Sustaining Biodiversity:
The Ecosystem Approach
Chapter 9
Section 9-1
WHAT ARE THE MAJOR THREATS
TO FOREST ECOSYSTEMS?
Forests vary in their age, makeup, and origins
• Natural and planted forests occupy about 30% of
the earth’s land surface (excluding Greenland and
Antarctica).
• Two major types based on their age and structure:
– Old growth forest: Uncut or regenerated primary forest
that has not been seriously disturbed by human activities
or natural disasters for several hundred years or more.
– Second-growth forest: A stand of trees resulting from
secondary ecological succession that develops after the
trees in an area have been removed by human activities
such as clear-cutting for timber or cropland or by natural
forces such as fire, hurricanes, or volcanic eruption.
Forests vary in their age, makeup, and origins
• A tree plantation (tree farm, commercial forest), is
a managed tract with uniformly aged trees of one
or two genetically uniform species that usually are
harvested by clear-cutting as soon as they
become commercially valuable.
• Forests provide important economic and
ecological services.
– Forests remove CO2 from the atmosphere and store it in
organic compounds (biomass) through photosynthesis.
– Forests help to stabilize the earth’s temperature and
slow projected climate change.
The short rotation cycle of cutting and
regrowth of a monoculture tree plantation
Weak trees
removed
25 yrs
Clear cut
30 yrs
15 yrs
Years of growth
Seedlings
planted
5 yrs
10 yrs
Fig. 9-3a, p. 176
Forests provide many important
economic and ecological services
Unsustainable logging is a major
threat to forest ecosystems
• The first step in harvesting trees is to build
roads for access and timber removal, but
they can cause the following problems:
– Increased erosion and sediment runoff into
waterways.
– Habitat fragmentation.
– Loss of biodiversity.
– Forest exposure to invasion by nonnative
pests, diseases, and wildlife species.
Unsustainable logging is a major
threat to forest ecosystems
• Methods of harvesting trees:
– Selective cutting.
– Clear-cut.
– Strip cutting.
Three major tree harvesting
methods
(a) Selective cutting
Clear
stream
Fig. 9-6a, p. 179
(b) Clear-cutting
Muddy
stream
Fig. 9-6b, p. 179
(c) Strip cutting
Uncut
Cut 1
year ago
Dirt road
Cut 3–10
years ago
Uncut
Clear
stream
Fig. 9-6c, p. 179
Aerial view showing clear-cut
logging, Washington state
Fire can threaten or benefit
forest ecosystems
• Surface fires usually burn only
undergrowth and leaf litter on the forest
floor.
– Kills seedlings and small trees but spares
most mature trees and allows most wild
animals to escape.
– Burns away flammable ground material and
may help to prevent more destructive fires.
– Frees valuable mineral nutrients tied up in
slowly decomposing litter and undergrowth.
Fire can threaten or benefit
forest ecosystems
– Releases seeds from the cones of lodgepole
pines.
– Stimulates the germination of certain tree
seeds (e.g. giant sequoia and jack pine).
– Helps to control tree diseases and insects.
• Crown fires are extremely hot fires that
leap from treetops, burning whole trees.
– Can destroy most vegetation, kill wildlife,
increase soil erosion, and burn or damage
human structures in their paths.
Surface fires and crown fires
Almost half of the world’s
forests have been cut down
• Deforestation is the temporary or permanent
removal of large expanses of forest for
agriculture, settlements, or other uses.
• Human activities have reduced the earth’s
original forest cover by about 46%, with most of
this loss occurring in the last 60 years.
• 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.
Almost half of the world’s
forests have been cut down
• Clearing large areas of forests, especially old-growth
forests, has important short-term economic benefits, but
it also has a number of harmful environmental effects.
• The net total forest cover in several countries changed
very little or even increased between 2000 and 2007.
Some due to natural reforestation by secondary
ecological succession on cleared forest areas and
abandoned croplands, or the spread of tree plantations.
