Environmental Science - 12e - Chapter 08.pdf - po ang - Januszek66

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Sustaining Biodiversity:

The Ecosystem Approach

Reintroducing Wolves to Yellowstone

CORE CASE STUDY

At one time, the gray wolf, also known as the eastern timber

wolf (Figure 8-1), roamed over most of North America. But be-

tween 1850 and 1900, an estimated 2 million wolves were shot,

trapped, and poisoned by ranchers, hunters, and government

employees. The idea was to make the West and the Great Plains

safe for livestock and for big-game animals prized by hunters.

It worked. When Congress passed the U.S. Endangered

Species Act in 1973, only a few hundred gray wolves remained

outside of Alaska, primarily in Minnesota and Michigan.

Ecologists recognize the important role this keystone preda-

tor species once played in parts of the West and the Great Plains.

These wolves culled herds of bison, elk, caribou, and mule deer,

and kept down coyote populations. They also provided uneaten

meat for scavengers such as ravens, bald eagles, ermines, grizzly

bears, and foxes.

In recent years, herds of elk, moose, deer, and antelope have

expanded. Their larger numbers have devastated some vegeta-

tion such as willow and aspen trees, increased erosion, and

threatened the niches of other wildlife species such as beavers

that help create wetlands.

In 1987, the U.S. Fish and Wildlife Service (USFWS) pro-

posed reintroducing gray wolves as a keystone species into the

Yellowstone National Park ecosystem as one way to help sustain

the biodiversity of the ecosystem and prevent further environmen-

tal degradation. The proposal brought angry protests, some from

ranchers who feared the wolves would leave the park and attack

their cattle and sheep. Other objections came from hunters who

feared the wolves would kill too many big-game animals, and

from mining and logging companies that feared the government

would halt their operations on wolf-populated federal lands.

Since 1995, federal wildlife officials have caught gray wolves

in Canada and relocated them in Yellowstone National Park and

northern Idaho. Scientists estimate that the long-term carrying

capacity of the park is 110 to 150 gray wolves. In 2007, the park

had 136 gray wolves.

Reintroducing this keystone species has sent ecological rip-

ples through the park’s ecosystem. With wolves around, elk are

gathering less near streams and rivers and their population

growth has slowed. This has spurred the growth of aspen, cot-

tonwoods, and willow trees. This in turn helped stabilize stream

banks, which lowered the water temperatures and made the

habitat better for trout. Beavers seeking willow and aspen have

returned. In addition, leftovers of elk killed by wolves are an im-

portant food source for grizzly bears and other scavengers such

bald eagles and ravens.

The wolves have also cut the population of coyotes—the top

predators in the absence of wolves—in half. This has reduced

coyote attacks on cattle in surrounding ranches. It has also in-

creased populations of smaller animals such as ground squirrels,

mice, and gophers hunted by coyotes, eagles, and hawks.

Since 1980, biodiversity (Figure 3-12, p. 48) has emerged

as one of the most important integrative principles of

biology. It is one of the four scientific principles of

sustainability . This chapter and the one that follows

are devoted to helping us understand and sustain the earth’s ter-

restrial and aquatic biodiversity.

Figure 8-1 Natural capital restoration: the gray wolf. Ranchers,

hunters, miners, and loggers have vigorously opposed efforts to return

this keystone species to its former habitat in the Yellowstone National

Park. Wolves were reintroduced beginning in 1995 and in 2007 num-

bered around 136.

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Key Questions and Concepts

8-1 How are we affecting the earth’s biodiversity and

why should we protect it?

CONCEPT 8-1A We are degrading and destroying biodiversity in

many parts of the world and these threats are increasing.

CONCEPT 8-1B We should protect biodiversity because it exists

and because of its usefulness to us and other species.

8-5 How should we manage and sustain parks

and nature reserves?

CONCEPT 8-5 Sustaining biodiversity will require protecting

much more of the earth’s remaining undisturbed land area, starting

with the most endangered biodiversity hot spots.

8-6 What is the importance of restoration ecology?

CONCEPT 8-6 Sustaining biodiversity will require a global effort

to rehabilitate and restore damaged ecosystems.

8-2 How should we manage and sustain forests?

CONCEPT 8-2 We can sustain forests by recognizing the

economic value of their ecological services, protecting old-growth

forests, harvesting trees no faster than they are replenished, and

making most paper from fast-growing plants and agricultural

residues instead of trees.

8-7 How can we help sustain aquatic biodiversity?

CONCEPT 8-7 We can sustain aquatic biodiversity by

establishing protected sanctuaries, managing coastal development,

reducing water pollution, and preventing overfishing.

8-3 How serious is tropical deforestation and how

can it be reduced?

