2
North America’s
Environmental
Setting
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LEARNING OUTCOMES
After reading this chapter, students should be able to:
• Explain the difference
between physical geography
and human geography.
•
•
•
Identify the major
geomorphic processes that
shaped the Appalachian
Mountains as compared
to the Rocky Mountains
through time.
List and describe North
America’s 12 major
physiographic provinces.
Compare and contrast
a shield volcano and a
composite cone volcano in
North America.
• Distinguish between an
ecosystem and a biome.
• Explain why environmental
planners often prefer to
use a map showing an
area’s watershed instead of
a map based on political
boundaries.
• List and discuss the
impacts of four climate
controls on weather and
climate in North America.
• Compare and contrast the
different kinds of landforms
created by continental
glaciers as compared to
alpine glaciers.
• Differentiate between
North America’s five major
river drainage systems
according to the general
direction of their flow
outward to the sea.
• Describe the major
temperature and moisture
properties of a Polar
continental air mass and a
Tropical maritime air mass.
• Differentiate between
North America’s
Mediterranean, Continental
Midlatitude, and West Coast
Marine climate zones.
• Explain why a comparison
of maps showing (1)
general climate zones; (2)
landforms; (3) soil types;
and (4) vegetation biomes
may prove useful for
geographic analysis.
The earth’s vegetation is part of a web of life in which there are intimate and
essential relations between plants and the earth, between plants and other plants,
between plants and animals. Sometimes we have no choice but to disturb these
relationships, but we should do so thoughtfully, with full awareness that what we
do may have consequences remote in time and place.
(Rachel Carson, Silent Spring, 1962, 64)
hysical geography is the study of the environmental characteristics of Earth, whereas human
geography focuses on human activity on the
planet. This chapter provides an overview of the physical geography of North America, with an emphasis on its
broad patterns of landforms, climate, hydrology, natural
vegetation, and ecosystems. The terrestrial portion of the
North American continent encompasses nearly 6.7 million
square miles (17 million square kilometers). Because it is
such a large continent, North America’s physical geography and related human patterns are extremely diverse.
Understanding North America’s physical patterns and
processes provides a great deal of insight into where human settlements were located historically and what environmental constraints influenced human decision making
over the years. Therefore, each of these environmental
variables is discussed here with reference to how they affected historic and present-day human landscapes to help
set the stage for the chapters that follow. We begin with
an overview of the processes that shaped North America’s
P
landforms, hydrology, and soils, and then we discuss the
continent’s predominant patterns of weather and climate,
vegetation, and ecosystems.
Landforms, Hydrology, Soils
Landforms and Geomorphic
Processes in North America
About one-third of the topography of North America is
mountainous, with older, more eroded mountains in the
eastern United States and southeastern Canada and more
recent and much higher mountains in the western parts
of the continent. Most of the mountain ranges in North
America have a north–south orientation (with a few exceptions such as the Ozark and Ouachita Mountains in
the Inland South and Alaska’s Brooks Ranges). An extensive plain covers the central portion of the continent.
Pine Creek cuts through rock embankments in Escalante, Utah, and exhibits climatic, geomorphic, and
ecological processes that shape the physical landscape
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4
THE GEOGRAPHY OF NORTH AMERICA
Alternating forces of erosion and deposition have
sculpted the Rocky Mountains and Appalachian chain,
as well as the continent’s valleys, coastal plains, and river
deltas. Over long periods of time, rivers can dramatically
erode land surfaces. This down-cutting has created the
Grand Canyon of the Colorado River and many other
well-known landforms throughout the United States and
Canada. Glaciers have also been at work over geologic
time eroding and depositing soil and rock and carving
out features such as the Great Lakes and thousands of
smaller lakes, as well as numerous high mountain valleys in parts of the United States and Canada.
Some of these topographic features have been barriers to travel and settlement, whereas others have provided resources for successful settlement. For example, if
you look at a map of cities on the East Coast you will
notice that Trenton, Philadelphia, Wilmington, Baltimore, Washington, and Richmond form a line in between and paralleling the coastline and the Appalachian
Mountains. These cities are located along the Fall Line,
an imaginary line connecting the head of navigation of
the Delaware, Susquehanna, Potomac, and other major
rivers that flow eastward from the Appalachians to the
Atlantic Ocean. Sites along the Fall Line were attractive
to settlers because they were accessible to ocean-going
ships, while waterfalls often provided power to support
water-powered grain mills and other industries at a time
prior to the invention of electricity. With a landing and a
mill site, a new community had advantages for growth.
The Appalachian Mountains also formed a topographic barrier to settlement in early America. From
the perspectives of westerners, this mountain chain
may not seem to be very high since the highest peak in
the Appalachians, Mount Mitchell in North Carolina, is
6684 feet above sea level (whereas many peaks in the
Rocky Mountains, Sierra Nevada, and Cascade Ranges
are more than 14,000 feet above sea level!). Nonetheless the Appalachian Mountains posed a considerable
barrier to travel and trade since mechanized transportation had not yet been invented and long-distance
trips could be taken only on foot, on horseback, or by
animal-powered stagecoaches or wagons. This was
enough to keep settlement primarily focused on the
eastern side of this mountain range during the earliest
years of post-indigenous settlement in North America.
In other places, however, topographic features encouraged trade and settlement .For example, during
the 17th century, French voyageurs based in Montreal
and Quebec City used canoes to travel as far west as
the Great Lakes in search of furs. In doing so, as discussed in more detail in Chapter 6, these early explorers contributed greatly to early geographic knowledge
of North America. In the early 19th century, financiers
in New York City recognized that the valley of the Mohawk River between the present-day cities of Albany
and Buffalo was the only flat land that extended all the
way across the Appalachian range from east to west.
As a result, these investors decided to finance the construction of the Erie Canal, which ultimately became
a major artery of commerce connecting the Atlantic
Coast with the Great Lakes states. This important canal
also ensured that New York would become the largest
city and major financial center of North America—a
position that it has retained to the present day, as discussed in Chapter 8.
Topographic features also determine political boundaries in Canada and the United States. The Bitteroot
Mountains separating Idaho from Montana, and the
crest of the Appalachians serving as a dividing line between North Carolina and Tennessee, were laid out
along the crest of mountain ranges. In other cases, rivers
were used to help define boundaries. Examples of this
important role of rivers as boundaries include the St.
John and St. Croix rivers forming part of the boundary
between Maine and New Brunswick, and several pairs
of U.S. states being separated by the Mississippi River.
120°E
60°W
140°E
160°E
180°
0
80°N
0
1,500
160°W
140°W
120°W
100°W
80°W
40°W
3,000 mi
20°W
0°
N
1,500 3,000 km
E
W
ARCTIC OCEAN
FIGURE 2.1 The tectonic base of the
North American continent
S
N O R T H
EURASIAN
PLATE
A M E R I C A N
60°N
P L A T E
E UR AS IAN
PLAT E
JUAN DE FUCA
PLATE
40°N
ATLANTIC
OCEAN
PACIFIC OCEAN
PHILIPPINE
PLATE
20°N
P A C I F I C
COCOS
PLATE
CAROLINE
P L A T E
PLATE
0°
BISMARCK PLATE
INDIAN-AUSTRALIAN
PLATE
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FIJI
PLATE
160°W
140°W
120°W
CARIBBEAN
PLATE
NAZCA
PLATE
100°W
80°W
SOUTH
AMERICAN
PLATE
AF R IC AN
PLAT E
20°W
0°
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CHAPTER 2 North America’s Environmental Setting
Earth’s surface is composed of more than 24 tectonic
plates that move against one another, producing folding,
faulting, earthquakes, and volcanoes (Figure 2.1). Most
of the North American continent is located on the North
American plate except for parts of the West Coast, which
lie on the Pacific Plate. The collision of these plates
causes the western margin of North America to be the
most tectonically active region of the continent.
Where tectonic plates collide or slide against one
another over time, earthquakes may occur along fault
lines. One of the best-known faults in the world is the
San Andreas Fault, which extends from the Salton Sea
area of Southern California to north of San Francisco.
From northern California to southern British Columbia,
the Juan de Fuca Plate rides under the North American
Plate while it pulls away from the Pacific Plate.
Crustal movement during orogeny (mountain building) can build up tremendous amounts of friction and
strain in rocks. When this occurs suddenly, energy is
released and may be felt as an earthquake. The seismic
release of energy is sometimes measurable at Earth’s
surface, and physical infrastructures are damaged. Many
earthquakes have been recorded in North America,
including the San Francisco earthquake in 1906 and the
1994 Northridge earthquake; the risk of earthquakes
is a fact of life on the West Coast of the United States.
Preventing large earthquakes is impossible, but it is
possible to help alleviate significant damage from earthquakes through monitoring and warning systems. As a
result, many places require building codes that specify
construction and design methods that help withstand
seismic movements and zoning codes that prohibit the
construction of buildings in fault zones.
Although earthquakes are much more common on
the West Coast than elsewhere in North America, major
earthquakes have struck other parts of the United
States and Canada at various times in recorded history. The most powerful of these was a series of earthquakes centered near the community of New Madrid,
Missouri, in 1811 and 1812. Geologists estimated that
5
these earthquakes were of magnitudes between 7.0 and
8.0 on the Richter scale, nearly as powerful as the San
Francisco earthquake of 1906. Fortunately, few people
lived in the New Madrid area in the early 19th century.
Today, however, an earthquake of similar magnitude
could devastate St. Louis, Memphis, and other nearby
cities and towns in the area.
Western North America also has approximately 70
volcanoes. Mount St. Helens, which experienced a
major eruption in 1980 and a minor but dramatic eruption in 2004, is perhaps the most famous of all the volcanoes in the Cascade Ranges (Figure 2.2) Volcanoes
in this part of North America are formed from magma
moving toward the surface through a central vent from
deep inside Earth. In volcanic areas along the Pacific
Coast and in places such as Yellowstone National Park,
the tremendous heat from the rising magma boils
groundwater, creating geothermal energy that can be
seen as geysers and thermal springs. When conditions
are right, eruptions occur, spreading lava, ash, and
other materials onto the landscape.
Volcanism in the Cascade Ranges has resulted in a
series of composite cone volcanoes. This type of volcano erupts explosively and shoots pyroclastic debris,
gases, and heat into the atmosphere. If this explosive
volcanic material reaches high altitudes, it may travel
long distances before being deposited elsewhere.
Chapter 16 provides more information about this form
of volcanism.
Hawai’i’s shield volcanoes have been created by a
different type of volcanism. They may also exhibit effusive lava flow eruptions capable of shooting fountains of
lava into the atmosphere. But this type of volcano is not
usually as violent as a composite cone type, although
shield volcanoes often do produce enormous amounts
of lava. These lava flows have a low viscosity that allows them to move easily over the landscape. As the
lava travels into the ocean it cools and creates new land.
