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The United States and Canada are rich in forests. Before the first white
settlers arrived in the 1600's, forests covered most of the land from
the Atlantic Ocean to the Mississippi River. Altogether, nearly 40 per
cent of the land north of Mexico was forested at that time. More than
half this forestland was in Canada and Alaska, where only a small portion
has been cleared. Even in the lower United States, forests still grow
on much of the original forestland. Today, the United States, excluding
Hawaii, has about 753 million acres (305 million hectares) of forests.
Canada has about 796 million acres (322 million hectares). In both countries,
forests cover about a third of the land area.
The forests of the United States and Canada include all the major formations
discussed in the previous section, except for tropical rain forests. The
U.S.-Canadian forests can be divided into many smaller formations. One
common system recognizes nine U.S.-Canadian formations. They are (1) subtropical
forests, (2) southern deciduous-evergreen forests, (3) deciduous forests,
(4) northern deciduous-evergreen forests, (5) temperate savannas, (6)
mountain evergreen forests, (7) Pacific coastal forests, (8) boreal forests,
and (9) subarctic woodlands.
Subtropical forests thrive along the coasts of the Atlantic Ocean
and the Gulf of Mexico in the Southeastern United States. In these regions,
the climate stays hot and humid throughout the year.
In southern Florida, raised areas of the swampy Everglades support forests
of live oak, mahogany, and sabal palm. These forests have a dense undergrowth
of ferns, shrubs, and small trees. Epiphytes and vines crowd the branches
of the taller trees. Broadleaf-evergreen forests grow farther north, along
the edges of the Atlantic and Gulf coasts. The dominant trees in these
forests are bay, holly, live oak, and magnolia. Thick growths of Spanish
moss, an epiphyte that looks like long gray hair, hang from the branches.
Southern deciduous-evergreen forests grow on the flat, sandy coastal
plains of the Southeastern United States. The forests extend along the
Atlantic Coastal Plain from New Jersey to Florida and along the Gulf Coastal
Plain from Florida to Texas. These regions have long, hot summers and
short winters.
Most of the forests consist of evergreen pine and deciduous oak. Pitch
pine is the most common evergreen in the northern part of these forests.
Going southward, pitch pine is replaced, in order, by loblolly, longleaf,
and slash pine.
Deciduous forests occupy a region bounded by the coastal plains
on the south and east, the Great Lakes on the north, and the Great Plains
on the west. This region has dependable rainfall and distinct seasons.
Severe frosts and heavy snows occur during winter in the northern parts
of this formation.
The northern part of the deciduous forest region was once covered by
glaciers. But the glaciers did not reach the southern portion, which has
the oldest and richest deciduous forest in North America. This forest
lies in the central Appalachian Mountains region. The dominant trees of
the forest include ash, basswood, beech, buckeye, cucumber magnolia, hickory,
sugar maple, yellow poplar, and several kinds of oaks.
In most deciduous forests outside the central Appalachians, fewer species
of trees dominate. For example, various kinds of oaks dominate the forests
from southern New England to northwestern Georgia. Hickory and tulip trees--and
in drier areas several species of pine--grow among the oak trees. Beech
and sugar maple trees dominate the northeastern and north-central deciduous
forests. However, these forests also have many other kinds of trees, such
as black cherry, red maple, red oak, and white elm. The northwestern deciduous
forests are dominated by basswood and maple. Some oak trees also grow
in these forests.
Northern deciduous-evergreen forests stretch from the Great Lakes
across southeastern Canada and northern New York and New England. In this
region of cold winters and warm summers, deciduous trees of the south
are mixed with conifers of the north.
The dominant evergreens throughout much of this region include white-cedar,
hemlock, and jack, red, and white pine. The chief broadleaf species include
basswood, beech, sugar maple, white ash, and yellow birch. In moist areas,
hemlock and white-cedar grow in mixed stands with black ash and white
elm. Drier areas have forests of red and white pine, which is mixed with
some ironwood and red oak. Areas that are neither especially dry nor moist
support maple or beech forests. The region's swamps are covered with black
spruce and larch.
Temperate savannas are found in areas of Canada and the United
States that have fairly light annual rainfall and a long season of dryness.
