LESSON
2
Forests and Their Resources
Guiding Question: How can resource managers strike a balance between
the ecological and economic value of forest resources?
• List some of the ecological and economical values of
forest resources.
• Describe the costs and benefits of the different
methods of timber harvesting.
• Discuss the current levels of deforestation in the
United States and in developing nations.
Reading Strategy Before you read, preview Figure 8. Note
any questions you have about it, and try to answer them as
you read.
Vocabulary even-aged, uneven-aged, clear-cutting,
seed-tree approach, shelterwood approach, selection system,
deforestation, old-growth forest
Forests cover about 30 percent of Earth’s land sur-
11.2 LESSON PLAN PREVIEW
Differentiated Instruction
Struggling students create a
T-chart to help them understand
the value of forests.
Real World Students consider
how logging could affect their
own lives.
Inquiry Students research
deforestation patterns in
various regions of the world.
11.2 Resources
Outdoors Activity, How Much Lumber? • Modeling Lab, Making Recycled
Paper • Real Data Online • Lesson 11.2
Worksheets and Assessment • Chapter 11 Overview Presentation
Source: U.S. Geological Survey
330 Lesson 2
face, as you can see in Figure 6. Most of the world’s remaining forests
are either boreal forest or tropical rain forest. Temperate forests cover a
much smaller area, in part because people have already cleared so many
of them.
Forests provide habitat for countless organisms; help maintain soil,
air, and water quality; and play key roles in our planet’s biogeochemical
cycles. Forests also have long provided people with wood for fuel, construction, paper production, and other uses.
Resource managers who manage public or private forests are called
foresters. Forest management is called forestry. Foresters aim to balance
the ecological importance of forests with the economic importance of
forests as resources for wood products.
Figure 6 Earth’s Forests About 30 percent of Earth’s land area is covered with
forests (as indicated by the green areas). Most of Earth’s forests are boreal forests
in the north and tropical rain forests in the south.
Forest Resources
Forest resources have great ecological and
economic value.
The complexity of forests makes their resources
enormously important, both within their ecosystems and in the world economy. A 2005 survey by
the United Nations showed that more than one third
of the world’s forests were used mostly for timber
production. But forests provide a wide variety of
other services and products, including conservation
of biodiversity; protection of soil and water quality; maintenance of biogeochemical cycles; food;
medicine; and “social services” such as recreation,
tourism, education, and conservation of culturally
important sites. In addition, some people live in
forests and depend on forests for all their needs.
Ecological Value Because forests are structur-
ally complex, they provide many different habitats
for plants and animals. As a result, forest ecosystems
have great biodiversity. You can see the complexity
of a mature forest’s structure and the diverse habitats within it in Figure 7. In general, forests with a
greater diversity of plants have a greater diversity
of other organisms as well. And in general, mature
forests, such as the old-growth forests remaining
at Clayoquot Sound, have more biodiversity than
younger forests.
Forests also provide many vital ecosystem services. Forest plants help prevent soil erosion. They
also help regulate the water cycle by slowing runoff,
reducing flooding, and purifying water as they take
it from the soil and release it to the atmosphere.
Forest plants also store carbon and release oxygen,
thereby helping to moderate climate. Because they
fulfill so many ecological functions, forests are necessary for our survival.
Canopy Some animals live in the
dense treetop canopy. Leaf-eating
insects there provide food for
many bird species.
Subcanopy Tree-dwelling mammals
such as squirrels, sloths, and monkeys
eat fruit and leaves in the canopy and
subcanopy. Other animals use tree
bark, branches, and trunks as places
to feed, nest, and rest.
Snag Snags are dead or dying
trees. Insects feed on snags and
then provide food for other
animals. Holes in snags provide
nest sites and shelter for many
vertebrate species.
Understory Understory plants, such as
rhododendrons, and groundcover plants,
such as ferns, provide varied habitats.
Stems, leaves, and roots also provide
food and shelter.
Figure 7 Mature Forest Structure Mature forests have
complex structures. The crowns of the largest trees form the
canopy, and smaller trees beneath them form the shaded
subcanopy and understory. Dead or dying trees, or snags,
are valuable for nesting and shelter. Shrubs and groundcover
grow just above the forest floor.
Forest floor Much biodiversity is
found on the forest floor, mostly as
insects and decomposers.