Kileauea, located on the big island of Hawai’i, has been
erupting since 1997. Other famous volcanoes of Hawai’i
FIGURE 2.2 Mount St. Helens in the Cascade
Range, 2004
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THE GEOGRAPHY OF NORTH AMERICA
are Mauna Loa and Mauna Kea and Haleakala on
Maui. Further discussion and a series of photographs of
Hawai’i’s volcanic landscapes are found in Chapter 17.
Glaciation has also helped shape the landforms of
North America. Glacial ice forms when snowpack in
high latitudes or high elevations does not completely
melt during the summer; more snow is added in
winter, and again, the snowpack does not melt. This
layering technique builds up snow layers that will
eventually transform into glacial ice under their own
weight. When enough ice has formed, the glacier will
begin to move down slope.
Most of northern North America was covered in
continental glaciers at periodic intervals that began
approximately 1.5 million years ago and ended about
10,000 years ago. During this time a great expanse of ice,
centering on what is now Hudson Bay, covered most of
Canada and Alaska and extended as far south as the
Ohio and Missouri rivers and the middle Columbia
River (Figure 2.3). Landscapes in the southward path
of a glacier were sculpted by both erosional and depositional processes. For instance, continental glaciers
carved out the Great Lakes, which are still rebounding
from having the great amount of weight lifted when the
glaciers retreated.
In some of the northern U.S. states such as New
York and Michigan, parallel hills called drumlins and
extensive systems of scoured and infilled glacial drift
sediments cover the landscape. Moraines are more
FIGURE 2.3 Prehistoric glaciation in
North America
common in parts of the upper Midwest, where glaciers
dumped their debris during periods of melting ice.
Another type of glaciation occurs in high mountain
areas where alpine glaciers have created many of the
most spectacular mountain scenery in on the continent.
Here, glaciers have carved dramatic horns and arêtes,
created alpine lakes called tarns, and eroded cirques
and u-shaped glaciated river valleys.
Karst landscapes are found in areas that have high
concentrations of soluble rock such as limestone, dolomite, and gypsum. Several conditions are necessary for
karst processes to form, including (1) a rock structure that
allows water to infiltrate into the subsurface; (2) a zone
containing air between the water table and the ground
surface; and (3) a type of vegetation cover with enough
organic acids to enhance the solution process. Karst can
weaken layers of soil above the water table, and the surface material begins to sink forming a circular depression
or a sinkhole (Figure 2.4). At times these sinkholes may
collapse and leave a deep depression in the landscape.
When this occurs under a road surface, cars are in danger
of falling in without prior warning. In areas where sinkholes are prevalent, such as Florida, Kentucky, and Indiana, autos, houses, and businesses have been destroyed.
Karst processes, therefore, are a reminder in this part of
North America that geomorphic processes may at times
be invisible to humans but are ongoing.
Coastal fluvial processes are also important agents of
change on Earth. Along the continent’s coastal margins,
70°N
Maximum extent of glaciation
Contemporary glaciers
0
0
250
500 mi
70°N
6
250 500 km
ARCTIC
OCEAN
30°W
°N
60
150°W
50°W
140°W
50
°N
PACIFIC
OCEAN
60°W
40
°N
130°W
N
40°
ATLANTIC
OCEAN
70°W
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CHAPTER 2 North America’s Environmental Setting
FIGURE 2.4 Sinkhole in karst soil, Columbia, South Carolina
both erosional and depositional forces form distinctive landforms. Waves are one of the most powerful
forces along shorelines, since they carry sediment onto
shore and also erode beaches with wave backwash.
Eroded coastlines in North America, particularly on
the West Coast, are usually rugged and have narrow
beaches. Other features such as sea cliffs, wave-cut
platforms, and sea stacks are common as well. In contrast, coastlines shaped by the depositional forces of
wave activity, such as are more common in eastern
North America, feature larger beaches; spits (arms of
deposited material attached to the shore), bay barriers,
and lagoons.
The force of wind can also affect landform development, especially in arid areas and along coastlines.
Winds can create or modify landforms in two ways,
deflation and abrasion. Deflation is the process of lifting and removing loose material. Fine particles can be
caught up in suspension and carried long distances
before being deposited. Wind process can sculpt rocks
into distinct angular landforms such as can be seen in
Arizona and Utah. When particles are deposited on
the landscape, dunes can form. Dunes can typically be
found along the Atlantic and Pacific coasts as well as
along the eastern shores of Lake Michigan. Loess, or
windborne clay deposits, may originate great distances
from where they are found. These particles bind together, weather, and erode into steep bluffs. In North
America extensive loess deposits are located in the
central Plains, in the Palouse Region of eastern Washington and Oregon, and along the lower reaches of the
Mississippi River. Smaller pockets of loess deposits can
also be found in southern Alberta and Manitoba, and
along the Missouri River in Iowa and South Dakota.
Hydrologic Patterns
Figure 2.5 shows major river drainage basins in
North America. East of the Continental Divide, there
are five prominent drainage systems including the
M02_HARD9671_00_SE_C02.indd 7
7
(1) Great Lakes-St. Lawrence system; (2) MississippiMissouri Basin; (3) major rivers of the West Coast; (4)
major rivers of the eastern United States; and (5) rivers draining into the Arctic Ocean. The Great LakesSaint Lawrence system is responsible for draining
areas in southeastern Canada and the northeastern
and north central United States. The Great Lakes, St.
Lawrence Seaway, and adjoining waterways, in fact,
are a major transportation artery that links central
Canada and the United States to the Atlantic Ocean
and the rest of the world.
Much of the central part of the continent is drained
by the Mississippi-Missouri system. The main stem
of the Mississippi River begins in Itasca State Park in
central Minnesota, and then this massive river flows
all the way south to the Gulf of Mexico near New
Orleans. This important waterway was historically
the gateway to the western part of the continent via
its tributary, the Missouri River. Another major tributary of the Mississippi is the Ohio River which flows
into the Mississippi River from the east. The Ohio
drains the northern Appalachian area and the eastern
portion of the Midwest. Many major cities including
Pittsburgh, Cincinnati, St. Louis, New Orleans, Memphis, Kansas City, and Minneapolis-St. Paul were
established on the banks of the Mississippi, Missouri, or Ohio rivers. During the early 20th century,
engineers reversed the flow of the Chicago River in
Chicago and constructed canals connecting the Great
Lakes with the Mississippi drainage basin, allowing
water trade and transportation from the mouth of the
Mississippi to the mouth of the St. Lawrence far to
the northeast.
The western United States drains to the Bering Sea
and the Pacific Ocean via the Fraser, Columbia, and
Sacramento-San Joaquin River systems and other, smaller
streams such as the coastal rivers and streams in western
California, Oregon, Washington, British Columbia, and
Alaska. Before it was dammed and used up for agricultural and domestic needs, the Colorado River flowed
from its source in the Rocky Mountains to the Sea of
Cortez in Mexico. However, due to overuse and evaporation from large reservoirs, this important western river
is completely used up before it reaches the international
boundary.
The eastern United States is drained by several
major rivers and their tributaries such as the Charles,
Connecticut, Hudson, Delaware, Susquehanna, Potomac, and James rivers. These rivers, though not as
long as the Mississippi, Missouri, Colorado, or Ohio
rivers to the west, were critically important for transportation, drinking water, and eventually water power
for Native Americans and later, for Euro-American
settlers. Most of the major cities of the East Coast including Boston, New York, Philadelphia, Baltimore,
Washington, and Richmond are located along major
rivers. To the north, the Mackenzie River flows into
the Arctic Ocean with many of central Canada’s rivers
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8
THE GEOGRAPHY OF NORTH AMERICA
80
7 0 °N
60°N
°N
Arctic
drainage
Sea
60°
N
ARCTIC OCEAN
Bering
Beaufort
Sea
Baffin Bay
Yu
kon
R.
Pacific
drainage
ic
ct
Ar rcle
Ci
YUKON
zie R.
ken
Mac
MACKENZIE
Labrador
Sea
Ar
drainctic
age
KEEWATIN
ce
PEACEATHABASCA
Hu
LOWER
COLORADO
Re d R
.
Susquehanna R.
Gulf/
Atlantic
drainage
E
as R .
TEXAS-GULF
RIO
GRANDE
E
SS
NE
TEN
A
dratlantic
ina
ge
110°W
90°W
ATLANTIC
OCEAN
SOUTH
ATLANTICGULF
N
30°
N
E
W
S
Gulf of
Mexico
of Ca
ncer
120°W
R.
O OHIO
ARKANSAS-WHITE-RED
Hudson R.
Delaware R.
o
Arkan
s
NORTH
ATLANTIC
Allegheny R.
UPPER
MISSISSIPPI
°N
40
St. Lawrence R.
GREAT
LAKES
hi
.
MARITIME
COASTAL
ST.
LAWRENCE
G
Atlaulf/
dra ntic
ina
ge
C
IA
Tropic
ic
nt
la
At age
h
n
t
i
r a
No dr
i R
RN
PACIFIC
COASTAL
oR
ad
or
l
o
°N
50
UN
DL
NORTH SLOPEGASPÉ
n
M ississipp
Internal Drainage
so
Gulf
/
drainAtlantic
age
500 mi
250 500 km
130°W
GREAT BASIN
IFO
0
250
CO U P P
L O ER
RA
DO
CAL
Pacific 334 (412,000)
Gulf/Atlantic 718 (886,000)
Atlantic 293 (361,000)
0
Missouri R .
MISSOURI
millions acre-feet per year
(millions m3 per year)
Continental divides
el
ASSINIBOINERED
COLUMBIA
OCEAN
UNITED STATES:
N
Pacific
drainage
PACIFIC
COASTAL
N
WF
O
NORTHERN
QUEBEC
dso
A nB
dra rctic ay/
ina
ge
SASKATCHEWAN
CANADA:
20°
c
ur
Ch
.
lR
hil
.
Saskatchewan R NELSON
DRAINAGE BASINS
Pacific 602,000 (488)
Arctic 440,000 (356)
Hudson Bay 682,000 (553)
Atlantic 670,000 (544)
Gulf PACIFIC
of Mexico 105 (0.9)
CHURCHILL
ca
as
ab
Ath
FRASER
millions m3 per year
(millions acre-feet per year)
ay
nB
dso ge
Hu raina
d
R.
R.
P ea
R.
PACIFIC
COASTAL
D
AN
PACIFIC
OCEAN
LABR
ADO
R-N
E
Hudson
Bay
LOWER MISSISSI .