• Concern about the growing amount of land occupied by
commercial tree plantations, because replacement of
old-growth forests by these biologically simplified tree
farms represents a loss of biodiversity, and possibly of
stability, in some forest ecosystems.
Harmful effects of deforestation
CASE STUDY: Many Cleared Forests
in the United States Have Grown Back
• Forests that cover about 30% of the U.S. land area
provide habitats for more than 80% of the country’s
wildlife species and supply about two-thirds of the
nation’s surface water.
• Today, forests in the U.S. cover more area than they did
in 1920, primarily due to secondary succession.
• Every year, more wood is grown in the U.S. than is cut
and the total area planted with trees increases.
• Protected forests make up about 40%.
• Since the mid-1960s, an increasing area of the nation’s
remaining old-growth and fairly diverse second-growth
forests has been cut down and replaced with biologically
simplified tree plantations.
Forest cover in the U.S.
Tropical forests are
disappearing rapidly
• Tropical forests cover about 6% of the earth’s land
area.
• At least half of the world’s known species of
terrestrial plants and animals live in tropical forests.
• Brazil has more than 30% of the world’s remaining
tropical rain forest in its vast Amazon basin.
• At the current rate of global deforestation, 50% of
the world’s remaining old-growth tropical forests will
be gone or severely degraded by the end of this
century.
Causes of tropical deforestation
are varied and complex
• There are a number of interconnected
underlying and direct causes.
– Pressures from population growth and poverty,
push subsistence farmers and the landless
poor into tropical forests, where they try to grow
enough food to survive.
– Government subsidies can accelerate the direct
causes such as logging and ranching by
reducing the costs of timber harvesting, cattle
grazing, and the creation of vast plantations of
crops such as soybeans.
Causes of tropical deforestation
are varied and complex
– Tropical forests in the Amazon and other South
American countries are cleared/burned for
cattle grazing and large soybean plantations.
– In Southeast Asia, tropical forests are being
replaced with vast plantations of oil palm,
whose oil is used in cooking, cosmetics, and
biodiesel fuel for motor vehicles.
– In Africa, people struggle to survive by clearing
plots for small-scale farming and by harvesting
wood for fuel, which is causing deforestation on
that continent.
Major underlying and direct causes of the
destruction and degradation of tropical forests
Section 9-2
HOW SHOULD WE MANAGE
AND SUSTAIN FORESTS?
We can manage forests more
sustainably
• Certification of sustainably grown timber
and of sustainably produced forest
products can help consumers.
• Removing government subsidies and tax
breaks that encourage deforestation would
also help.
Ways to grow and harvest trees
more sustainably
We can improve the
management of forest fires
• In the United States, the Smokey Bear
educational campaign has:
– prevented countless forest fires, saved many lives
and prevented billions of dollars in loss of trees,
wildlife, and human structures.
– convinced the public that all forest fires are bad and
should be prevented or put out.
• Trying to prevent all forest fires can make
matters worse by increasing the likelihood of
destructive crown fires due to the accumulation
of highly flammable underbrush and smaller
trees in some forests.
We can improve the
management of forest fires
• Strategies for reducing fire-related harm:
– Prescribed burns are small, contained surface fires to
remove flammable small trees and underbrush in the
highest-risk forest areas.
– Allow some fires on public lands to burn, thereby
removing flammable underbrush and smaller trees, as
long as the fires do not threaten human structures and
life. Protect houses/buildings in fire-prone areas by
thinning a zone of about 60 meters (200 feet) around
them and eliminating the use of flammable building
materials such as wooden shingles.
– Thin fire-prone areas by clearing small fire-prone trees
and underbrush under careful environmental controls.
We can reduce the demand for
harvested trees
• Reduce inefficient use of construction
materials, excess packaging, overuse of
junk mail, inadequate paper recycling, and
failure to reuse or find substitutes for
wooden shipping containers.
• Paper can be made from fiber that does
not come from trees.
