that become stable behind their dams become highly productive and support flora and fauna much like those of large lakes. Among the beneficiaries of that change are numerous nonnative fish species, from Striped Bass to Channel Catfish, that live in reservoirs and rivers. Changed aquatic populations have benefited predatory species, such as Bald Eagles, which now concentrate in winter in such fish-rich places as the Colorado River below Glen Canyon Dam.

Reservoirs also have detrimental effects on plants and animals. Those with a fluctuating water level become relatively sterile, with no permanent shallow water in which plants can take root and a very sparse food web. Some reservoirs release water from their bottom that is very cold; the change in temperature can be very harmful to the flora and fauna of the channels into which the water is released.

Freshwater Swamps, Marshes, and Bogs

Freshwater swamps, marshes, and bogs are wonderful, rich habitats that are biologically fascinating and ecologically important. They help keep rivers and lakes clean by filtering out impurities and pollution. Their soils act as sponges during spring flood seasons, absorbing and holding rain overflow and flood waters, and later recharging the water table. They also provide food and shelter for an array of animals from dragonflies to American Alligators. Botanists search out rare orchids and bizarre insect-eating plants in wetlands, and birders look for furtive rails and bitterns there. Getting around on foot in the muck of swamps and marshes can be a tricky business, but walking is sometimes eased by raised paths or boardwalks. In the end, the rewards are always worth the effort.

Freshwater Marshes

A marsh is a wetland with shallow standing water, usually throughout the year, saturated soil, and few or no trees. Marshes form along slow-moving streams and at pond and lake borders, and may be alkaline or acidic. Marsh plants, generally herbaceous, may be emergent (rooted in shallow water) or floating species. Reeds, sedges, rushes, tules, and grasses are most numerous, and arrowheads, cattails, water lilies, and bur-marigolds are also common. The cattail is one of the most common marsh plants but in many areas it is being muscled out by the non-native, invasive Purple Loosestrife and Common Reed.

Marsh habitats support many vertebrates, including a number of frog species, the Red-winged Blackbird, and the Common Muskrat. The notoriously shy American Bittern makes its home in marshes, where it easily finds itself a hiding place among the cattails. Like other wetlands, marshes feature abundant insect life. Insects provide food for reptiles, amphibians, birds, and mammals. Mosquitoes are a prime food item for gloriously colored and patterned skimmers, emeralds, gliders, amberwings, and other dragonflies.

The Everglades of Florida is a 4,000-square-mile freshwater marsh, featuring lush stands of sawgrass up to ten feet tall and supporting immense flocks of wading birds, fish, exotic plants, and, of course, alligators.

Wet Prairies and Savannas

Wet prairies and savannas of the southeastern United States occupy a niche between a freshwater marsh and a dry prairie. Wet prairies, a prime habitat for American Alligators, are marshy ponds that usually remain wet year-round. Savannas are soggy expanses dominated by grasses, sedges, and other plants and maintained by frequent fires. Although most of these wetlands have been converted to agricultural lands or altered by wildfire suppression, a few sites remain intact. Black Bears often inhabit wet prairies, which contain a wide assortment of plants and small animals on which bears can feed. During spring, summer, and early fall, showy composites, figworts, and milkweeds adorn the prairies.

Some of the most characteristic wet prairies occur in Georgia’s Okefenokee Swamp. Mississippi’s Jackson Prairie, in Bienville National Forest, consists mostly of wet prairie islands surrounded by forest. Paynes Prairie, near Gainesville, Florida, is noted for its abundant populations of frogs and snakes.

Swamps

Swamps are freshwater wetlands with shrubs or trees, rather than just herbaceous plants, as in marshes. Common throughout eastern North America, swamps tend to have one or two dominant trees species, although numerous tree species may occur.