PPI
°N
50
Gulf of
Alaska
ARCTIC COAST AND ISLANDS
20°N
80°W
FIGURE 2.5 Major drainage basins of North America
flowing into the Hudson Bay, an arm of the Arctic,
although the Arctic is much less feasible for transportation and access to distant markets than the Atlantic
and the Pacific oceans.
Some parts of North America have no external drainage. This type of internal drainage occurs in the Great
Basin states of Nevada, Utah, and a part of California.
Water that comes into these areas flows into shallow or
dry lakes known as wadis and then is evaporated or
percolated into the soil.
River systems in North America were essential
for long-distance transportation prior to the development of railroads and automobiles, and some remain important for this purpose even today. Some of
M02_HARD9671_00_SE_C02.indd 8
the rivers and river basins that were located in close
proximity to each other were connected by canal systems with most located in eastern Canada and the
United States.
Soils North America contains some of the most productive agricultural soils on Earth. The distinctive characteristics of soils are very site-specific, but may be
generalized into the classifications called soil orders as
shown on the map in Figure 2.6.
Soils are formed by weathering of surface rocks, the
mixing of this material with organic matter, and moisture. Climate is perhaps the most influential factor in
determining the geographic distribution of soils in
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9
80°
70°N
CHAPTER 2 North America’s Environmental Setting
N
60°
N
60
°N
50°N
40
°N
0
500
0
500
1000 mi
40°
1000 km
N
SOIL TYPES
N
Alfisols
Aridisols
E
W
Entisols
S
Histosols
30°N
Inceptisols
Mollisols
Andisols
Spodosols
Ultisols
Vertisols
Complex soil region
Areas with little or no soil
120°W
110°W
80°W
70°W
FIGURE 2.6 General soil types in North America
North America. Temperature and moisture determine
how weathering takes place and how much moisture
will support the development of biota (living organisms). Some of the best agricultural soils on Earth are
found in the Middle West and the Great Plains. It is interesting to compare the soils map shown in Figure 2.6
with the map of natural vegetation shown in Figure
2.16. Compare these maps with Figure 1.8 of current
agricultural patterns in North America to see how successful agricultural production depends on both the
quality and type of soil in an area as well as its moisture availability.
It is interesting to note that the extremely fertile
soils of the Great Plains were not used for farming
until the technology for drawing well water, plowing
the deep grassland soils, and fencing large areas from
M02_HARD9671_00_SE_C02.indd 9
livestock was developed. In other places, such as the
American Southeast, soils are lower in fertility and
have historically been misused through agricultural
practices that did not allow for nutrient regeneration
and through planting crops such as cotton that expose
soil to erosion. These soils often are a reddish color
because they contain substantial amounts of iron and
aluminum oxide.
CONCEPTUAL CHECKPOINT 2.1
Develop a presentation based on a set of comparative
maps of your local region (e.g., landforms, vegetation,
climate, soils maps) that defends some of the reasons
why many of the patterns shown on these maps look
the same.
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10
THE GEOGRAPHY OF NORTH AMERICA
North America’s
Physiographic Provinces
Environmentally defined parts of North America that
feature interrelated patterns of landforms, vegetation,
soils, and hydrology are known as physiographic provinces. Each of the twelve major physiographic provinces
in North America (as shown on the map in Figure 1.9 in
Chapter 1) are discussed below to provide an environmental context for understanding the various geographic
regions covered in the chapters that follow.
The first of these physiographic provinces is the
Atlantic and Gulf Coastal Plain, a lowland area that
flanks the Atlantic Ocean all the way from New York
south to the tip of Florida and then west along the Gulf
of Mexico. This province is characterized by some of the
flattest terrain on the continent that gently slopes toward
the sea. Wetland areas here provide habitat for waterfowl
and other wildlife in fertile estuaries, swamps, marshes,
and lagoons. These include estuaries such as Chesapeake
and Delaware Bays and the well-known Great Dismal
Swamp of Virginia and North Carolina and Okefenokee
Swamp of Georgia. Farther west, the coastal plains at the
mouth of the Mississippi River deposit tons of sediment
into the Gulf of Mexico. As the velocity of the river slows
due to the decreasing slope of this area, a heavy sediment load is deposited to form the Mississippi Delta.
In recent decades, land rejuvenated from sedimentation
has not kept up with loss of land by sea-level rises and
levees. Another significant part of the coastal plain includes a chain of offshore islands (fittingly called barrier
islands) that protect coastal shipping and shoreline land
development from Atlantic storms.
The Appalachian Mountain province is an ancient
assembly of parallel mountains and valleys that trend
southwest to northeast along the eastern portion of the
North American continent. Its easternmost component
is the Piedmont (literally, the “foot of the mountains”),
an area of low, rolling hills with moderate relief. The
Piedmont was important in colonial times for cotton and
tobacco farming, but these crops are now grown farther
west due to overuse of previously fertile Piedmont soils.
West of the Piedmont, the Appalachians extend from
Newfoundland to central Alabama. The highest part of
this mountain range is the Blue Ridge (4000 to 6000
feet; 1219 to 1828 meters), which marks the drainage
divide between easterly flowing streams that flow into
the Atlantic and westerly flowing streams that eventually join the Mississippi River drainage system.
The Interior Uplands province is not directly connected with the southern Appalachians, but is very similar
to it. This area includes the Ozark Mountains in southern
Missouri and northern Arkansas and the Ouachita Mountains in western Arkansas and eastern Oklahoma.
The Interior Plains province is located west of the
Appalachian Mountains and north of the coastal plains.
Several different sections comprise this now heavily
industrialized and urbanized physiographic province.
M02_HARD9671_00_SE_C02.indd 10
The first is the St. Lawrence Valley, the transition zone
between the Appalachians and the Mississippi River
Valley. This area is famous for its lime-rich soils, which
create good pasture for raising livestock such as the famous racehorse farms of Kentucky Bluegrass country.
The second main subregion of this physiographic province is the Mississippi–Great Lakes section. The level
nature of this part of the province is due to its heavy
glaciation. The Balcones Escarpment in Texas marks its
southwestern boundary.
The Great Plains’ gently rolling grasslands have
been shaped primarily by the wind and water through
time. Along this physiographic province’s western
border, the erosional forces of wind and water can be
seen in the sculpted South Dakota Badlands and Sand
Hills of Nebraska. Historical settlement in this part
of North America was filled with use and misuse of
the land, including cattle drives, railroad promotion
schemes, and damaging farming operations. Examples
of results of the overuse of resources here include the
Dust Bowl in the 1930s (caused by drought and other
climatic challenges and poor farming techniques), and
this area’s continuing overdependence on groundwater for agricultural and urban use today.
The Rocky Mountains or Cordilleran province
trending in a north–south direction was formed by uplift, folding, and faulting processes. This province extends from New Mexico to the Liard River in Canada.
Mining, ranching, recreation, and tourism are important
economic activities here. In the far north, the Northwestern Highlands extend this province’s boundaries as far
north as Alaska. This area has also been shaped by volcanism. The Continental Divide, a line demarcating where
water falling on the east flows into the Gulf of Mexico
and water from the mountain’s western slopes flows into
the Pacific Ocean, is located along the high peaks of the
Rockies from New Mexico northward to Alberta, British
Columbia, and Alaska (Figure 2.7).
The Intermontane is located between the Rocky
Mountains and the Pacific Coast mountains. This region
has been shaped by both wind and water, and it often
features spectacular scenery. Several subregions are
important here, including the Colorado Plateau where
the Colorado River and its tributaries have greatly incised the landscape to create steep canyons and a series of mesas and buttes (Figure 2.8). Wind erosion and
volcanism have also helped shape this southwestern
landscape. Adjacent to the Colorado Plateau is basinand-range country that includes the Great Basin and
Death Valley. This distinct area is characterized by short,
rugged mountain ranges intermingled with flat valleys
and no drainage to the sea. Much of the annual rainfall
in this region evaporates quickly, thereby creating the
extremely dry conditions that characterize this province.
In many places, the landscape is barren of most vegetation and is subjected to extensive erosion by wind.
The northernmost section of the Intermontane in the
United States features the plateaus and basins of the
18/05/11 8:17 PM
CHAPTER 2 North America’s Environmental Setting
11
FIGURE 2.7 Rocky Mountains above tree line have
conditions similar to polar conditions
Snake River in southern Idaho and the Columbia River
of eastern Washington. Here, evidence of the giant glacial Lake Missoula floods that occurred 15,000 years
ago is visible in deeply incised canyons. The Columbia and Snake rivers have cut into this area’s volcanic
landscape, creating deep canyons and dramatic waterfalls. The northernmost portion of the Intermontane
extends from the Canadian-U.S. border north to the
central Yukon and northern British Columbia. Portions
of this subregion are flat, with other parts of it covered
by dissected plateaus much like the Intermontane.
The Pacific Coast province extends along the West
Coast of North America from Southern California all
the way north to western Alaska. Although this may
look like one long province on a map, the landscape is
varied here due to climate differences and the various
geomorphic processes that have shaped it. All along
the shoreline, for example, coastal processes are at
work with steep cliffs that have been cut by wave action and beaches that are continually being expanded
or eroded by powerful waves. In more northerly
coastal locations bays, fjords, and offshore islands
WYOMING
N EVA DA
ive
r
C
ol
or
ad
o
R
U TA H
FIGURE 2.8 Mesas and buttes
in southwestern Utah
M02_HARD9671_00_SE_C02.indd 11
18/05/11 8:17 PM
12
THE GEOGRAPHY OF NORTH AMERICA
have been created by these coastal processes as well as
by ancient glacial activity.
In this Pacific Coast province, a host of mountain
ranges such as the Cascade Ranges, Coast Ranges,
Sierra Nevada, and Olympic Mountains provide evidence of volcanism and widespread tectonic uplift.
This area is also marked with several structural depressions, including the Willamette Valley in Oregon,
Puget Sound in Washington, and the Central Valley of
California. These fertile valleys provide fertile land for
agricultural production as well as ample level land for
urban development.
The huge physiographic province known as the
Canadian Shield covers more than half of Canada, all
of Greenland, and the far northern parts of Minnesota
and upstate New York. This area is a wide expanse
of ancient rock that has been greatly compressed by
ice and then contorted into the rugged landscape that
is visible today. The Shield is rich in valuable minerals such as iron ore, silver, nickel, and gold. There
are also numerous rivers and lakes here, connected
by a network of streams. The southern portion of the
Canadian Shield is covered with slow-growing boreal
vegetation, which transitions into bogs and tundra
in more northern locations. Land use in most of this
province is limited to extractive or primary industries
such as fishing, forestry, and mining with settlements
small and widely dispersed.