Ways to reduce tropical
deforestation
• Debt-for-nature swap can make it
financially attractive for countries to protect
their tropical forests.
• Conservation concessions occur when
governments or private conservation
organizations pay nations for agreeing to
preserve their natural resources.
Ways to reduce tropical
deforestation
• Consumers can reduce the demand for
products that are supplied through illegal
and unsustainable logging in tropical forests.
– For building projects, use recycled waste
lumber or wood alternatives, such as recycled
plastic building materials and bamboo.
– Reduce the use of throwaway paper products
and replace them with reusable plates, cups,
and cloth napkins and handkerchiefs.
• Individuals can plant trees.
Ways to protect tropical forests
and use them more sustainably
Section 9-3
HOW SHOULD WE MANAGE
AND SUSTAIN GRASSLANDS?
Some rangelands are
overgrazed
• Grasslands provide many important ecological
services, including soil formation, erosion
control, nutrient cycling, storage of atmospheric
carbon dioxide in biomass, and maintenance of
biodiversity.
• Rangelands are unfenced grasslands in
temperate and tropical climates that supply
forage, or vegetation, for grazing (grass-eating)
and browsing (shrub-eating) animals.
Some rangelands are
overgrazed
• Livestock also graze in pastures, which are
managed grasslands or enclosed meadows
usually planted with domesticated grasses or
other forage.
• Overgrazing occurs when too many animals
graze for too long and exceed the carrying
capacity of a rangeland area.
• Limited data from surveys in various countries
indicate that overgrazing by livestock has
caused a loss in productivity in as much as 20%
of the world’s rangeland.
Left of fence: overgrazed land
Right: lightly grazed land
We can manage rangelands
more sustainably
• Control the number of grazing animals and the
duration of their grazing in a given area so the
carrying capacity of the area is not exceeded.
– Rotational grazing: confine cattle to one area via portable
fencing for a short time (1–2 days) and then moved.
– Provide supplemental feed at selected sites and
strategically locate water holes and tanks and salt blocks
to reduce overgrazing.
– Suppress the growth of unwanted invader plants by use
of herbicides, mechanical removal, or controlled burning
or use controlled, short-term trampling by large numbers
of livestock.
Restoration via secondary
ecological succession
Section 9-4
HOW SHOULD WE MANAGE
AND SUSTAIN PARKS AND
NATURE RESERVES?
National parks face many
environmental threats
• More than 1,100 major national parks are located in
more than 120 countries.
• Most too small to sustain many large animal species.
• Many parks suffer from invasions by nonnative
species that compete with and reduce the populations
of native species.
• Some parks are so popular that large numbers of
visitors are degrading the natural features that make
them attractive.
• Parks in less-developed countries have the greatest
biodiversity of all parks, but only about 1% of these
parklands are protected.
CASE STUDY: Stresses on
U.S. Public Parks
• The U.S. national park system, established in 1912,
includes 58 major national parks, along with 335
monuments and historic sites. States, counties, and
cities also operate public parks.
• Popularity is one of the biggest problems. Noisy and
polluting vehicles degrade the aesthetic experience
for many visitors, destroy or damage fragile
vegetation, and disturb wildlife.
• Many suffer damage from the migration or deliberate
introduction of nonnative species.
• Native species—some of them threatened or
endangered—are killed or removed illegally.
Nature reserves occupy only a
small part of the earth’s land
• As of 2010, less than 13% of the earth’s land area
was strictly or partially protected in nature reserves,
parks, wildlife refuges, wilderness, and other areas.
• No more than 5% of the earth’s land is strictly
protected from potentially harmful human activities.
• Conservation biologists call for full protection of at
least 20% of the earth’s land area in a global system
of biodiversity.
• Developers and resource extractors oppose
protection and contend that these areas might
contain valuable resources that would add to current
economic growth.
Nature reserves occupy only a
small part of the earth’s land
• Ecologists and conservation biologists view
protected areas as islands of biodiversity and
natural capital that help to sustain all life and
economies and serve as centers of evolution.