Red Maple Swamps

Red Maple swamps, named for their dominant tree species, are the most common wetland habitat in the southern part of New England. There are 300,000 acres of Red Maple swamp in Massachusetts alone, and 200 vertebrate and more than 400 plant species have been counted in these richly diverse environments. Skunk Cabbage blossoms with the earliest thaws, while the Cinnamon Fern’s massive fronds add to the swamp’s summer splendor. Red Maples are often the first trees to show their color in fall.

Cypress Swamps

The swollen base, tall, straight trunk, and watery habitat of the Bald Cypress and somewhat shorter Pond Cypress make them two of the most distinctive trees of the southeastern United States. Widespread from South Carolina to Louisiana and Mississippi, cypress swamps occur in several forms. Cypress ponds have an irregular profile, while cypress domes, also called cypress heads, have a rounded contour, with the oldest and tallest trees in the center of the dome. Vegetation in cypress wetlands includes a variety of heaths, as well as Golden Club, Maidencane, and Peat Moss. Cypresses create a habitat for many other species, including such colorful epiphytes (air plants) as bromeliads, orchids, and ferns, which grow on their trunks and branches.

The massive Okefenokee Swamp of southeastern Georgia, essentially a huge, peat-filled lake that encompasses several wetland habitats, is noted for its extensive cypress stands, which are often referred to as cypress bays or cypress forests. The swamp, now a 396,000 national wildlife refuge, is home to 15,000 American Alligators, 90 species of reptiles and amphibians, 233 species of birds, and 42 species of mammals.

Bay Swamps and Gum Ponds

Other types of freshwater swamps found in the Southeast are gum ponds and bay swamps. Gum ponds, named for the Black Gum trees that dominate the overstory, occur mainly on the coastal plain but occasionally inhabit low-lying areas in the Piedmont. Bay swamps, also known locally as bays, bay heads, or pocosins, are evergreen wetlands dominated by Red Bay, Sweet Bay Magnolia, and Loblolly Bay. They are situated on flat, shallow areas at the heads of streams, in coastal plain sandhill depressions, or in seepage areas. With a plentiful water supply from below-ground seepage, bay swamps are continually wet but seldom flooded.

Carolina bays are ancient bay swamps (some date back 250,000 years) found mainly on the lower coastal plain of North and South Carolina and eastern Georgia. Most are elliptical, oval, or tear-shaped, peat-filled depressions that contain standing water much of the year. They tend to lie along a northwest-southeast axis, range from several hundred feet to more than five miles long, and can be thirty feet deep. Many shrubs and herbaceous plants thrive in Carolina bays, such as Black Gum, Titi, Pond Pine, Giant Plume Grass, and Sweet Pepperbush. The Small-tailed Muskrat, a rarely seen wetland rodent, and the striking Marbled Salamander are known to inhabit Carolina bays.

Bogs

Wet, spongy areas rich in plant residue, bogs are home to many unusual life-forms. Bogs form where water accumulates and sits. Lack of water movement produces low oxygen levels and high acidity, conditions few plants can tolerate. Carnivorous plants, including sundews and pitcher plants, and other bog plants, such as sedges, heaths, bog orchids, and sphagnum mosses, are chemically adapted to survive in this nutrient-poor environment and often grow in a thick mat. Surrounded by tree species that vary by locale, including Tamaracks, Red Spruces, and Pitch Pines, bog waters are usually tea-colored, the result of tannins from fallen leaves leaching into the water.

Bogs are most common in northern coniferous areas, where glacial depressions with no outlets for water flow gradually filled with sediment, providing micro-habitats for plants that survive best in nutrient-poor, acidic environments. New England bogs are an excellent habitat for Four-toed Salamanders and dragonflies of many types, including species that are otherwise rare in the region. Other bogs are found below the southern reach of the glaciers, such as in the New Jersey Pine Barrens. So-called herb bogs occur in seepage zones between pinewoods and swamps or streams in Florida and southeastern Georgia. Named for their lush herbaceous ground cover, herb bogs support large populations of insectivorous pitcher plants and sundews.


Birding Genealogy

Home

Railroading
Revised: 22 Nov 2002 11:46 AM