North of the Canadian Shield is the Hudson Bay
Lowland-High Arctic Mountain Province. Both are very
sparsely populated. Here, the Yukon Basin and Northwestern Highlands occupy most of central Alaska and
the southern part of the Yukon Territory where most of
the land is hilly or mountainous.
Last, but certainly not least of the 12 major physiographic regions discussed in this chapter, is the
Hawai’ian province. Here, the impacts of volcanism,
a warm tropical climate, and tourism come together
to form a unique part of the greater North American
region that is geographically disconnected from the
mainland of the continent by more than 2000 miles.
CONCEPTUAL CHECKPOINT 2.2
Develop a promotional brochure to advertise one of
North America’s physiographic provinces as an appropriate site for development of a new ecotourism resort.
Weather and Climate
Weather refers to day-to-day atmospheric conditions
(or what you experience when you walk out the door in
the morning!), while the term climate refers to the longterm pattern of weather and atmospheric conditions on
Earth’s surface. Climatologists deal primarily with four
basic elements of weather and climate—temperature,
atmospheric pressure, wind, and precipitation.
The factors that influence weather and climate are
numerous and interrelated. These important control
factors include latitude, a critically important variable
that determines the amount of solar radiation received
at selected points and the length of daylight in each
24-hour period. Differences in latitude help explain why
places located near the equator are generally warmer
than places located farther away from it because they
receive more direct rays of the sun through the atmosphere. Figure 2.9 symbolizes such a place. Likewise,
polar areas receive less direct solar energy, particularly
in winter, when they experience days of 24-hour darkness. In general, the farther a location is from the equator, the less solar energy is received throughout the year.
Differences in the heating and cooling potential of
land and water are another important climatic control.
Land surfaces do not allow radiation to pass through,
and thus they heat and cool very rapidly. Water surfaces, on the other hand, heat and cool more slowly
than do land surfaces. This means that places located close to the ocean tend to have less temperature
FIGURE 2.9 The southern most bar in the United States
at 19º latitude on the Big Island of Hawai’i. In business,
it is often said that location is everything.
M02_HARD9671_00_SE_C02.indd 12
18/05/11 8:18 PM
CHAPTER 2 North America’s Environmental Setting
FIGURE 2.10 Mean annual temperatures (in centigrade) for North
America in January and July
-24
°
-12
°
0°
50°N
-30°
Isotherms
bend
equatorward
6°
40°N
12°
30°N
18°
WINTER
6°
6°
60°N
50°N
12°
18°
30°N
30°N
°
27
Isotherms
bend
poleward
30°
27°
24°
24
°
SUMMER
°
M02_HARD9671_00_SE_C02.indd 13
winds. In contrast, however, Chinook winds in Colorado often bring welcome relief from bitter cold winters
to residents of the northern and central Great Plains.
Frontal storms are common in many parts of North
America as well. A front is the point of contact between
two different air masses. When a warmer (and usually
moister) air mass is forced to rise above cooler air, a
discontinuity of surface temperature and air pressure
is created and precipitation may occur. As warm air is
pushed off the ground, cold temperatures and gusty
winds mark the passage of the front with cloud formations also marking the progress of frontal storms.
Average summer and winter temperatures in North
America are shown in Figure 2.10. Contour lines of
equal temperature, as shown on this map, are called
isotherms. The hottest average annual temperatures in
North America are found in the deserts of Arizona and
southeastern California. The highest surface temperature ever recorded in North America was 134°F at Death
Valley, California, where temperatures over 115 degrees
occur regularly in July and August. Death Valley is also
the driest location in North America, with some portions
recording only an inch of precipitation per year on average. In contrast, average temperatures decrease with
latitude. A combination of high latitude, high elevation,
and distance from water has contributed to the coldest
recorded temperature in continental North America at
–81°F (–63°C) at a place called Snag, in the Yukon Territory of Canada.
30
variation than do places further inland. These differences between coastal and inland climates can be measured by comparing the average summer and winter
temperatures of places such as Vancouver, British Columbia and Winnipeg, Manitoba. Both of these cities
are located at approximately the same latitude, but
Vancouver has a July mean temperature of 71°F (22°C)
and a January mean temperature of 42°F (6°C), resulting in an annual temperature range of 29°F (16°C). In
contrast, the July mean temperature in Winnipeg, located more than a thousand miles (1600 kilometers) inland from the Pacific Coast, in contrast, is 79°F (26°C)
and the January mean temperature is 9°F (–13°C)—an
annual range of 70°F (39°C). This comparison of temperature averages in Vancouver and Winnipeg illustrates the general principle that the further away from
large bodies of water a place is located, the greater the
range (high summer–low winter) of its temperatures.
The force or weight exerted by air on a unit area
on Earth’s surface is known as atmospheric pressure.
Pressure differences at the surface reflect whether the
air is slowly rising or descending. These vertical motions often reflect the temperature of the air and are
measured with a barometer. We feel the movement of
air from an area of high pressure toward an area of low
pressure (called a pressure gradient) as wind.
Elevation is another important climatic control. On
average, temperatures decline with elevation at a rate of
about 2.5 degrees Fahrenheit every 1000 feet (2 degrees
Celsius with every 300 meters) of elevation. This rate of
decline is called the normal lapse rate. Thus, Denver at
5280 feet (1610 meters) elevation has an average temperature in January of 29.7°F (–1.3°C), whereas nearby
Aspen at 7907 feet (2410 meters) has an average January
temperature of only 20.7°F (–6.3°C).
Mountain barriers may also exert an influence on precipitation patterns. Orographic precipitation, caused
by the cooling of air as it is uplifted, is especially common in parts of the world where moist air masses come
in contact with high mountain barriers. One example of
this is the impact of the Coast Ranges and Sierra Nevada
Mountains in California that block the passage of maritime air from the west. The result is more abundant
precipitation to the west of this mountain barrier along
the Pacific Coast of California and the immense and
very dry Great Basin desert in the rain shadow on the
downwind side of these mountains.
Other topographically caused winds include the
Chinook winds in the Rocky Mountains and Southern
California’s infamous Santa Ana winds. Both are hot,
dry regional winds that descend from high to low elevations over a mountain barrier or a high plateau. Santa
Ana winds are perceived negatively in Southern California: It has been documented that homicide and assault
rates increase in the Los Angeles basin when this fierce
wind blows. Numerous wildfires and losses of residential homes in the mountains rimming the Los Angeles
basin also are associated with these often damaging
13
18/05/11 8:18 PM
14
THE GEOGRAPHY OF NORTH AMERICA
There are also significant geographical variations in
climate at the local level. For example, large cities generally experience temperatures that are several degrees
warmer than those in the surrounding countryside. This
urban heat island is associated with heat generated from
human activity such as the injection of pollutants into the
atmosphere, heat retention of roofs and parking lots, and
the effects of tall buildings on local wind patterns.
As mentioned previously, air masses are very large
bodies of relatively stable air. They are called Continental
10°
Sea surface temerature in °C
SH
Specific humidity
5°
or Maritime air masses depending on whether they originate over land masses and are dry (continental) or over
oceans or large lakes and are more moist (maritime).
Other types of air masses are identified according to their
temperatures as either Tropical (hot) or Polar (cold).
Warmer air masses can carry relatively more moisture
than colder ones.
Figure 2.11 shows the general patterns of summer and
winter air masses over North America. Polar air masses
form at high latitudes (centered at approximately 55°N),
FIGURE 2.11 Air mass regions of North
America in (a) winter and (b) summer
Continental arctic
cold, very dry, stable
cA Very(avg.
SH 0.1 g/kg)
Continental polar
(n. Hemi. only) cold, dry,
stable. and high pressure
(avg. SH 1.4 g/kg)
mP
Maritime polar
Cool, humid,
unstable all year
(avg. SH 4.4 g/kg)
0°
mP
Maritime polar
Cool, humid,
unstable all year
(avg. SH 4.4 g/kg)
cP
5°
15°
10°
22°
15°
20°
Maritime tropical
Warm, humid, unstable
(avg. SH 14 g/kg)
Maritime tropical
Warm, humid, stable to
conditionally unstable
(avg. SH 10 g/kg)
mT
mT
a) Winter pattern
10°
Sea surface temerature in °C
SH
Specific humidity
5°
A
Continental polar
Cool, dry, moderately stable
10°
mP
cP
Maritime polar
Cool, humid,
unstable all year
(avg. SH 4.4 g/kg)
mP
Maritime polar
10° Cool, humid,
unstable all year
(avg. SH 4.4 g/kg)
15°
20°
25°
15°
cT
25°
mT
28°
28°
mT
28°
Maritime tropical
Warm, humid, very unstable
(avg. SH 17 g/kg)
Maritime tropical
Warm, humid, stable to
Conditional tropical
conditionally unstable Hot, low relative humidity
(avg. SH 13 g/kg) stable aloft, unstable at surface,
turbulent in summer
(avg. SH 10 g/kg)
b) Summer pattern
M02_HARD9671_00_SE_C02.indd 14
18/05/11 8:18 PM
CHAPTER 2 North America’s Environmental Setting
Air Masses of North America
TABLE 2.1
Source Region
Temperature
and Moisture
Characteristics in
Source Region
cA
Arctic basin and
Greenland ice cap
cP
Air
Mass
mP
15
Stability in
Source Region
Associated Weather
Bitterly cold and
very dry in winter
Stable
Cold waves in winter
Interior Canada and
Alaska
Very cold and dry
in winter
Stable entire year
a. Cold waves in winter
North Pacific
Mild (cool) and
humid entire year
Unstable
in winter
b. Modified to cPk in winter over Great Lakes bringing
“lake-effect” snow to leeward shores
a. Low clouds and showers in winter
Stable in summer
b. Heavy orographic precipitation on windward side of
western mountains in winter
c. Low stratus and fog along coast in summer; modified
to cP inland
mP
cT
mT
Northwestern
Atlantic
Cold and humid
in winter
Unstable
in winter
a. Occasional “nor’easter” in winter
Cool and humid
in summer
Stable in summer
Northern interior
Mexico and
southwestern U.S.
(summer only)
Hot and dry
Unstable
Gulf of Mexico,
Caribbean Sea,
western Atlantic
Warm and humid
entire year
b. Occasional periods of clear, cool weather in summer
a. Hot, dry, and cloudless, rarely influencing areas
outside source region
b. Occasional drought to southern Great Plains
Unstable entire
year
a. In winter it usually becomes mTw moving northward
and brings occasional widespread precipitation or
advection fog
b. In summer, hot and humid conditions, frequent
cumulus development and showers or
thunderstorms
mT
Subtropical Pacific
Warm and humid
entire year
Stable entire year
a. In winter it brings fog, drizzle, and occasional
moderate precipitation to N.W. Mexico and S.W.