CONCEPT 8-3 We can reduce tropical deforestation by

protecting large forest areas, teaching settlers about sustainable

agriculture and forestry, using government subsidies that encourage

sustainable forest use, reducing poverty, and slowing population

growth.

8-8 What should be our priorities for protecting

biodiversity?

CONCEPT 8-8 Sustaining the world’s biodiversity requires

mapping terrestrial and aquatic biodiversity, protecting terrestrial

and aquatic hotspots and old-growth forests, initiating ecological

restoration projects worldwide, and making conservation

profitable.

8-4 How should we manage and sustain grasslands?

CONCEPT 8-4 We can sustain the productivity of rangeland by

controlling the number and distribution of livestock and by

restoring degraded rangeland.

Note: Supplements 3, 4, 5, 6, 11, and 13 can be used with this chapter.

Forests precede civilizations,

deserts follow them.

FRANCOIS-AUGUSTE-RENÉ DE CHATEAUBRIAND

How Are We Affecting the Earth’s Biodiversity

and Why Should We Protect It?

8-1

CONCEPT 8-1A We are degrading and destroying biodiversity in many parts of the world

and these threats are increasing.

CONCEPT 8-1B We should protect biodiversity because it exists and because of its useful-

ness to us and other species.

Human Activities Are Destroying

and Degrading Biodiversity

We have depleted and degraded some of the earth’s

biodiversity, and these threats are expected to increase

( Concept 8-1A ). You can get an idea of our impact on

the earth’s natural systems by comparing a map of

those systems (Figure 1 on pp. S12–S13 in Supple-

ment 4 and Figure 5-8, p. 81) with maps showing our

large and growing ecological footprints (Figures 3 on

pp. S16–S17 and Figure 7 on pp. S20–S21 in S upple-

ment 4) ( Concept 1-3 , p. 11). According to

biodiversity expert Edward O. Wilson, “The

natural world is everywhere disappearing before our

eyes—cut to pieces, mowed down, plowed under, gob-

bled up, replaced by human artifacts.”

According the 2005 Millennium Ecosystem Assess-

ment and other studies, humans have disturbed to

150

Links:

refers to the Core Case Study.

refers to the book’s sustainability theme.

indicates links to key concepts in earlier chapters.

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some extent at least half and probably about 83% of

the earth’s land surface (excluding Antarctica and

Greenland). Most of this disturbance involves filling in

wetlands or converting grasslands and forests to crop

fields and urban areas.

The global area of temperate forests increased by

1% during the 1990s. But the area of tropical forests

decreased by 7%. As grasslands were converted to

cropland between 1970 and 2000, the populations of

wild species in temperate grasslands dropped by 7%

while those in tropical grasslands declined by a stag-

gering 80%.

Human activities are also degrading the earth’s

aquatic biodiversity. About half of the world’s wetlands

(including half of U.S. wetlands) were lost during the

last century. An estimated 15% of the world’s biologi-

cally rich coral reefs—the “rain forests of the sea”—

have been destroyed, and another 20% have been

damaged, mostly by human activities (Figure 5-27,

right, p. 99). According to a 2006 report by NOAA’s

U.S. Coral Reef Task Force, 60% of the world’s coral

reefs may be severely damaged or destroyed in less

than 25 years due to pollutants and global warming—a

major loss of the world’s aquatic biodiversity.

Three-fourths of the world’s 200 commercially

valuable marine fish species are either overfished or

fished to their estimated sustainable yield, and 29%

have collapsed, with a resulting 90% decline in their

catch. According to a 2006 report by Redefining

Progress, the Ocean Project, and the Center for Sus-

tainable Economy, the world’s ecological fishprint is un-

sustainable. The study estimated that to sustain 2003

levels of seafood consumption, humans would need

more than 2.5 times the area of all of the earth’s

oceans. Some 91 countries have exceeded the biologi-

cal capacity of the waters under their control, with

Japan, Indonesia, and China leading the pack.

The ocean is a great recycler. It converts sewage

into nutrients, removes some toxins from water, pro-

duces food, adds oxygen to water and the atmosphere,

and reduces the threat of global warming by removing

carbon dioxide from the atmosphere. But these vital

ecological and economic services (Figure 5-21, p. 94)

depend on maintaining, not depleting, the millions of

marine plants and animals whose biodiversity and in-

teractions supply such natural capital.

Freshwater streams and rivers, which make up only

about 2.5% of the earth’s water, face intense environ-

mental pressures as we dam and pollute them and

withdraw more than half of the their runoff to grow

crops and support cities.

Human activities also contribute to the premature

extinction of species. Biologists estimate that the current

global extinction rate of species is at least 100 times

and probably 1,000–10,000 times what it was before

humans existed. Mostly because of their small volume,

freshwater ecosystems have a higher rate of endan-

gered species per unit of area than terrestrial ecosys-

tems have. These threats to the world’s species are

projected

increase

sharply

during

the

few

decades, as discussed in Chapter 9.