Forestry and Resource Management 331
Economic and Medicinal Value The use of forest resources is
essential to our lifestyle. Forests provide timber, which can be made into
thousands of economically valuable products. And for thousands of years,
wood from forests has fueled the fires that have kept people warm and
well fed. Wood has also built the houses that have kept people sheltered.
It has built the ships that have carried people and their cultures from one
region to another. And wood has enabled us to make paper, which has
helped people to share knowledge.
Forest plants also provide food and medicine. Many fruits, nuts,
spices, and herbs come from forest plants. Forest plants have also yielded
many modern medicines. The drug paclitaxel, which treats several kinds
of cancer, was discovered in the Pacific yew tree. Madagascar rosy periwinkle, a flowering forest plant that is endangered in much of its range,
is the source of treatments for leukemia and Hodgkin’s lymphoma. Other
cancer treatments and treatments for other illnesses have also been
derived from plants.
ANSWERS
Real Data
1. 1970: 130 million tons; 1980: 180
million tons; 1990: 250 million
tons; 2000: 350 million tons
(answers are approximate)
2. 1970–1980: 38%; 1980–1990: 39%;
1990–2000: 40%
3. About 23%
4. Answers will vary.
Timber Harvesting
There are costs and benefits to every method of timber
harvesting.
Today, most commercial timber harvesting, or logging, takes place in
Canada, Russia, and other nations with large boreal forests, and in nations
with large tropical rain forests, such as Brazil. In the United States, most
logging takes place in the conifer forests of the West and on the pine plantations of the South, on both private and public lands.
Real Data
From Trees to Paper
332 Lesson 2
Global Consumption of Paper
and Paperboard 1970–2000
120
Paper and paperboard
consumed (millions of tons)
The invention of the movable-type printing press by
Johannes Gutenberg in 1450 created a demand for
paper that continues to increase even today. Because
most fiber for paper production comes from wood, a
high demand for paper results in a high demand for
timber. Examine the graph and answer the questions.
1. Interpret Graphs About how many millions of
tons of paper and paperboard were consumed
worldwide in 1970? 1980? 1990? 2000?
2. Calculate By about what percentage did global
consumption increase from 1970 to 1980? From
1980 to 1990? From 1990 to 2000?
3. Calculate According to the United Nations’ Food
and Agriculture Organization, worldwide paper
consumption was expected to be about 431 million
tons in 2010. By what percentage was world paper
consumption expected to increase from 2000 to 2010?
1970
1980
1990
2000
100
80
60
40
20
0
Af
ric
a
As
ia
r
Eu
op
e
Am
er
ica
Am
r th
o
N
Continent
t
La
in
er
ica
e
Oc
an
ia
Data from the Food and Agriculture Organization of the United Nations
4. Propose a Solution List three steps that your
school could take to reduce its paper consumption.
When timber companies harvest trees, they use
one or more of the methods shown in Figure 8—clearcutting, the seed-tree approach, the shelterwood
approach, or a selection system. These methods fall
into two categories: those that result in even-aged
stands of trees and those that result in uneven-aged
stands of trees. Even-aged stands result from the
regrowth of trees that were mostly all cut at the same
time, as with clear-cutting (Figure 9). Uneven-aged
stands result from the regrowth of trees that were cut
at different times, as with selection systems.
Uneven-aged stands typically have more biodiversity, because the regrown trees of different ages offer a
greater variety of habitats. But all methods of logging
disturb forest communities. Logging changes forest
structure and composition, as the larger trees forming
the canopy and subcanopy are often removed. Most
logging methods also increase soil erosion, which can
lead to muddy waterways that degrade animal habitats
and lower drinking-water quality. And most methods
also increase runoff, sometimes causing flooding, or
even landslides.
Figure 9 Clear-Cutting During clear-cutting
all the mature trees in an area are cut at once. The
result is regrowth that is even-aged, like the short
trees in the foreground.
Figure 8 Timber
Harvesting Methods
Different methods of
timber harvesting lead
to different patterns of
regrowth.
BIG QUESTION
Original forest
HARVEST
(a) Clear-cutting
(b) Seed-tree or shelterwood approach
REGROWTH FOLLOWING HARVEST
(c) Selection system
How can we use Earth’s
resources sustainably?
Perspective After students
have read about the methods
of timber harvesting, ask each
student to develop a few
questions a timber company
executive might consider
when determining what
method of harvesting to use
in a particular area. Have
students share and discuss the
questions they develop.