United States
b. In summer this air mass occasionally reaches the
western United States and is a source of moisture for
infrequent convectional thunderstorms.
and tropical air masses form at low latitudes (centered
at approximately 25°N). These characteristics combine
to form different air masses that then dominate weather
and climate in North America. Table 2.1 provides more
details on the characteristics of each of these types of air
masses.
High-latitude air masses are associated with cool
summer weather and bitterly cold winters in the
northern interior. Polar continental (cold, dry) air
masses filter air into northern Canada bringing extremely frigid temperatures but not producing much,
if any, precipitation. Locations such as Fairbanks,
Alaska may experience temperatures as low as –50°F
(–46°C) when continental Arctic air masses arrive
in winter. These air masses sometimes spill into the
United States in winter, bringing frigid temperatures
as far south as Texas. In winter, the weather in northern West and East Coast locations is often dominated
M02_HARD9671_00_SE_C02.indd 15
by Polar maritime (cold, moist) air masses. Locations
that are influenced by maritime polar air masses,
such as Juneau, Alaska, tend to experience wet winter
weather and cool summers. The movement of these
maritime polar air masses brings heavy snow to the
eastern and central parts of Canada and the United
States in winter.
Tropical maritime (warm, moist) air masses generate strong flows of warm, wet air into areas of the
southern United States. These air masses are responsible for the warm, humid conditions experienced in
the American Southeast during the summer. Tropical
continental (warm, dry) air flows from central Mexico
into the interior of the United States but is typically
only a major influence on weather during the summer
months, when hot, dry weather invades the central
United States. Occasionally, these air masses bring unusual heat as far north as Saskatchewan and Manitoba.
18/05/11 8:18 PM
16
THE GEOGRAPHY OF NORTH AMERICA
The high-altitude jet stream often discussed on
the Weather Channel can bend as far south as Texas
while funneling cold air into the United States in the
winter and influencing eastward-moving storm systems. At other times, the jet stream may move north to
the Prairie Provinces in Canada and bring warm, dry
weather to southern Alberta, Saskatchewan, and Manitoba. During the summer, the jet stream has less of an
influence on day-to-day weather in the United States
and southern Canada because it stays in the higher
latitudes.
North America’s climate is greatly influenced by
subtropical high-pressure systems that form the basis
of the westerly winds that move weather systems
in a west-to-east pattern across the continent. These
pressure systems migrate seasonally so that the subtropical high-pressure cell that lies just to the southwest of California during the winter shifts northward
and westward as July approaches. More northerly
locations face weather and winds associated with the
subpolar low-pressure systems. Because winds blow
from areas of high pressure to areas of low pressure,
interior Canada and other parts of the continent may
experience variable weather due to its being influenced by both subtropical high- and subpolar lowpressure systems.
The Westerlies also carry moisture onto the continent from the Pacific Ocean, with the Pacific Northwest
coast of the United States and Canada’s southwest
coast receiving the most annual precipitation from this
flow. Henderson Lake in British Columbia holds the
record for the greatest average annual precipitation of
262 inches (665 centimeters). North America’s highest snowfall in one season (1027 inches or 2600 centimeters) occurred in this same part of the continent in
Washington State’s Cascade Ranges.
Figure 2.12 provides a summary of North America’s
average annual precipitation. The southeastern states
generally receive the second highest annual precipitation; these states comprise the driest part of North
America, including parts of eastern California at
Death Valley, and Nevada, Utah, and Arizona, where
continental air masses dominate and mountains block
the arrival of maritime air from the Pacific Ocean. In
contrast, the windward side of these mountains, such
as at Donner Pass, California, receives the highest annual snowfall in the world. Also for the record books,
Mt. Waialiale in Hawai’i boasts the highest rainfall
in the world, with an average of 460 inches (1170
centimeters) per year as discussed in Chapter 17. A
summary of the results of all of these processes is provided on the map of North American climate zones
shown in Figure 2.13.
But how will global climate change affect the patterns of weather and climate in North America? Although many uncertainties remain in predicting the
precise impacts of climate change at this point in
M02_HARD9671_00_SE_C02.indd 16
time, one thing is abundantly clear: climate change is
happening at a seemingly unprecedented rate in recorded history. The many impacts of this crisis are already being felt in North America and other parts of
the world. Over the last two centuries there has been
a noticeable rise in sea level along both the Atlantic
and Gulf coasts of North America (see Figure 2.14), no
doubt owing to the impact of global warming of melting ice. As a result, local governments in some of North
America’s most fragile coastal areas now restrict construction near active shorelines.
Average annual temperatures are increasing over
most of Earth’s land and water surfaces but not at
the same rates. It has been proven that polar environments are experiencing greater temperature increases
than the tropical areas at the present time. And these
higher average temperatures are creating longer growing seasons that will, in turn, affect plant distribution
patterns.
Increases in average temperatures may also affect
the shifting location patterns and amounts of precipitation in particular areas. While the amount of
rainfall is increasing in some places and decreasing
in others, it has not yet been adequately predicted
exactly where this change will occur and to what degree. Snowfall has been decreasing worldwide in recent decades as well. Storms very likely may become
more severe, but again, we don’t know where or
when these increases will occur. Likewise, the number and severity of floods may increase due to greater
rainfall levels and less water storage in snowfields.
Related to the loss polar ice, sea levels are rising. In
many of the midlatitude zones of places like North
America, grasslands are turning to desert conditions
without irritation.
The patterns of weather and climate in North
America are currently undergoing a dramatic but unpredictable period of change within the time period of
an average human life. Understanding the processes
that shape these patterns will no doubt continue to
prove helpful in finding new ways to predict what
changes lie ahead and how these changes may impact
human systems at local levels. Some of the local implications of climate processes bear examination in
the next section.
CONCEPTUAL CHECKPOINT 2.3
Speculate on some of the impacts of global climate
change on a group of local indigenous residents who live
in a small village located on edge of the Hudson Bay in
the Canadian Arctic region.
North American Climate Zones
Based on the work of early climatologist Vladimir Koeppen, six major climatic zones have been identified on
18/05/11 8:18 PM
CHAPTER 2 North America’s Environmental Setting
17
JANUARY
45°
N
40°
N
40°N
ATLANTIC
OCEAN
35°N
35°N
PACIFIC
OCEAN
30°N
0
Centimeters
Over 40
Over 16
8–16
10–20
4–8
5–10
2–4
2.5–5
110
1–2
Below 2.5
1000 mi
0 500 1000 km
Inches
20–40
500
Gulf of
Mexico
25°N
Below 1
95°W
85°W
80°W
JULY
45°
N
40°
N
40°N
ATLANTIC
OCEAN
35°N
35°N
PACIFIC
OCEAN
0
30°N
Centimeters
Over 40
Over 16
8–16
10–20
4–8
5–10
2–4
2.5–5
110
1–2
Below 2.5
1000 mi
0 500 1000 km
Inches
20–40
500
Gulf of
Mexico
25°N
Below 1
95°W
85°W
80°W
FIGURE 2.12 North American precipitation patterns in winter and summer
Earth. Figure 2.13 shows the distribution of these climatic zones in North America based on the following
system of lettering:
Tropical Humid “A” Climates are characterized by
warm and humid weather year-round. In North America, they are limited to southern Florida and Hawai’i.
Both of these areas are influenced by maritime tropical air masses bringing moisture-laden warm air into
the region. However, because both areas are nearly
surrounded by water, temperatures are not as hot in
M02_HARD9671_00_SE_C02.indd 17
summer as is the case in the continental southeastern
United States, and hence many “A” climate dwellers
regard their weather as less oppressive.
Dry “B” Climates are found where less than 20
inches of precipitation falls annually. Climatologists
generally divide these climates into steppe climates,
with 10 to 20 inches of rain per year, and desert climates, with less than 10 inches of rain per year. Death
Valley, as we have seen, is an extreme example of a
desert climate. Desert climates are found in much of
18/05/11 8:18 PM
THE GEOGRAPHY OF NORTH AMERICA
Anchorage
Churchill
15
40
10
20
ARCTIC
OCEAN
100
hi
lo
Temperature (°F)
ET
Vancouver
BRITISH COLUMBIA
25
20
60
15
40
10
20
10
20
-20
Dfc
5
J FMAM J J A SOND
Annual Precip.: 32.2
0
°N
50
Columbus
Dfb
Dfb
Cheyenne
15
40
10
20
-20
Philadelphia
Cheyenne
J FMAM J J A SOND
Annual Precip.: 14.4
0
N
0
250
250
500 mi
H
BSk
BSk
Cfa
BWh
Los Angeles
0
150 mi
Af
158°W
40
10
20
-20
156°W
A TROPICAL HUMID CLIMATES
20
80
15
5
0
75 150 km
160°W
60
100
hi
lo
Temperature (°F)
75
J FMAM J J A SOND
Annual Precip.: 15.0
0
C MILD MIDLATITUDE CLIMATES
Af
Tropical wet
climate
Cfa
Humid subtropical, without
dry season, hot summers
Aw
Tropical savanna
climate
Cfb
Marine west coast, without dry
season, warm to cool summers
Cs
Mediterranean summer—dry
Cfc
Marine west coast,
short, cool summers
B DRY CLIMATES
BWh Subtropical desert
BSk
Midlatitude steppe
PENNSYLVANIA
25
15
40
10
20
5
0
-20
J FMAM J J A SOND
Annual Precip.: 41.4
0
Miami
TEXAS
25
20
60
15
40
10
20
Aw
Miami
5
0
-20
0
20
60
Dallas
25
Precipitation (in.)
HAWAII
80
hi
lo
Temperature (°F)
PACIFIC
OCEAN
CALIFORNIA
ATLANTIC
OCEAN
Dallas
500 km
100
J FMAM J J A SOND
Annual Precip.: 37.9
80
Los Angeles
22°N
0
100
BWh
Cs
5
Philadelphia
Columbus
H
5
0
Dfa
10
20
Precipitation (in.)
60
15
40
0
Toronto
BSk
hi
lo
Temperature (°F)
20
Precipitation (in.)
80
BSk
20
60
J FMAM J J A SOND
Annual Precip.: 32.3
100
FLORIDA
80
20
60
15
40
10
20
5
0
-20
0
80°W
D CONTINENTAL
MIDLATITUDE CLIMATES
Dfa
Humid continental,
warm summer
Dfb
Humid continental,
cool summer
Dfc
Subarctic
25
Precipitation (in.)