• The buffer zone concept strictly protects an inner
core of a reserve and establishes buffer zones in
which local people can extract resources
sustainably without harming the inner core.
• By 2010, the United Nations had used this
principle to create a global network of 553
biosphere reserves in 109 countries.
CASE STUDY: Costa Rica—A
Global Conservation Leader
• Tropical forests once completely covered Costa
Rica, but between 1963 and 1983 much of the
country’s forests were cleared to graze cattle.
• Costa Rica is a superpower of biodiversity, with
an estimated 500,000 plant and animal species.
• Costa Rica now has a system of nature reserves
and national parks that, by 2010, included about
a quarter of its land.
• Costa Rica now devotes a larger proportion of its
land to biodiversity conservation than does any
other country
CASE STUDY: Costa Rica—A
Global Conservation Leader
• The country’s largest source of income is its $1billion-a-year tourism industry, almost two-thirds of
which involves ecotourism.
• To reduce deforestation, the government has cut
subsidies for converting forest to rangeland.
• The government pays landowners to maintain or
restore tree cover.
• Between 2007 and 2008, the government planted
nearly 14 million trees.
• Went from having one of the world’s highest
deforestation rates to having one of the lowest.
Costa Rica’s eight megareserves
Nicaragua
Caribbean Sea
Costa
Rica
Panama
Pacific Ocean
National parkland
Buffer zone
Fig. 9-20, p. 191
Protecting wilderness is an important
way to preserve biodiversity
• One way to protect undeveloped lands is to set
them aside as wilderness, land officially designated
as an area where natural communities have not
been seriously disturbed by humans and where
human activities are limited by law.
• Some critics oppose protecting large areas for their
scenic and recreational value for a relatively small
number of people.
• Conservation biologists support protecting
wilderness in order to preserve biodiversity and as
centers for evolution.
CASE STUDY: Controversy over
Wilderness Protection in the United States
• Conservationists have been trying to save
wild areas from development since 1900.
• The Wilderness Act (1964) allowed the
government to protect undeveloped tracts of
public land from development as part of the
National Wilderness Preservation System.
• Only about 2% of the land area of the lower
48 states is protected, most of it in the West.
Section 9-5
WHAT IS THE ECOSYSTEM
APPROACH TO SUSTAINING
BIODIVERSITY?
Here are four ways to protect
ecosystems
• Most biologists and wildlife
conservationists believe that the best way
to keep from hastening the extinction of
wild species through human activities is
the ecosystems approach, which protects
threatened habitats and ecosystem
services.
Here are four ways to protect
ecosystems
• Four-point plan of the ecosystems approach:
– Map the world’s terrestrial and aquatic
ecosystems and create an inventory of the
species contained in each of them and the
ecosystem services they provide.
– Locate and protect the most endangered
ecosystems and species, with emphasis on
protecting plant biodiversity and ecosystem
services.
– Seek to restore as many degraded ecosystems
as possible.
Protecting global biodiversity
hotspots is an urgent priority
• Some biodiversity scientists urge adoption of an
emergency action strategy to identify and quickly
protect biodiversity hotspots, areas especially rich in
plant species that are found nowhere else and are in
great danger of extinction .
• These hotspots cover only a little more than 2% of
the earth’s land surface, they contain an estimated
50% of the world’s flowering plant species and 42%
of all terrestrial species.
• These hotspots are home for a large majority of the
world’s endangered or critically endangered species,
and one-fifth of the world’s population.
Biodiversity hotspots
We can rehabilitate and restore
ecosystems that we have damaged
• Almost every natural place on the earth
has been affected or degraded to some
degree by human activities.
• We can at least partially reverse much of
this harm through ecological restoration:
the process of repairing damage caused
by humans to the biodiversity and
dynamics of natural ecosystems.