Forestry and Resource Management 333
1
A Tree’s History
5 of
6 the7
1 Examine
2 3 the
4 photo
1
2
8
tree-trunk slice, or tree
cookie, below. Observe the
light-colored and darkcolored rings. Each pair of
rings represents a year of the
tree’s growth.
5 A6 and7B. Note
8 9
2 Observe
3 4 areas
any differences.
6 C,
7 which
8 was
9
3 Observe
4 5 Area
blackened by a fire.
Analyze and Conclude
1. Calculate Approximately
how old was this tree when it
was cut down?
2. Infer Areas A and B were
both produced by four years
of growth. What conditions might account for their
difference?
3. Interpret Visuals How are
the ring widths in Area C
different from the widths
elsewhere? Given these differences, explain how the tree
grew after the fire.
4. Communicate Using evidence from this tree cookie,
write a paragraph that summarizes the history of the
tree. Include as many details
as possible in your paragraph.
B
C
9
Clear-Cutting From the 1950s through the 1970s, timber was largely
harvested by clear-cutting, a method in which all of the trees in an area are
cut at once. Clear-cutting is generally the most cost-efficient method for
timber companies, but it also has the greatest impact on forest ecosystems.
Clear-cutting results in even-aged stands of regrowth. Sometimes
clear-cutting can mimic the effects of natural disasters such as fires,
tornadoes, or windstorms that knock down large areas of trees. Usually, however, clear-cutting destroys or displaces entire communities of
organisms, causes soil erosion, and increases the penetration of sunlight
to ground level. Because it changes light, precipitation, wind, and temperature conditions, clear-cutting can lead to a new microclimate. The
new microclimate allows different types of plants to replace those of the
original forest. Essentially, clear-cutting sets in motion secondary succession in which the resulting climax community may turn out to be different from the original climax community.
Seed-Tree and Shelterwood Approaches When timber is harvested with the seed-tree approach, small numbers of mature and healthy
seed-producing trees are left standing so that they can reseed the logged
area. In the shelterwood approach, small numbers of mature trees are
left in place to provide shelter for seedlings as they grow. Although both
methods are less harmful to forest communities than clear-cutting, both
lead to regrowth that is mostly even-aged.
Selection Systems Selection systems, in contrast, result in uneven-
aged stands of regrown trees. In a selection system, only some of the trees
in a forest are cut at once. Selection systems include single-tree selection,
in which trees spaced widely apart are cut one at a time, and group selection, in which small patches of trees are cut.
Timber companies pursued a form of selection harvesting at Clayoquot Sound after old-growth advocates applied pressure and the government researched the issue. Not wanting to bring a complete end to
logging when so many local people depended on the industry for work,
the activists promoted a method they considered more environmentally
friendly. After some research, the government agreed.
However, selection systems are by no means ecologically harmless.
Moving trucks and machinery over roads and trails to get to individual
trees compacts the soil and disturbs the forest floor. In addition, selection
methods are unpopular with timber companies because they are more
expensive than clear-cutting. For example, cut trees must sometimes
be removed by helicopters. Loggers dislike selection systems because
they are more dangerous than clear-cutting. In clear-cutting, loggers are
largely protected from falling trees by the heavy machinery they operate;
when cutting selectively, loggers must spend more time on the ground, in
danger both from equipment and from falling trees.
Reading
Checkpoint
A
334 Lesson 2
What are two different selection systems?
Deforestation
ANSWERS
Deforestation may help nations develop, but it can be
ecologically destructive in the long run.
We all depend on wood, from the herder in Nepal cutting trees for
firewood to the American high school student using tons of paper while
earning a diploma. For such reasons, people have cut forests for timber
for thousands of years. Forests are also cleared to make way for farming. Deforestation is the clearing of a forest and the replacement of it by
another land use. It has altered the landscapes and ecosystems of much
of our planet. Deforestation has provided warmth, shelter, and trade for
many human communitites, even as it has caused soil degradation and
species population declines for other communities.
The negative effects of deforestation are greatest in tropical regions
because of the potential massive loss of biodiversity, and in arid regions
because of loss of soil productivity. In addition, deforestation has a global
impact. It adds carbon dioxide (CO2) to the atmosphere in two ways. CO2
is released when plant matter is burned or decomposed, and after burning, less vegetation remains to use CO2. Because CO2 in the atmosphere
contributes to the greenhouse effect that can cause global warming, widespread deforestation can contribute to global warming.