From this brief overview, you can see why protect-

ing and sustaining the genes, species, ecosystems, and

ecological functions that make up the world’s biodi-

versity is such an important and urgent environmental

issue. Let’s explore these reasons more fully.

Why Should We Protect

Biodiversity?

Biodiversity researchers contend that we should act to

preserve the earth’s overall biodiversity, which includes

genes, species, ecosystems, and ecological processes,

because it has two types of value. One is intrinsic

value —the fact that these components of biodiversity

exist, regardless of their use to us ( Concept 8-1B ). Pro-

tecting biodiversity on this basis is essentially an ethical

decision.

The other is instrumental value —their useful-

ness to us in the form of economic and ecological serv-

ices (Figure 1-3, p. 8) ( Concept 8-1B ). For example,

more than half the world’s people depend directly on

forests, rangelands, croplands, and fisheries for their

livelihoods.

Biodiversity provides economic benefits and pleas-

ure from recreation and tourism. It also helps maintain

the structure and function of ecosystems (Figure 3-11,

p. 47) and plays a role in controlling the populations of

the earth’s species. Biodiversity also helps nature to

adapt to environmental change through natural selec-

tion ( Concept 4-1B , p. 64) and supplies us

with food and a variety of medicines and

drugs. In other words, biodiversity is one of the most

important forms of natural capital (Figure 1-3, p. 8).

The other form of instrumental values is nonuse val-

ues. For example, there is existence value —the satisfaction

of knowing that a redwood forest, a wilderness, or ang-

utans (Figure 8-2, p. 152), and wolf packs ( Core

Case Study ) exist, even if we will never see

them or get direct use from them. Aesthetic value is an-

other nonuse value. Many people, for example, appre-

ciate a tree, a forest, a wild species such as a parrot (see

photo 3, p. vii), or a vista because of its beauty. Bequest

value, a third type of nonuse value, is based on the will-

ingness of some people to pay to protect some forms of

natural capital for use by future generations.

THINKING ABOUT

Orangutans

If orangutans become extinct, mostly because of human activ-

ities, what difference might this make to you and to any chil-

dren you may have?

RESEARCH FRONTIER

Improving estimates of the economic values of the ecological

services provided by ecosystems

151

CONCEPTS 8-1A AND 8-1B

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Figure 8-2 Endangered orangutans in a

tropical forest. In 1900, there were over

315,000 wild orangutans. Now there are

less than 20,000 and they are disappearing

at a rate of over 2,000 per year. An illegally

smuggled orangutan typically sells for a

street price of $10,000. Question: How

would you go about trying to set a price on

the ecological value of an orangutan?

How Should We Manage and Sustain Forests?

8-2

CONCEPT 8-2 We can sustain forests by emphasizing the economic value of their eco-

logical services, protecting old-growth forests, harvesting trees no faster than they are re-

plenished, and making most paper from fast-growing plants and agricultural residues instead

of trees.

Forests Provide Important

Economic and Ecological Services

Figure 5-8 (p. 81) shows the distribution of the world’s

boreal, temperate, and tropical forests, which occupy

about 30% of the earth’s land surface (excluding

Greenland and Antarctica). They provide many impor-

tant ecological and economic services (Figure 8-3). For

example, through photosynthesis, forests remove CO 2

from the atmosphere and store it in organic com-

pounds (biomass). By performing this ecological serv-

ice, forests help stabilize the earth’s temperature and

slow global warming as a part of the global carbon cy-

cle (Figure 3-19, 56).

There have been efforts to estimate the economic

value of the ecological services provided by the world’s

forests and other ecosystems (Science Focus, at right).

activities or natural disasters for a hundred years or

more (Figure 8-4, p. 154, and Figure 5-14, top photo,

p. 87). Old-growth forests are storehouses of biodiver-

sity because they provide ecological niches for a multi-

tude of wildlife species (Figure 5-15, p. 88, and Fig-

ure 5-16, p. 89).

The second type is a second-growth forest: a stand

of trees resulting from secondary ecological succ ession

( Concept 6-4A , p. 115; Figure 6-9, p. 116; and

Figure 5-14, middle photo, p. 87). These

forests develop after the trees in an area have been re-

moved by human activities (such as clear-cutting for

timber or conversion to cropland) or by natural forces

(such as fire, hurricanes, or volcanic eruption).

A tree plantation, also called a tree farm (Fig-

ure 8-5, p. 154, and photo 1, p. vi), is a managed tract

with uniformly aged trees of one or two genetically

uniform species that are harvested by clear-cutting as

soon as they become commercially valuable. The land

is then replanted and clear-cut again in a regular cycle.