Temperate savannas dominated by aspen grow in North Dakota, Manitoba,
Saskatchewan, and Alberta. Outside this region, oak, pine, or both oak
and pine dominate the temperate savannas of North America. Savannas of
bur oak, mixed in some areas with other oaks or hickory, extend in a belt
from Manitoba through Texas. Coniferous savannas of juniper and pinon
pine cover the dry foothills of the mountainous regions of the Southwestern
United States from Texas to Arizona, and the southern half of Mexico.
In California, the foothills of the Sierra Nevada have similar savannas
of blue oak and digger pine. Along the coast of southern California, the
climate supports a broadleaf savanna of various species of oaks.
Mountain evergreen forests grow above the foothill savannas of
the mountains of the western United States and Canada. In general, the
climate in the mountains becomes colder, wetter, and windier with increasing
altitude. The forests of the lower and middle slopes are called montane
forests. Those of the upper slopes are known as subalpine forests.
In the Rockies, the lower montane forests consist of unmixed stands of
ponderosa pine. At higher elevations, Douglas-fir becomes dominant. Douglas-fir
is mixed with grand fir in the northern Rockies and with blue spruce and
white fir in the southern Rockies. Above this zone lie the cold, snowy
subalpine forests, which are dominated by Engelmann spruce and subalpine
fir. Lodgepole pine is also common in both the montane and subalpine zones,
especially in areas that have been affected by fire. The highest elevation
at which trees can grow is called the timber line. Beyond this point,
the climate is too severe for tree growth. In the timber-line regions,
the trees grow in a scattered, savannalike way. The timber-line regions
are dominated by bristlecone pine in the southern Rockies, by limber pine
in the central Rockies, and by Lyall's larch and whitebark pine in the
northern Rockies.
In the Sierra Nevada, incense-cedar grows in moist areas of the lower
montane forests. Douglas-fir, Jeffrey pine, ponderosa pine, and sugar
pine thrive on drier slopes. In central California, magnificent stands
of giant sequoia trees grow on the western slopes of the Sierra Nevada.
The sequoias are the bulkiest, though not the tallest, of all the world's
trees. The largest sequoias measure about 100 feet (30 meters) around
at the base. White fir dominates the upper montane forests of the Sierra
Nevada. At subalpine elevations, the mountains support forests of red
fir mixed with lodgepole pine and mountain hemlock. These subalpine forests
thin out into savannas of bristlecone and whitebark pine at elevations
near the timber line.
Pacific coastal forests extend along the Pacific Ocean from west-central
California to Alaska. The warm currents of the Pacific help give this
region a mild climate the year around. Warm, moisture-filled winds from
the ocean bring heavy annual precipitation.
Huge conifers dominate the Pacific coastal forests. Forests of redwood,
one of the world's tallest trees, grow along a narrow coastal strip from
central California to southern Oregon. Many of these giants tower more
than 300 feet (91 meters). Inland from the redwoods and to the north,
grow magnificent forests of Douglas-fir, Sitka spruce, western hemlock,
and western redcedar. Along the coast of northern Washington and southern
British Columbia, the high annual precipitation supports thick temperate
rain forests. These forests, with their moss-covered Douglas-fir, Sitka
spruce, and western redcedar, make up a damp, green wilderness found nowhere
else in North America.
Boreal forests sweep across northern North America from northwestern
Alaska to Newfoundland. In this region of severe cold and heavy snowfall,
winter lasts seven to eight months. However, the short growing season
has dependable rainfall and many hours of daylight each day. The boreal
forests are dominated by coniferous evergreens, chiefly balsam fir, black
spruce, jack pine, and white spruce. Some areas support stands of larch,
which is a deciduous conifer. Such deciduous broadleaf trees as balsam
poplar, trembling aspen, and white birch grow in areas that have been
burned over by forest fires. The boreal forests have many bogs (areas
of wet, spongy ground). Some of the bogs are treeless. Other bogs, called
muskegs, are covered by a deep mat of moss on which dwarfed conifers grow.
Subarctic woodlands lie along the northern edge of the boreal
forests. The climate in this region is bitterly cold, with low precipitation
and an extremely brief growing season. These conditions force the trees
to grow in a widely spaced, savannalike fashion. Black spruce dominates
most of the region. Other boreal trees, such as aspen, larch, white birch,
and white spruce, grow in some places. North of the woodlands lies the
Arctic tundra, where trees cannot survive.
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