Quick Lab
1. About 28 years old
2. Sample answer: Rainfall and temperature; the years in which Area A
grew might have had more rainfall
and temperatures that were better
suited for growth
3. The tree added more new wood on
the side away from the fire than on
the side of the fire.
4. Answers will vary. Answers should
account for differences in the
widths of the tree rings (specifically the areas marked A and B ),
mention the fire and how it damaged the outmost growing regions
of the tree in Area C, and mention
the fact that the tree survived the
fire (as evidenced by continued
growth in other parts of tree).
Reading Checkpoint Single-tree
selection and group selection
United States Deforestation for timber and farmland enabled the
United States to expand across the continent. The vast deciduous forests
of the East were virtually stripped of their trees by 1850, making way
for countless small farms. Timber from eastern forests built the cities of
America’s East Coast. Later, midwestern cities such as Chicago were constructed with timber cut in the forests of Wisconsin and Michigan.
As the U.S. farming economy shifted to an
industrial one, wood was used to fuel the Industrial Revolution. Logging
operations moved south to Texas, Florida, and the Carolinas. Once most
mature trees there were cut, timber companies moved west, cutting the
continent’s biggest trees in the Rocky Mountains, the Sierra Nevada, the
Cascade Mountains, and the Pacific Coast ranges. By the early 1900s, very
little old-growth forest—forest that has never been logged—remained in
the United States, as you can see in Figure 10.
▶ The Industrial Revolution
1620
Figure 10 Deforestation in the
United States When Europeans began
colonizing the area that would become
the United States (left map), the entire
eastern half and large parts of the
western half were forested (green). By
1920, the vast majority of these forests
had been cut (right map).
1920
Source: Williams, M. 1989. Americans and their forests. Cambridge: Cambridge University Press. As adapted by Goudie, A., 2000. The human impact. Cambridge, MA: MIT Press.
Forestry and Resource Management 335
Today, not even the largest oaks and maples in eastern North
America, or even most redwoods of the California coast, are old-growth
trees. The scarcity of old-growth trees in North America today explains
the concern that scientists have for old-growth ecosystems and the passion with which environmental advocates have fought to preserve them
in areas such as Clayoquot Sound. While some former farms and pastures
of eastern North America are slowly regaining forest cover, this process is
basically secondary succession. Once old-growth forest is cut, it may need
hundreds of years of undisturbed growth in order to recover.
▶ Today
Developing Nations Old-growth tropical rain forests still remain
ANSWERS
Lesson 2 Assessment For answers
to the Lesson 2 Assessment, see page
A–17 at the back of the book.
in many developing nations, and these nations are in the position the
United States once was: They have a vast frontier that they can develop
and use for income. Today’s advanced technology, however, has allowed
these nations to exploit their resources much faster than the United States
did. As a result, deforestation has been rapid in the tropical rain forests of
developing nations, such as Brazil and Indonesia (Figure 11). Because rain
forests are the most diverse biomes, a
great diversity of species—some perhaps
still undiscovered—are being affected by,
or even lost to, deforestation. And recall
that large-scale forest loss has global consequences. It can worsen global warming by increasing carbon dioxide in the
atmosphere, especially if trees are cleared
by burning, as they often are in tropical
rain forests.
Figure 11 Rainforest Deforestation
Brazil produces more charcoal than any other
nation. Both farmed trees and rainforest
trees are cut and burned to make charcoal.
About 350,000 Brazilians work in unhealthy,
often exploitative conditions in the charcoal
industry.
2
1. Review What is one way a forest is ecologically
valuable? What is one way a forest is economically
valuable?
2. Compare and Contrast How are clear-cutting and
the shelterwood approach similar? How are they different? How do both differ from selection systems?
3. Predict What, generally, is the current level of
deforestation in the United States? In developing
nations? How would you expect the deforestation
in developing nations to change in the next 100
years? Explain.
336 Lesson 2
4.
People in developed
nations often warn people in developing nations
to stop destroying rain forests. People of developing nations often respond that this is hypocritical,
because many of the developed nations became
wealthy by deforesting their land and exploiting its
resources. What would you say to the leader of a
developing nation that is seeking to clear much of
its forest?