Forest

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This article is about a community of trees. For other uses, see Forest (disambiguation).

A 'Forest is a large area of land covered with trees or other woody vegetation.[1] Hundreds of more precise definitions of “Forest” are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing and ecological function.[2][3][4] According to the widely-used[5][6] United Nations Food and Agriculture Organization definition, forests covered an area of four billion hectares (15 million square miles) or approximately 30 percent of the world's land area in 2006.[4]

Forests may provide a diversity of ecosystem services including recycling carbon dioxide into oxygen, acting as a carbon sink, aiding in regulating climate, purify water, mitigating natural hazards such as floods, and serving as a genetic reserve. Forests also serve as a source of lumber and as recreational areas.

It is often forgotten that forests do not only provide benefits, but can also incur large and significant costs to humans.[7] [8] Forests may impose a considerable economic burden [9][10],diminish the enjoyment of natural areas,[11] cause a dramatic decline in the food producing capacity of grazing land [12] and cultivated land,[13] reduce biodiversity [14][15] remove available water for humans and wildlife, [16][17], harbour dangerous and destructive wildlife,[18] [19] and act as reservoirs of human and livestock disease.[20][21]

Definition[edit]

Although forest is a term of common parlance, there is no universally recognised precise definition, with more than 800 definitions of forest used around the world.[4] Although a forest is usually defined by the presence of trees, under many definitions an area completely lacking trees may still be considered a forest if it grew trees in the past, will grow trees in the future,[22] or was legally designated as a forest regardless of vegetation type.[23][24]

There are three broad categories of forest definitions in use: administrative, land use, and land cover.[23] Administrative definitions are based primarily upon the legal designations of land, and commonly bear no relationship to the vegetation growing on the land: land that is legally designated as a forest is defined as a forest even if no trees are growing on it.[23] Land Use definitions are based upon the primary purpose that the land serves. For example, a forest may defined as any land that is used primarily for production of timber. Under such a Land Use definition, cleared roads or infrastructure within an area used for forestry, or areas within the region that have been cleared by harvesting, disease or fire are still considered forests even if they contain no trees. Land Cover definitions define forests based upon the type and density of vegetation growing on the land. Such definitions typically define a forest as an area growing trees above some threshold. These thresholds are typically the number of trees per area (density), the area of ground under the tree canopy (canopy cover) or the section of land that is occupied by the cross-section of tree trunks (basal area).[23] Under such Land Cover definitions, and area of land only be defined as forest if it is growing trees. Areas that fail to meet the Land Cover definition may be still included under while immature trees are establishing if they are expected to meet the definition at maturity.[23]

Under land use definitions, there is considerable variation on where the cutoff points are between a forest, woodland, and savanna. Under some definitions, forests require very high levels of tree canopy cover, from 60% to 100%,[25] excluding savannas and woodlands in which trees have a lower canopy cover. Other definitions consider savannas to be a type of forest, and include all areas with tree canopies over 10%.[22]

Etymology[edit]

Since the 1200s this forest has had special use and protection in Poland. In this view from space, different coloration can indicate different functions.[26]

The word forest comes from Middle English, from Old French forest (also forès) "forest, vast expanse covered by trees"; first introduced in English as the word for wild land set aside for hunting[27] without the necessity in definition for the existence of trees (James 1981;Muir 2000,2008).[28] Possibly a borrowing (probably via Frankish or Old High German) of the Medieval Latin word foresta "open wood", foresta was first used by Carolingian scribes in the Capitularies of Charlemagne to refer specifically to the king's royal hunting grounds. The term was not endemic to Romance languages (e.g. native words for "forest" in the Romance languages evolved out of the Latin word silva "forest, wood" (English sylvan); cf. Italian, Spanish, Portuguese selva; Romanian silvă; Old French selve); and cognates in Romance languages, such as Italian foresta, Spanish and Portuguese floresta, etc. are all ultimately borrowings of the French word.

The exact origin of Medieval Latin foresta is obscure. Some authorities claim the word derives from the Late Latin phrase forestam silvam, meaning "the outer wood"; others claim the term is a latinisation of the Frankish word *forhist "forest, wooded country", assimilated to forestam silvam (a common practice among Frankish scribes). Frankish *forhist is attested by Old High German forst "forest", Middle Low German vorst "forest", Old English fyrhþ "forest, woodland, game preserve, hunting ground" (English frith), and Old Norse fýri "coniferous forest", all of which derive from Proto-Germanic *furhísa-, *furhíþija- "a fir-wood, coniferous forest", from Proto-Indo-European *perkwu- "a coniferous or mountain forest, wooded height".