When managed carefully, such plantations can produce

wood at a fast rate and increase profits, but they are

much less biologically diverse and sustainable than old-

growth and second-growth forests. In addition, re-

peated cycles of cutting and replanting can eventually

deplete the soil of nutrients and hinder the growth of

any type of forest on the land.

We Have Old-Growth

and Second-Growth Forests

and Tree Plantations

Forest managers and ecologists classify forests into two

major types based on their age and structure. The first

type is an old-growth forest: an uncut or regenerated

forest that has not been seriously disturbed by human

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CHAPTER 8

Sustaining Biodiversity: The Ecosystem Approach

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We Have Cut Down Almost Half

of the World’s Forests

Deforestation is the temporary or permanent re-

moval of large expanses of forest for agriculture or

other uses. Surveys by the World Resources Institute

(WRI) indicate that over the past 8,000 years, human

activities have reduced the earth’s original forest cover

by about 46%, with most of this loss taking place

since 1950.

Deforestation is continuing at a rapid rate in many

parts of the world. The FAO and WRI surveys indicate

that the global rate of forest cover loss between 1990

and 2005 was between 0.2% and 0.5% per year, and

that at least another 0.1–0.3% of the world’s forests

were degraded annually, mostly to grow crops and

graze cattle.

If these estimates are correct, the world’s forests

are being cleared or degraded exponentially at a rate

of 0.3–0.8% per year, with much higher rates in some

areas. These losses are concentrated in developing

countries, especially those in the tropical areas of Latin

America, Indonesia, and Africa. According to the WRI,

if current deforestation rates continue, about 40% of

the world’s remaining intact forests will have been

logged or converted to other uses within two decades,

if not sooner.

Cutting down large areas of forests, especially old-

growth forests, has important short-term economic

NATURAL

CAPITAL

Forests

Ecological

Services

Economic

Services

Support energy flow and chemical cycling

Fuelwood

Lumber

Reduce soil erosion

Pulp to make

paper

Absorb and release water

Purify water and air

Mining

Livestock

grazing

Influence local and regional climate

Store atmospheric carbon

Recreation

Provide numerous wildlife habitats

Jobs

Figure 8-3 Major ecological and economic services provided by forests ( Con-

cept 8-1B ). Question: Which two ecological services and which two economic

services do you think are the most important? Why?

SCIENCE FOCUS

Putting a Price Tag on Nature’s Ecological Services

stroying or degrading these ecological serv-

ices? One reason is that economic savings

provided by conserving natural resources ben-

efit everyone now and in the future, whereas

the profits made by exploiting these resources

are immediate, and they benefit a relatively

small group of people who have the motiva-

tion and means to develop them.

A second reason is that many government

subsidies and tax incentives support unsustain-

able use of forests and other ecosystems for

short-term economic gain. Finally, most people

are unaware of the value of the ecological

services and biological income provided by

forests and other ecosystems.

he long-term health of an economy

cannot be separated from the health

of the natural systems that support it. Cur-

rently, forests and other ecosystems are val-

ued mostly for their economic services (Figure

8-3, right). But suppose we took into account

the monetary value of the ecological services

provided by forests (Figure 8-3, left).

In 1997, a team of ecologists, economists,

and geographers—led by ecological econo-

mist Robert Costanza of the University of

Vermont—estimated the monetary worth of

the earth’s ecological services and the biologi-

cal income they provide. They estimated the

latter to be at least $33.2 trillion per year—

close to the economic value of all of the

goods and services produced annually

throughout the world. To provide this income,

the world’s natural capital would have a value

of at least $500 trillion—an average of about

$82,000 for each person on earth!

According to this study, the world’s forests

provide us with ecological services worth at

least $4.7 trillion per year—hundreds of times

more than their economic value. And these

are very conservative estimates.

The authors of such studies warn that un-

less we include the financial value of ecologi-

cal services in deciding how to use forests and

other natural resources, they will be destroyed

or degraded for short-term economic gain.

These researchers hope their estimates will

alert people to three important facts: the

earth’s ecosystem services are essential for all

humans and their economies; their economic

value is huge; and they are an ongoing source

of ecological income as long as they are used

sustainably.

According to Costanza, “We have been

cooking the books for a long time by leaving

out the worth of nature.” Biologist David

Suzuki warns, “Our economic system has

been constructed under the premise that

natural services are free. We can’t afford that

luxury anymore.”

Why haven’t we changed our accounting

systems to reflect the values of these re-

sources and the losses that result from de-

Critical Thinking

Some analysts believe that we should not try

to put economic values on the world’s irre-

placeable ecological services because their

value is infinite. Do you agree with this view?

Explain. What is the alternative?

153

CONCEPT 8-2

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