Forests and their Roles

Study Notes

Forests occupy less than one-third of Earth's total land area but provide many goods and services to support human society.

Trees regulate global biogeochemical cycles, such as those for carbon and nitrogen.
Photosynthesis removes large quantities of heat-trapping carbon dioxide from the atmosphere and fixes it into carbon compounds.
Oxygen is released back into the atmosphere during photosynthesis.

Trees act as carbon "sinks," which may help mitigate climate warming.
Tree roots hold vast tracts of soil in place, reducing erosion and mudslides.
Forests protect watersheds and moderate water flow, providing a more regulated flow of water downstream.

Management for timber production disrupts a forest's natural condition and alters its species composition and other characteristics.

Monoculture is a type of ecological simplification in which only one type of plant is cultivated over a large area.
Monocultures are at increased risk of damage from insect pests and disease-causing microorganisms.

Sustainable forestry is the use and management of forest ecosystems in an environmentally balanced and enduring way.

Wildlife corridors are protected zones that connect isolated unlogged or undeveloped areas.

Approximately 3.5 million m3 (120 million ft3) of wood are harvested annually for fuelwood, timber, and other products.
The top 5 countries with the greatest tree harvests are the United States, Canada, Russia, Brazil, and China.
About 50% of harvested wood is burned directly as fuelwood or used to make charcoal.

Selective cutting: mature trees are cut individually or in small clusters, allowing the forest to regenerate naturally.
Shelterwood cutting: removal of all mature trees in an area over an extended period, with subsequent harvests occurring at intervals of several years.
Seed tree cutting: almost all trees are harvested from an area, leaving a scattering of desirable trees to provide seeds for regeneration.
Clear-cutting: a logging practice in which all trees in a stand of forest are cut, leaving just the stumps.

Deforestation is the temporary or permanent clearance of large expanses of forest for agriculture or other uses.
Causes of deforestation include fires, land clearing, expansion of agriculture, construction of roads, tree harvests, insects, disease, and mining.
Most of the world's deforestation is currently taking place in Africa and South America.

Decreased soil fertility
Uncontrolled soil erosion
Increased sedimentation of waterways, harming downstream fisheries
Formation of deserts
Disruption of water flow regulation, leading to alternating periods of flood and drought
Extinction of many species
Habitat modification and destruction
Regional and global climate changes, including an increase in global temperature by releasing carbon dioxide into the atmosphere
Specific impact on boreal forests, which have experienced extensive deforestation due to logging since the late 1980s.