• Examples of restoration include:
– replanting forests
We can rehabilitate and restore
ecosystems that we have damaged
– restoring grasslands
– restoring coral reefs
– restoring wetlands and stream banks
– reintroducing native species
– removing invasive species
– freeing river flows by removing dams.
We can rehabilitate and restore
ecosystems that we have damaged
• Four steps to speed up repair operations
include the following:
– Restoration.
– Rehabilitation.
– Replacement.
– Creating artificial ecosystems.
We can rehabilitate and restore
ecosystems that we have damaged
• Researchers have suggested a science-based,
four-step strategy for carrying out most forms of
ecological restoration and rehabilitation:
– Identify the causes of the degradation.
– Stop the abuse by eliminating or sharply reducing
these factors.
– If necessary, reintroduce key species to help restore
natural ecological processes.
– Protect the area from further degradation and allow
secondary ecological succession to occur.
We can share areas we
dominate with other species
• Reconciliation ecology is the science that
focuses on inventing, establishing, and
maintaining new habitats to conserve
species diversity in places where people
live, work, or play.
• Examples include:
– Protecting local wildlife and ecosystems can
provide economic resources for their
communities by encouraging sustainable forms
of ecotourism.
We can share areas we
dominate with other species
– Protecting vital insect pollinators such as native
butterflies and bees by reducing the use of
pesticides, planting flowering plants as a source
of food for pollinating insect species, and
building structures which serve as hives for
pollinating bees.
– Protecting bluebirds within human-dominated
habitats where most of the bluebirds’ nesting
trees have been cut down by using nesting
boxes and keeping house cats away from
nesting bluebirds.
Ways you can help sustain
terrestrial biodiversity
Section 9-6
HOW CAN WE HELP TO
SUSTAIN AQUATIC
BIODIVERSITY?
Human activities are destroying
and degrading aquatic biodiversity
• Human activities have destroyed or degraded a
large portion of the world’s coastal wetlands,
coral reefs, mangroves, and ocean bottom, and
disrupted many of the world’s freshwater
ecosystems.
• Rising sea levels are likely to destroy many coral
reefs and flood some low-lying islands along
with their protective coastal mangrove forests.
• Loss and degradation of many sea-bottom
habitats caused by dredging operations and
trawler fishing boats.
Human activities are destroying
and degrading aquatic biodiversity
• In freshwater aquatic zones, dam building and
excessive water withdrawal from rivers for
irrigation and urban water supplies destroy
aquatic habitats, degrade water flows, and
disrupt freshwater biodiversity.
• The deliberate or accidental introduction of
hundreds of harmful invasive species threatens
aquatic biodiversity.
• Thirty-four percent of the world’s known marine
fish species and 71% of the world’s freshwater
fish species face premature extinction.
Before and after a trawler net
Overfishing: gone fishing; fish
gone
• A fishery is a concentration of a particular wild
aquatic species suitable for commercial
harvesting in a given ocean area or inland body
of water.
• The fishprint is defined as the area of ocean
needed to sustain the consumption of an
average person, a nation, or the world.
• Fifty-two percent of the world’s fisheries are fully
exploited, 20% are moderately overexploited,
and 28% are overexploited or depleted.
Overfishing: gone fishing; fish
gone
• Overharvesting has led to the collapse of some
of the world’s major fisheries.
• When overharvesting causes larger predatory
species to dwindle, rapidly reproducing invasive
species can more easily take over and disrupt
ocean food webs.
The collapse of Canada’s 500year-old Atlantic cod fishery
900,000
800,000
Fish landings (tons)
700,000
600,000
500,000
400,000
1992
300,000
200,000
100,000
0
1900
1920
1940
1960
Year
1980
2000
Fig. 9-25, p. 197
CASE STUDY: Industrial Fish
Harvesting Methods
• Industrial fishing fleets dominate the world’s marine
fishing industry, using global satellite positioning
equipment, sonar fish-finding devices, huge nets and
long fishing lines, spotter planes, and gigantic
refrigerated factory ships that can process and freeze
their catches.
