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Sustaining Biodiversity: The Ecosystem Approach. Chapter 9. Section 9-1. What are the major threats to forest ecosystems?. 2 types of forests. Two major types based on their age and structure:

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Sustaining Biodiversity: The Ecosystem Approach

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Sustaining Biodiversity: The Ecosystem Approach

Chapter 9

Section 9-1

What are the major threats to forest ecosystems?

2 types of forests

  • 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.

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

  • Problems associated with harvesting trees:

    • Increased erosion and sediment runoff into waterways.

    • Habitat fragmentation.

    • Loss of biodiversity.

    • Forest exposure to invasion by nonnative pests, diseases, and wildlife species.

Know this!

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

Cut 1 year ago


Dirt road

Cut 3–10 years ago


Clear stream

Fig. 9-6c, p. 179

  • Know the best type of logging (strip cutting) and the differences between the 3 types.

Aerial view showing clear-cut logging, Washington state


  • Surface fires

  • Crown fires

Fire can threaten or benefit forest ecosystems

  • Surface firesusually 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

  • Crown firesare 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


  • Deforestation is the temporary or permanent removal of large expanses of forest for agriculture, settlements, or other uses.

Harmful effects of deforestation

  • What are the problems associated with deforestation?

Forest cover in the U.S.

Carolina Parakeet

The Carolina Parakeet was the only parrot species native to the eastern United States. It was found from southern New York and Wisconsin to Kentucky, Tennessee and the Gulf of Mexico, and lived in old forests along rivers.

Tropical forests are disappearing rapidly

  • At least half of the world’s known species of terrestrial plants and animals live in tropical forests.

Tropical Forests

  • 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: population growth

  • 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.

Causes of tropical deforestation: government subsidies

  • 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

  • Tropical forests in the Amazon and other South American countries are cleared/burned for cattle grazing and large soybean plantations.

Causes of tropical deforestation

  • 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.

Causes of tropical deforestation

  • 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

Possible test question

  • List 3 causes of deforestion

Section 9-2

How should we manage and sustain forests?

Ways to grow and harvest trees more sustainably

Know this!

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.

We can improve the management of forest fires

  • Strategies for reducing fire-related harm:

    • Prescribed burnsaresmall, contained surface fires to remove flammable small trees and underbrush in the highest-risk forest areas.

Know this!

  • Be able to list the advantages and disadvantages of forest fires.

  • 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.

Construction Materials

  • 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.

We can reduce the demand for harvested trees

  • Paper can be made from fiber that does not come from trees.

Debt for nature swap

  • Debt-for-nature swap can make it financially attractive for countries to protect their tropical forests.

    •  financial transactions in which a portion of a developing nation's foreign debt is forgiven in exchange for local investments in environmental conservation measures.

Conservation concessions

  • 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?

Ecological Services of Grasslands

  • Grasslands provide many important ecological services, including:

    • soil formation,

    • erosion control,

    • nutrient cycling,

    • storage of atmospheric carbon dioxide in biomass,

    • 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.


  • Overgrazing occurs when too many animals graze for too long and exceed the carrying capacity of a rangeland area.

Left of fence: overgrazed landRight: 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.

Restoration via secondary ecological succession

Section 9-4

How should we manage and sustain parks and nature reserves?

National parks face many environmental threats

  • 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.

Section 9-5

What is the ecosystem approach to sustaining biodiversity?

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.

    • Seek to restore as many degraded ecosystems as possible.

    • Make development biodiversity-friendly by providing financial incentives (tax-breaks) to private landowners who agree to help protect endangered ecosystems.

Protecting global biodiversity hotspots

  • Biodiversity hotspots – areas especially rich in plant species that are found nowhere else and are in great danger of extinction.

    Know this term!

Biodiversity hotspots

We can rehabilitate and restore ecosystems that we have damaged

  • We can reverse much of this harm through ecological restoration: the process of repairing damage caused by humans to the biodiversity and dynamics of natural ecosystems.

We can rehabilitate and restore ecosystems that we have damaged

  • Examples of restoration include:

    • replanting forests

    • 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.

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.

Before and after a trawler net

Overfishing: gone fishing; fish gone

  • A fisheryis a concentration of a particular wild aquatic species suitable for commercial harvesting in a given ocean area or inland body of water.

  • The fishprintis defined as the area of ocean needed to sustain the consumption of an average person, a nation, or the world.

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 500-year-old Atlantic cod fishery

Ways to manage fisheries more sustainably and protect marine biodiversity


Marine Reserves


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