Uses of the word "forest" in English to denote any uninhabited area of non-enclosure are now considered archaic.[29] The word was introduced by the Norman rulers of England as a legal term (appearing in Latin texts like the Magna Carta) denoting an uncultivated area legally set aside for hunting by feudal nobility (see Royal Forest).[29][30] These hunting forests were not necessarily wooded much, if at all. However, as hunting forests did often include considerable areas of woodland, the word "forest" eventually came to mean wooded land more generally.[citation needed] By the start of the fourteenth century the word appeared in English texts, indicating all three senses: the most common one, the legal term and the archaic usage.[29]

Other terms used to mean "an area with a high density of trees" are wood, woodland, wold, weald, holt, frith and firth. Unlike forest, these are all derived from Old English and were not borrowed from another language. Some classifications now reserve the term woodland for an area with more open space between trees and distinguish among woodlands, open forests, and closed forests based on crown cover.[31]

Distribution[edit]

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.

Forests sometimes contain many tree species only within a small area (as in tropical rain and temperate deciduous forests), or relatively few species over large areas (e.g., taiga and arid montane coniferous forests). Forests are often home to many animal and plant species, and biomass per unit area is high compared to other vegetation communities. Much of this biomass occurs below ground in the root systems and as partially decomposed plant detritus. The woody component of a forest contains lignin, which is relatively slow to decompose compared with other organic materials such as cellulose or carbohydrate.

Forests are differentiated from woodlands by the extent of canopy coverage: in a forest, the branches and the foliage of separate trees often meet or interlock, although there can be gaps of varying sizes within an area referred to as forest. A woodland has a more continuously open canopy, with trees spaced farther apart, which allows more sunlight to penetrate to the ground between them (also see: savanna).

Among the major forested biomes are:

Types of forests[edit]

Spiny forest at Ifaty, Madagascar, featuring various Adansonia (baobab) species, Alluaudia procera (Madagascar ocotillo) and other vegetation
Even, dense old-growth stand of beech trees (Fagus sylvatica) prepared to be regenerated by their saplings in the understory, in the Brussels part of the Sonian Forest.
Trees on a mountain in northern Utah during early autumn.

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.

A number of global forest classification systems have been proposed, but none has gained universal acceptance.[32] UNEP-WCMC's forest category classification system is a simplification of other more complex systems (e.g. UNESCO's forest and woodland 'subformations'). This system divides the world's forests into 26 major types, which reflect climatic zones as well as the principal types of trees. These 26 major types can be reclassified into 6 broader categories: temperate needleleaf; temperate broadleaf and mixed; tropical moist; tropical dry; sparse trees and parkland; and forest plantations. Each category is described as a separate section below.

Temperate needleleaf[edit]

Temperate needleleaf forests mostly occupy the higher latitude regions of the northern hemisphere, as well as high altitude zones and some warm temperate areas, especially on nutrient-poor or otherwise unfavourable soils. These forests are composed entirely, or nearly so, of coniferous species (Coniferophyta). In the Northern Hemisphere pines Pinus, spruces Picea, larches Larix, firs Abies, Douglas firs Pseudotsuga and hemlocks Tsuga, make up the canopy, but other taxa are also important. In the Southern Hemisphere, most coniferous trees (members of the Araucariaceae and Podocarpaceae) occur in mixtures with broadleaf species, and are classed as broadleaf and mixed forests.

Temperate broadleaf and mixed[edit]

Temperate broadleaf and mixed forests include a substantial component of trees in the Anthophyta. They are generally characteristic of the warmer temperate latitudes, but extend to cool temperate ones, particularly in the southern hemisphere. They include such forest types as the mixed deciduous forests of the United States and their counterparts in China and Japan, the broadleaf evergreen rainforests of Japan, Chile and Tasmania, the sclerophyllous forests of Australia, central Chile, the Mediterranean and California, and the southern beech Nothofagus forests of Chile and New Zealand.

