Forest
Introduction
A forest is a large area dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing and ecological function. According to the widely accepted United Nations Food and Agriculture Organization definition, forests covered approximately four billion hectares (15 million square miles) or approximately 30 percent of the world's land area in 2006.
Forest Ecology
Forests are areas with a high density of trees. These habitats can cover vast areas of land and serve as homes for many organisms, from insects and birds to larger mammals. Forests are an integral part of the planet's carbon cycle, acting as a reservoir for carbon dioxide through a process called photosynthesis.
Forests can be found in all regions capable of sustaining tree growth, at altitudes up to the tree line, except where natural fire frequency or other disturbance is too high, or where the environment has been altered by human activity. The latitudes 10° north and south of the Equator are mostly covered in tropical rainforest, and the latitudes between 53°N and 67°N have boreal forest. As a general rule, forests dominated by angiosperms (broadleaf forests) are more species-rich than those dominated by gymnosperms (conifer, montane, or needleleaf forests), although exceptions exist.
Forest Types
Forests can be classified in different ways and to different degrees of specificity. One such way is in terms of the "biome" in which they exist, combined with leaf longevity of the dominant species (whether they are evergreen or deciduous). Another distinction is whether the forests are composed predominantly of broadleaf trees, coniferous (needle-leaved) trees, or mixed.
Boreal Forests
Boreal forests, also known as taiga, represent the world's largest terrestrial biome. They occupy the high latitudes of the northern hemisphere in North America, Europe, and Asia. Boreal forests are characterized by their coniferous trees and long, cold winters.
Temperate Forests
Temperate forests are found in eastern North America, northeastern Asia, and western and central Europe. Well-defined seasons with a distinct winter characterize this forest biome. Temperate deciduous forests, the "signature" temperate forest type, reach their greatest ecological complexity in the eastern United States and southeastern Canada, in the Appalachian mixed deciduous forests and the Atlantic coastal forests.
Tropical Forests
Tropical forests are characterized by the greatest diversity of species. They occur near the equator, within the area bounded by latitudes 23.5 degrees N and 23.5 degrees S. One of the major characteristics of tropical forests is their distinct seasonality: winter is absent, and only two seasons are present (rainy and dry).
Forest Functions
Forests perform important ecological functions, including the sequestration of atmospheric carbon, which could potentially mitigate climate change. Forests also affect the water cycle; they extract groundwater and release it into the atmosphere through transpiration. Forests can also act as a "sink" for various pollutants, purifying the environment.
Forest Management
Forest management has changed considerably over the centuries. Today, it involves a range of interventions that aim to create a stable and productive forest, capable of meeting diverse needs. In many cases, forests are managed to provide timber for wood and paper products. In other cases, forests may be managed for conservation, recreation, or watershed protection.
Threats to Forests
Forests around the world are under threat from deforestation, largely due to human activities such as logging, mining, and conversion to farmland. Climate change also poses a significant threat to forests, altering their distribution and the species they support.