25
Precipitation (in.)
WYOMING
25
80
Cfb
100
OHIO
100
Precipitation (in.)
H
Vancouver
hi
lo
Temperature (°F)
0
hi
lo
Temperature (°F)
J FMAM J J A SOND
Annual Precip.: 57.4
PACIFIC
OCEAN
hi
lo
Temperature (°F)
15
40
Hudson
Bay
Churchill
25
5
0
20°N
0
20
60
0
ET
Dfc
Precipitation (in.)
hi
lo
Temperature (°F)
80
0
ONTARIO
80
Cfb
30°
J FMAM J J A SOND
Annual Precip.: 16.0
Toronto
Anchorage
-20
5
ET
Cfc
-20
10
20
B a f fi n
Bay
Dfc
100
15
40
-20
ET
20
60
0
EF
ET
0
25
60
J FMAM J J A SOND
Annual Precip.: 15.8
MANITOBA
80
5
0
-20
ET
hi
lo
Temperature (°F)
20
60
Precipitation (in.)
hi
lo
Temperature (°F)
80
100
Precipitation (in.)
25
°N
ALASKA
100
Precipitation (in.)
18
J FMAM J J A SOND
Annual Precip.: 57.1
0
E POLAR CLIMATES
ET
Tundra
EF
Ice cap
H HIGHLAND
H
Complex
mountain
climates
FIGURE 2.13 Climate regions of North America
M02_HARD9671_00_SE_C02.indd 18
18/05/11 8:18 PM
CHAPTER 2 North America’s Environmental Setting
19
FIGURE 2.14 Rising sea levels and erosion threatens
beach front houses, North Topsail Beach, North
Carolina. Sea levels have risen at a mean rate of
1.8 mm a year for the past century, but this yearly
rate has increased to 2.8–3.1 mm in recent years.
western North America between the Sierra Nevada
and Cascades to the west and the western Great Plains
to the east.
In areas with desert and steppe climates, subtropical
high-pressure systems bring subsiding air with low relative humidity into these areas. Adiabatic heating (the
warming of air as it descends in elevation) also adds to
the arid and semiarid conditions of this geographic region. As mentioned earlier in this chapter, orographic
uplift (air that is forced up by blocking landforms)
pushes moisture-laden air over the western mountains.
As these parcels expand and cool, water vapor changes
from a gas to a liquid, resulting in clouds and then precipitation. The air then descends on the leeward side of
the mountains and is warmed in the process. The capacity of descending (warming) air for holding water
vapor is increased, so the land in the rain shadow is relatively dry. Such arid conditions are found in southeast
California, along the southern and central portions of
Arizona, in New Mexico, and along the southwest margin of Texas, spilling over into Mexico. The southern
portions of Utah and Nevada also experience desertlike conditions. These arid climates are characteristic of
cities such as Phoenix, Las Vegas, and El Paso.
Mild Midlatitude “C” Climates are located primarily along the Atlantic and Pacific coasts of the continent.
This climatic zone runs the entire length of the West
Coast of North America from southeastern Alaska to
Southern California. East of the Rocky Mountains, these
midlatitude climates can be found in a region from the
Atlantic to about the 98° W longitude (that is, as far west
as Oklahoma City, Dallas, and San Antonio) and northward to about the 40th parallel of latitude (that is, as far
north as Philadelphia, Indianapolis, and Kansas City).
There are several distinct types of mesothermal climates. The southeast region is classified as having
a humid subtropical climate, while Mediterranean
M02_HARD9671_00_SE_C02.indd 19
climate and marine west coast climates dominate along
the West Coast. The humid subtropics receive precipitation all year, with mild winters and hot summers. The
moist unstable air mass brought in by the wind from
the warm-water source region of the southern Atlantic
Ocean and Gulf of Mexico can produce convectional
rain showers over the area. Hurricanes can dump large
quantities of rain in this area, many times causing severe
flooding due to the already saturated soils as occurred
in the devastating Katrina storm of fall 2005 on the Gulf
Coast of the United States and in the earlier hurricaneflood of 1900 in Galveston, Texas. Other severe weather
is generated from cyclonic storms or frontal activities
produced from the clash of a continental polar air mass
from the north and a maritime tropical air mass from the
south. In portions of the Appalachian highlands, higher
elevations result in lower summer temperatures. The
Great Smoky Mountains National Park and nearby communities such as Asheville, North Carolina, and Gatlinburg, Tennessee, are popular with tourists wishing to
escape from heat and humidity at lower elevations.
Tornadoes are another form of midcontinent extreme
weather event and are discussed in Chapter 11.
Most of coastal California, including the metropolitan areas of Los Angeles, San Francisco, Sacramento,
and San Diego, has a Mediterranean climate. Places
with this type of midlatitude climate receive most of
their annual precipitation during the winter months
and experience a dry summer season, which is the opposite of most other areas of North America. This pattern of precipitation is due to subtropical high-pressure
blocking winds that would otherwise bring moisture
to the area from the maritime polar air mass during
the summer. In winter the subtropical high pressure
shifts away from the coast and allows moisture-laden
air to flow in from the Gulf of Alaska. Summer fogs
often occur along the West Coast, in places with
18/05/11 8:18 PM
THE GEOGRAPHY OF NORTH AMERICA
80
°N
60°
60
°N
N
°N
M02_HARD9671_00_SE_C02.indd 20
50
Mediterranean climates. The term Mediterranean used
to describe this type of rainy season-dry season climate
refers to the fact that this climate is also characteristic
of countries like Spain, Italy, and Greece which border
the Mediterranean Sea.
Farther north, in the Pacific Northwest, maritime
polar air masses dominate for longer periods of time
over the course of the year, resulting in a marine west
coast climate. This climate is associated with cooler
summers, rainier winters, and more unpredictable
weather patterns as compared to the humid subtropical climate and the Mediterranean climate. Winter
fogs occur frequently. They are created by the flow of
relatively warm moist air flowing over the moderating
effect of very cold water. Marine west coast climates
associated with coastal areas of Oregon, Washington,
British Columbia, and southeastern Alaska affect cities
such as Portland, Seattle, Vancouver, and Juneau.
Continental Midlatitude “D” Climates are found
along the northern tier of the United States from the
East Coast to the upper Midwest and throughout
most of Canada. They are associated with longer,
colder winters relative to Mild Midlatitude climates.
Typically, average temperatures are below freezing for
several months each winter. The Humid Continental
hot summer locations on Figure 2.13 are influenced
by the continental polar air mass but can also be affected by continental tropical and maritime air masses
throughout the year. When the colder, drier air from
the north clashes with the warmer, wetter air from
the south, violent storms can erupt, dumping large
quantities of rain or snow on the landscape, similar to
what occurs in the Southeast. Cities in the central area
of the United States such as Des Moines and Omaha
have humid continental climates with hot summers
and cold winters.
Higher latitude, humid continental mild summer
climates are characterized by a frost-free period of
at least three months and less precipitation than the
humid continental hot summer climates or the mesothermal climates. In North America, the Great Lakes
moderate winter cold and reduce summer heating in
places like upstate New York and southern Ontario.
Thus, while the lake effect snow in winter months
may pose challenges for residents, moderate temperatures support vineyards for wine grapes in this part of
North America. Parts of the New England states and
the Atlantic provinces of Canada also experience this
type of climate.
The Subarctic subregion of the midlatitude climates
is located poleward of the humid continental mild
summer zone. This area experiences dry conditions
compared to its lower latitude counterparts. Here,
cooler summers with short growing seasons and long,
cold winters are common. Parts of the Subarctic also
lie within the permafrost zone, where soils are totally
or partially frozen all year (Figure 2.15). The short
growing season here often makes agriculture risky
70°N
20
50
N
40
°N
W
°N
E
40°
S
0
500
1,000 mi
N
30°N
0 500 1,000 km
Continuous
permafrost
20°
N
Discontinuous
permafrost
Sporadic
permafrost
130°W
120°W
110°W
100°W
90°W
80°W
FIGURE 2.15 Permafrost zones in North America
and unprofitable, so most areas with subarctic climates
support very few people. Exceptions are mining and
other communities with economies not dependent on
agriculture such as Schefferville, Quebec, and Thompson, Minnesota.
Polar “E” Climates are found in the extreme north
of Alaska, Canada, and Greenland where locations are
influenced by continental Arctic and polar air masses.
There is no true summer in this zone since monthly
average temperatures never rise above 50°F or 10°C.
Because of its extreme northern location, the sun does
not rise for several weeks during the winter, producing continuous night. Snow covers the landscape for
as much as eight to ten months of the year causing
either permafrost or ground ice conditions. When
the snow melts, tundra plants appear such as sedges,
mosses, lichens, and some flowering plants. Few
settlements dot the polar climate landscape. Polar regions are also areas of low precipitation with less than
10 inches (25 centimeters) per year, and thus are technically deserts. North American polar areas are feeling the effects of ongoing global climate change more
than any other region. In fact, due to melting sea ice
caused by global warming, it is now possible for ships
to go from the Atlantic Ocean to the Pacific Ocean
across the formerly frozen Arctic Ocean during the
summer season.
Semidry climates in North America include areas
to the east of the Rocky Mountains through northern
New Mexico and north and west Texas, as well as the
western margin of the Great Plains. Cities such as Denver, Cheyenne, Great Falls, and Calgary have semiarid
climates.
18/05/11 8:18 PM
CHAPTER 2 North America’s Environmental Setting
The Highland “H” Climate realm is located in
places where the presence of high mountains causes
extensive local climatic variation. There are a few
pockets of highland climates in North America, including a finger that extends from southeastern California and northwestern Arizona through western
Nevada and eastern Oregon and Washington; a larger
area in eastern British Columbia, mid- and southern Alberta, Idaho, western Montana, and northern
Utah; and a pocket in Colorado. Resort communities such as Aspen, Vail, and Steamboat Springs, as
well as many popular national parks in the United
States and Canada, including Yellowstone, Glacier,
Jasper, and Banff, are included in the highland climate region. These locations are unique because, although some are located at fairly low latitudes, their
high elevations produce climates similar to those
found at higher latitudes. Landscapes at these higher
21
elevations mimic those of the polar climates, ranging
from short grasses, sedges, and mosses to a constant
cover of snow and/or ice.