• Trawler fishing is used to catch fish and shellfish by
dragging a funnel-shaped net held open at the neck
along the ocean bottom.
• Purse-seine fishing, is used to catch surface-dwelling
fish by using a spotter plane to locate a school; the
fishing vessel then encloses it with a large net called a
purse seine.
CASE STUDY: Industrial Fish
Harvesting Methods
• Longlining involves lines up to 130 kilometers (80 miles)
long, hung with thousands of baited hooks to catch
open-ocean fish species or bottom fishes.
• Drift-net fishing catches fish with huge drifting nets that
can hang as deep as 15 meters (50 feet) below the
surface and extend to 64 kilometers (40 miles) long.
• Drift-nets can trap and kill large quantities of unwanted
fish, called bycatch, along with marine mammals, sea
turtles, and seabirds.
• Almost one-third of the world’s annual fish catch by
weight consists of bycatch species, which are mostly
thrown overboard dead or dying.
Major commercial fishing
methods
Fish farming
in cage
Trawler
fishing
Spotter airplane
Purse-seine
Sonar fishing
Drift-net fishing
Long line
fishing
Float Buoy
lines with
hooks
Deep sea
aquaculture
cage
Fish caught by gills
Fig. 9-26, p. 198
We can protect and sustain
marine biodiversity
• Protecting marine biodiversity is difficult for
several reasons.
– The human ecological footprint and fishprint
are expanding so rapidly into aquatic areas
that it is difficult to monitor the impacts.
– Much of the damage to the oceans and other
bodies of water is not visible to most people.
We can protect and sustain
marine biodiversity
– Many people incorrectly view the seas as an
inexhaustible resource that can absorb an
almost infinite amount of waste and pollution
and still produce all the seafood we want.
– Most of the world’s ocean area lies outside
the legal jurisdiction of any country and is thus
an open-access resource and subject to
overexploitation.
We can protect and sustain
marine biodiversity
• Several ways to protect and sustain
marine biodiversity:
– Protect endangered and threatened aquatic
species.
– Establish protected marine sanctuaries.
– Protect whole marine ecosystems within a
global network of fully protected marine
reserves.
Ways to manage fisheries more sustainably
and protect marine biodiversity
Taking an Ecosystem Approach to
Sustaining Aquatic Biodiversity
• Strategies for applying the ecosystem
approach to aquatic biodiversity include:
– Complete the mapping of the world’s aquatic
biodiversity, identifying and locating as many
plant and animal species as possible.
– Identify and preserve the world’s aquatic
biodiversity hotspots and areas where
deteriorating ecosystem services threaten
people and other forms of life.
Taking an Ecosystem Approach to
Sustaining Aquatic Biodiversity
– Create large and fully protected marine reserves
to allow damaged marine ecosystems to recover
and to allow fish stocks to be replenished.
– Protect and restore the world’s lakes and river
systems (the most threatened ecosystems of all).
– Initiate worldwide ecological restoration projects
in systems such as coral reefs and inland and
coastal wetlands.
– Find ways to raise the incomes of people who live
in or near protected lands and waters so that they
can become partners in the protection and
sustainable use of ecosystems.
Taking an Ecosystem Approach to
Sustaining Aquatic Biodiversity
• The harmful effects of human activities on aquatic
biodiversity and ecosystem services could be
reversed over the next 2 decades if an ecosystem
approach is implemented, at a cost one of penny
per cup of coffee consumed in the world each
year.
Three big ideas
• The economic values of the important ecological
services provided by the world’s ecosystems are far
greater than the value of raw materials obtained from
those systems.
• We can sustain terrestrial biodiversity by protecting
severely threatened areas, protecting remaining
undisturbed areas, restoring damaged ecosystems,
and sharing with other species much of the land we
dominate.
• We can sustain aquatic biodiversity by establishing
protected sanctuaries, managing coastal development,
reducing water pollution, and preventing overfishing.