Download Concept Review

Concept Review
World Land Uses
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Twenty-nine percent of the earth is land, approximately 133 million km 2.
Two-thirds of the land on earth is forest, grassland, and agriculture.
Nearly 10 percent of the land is protected in parks and nature preserves.
As human populations grow, land use changes throughout the world.
o Forests are cleared for agriculture.
o Grasslands are used for grazing or cropland.
o Dry forests have been overharvested and turned into deserts.
World Forests
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More than half the world’s forests have been converted to cropland.
Of the forests that remain, about four-fifths are closed canopy and onefifth is open canopy forest.
Old-growth forests are not significantly modified by human activities and
contain much of the world’s biodiversity as a result.
Remote locations, rather than legislation, protect undisturbed old-growth
forests.
Secondary forests have restored the complexity of the ecosystem through
successional stages.
Global wood consumption has doubled over the last 50 years and is
expected to increase another 50 percent by 2050.
Tropical hardwoods are being cut at an unsustainable rate.
Developed countries produce less than half of the wood but consume 80
percent.
One-third of the people in the world depend upon firewood for heating and
cooking.
Approximately 25 percent of the world’s forests are managed for wood
production.
o Cut trees are replaced by new seedlings.
o Replanting of trees reduces flooding and erosion.
Monoculture forestry involves planting large plantations of one species of
tree as a crop that can be easily clear-cut.
Mixed species planting can be used for a variety of purposes and can
protect the ecosystem.
Tropical Forests
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Tropical forests are the most diverse ecosystems on earth even though
they occupy less than 10 percent of the land.
More than two-thirds of the plant species and one-half of plant, animal,
and microbial species occupy these forests.
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The rate of deforestation is hard to determine but satellite data provide the
best estimates.
The Congo and Amazon River Basin have the highest rates of
deforestation, mainly to make way for farming and grazing.
Indigenous people practice swidden agriculture, which can be sustainable
if done in moderation.
o Plots of land are cleared.
o Branches and leaf litter are burned to make a seed bed.
o Up to 80 types of fast-growing crops are planted.
o After several years, forest succession takes place and the farmer
moves to a new location.
Conservation organizations, such as the Nature Conservancy, use debtfor-nature swaps to protect tropical forests.
Temperate Forests
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Temperate forests are being overharvested, especially in eastern Russia.
Timber management is an issue in the United States and Canada.
Less than 10 percent of the temperate rainforest in the United States
remains today.
A compromise forest management plan has been developed to allow
some cutting while protecting a high percentage of forest.
Most lumber and pulpwood is harvested using clear-cutting techniques in
which every tree is cut regardless of size.
The least disruptive harvest method is selective cutting, in which only a
small percentage of trees are harvested in a 10- to 20-year rotation.
U.S. Forest Management
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The U.S. Forest Service’s mission is to provide cheap timber for
home builders.
Subsidized logging costs taxpayers because the lumber industry does not
pay for the roads and cleanup associated with the logging operation.
The Bush administration’s “Healthy Forests Initiative” has opened more
public land to logging, mining, and oil and gas drilling.
Until recently, the U.S. Forest Service had a policy of fire suppression.
By eliminating fires from forested lands, regeneration and clearing through
natural processes were unable to take place.
Forty million people live in areas with a high potential for wildfires.
Forest thinning and salvage logging are being used to reduce the risk
of wildfires.
Logging is not the only way to make a living from forest products—other
sustainable crops include fruits, nuts, mushrooms, latex, and gum.
Grasslands
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Grasslands occur where there is enough rainfall to support droughttolerant plants but not enough to support forests.
Overgrazing, soil erosion, and degradation contribute to grassland losses.
When animal herds are migratory, grasslands remain healthy.
When plants are unable to recover and weedy invaders move in,
desertification occurs.
Native animals forage more efficiently than domestic livestock.
In the United States, grazing exceeds the carrying capacity of the range.
Rotational grazing helps keep weeds in check and encourages the growth
of forage plant species.
Landownership and Land Reform
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The largest landowners have the most power and reap the most benefits.
Land reform seeks to shift the balance of landownership to a more
equitable distribution.
Owner-operated farms are more productive, owners typically give their
land more attention.
Indigenous people play an important role in guarding wildlife and forests.
Many governments do not recognize indigenous people’s rights to
the land.