Biogeography and Ecology
Vegetation is a mirror of climate, hydrology, and soil
types. Note that “natural” vegetation is the term used
to identify plant species that were in a particular place
before Europeans appeared in the 17th century. Natural
vegetation is often a key indicator of what kinds of soils
were beneath and what kinds of climatic cycles to expect. The natural vegetation map in Figure 2.16 may be
compared to the soils and climate maps (Figures 2.6 and
2.13) to visualize some of these relationships. For example, annual rainfall totals are especially significant for
vegetation patterns and the availability of precipitation
80°N
70°N
FIGURE 2.16 North American vegetation zones
60°
N
60
°N
50°N
40
°N
0
500
0
500
40°
1000 mi
N
1000 km
N
VEGETATION ZONES
E
W
Broadleaf deciduous forest
S
Mixed broadleaf deciduous and
needleleaf evergreen forest
30°N
Needleleaf evergreen forest
Grassland
Mixed grassland and mesquite
Broadleaf evergreen shrubland
Mediterranean shrubland
Tundra
Little or no vegetation
120°W
M02_HARD9671_00_SE_C02.indd 21
110°W
80°W
70°W
18/05/11 8:18 PM
THE GEOGRAPHY OF NORTH AMERICA
80°N
70°N
22
60°
17
N
16
60
°N
17
13
50
°N
15
16
3
12
14
40
14
4
1
50
°N
°N
4
N
40
2
E
S
30
22
19
W
20
11
°N
18
°N
5
7
30°
8
N
6
21
20°
N
0
500
9
1000 mi
23
0
500
140°W
1000 km
10
130°W
120°W
110°W
21
20°N
80°W
70°W
1
Sitkan
7
Californian
12
Aleutian Islands
18
Grasslands
2
Oregonian
8
Sonoran
13
Alaskan tundra
19
Rocky Mountains
3
Yukon taiga
9
Chihuahuan
14
Canadian tundra
20
Sierra Cascade
4
Canadian taiga
10
Tamaulipan
15
Arctic Archipelago
21
Madrean-Cordilleran
5
Eastern forest
11
Great Basin
16
Greenland tundra
22
Great Lakes
6
Austroriparian
17
Arctic Desert and Icecap
23
Everglades
FIGURE 2.17 Bioregions of North America
determines whether an area is desert, grassland, or
forest. This is true regardless of temperature, soil characteristics, or topography. Figure 2.17 shows the combined soil, climate, and vegetation patterns as biomes
or bioregions.
The number, range, and specific characteristics of
species within a biome are influenced by soil type, topography (including elevation and sun angles), temperature, moisture, and human factors. As such, there
are tropical rain forests in Hawai’i and boreal forests
M02_HARD9671_00_SE_C02.indd 22
in Alaska. You may see from examining the vegetation
map in this chapter that deserts, grasslands, and forests
occur naturally at most latitudes.
In contrast, biomes such as midlatitude temperate deserts in North America are generally hot in the
summer and have cold winters, but support a variety
of succulents, shrubs, and seasonal wildflowers. Desert
soils are almost always nutrient deficient because the
growth rates of plants are slow and there is little biomass to decompose into humus.
18/05/11 8:18 PM
CHAPTER 2 North America’s Environmental Setting
Neither desert nor forest, the Mediterranean scrub
biome, found in California and southern Oregon,
is a greater reflection of the influence of climate on
vegetation than the other biomes. Its deep-rooted,
small-leaved, perennial shrubs mixed with scattered,
savanna-like woodland is particularly adapted to summer drought and mild winters. When irrigated during dry months of the year, this environment becomes
highly productive for agriculture because many of its
soils are deep and fertile. Warm, sunnier summers also
have resulted in these regions becoming the focus of
tourism and resort industries.
Six broad patterns and locations of North American
biomes are shown in Figure 2.17: forest, tundra, grassland, scrubland, desert and steppe, and subtropical
wetland. Each type is discussed in the following sections. As on the other large-scale maps shown in this
chapter, note that local conditions may vary from the
broad patterns shown at macro scale on Figure 2.17 since
biomes transition across climate and soil-type boundaries. In addition, the general distribution patterns of biomes or bioregions in North America greatly overlap
each other (further distorting the patterns shown on
these maps).
Forests
Forests (Regions 1 through 6 and 19 through 21) occur in undisturbed areas where rainfall patterns are
regular and average over 30 inches (75 centimeters) per
year. The primary requisite for tree cover is adequate
year-round rainfall. The various forest types of North
America include tropical and temperate rain forests,
broadleaf deciduous forest, mixed broadleaf deciduous and evergreen needle leaf forests, and coniferous
forests. The only location in our definition of North
America that possesses a tropical rain forest is Hawai’i.
Temperate rain forests correspond with marine west
coast climates and are therefore found in the western
portions of the Pacific Northwest of the United States
and along the western margin of Canada. These forests
support a lush mix of broadleaf and needleleaf trees.
However, fewer tree species are found here relative
to their tropical counterparts. These rain forests are
unique not only because they are found at higher latitudes but also because they receive a large amount of
moisture from summer fog and the maritime polar air
mass. North America’s temperate rain forests house the
tallest trees found on Earth—coastal redwoods (Sequoia
sempervirens). They also contain commercially valuable species such as Douglas fir, spruce, hemlock, and
cedar. Few areas of this type of forest are native “old”
growth; most are secondary growth forests, meaning
that in the past these forests were cut down and were
either replanted or left to regenerate naturally. Poor
timber management plans have plagued these areas
in the past, but better management practices in recent
M02_HARD9671_00_SE_C02.indd 23
23
years have been put in place in an attempt to achieve
sustainable levels of production.
Broadleaf deciduous forests with oak, hickory,
beech, and maple trees are located in places with warm
to hot summers and cool to cold winters. Thus, they
correspond to the humid subtropical and continental
climates of the eastern United States and southeastern
Canada. Continuing northward into cooler and drier
regions, deciduous and mixed forests are replaced by
needle leaf evergreen forests dominated by firs, pines,
and spruces. These forests are also termed boreal forests or taigas. This is perhaps the largest biome in
North America in terms of areal extent. It extends over
most of Canada, all of the Upper Peninsula of Michigan, and northern Wisconsin and Minnesota. Signs of
the influence of global warming are beginning to be
seen in many boreal forests. The warmer temperatures
are thawing more of the active layer of soil, causing
waterlogging of soils, which these tree species cannot
tolerate. The ultimate result is a dying off of these trees
in response to the excess of water in many parts of the
Far North.
Tundra
The tundra biome (Regions 12 through 17) is found
in the highest latitudes of North America that can sustain vegetation. This zone corresponds closely to polar
climates where soils are poorly drained and exhibit a
thinner permafrost layer than the soils of needle leaf
forests. This biome consists of vegetation that can endure cold winters, low amounts of heating, and little
sunlight with a short growing season. This biome includes grasses, sedges, lichens, and some low shrubs.
Tundra locations are also excellent breeding habitats
for waterfowl such as geese and swans, and grazing areas for mountain goats and bighorn sheep. Areas along
the Arctic coast of Alaska and Canada contain this tundra vegetation.
Grasslands and Steppes
Grasslands (Region 18) are located in the Great Plains
region of the continent. The 98th to the 100th meridian
divides the short-grass from the tall-grass prairie. This
demarcation is the result of a difference in precipitation, with areas to the east experiencing more rainfall
than evaporation. To the west, potential evaporation
exceeds precipitation. In Chapter 11, we discuss major consequences in historical settlement of the Great
Plains that are related to these phenomena. Naturally
occurring trees found in the grassland biome are generally restricted to stream and river corridors. However,
people have also planted and cultivated large numbers
of trees in cities and towns and near farmsteads in order to provide shade and windbreaks, as well as for
aesthetic reasons.
18/05/11 8:18 PM
24
THE GEOGRAPHY OF NORTH AMERICA
Temperate grasslands tend to have limited and irregular rainfall and a large seasonal temperature range
(warm summers and cold winters). Most are located in
the centers of land masses away from the moderating
influence of oceans. Soils in the temperate grasslands
are among the best on Earth for field agriculture and
produce a major portion of the world’s wheat, maize
(corn), livestock, and vegetables. The deep top soils are
very fertile due to their large humus content. Nutrients
are stored in the soil rather than in the living biomass
(as in forest ecosystems).
Today, less than 1 percent of the original midcontinent grasslands in North America remain in their original state, having been heavily used because of high soil
fertility, value for grazing livestock, and improved irrigation technology. This biome is the most modified
by humans because it is the area of greatest crop and
livestock agricultural production.
Deserts and Steppes
West of the grassland biome is the driest, least vegetated
biome of the continent. This desert and steppe biome
(Regions 8, 9, and 11) is associated with an extremely dry
type of “B” climate. In this region, annual rainfall totals
are less than 10 inches (25 centimeters). This low amount
of precipitation and high potential evapotranspiration
defines these dry areas as a desert biome. Vegetation that
survives in this landscape must not only tolerate very little water on average but also must be rooted well enough
to withstand flash flooding. This biome is increasing in
areal extent as desertification takes place, owing mainly
to native vegetation removal, intensive agricultural practices, and poor soil moisture management, which can
lead to increased erosion and salinization.
Mediterranean Scrub
To the west, the desert biome gives way to the Mediterranean scrubland (Region 7) of western California and
southern Oregon. This area corresponds with the Mediterranean climate zone and is located north of the area’s
shifting subtropical high-pressure cells. Because of the
dry conditions that exist, fire is a constant possibility and,
in fact, was historically part of the natural ecosystem.
Vegetation in these fire-prone areas, called chaparral in
California, is well adapted to this hazard because it has
deep root systems and the ability to re-sprout roots after
a fire episode. Chaparral typically includes blue and live
oak, Toyon, Manzanita, and many other shrub species.
The climate and soils of this region allow for subtropical fruits, vegetables, and nuts to be grown. European
wine grapes are particularly profitable. Some other crops
include citrus fruits, olives, avocados, artichokes, and almonds, most of which are grown only in this biome in
North America and very few other parts of the world.
M02_HARD9671_00_SE_C02.indd 24
Subtropical Wetland
The Subtropical (Everglades) Wetland (Region 23) is a
comparatively tiny region. It is critically important to
the survival of many plant and animal species, however, and consists mostly of protected marshes and
mangrove zones in and around Everglades National
Park. It has recently become well known as the part
of North America (excluding Hawai’i) that is most
impacted by the illegal introduction of many tropical
plants and animals.
Ecosystems and Watersheds
It has long been a major challenge to accurately map
the physical systems of an area as compared to the
patterns of human settlement and economic activities. One way to accomplish this objective is to use
Geographic Information System (GIS) software to
combine, display, and compare multiple layers of information. The GIS-based map shown in Figure 2.18
shows 76 different ecoregions that have been identified by “overlapping” the distributions of precipitation, temperature, elevation, hydrology, geology,
soils, vegetation, and human impact. It is similar to
Figure 2.17 but much more detailed. A problem facing
cartographers interested in mapping biogeographic
information lies in selecting an appropriate scale that
is compatible with other variables to be shown on the
map. The use of ecoregions helps solve this problem
since ecoregions are an intermediate level of scale
(in between a very generalized description of global
biomes and a more site-specific biotic community at
the local scale). The U.S. Environmental Protection
Agency and other federal agencies use four levels of
detail on ecoregional maps depending on their needs.
