Forests and their Roles

Forests and Their Roles

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

Goods and Services Provided by Forests

• Timber is used for fuel, construction materials, and paper products.
• Forests supply nuts, mushrooms, fruits, and medicines.
• They provide employment for millions of people worldwide.
• Forests offer recreation and spiritual sustenance.

Role of Forests in the Hydrologic Cycle

• 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.

Forests as Carbon Sinks

• 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.

Forest Soils and Water Quality

• Forest soils remove impurities from water, improving its quality.

Forests as Habitats

• Forests provide a variety of essential habitats for many organisms.

Forest Management

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

Monoculture and Its Disadvantages

• 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

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

Wildlife Corridors

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

Wood Harvesting

• 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.

Harvesting Methods

• 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

• 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.

Consequences of Deforestation

• 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.