Ansley Kenney’s Chapter 18 – Part 2 (Pages 412 – 423)
•Trends in Tropical Forests: Two types of tropical rainforests:
-Tropical rain forests: climate warm and moist throughout the year
-Tropical dry forest: annual precipitation is less but is still enough to support trees
•Why are tropical rain forests disappearing?
Correlation between population growth and deforestation.
-Subsistence agriculture: A family produces just enough food to feed itself, accounts
for 60% of tropical deforestation.
-Commercial Logging: 20% of tropical deforestation is due to this harvesting for
export abroad. Slash-and burn agriculture.
-Cattle Ranching and Agriculture for Export: 12% of tropical deforestation is carried
out to provide open range for cattle. A considerable portion is cleared for
plantation-style agriculture. Shrubby plants, known as Shrub Savana, take over the
•Why are tropical dry forests disappearing?
They are being destroyed at a rapid rate primarily for fuel wood.
•Boreal Forests and Deforestation
-Boreal forests occur in Alaska, Canada, Scandinavia, and northern Russia.
-They comprise the world’s largest biome covering 11% of Earth’s land area.
-Boreal forests are harvested primarily by clear-cut logging, and are currently the
primary source of the world’s industrial wood and wood fiber.
•Rangelands: grasslands in both temperate and tropical climates that serve as
important areas of food production for humans by providing fodder for livestock.
-They are also mined for minerals and energy resources, used for recreation, and
preserved for biological habitat, and for soil and water sources.
•Rangeland Degradation and Desertification
-The grasses of rangelands have a fibrous root system, in which many roots form a
diffuse network in the soil to anchor the plant.
-The carrying capacity is the maximum number of animals the rangeland plants can
sustain over an indefinite period without deterioration.
-Overgrazing: destruction of vegetation caused by too many grazing animals
consuming the plants in a particular area so they cannot recover.
-Overgrazing results in barren, exposed soil susceptible to erosion; if this land
degradation continues, it contributes to desertification.
-Land degradation: the natural or human-induced process that decreases the future
ability of the land to support crops or livestock.
-Desertification: degradation of once-fertile rangeland or tropical dry forest into
•Rangeland Trends in the United States
-Rangelands make up 30% of the total land area of the United States.
-The federal government owns much of the remaining land and the BLM manages
most of these lands, with the rest overseen by the USFS.
-Taylor Grazing Act of 1934, Federal Land Policy and Management Act of 1976, and
the Public Rangelands Improvement Act of 1978 manage most of the approximately
69 million hectares of public rangelands.
-Issues involving public rangelands: federal government distributes permits to
private livestock operators to allow them to use public rangelands for grazing in
exchange for a fee. Some environmental groups are concerned about the ecological
damage caused by overgrazing of public rangelands. Also wild horses and burros
roam public rangelands.
•Conservation Easement: is a legal agreement that protects privately owned forest
or other property from development for a specified number of years.
-The US has more than 121 million hectares of prime farmland that has the soil type,
growing conditions, and available water to produce food, forage, fiber, and oilseed
-Larger agribusiness conglomerates that operate more efficiently are rapidly
replacing the family farm.
-The 1996 Farm Bill included funding for the establishment of a national Farmland
-Agricultural lands are threatened by expanding urban and suburban sprawl.
-Lands that are usually covered by shallow water for at least part of the year and
that have the characteristic soils and water-tolerant vegetation.
-Wetlands recharge groundwater and reduce damage from flooding because they
hold excess water when rivers flood their banks.
-Human activities such as drainage for agriculture, mosquito control, and dredging
for navigation threaten wetlands.
-Clean Water Act of 1972: legislation controls the loss of wetlands.
-Emergency Wetlands Resources Act of 1986: inventories and maps U.S. wetlands.
-Congress authorized the establishment of the Wetlands Reserve Program under the
Food Security Act of 1985.
-Coastal wetlands, also called saltwater wetlands, provide food and protective
habitats for many aquatic animals.
-Most legislation protects beaches at the shoreline from seawalls by rolling
easements, which prioritize public access to the shore over property owners’ rights
to build walls.
-Many coastal areas are overdeveloped, highly polluted, and overfished.
•National Marine Sanctuaries
-A marine ecosystem set aside to minimize human impacts and protect unique
natural resources and historical sites.
-The U.S. has 12 national marine sanctuaries.
-The National Marine Sanctuary Program, which is part of the National Oceanic and
atmospheric Administration, administers the sanctuaries.
•The Three Most Endangered Ecosystems in the United States
-South Florida Landscape
-Southern Appalachian spruce-fir forests
-Longleaf pine forests and savannas
(For a quick review of objectives and key terms for the entire chapter turn to pages
424 – 425)