Thus, Figure 2.18 shows North America at a Level II
scale, while Level I is more generalized and Level III
is more regionally specific.
Estimates of the degree of correspondence or
overlap of different kinds of regions also provide insights into what regional factors may have influenced
human decisions regarding settlement patterns, land
use, or cultural imprints. The use of watersheds
(Figure 2.5), for example, makes it possible to analyze the physical features of the surface of Earth as
they are bounded by common drainage systems. Resource planners and managers also use watershed
maps because these regions are often inhabited by
people with common interests, making them culturally identifiable regions (as well as physical regions).
There are almost an infinite number of watersheds in
North America, with many identified for flood control management, habitat restoration, and other conservation-related projects. In recent years, a number
of environmental planners have suggested that local
political boundaries should be redrawn to follow
18/05/11 8:18 PM
CHAPTER 2 North America’s Environmental Setting
25
80
°N
70°
1.1
N
1.1
2.1
1.1
2.1
2.1
2.3
2.2
2.2
6.1
50°
2.1
3.1
7.1
N
2.2
1.1
2.1
3.1
7.1
1.1
2.1
2.1
6.1
1.1
1.1
2.1
N
N
2.2
2.2
6.1
60°
60°
2.1 1.1
2.1
2.1
2.1
2.1
1.1
2.2
2.4
6.1
2.1
2.1
3.2
7.1
2.1
2.1
2.1
7.1
2.1
7.1
2.4
2.4
3.3
2.1
1.1
2.4
6.1
3.4
0
500
3.4
1000 mi
50
3.4
°N
2.4
0
40
6.2
1000 km
500
5.1
5.4
4.1
°N
5.1
7.1
9.2
8.1
5.1
5.3
10.1
6.2
8.1
6.2
9.2
7.1
6.2
10.1
5.2
LEVEL ONE ECOREGIONS
1.0
Tundra
Taiga
4.0
Hudson Plain
6.2.
8.1
7.1
8.1
6.2
Northwestern forested mountains
7.0
Marine west coast forest
Eastern temperate forests
9.0
Great Plains
10.0
Deserts and steppes
11.0
Mediterranean California
12.0
Southern semi-arid highlands
13.0
Temperate sierras
14.0
Tropical dry forests
9.4
13.1
13.1
10.2
S
8.4
13.1
8.5
8.3
8.3
12.1
8.5
9.4
14.3
9.5
10.2
10.2
13.2
9.6
10.2
14.6
Tropical wet forests
15.4
14.3
13.2
20°
12.1
120°W
110°W
13.4
13.5
14.5
N
13.3
15.5
130°W
N
W
8.3
8.3
13.1
30°
E
8.3
10.1
11.1
N
8.4
Boreal forests
8.0
8.5
8.2
6.2
°N
8.5
9.2
10.1
10.1
40
8.5
5.3
5.3
7.1
6.0
15.0
5.2 8.2
6.2
3.0
5.0
5.3
9.3
6.2
Arctic Cordillera
2.0
5.3
5.3
5.2
14.2
14.1
15.1
12.2
13.4
15.2
14.1
80°W
LEVEL TWO ECOREGIONS
1.1
Arctic Cordillera
8.1
Mixed wood plains
13.2
Western Sierra Madre
2.1
Northern Arctic
8.2
Central USA plains
13.3
Eastern Sierra Madre
2.3
Alaskan tundra
8.3
Southeastern USA plains
13.4
Transversal neo-volcanic system
2.4
Brooks Range tundra
8.4
Ozark, Ouachita-Appalachian forests
13.5
Southern Sierra Madre
3.1
Alaskan boreal interior
8.5
Mississippi alluvial and southeast USA coastal plains
13.6
Central American Sierra Madre and Chiapas highlands
3.2
Taiga cordillera
9.2
Temperate prairies
14.1
Dry Gulf of Mexico coastal plains and hills
3.3
Taiga plain
9.3
West-central semi-arid prairies
14.2
Northwestern plain of the Yucatan Peninsula
3.4
Taiga shield
9.4
South-central semi-arid prairies
14.3
Western pacific coastal plain, hills and canyons
4.1
Hudson Plain
9.5
Texas-Louisiana coastal plain
14.4
Interior depressions
5.1
Softwood shield
9.6
Tamaulipas-Texas semi-arid plain
14.5
Southern pacific coastal plain and hills
5.2
Mixed wood shield
10.1
Cold deserts and steppes
14.6
Sierra and plains of El Cabo
5.3
Atlantic Highlands
10.2
Warm deserts and steppes
15.1
Humid Gulf of Mexico coastal plains and hills
5.4
Boreal plain
11.1
Mediterranean California
15.2
Plain and hills of the Yucatan Peninsula
6.1
Boreal cordillera
12.1
Western Sierra Madre piedmont
15.3
Sierra Los Tuxtlas
6.2
Western cordillera
12.2
Mexican high plateau
15.4
Everglades
7.1
Marine west coast forest
13.1
Upper Gila mountains
15.5
Western pacific plain and hills
15.6
Coastal plain and hills of Soconusco
FIGURE 2.18 Level Two Ecoregions of North America
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26
THE GEOGRAPHY OF NORTH AMERICA
watershed boundaries before making important decisions related to resource use and conservation.
CONCEPTUAL CHECKPOINT 2.4
Develop a list of recommendations for preserving the natural vegetation and streamflow patterns of an ecosystem located near your home town that is slated for development.
Conclusions
The physical geography of North America has been discussed in this chapter at a general scale from the perspective of the patterns that existed on the continent
prior to Euro-American contact. As people from other
places settled in North America in the post-indigenous
era, they either adapted to the physical setting or began
to change it significantly. Many of these changes had disastrous consequences, resulting in disturbances such
as soil erosion, flooding, deforestation and unwise land
uses in certain places.
As a result, by the early 21st century very few populated areas on the continent looked anything like
the 16th-century landscape. This historical process of
landscape modification sets the stage for the story of
how North America was settled by the mix of diverse
peoples discussed in the following chapter.
Study Questions
Part I: Individual Review Questions
1. How are the location patterns of earthquakes, volcanoes, and fault lines in North America related to
its tectonic plate boundaries?
2. What have been some of the different erosional
impacts of glaciers, running water, wind, and
wave action on the geomorphology of the American and Canadian West?
3. What are some examples that illustrate the relationship between topographic barriers and human settlement on the North American continent
during the Euro-American era?
4. How do the barriers posed by high mountains influence precipitation patterns on the windward
side as compared to the leeward side of a range?
5. Why are watershed maps useful to environmental
planners and other local decision makers in delineating appropriate places for preserving natural
systems and eschewing economic development?
6. How are the landforms common to North America’s Intermontane physiographic province different from those that are visible in the Great Plains
province?
7. Specify four types of biomes that are found in
North America based on their general location
on the continent and their interrelated patterns of
natural vegetation and climate.
8. What evidences seen in the physical environment
of a particular area indicate that it was shaped by
continental glaciation in the past?
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9. What is the name of at least one major river system that flows into the Arctic, Pacific, and Atlantic
oceans?
10. What are three examples of rivers or other topographic features that have been used to delineate
political boundaries in North America?
Part II: Group Study Questions
and Learning Activities
1. Your group has been hired by a transportation planner to provide assistance determining the route of a
newly proposed hybrid bus line through a large regional park. The goal of your assignment is to suggest a route that minimizes environmental impacts
in the park. Using a GIS map showing the interrelationships of the area’s natural vegetation, stream
drainage patterns, and landform features, draft
a list of recommendations that can be included in
this planner’s final report.
2. It is three centuries ago, and your group has just
arrived in northeastern North America as colonizers from France. Select an ideal site to locate your
first settlement based on its potential for successful agriculture and the possibility of establishing
transportation linkages both with the interior of
eastern North America and with Europe.
3. Describe three different scenarios that illustrate
when the use of a bioregions map of North America as compared to a map showing the continent’s
physiographic provinces would prove to be most
useful in defending a plan to protect the natural
resource base of your state or province.
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CHAPTER 2 North America’s Environmental Setting
27
Suggestions for Further Reading
Bailey, Robert G. 1995. Descriptions of the EcoRegions of the
United States, 2nd ed. Washington, DC: U.S. Department
of Agriculture, Forest Service.
As the title suggests, this small, but fact-filled, book includes a large reference map and details about how all of
the ecosystems in the country are classified.
Chris, Daniel, and John Reganold. 2010. Natural Resource
Conservation Management for a Sustainable Future. Englewood Cliffs, NJ: Pearson.
A helpful guide that illustrates how environmental geography can be useful in conservation practices.
Christopherson, Robert W. 2003. Geosystems: An Introduction
to Physical Geography. Englewood Cliffs, NJ: Prentice Hall.
This widely used physical geography textbook is based on
the systems approach to understanding Earth’s physical
geography.
Daniels, Tom, and Katherine Daniels. 2003. The Environmental
Planning Handbook for Sustainable Communities and Regions.
Chicago: American Planning Association.
This book provides information about how to develop sustainable management practices geared to the wise use of
resources.
Diamond, Jared. 1997. Guns, Germs, and Steel: The Fates of
Human Society. New York: W.W. Norton.
Marsh, William M. 2005. Landscape Planning: Environmental
Implications. New York: John Wiley & Sons.
A “how-to” manual designed to help planners deal with
various environmental issues in land-use planning and land
development in North America.
Orme, Anthony R., ed. 2002. The Physical Geography of North
America. New York: Oxford University Press.
This book includes 25 articles on various aspects of the
physical geography of North America.
Ricketts, Taylor H., et al. 1999. Terrestrial Ecoregions of North
America: A Conservation Assessment. Covelo, CA: Island
Press.
The authors of this book argue that the use of an ecoregionbased assessment of biodiversity is the most effective way
to implement conservation planning.
Vale, Thomas R. 2005. The American Wilderness: Reflections on
Nature Protection in the United States. Charlottesville: University of Virginia Press.
This important publication examines the various meanings we attribute to nature as expressed through protected landscapes in the United States at scales ranging
from the wooded corners of city parks to vast wilderness
areas such as Yosemite, the Everglades, and Okeefenokee
Swamp.
A Pulitzer Prize–winning book that integrates the human and
environmental history of Earth in an engrossing popular style.
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