Tropical moist[edit]

There are many different types of tropical moist forests, although most extensive are the lowland evergreen broad leaf rainforests, for example várzea and igapó forests and the terra firma forests of the Amazon Basin; the peat swamp forests, dipterocarp forests of Southeast Asia; and the high forests of the Congo Basin. Forests located on mountains are also included in this category, divided largely into upper and lower montane formations on the basis of the variation of physiognomy corresponding to changes in altitude.[33]

Tropical dry[edit]

Tropical dry forests are characteristic of areas in the tropics affected by seasonal drought. The seasonality of rainfall is usually reflected in the deciduousness of the forest canopy, with most trees being leafless for several months of the year. However, under some conditions, e.g. less fertile soils or less predictable drought regimes, the proportion of evergreen species increases and the forests are characterised as "sclerophyllous". Thorn forest, a dense forest of low stature with a high frequency of thorny or spiny species, is found where drought is prolonged, and especially where grazing animals are plentiful. On very poor soils, and especially where fire is a recurrent phenomenon, woody savannas develop (see 'sparse trees and parkland').

Sparse trees and parkland[edit]

Taiga forest near Saranpaul in the northeast Ural Mountains, Khanty–Mansia, Russia. Trees include Picea obovata (dominant on right bank), Larix sibirica, Pinus sibirica, and Betula pendula.

Sparse trees and parkland are forests with open canopies of 10–30% crown cover. They occur principally in areas of transition from forested to non-forested landscapes. The two major zones in which these ecosystems occur are in the boreal region and in the seasonally dry tropics. At high latitudes, north of the main zone of boreal forest or taiga, growing conditions are not adequate to maintain a continuous closed forest cover, so tree cover is both sparse and discontinuous. This vegetation is variously called open taiga, open lichen woodland, and forest tundra. It is species-poor, has high bryophyte cover, and is frequently affected by fire.

Forest plantations[edit]

Forest plantations, generally intended for the production of timber and pulpwood increase the total area of forest worldwide. Commonly mono-specific and/or composed of introduced tree species, these ecosystems are not generally important as habitat for native biodiversity. However, they can be managed in ways that enhance their biodiversity protection functions and they are important providers of ecosystem services such as maintaining nutrient capital, protecting watersheds and soil structure as well as storing carbon. They may also play an important role in alleviating pressure on natural forests for timber and fuelwood production.[citation needed]

Forest categories[edit]

A temperate deciduous broadleaf forest, the Hasenholz, southeast of Kirchheim unter Teck, Baden-Württemberg, Germany
Redwoods in old growth forest in Muir Woods National Monument, Marin County, California
Parambikulam Forest Inside view, Kerala, India

28 forest categories are used to enable the translation of forest types from national and regional classification systems to a harmonised global one:

Temperate and boreal forest types[edit]

  1. Evergreen needleleaf forest – Natural forest with > 30% canopy cover, in which the canopy is predominantly (> 75%) needleleaf and evergreen.
  2. Deciduous needleleaf forests – Natural forests with > 30% canopy cover, in which the canopy is predominantly (> 75%) needleleaf and deciduous.
  3. Mixed broadleaf/needleleaf forest – Natural forest with > 30% canopy cover, in which the canopy is composed of a more or less even mixture of needleleaf and broadleaf crowns (between 50:50% and 25:75%).
  4. Broadleaf evergreen forest – Natural forests with > 30% canopy cover, the canopy being > 75% evergreen and broadleaf.
  5. Deciduous broadleaf forest – Natural forests with > 30% canopy cover, in which > 75% of the canopy is deciduous and broadleaves predominate (> 75% of canopy cover).
  6. Freshwater swamp forest – Natural forests with > 30% canopy cover, composed of trees with any mixture of leaf type and seasonality, but in which the predominant environmental characteristic is a waterlogged soil.
  7. Sclerophyllous dry forest – Natural forest with > 30% canopy cover, in which the canopy is mainly composed of sclerophyllous broadleaves and is > 75% evergreen.
  8. Sparse trees and parkland – Natural forests in which the tree canopy cover is between 10–30%, such as in the steppe regions of the world. Trees of any type (e.g., needleleaf, broadleaf, palms).
  9. Disturbed natural forest – Any forest type above that has in its interior significant areas of disturbance by people, including clearing, felling for wood extraction, anthropogenic fires, road construction, etc.
  10. Exotic species plantation – Intensively managed forests with > 30% canopy cover, which have been planted by people with species not naturally occurring in that country.
  11. Native species plantation – Intensively managed forests with > 30% canopy cover, which have been planted by people with species that occur naturally in that country.
  12. *Unspecified forest plantation – Forest plantations showing extent only with no further information about their type, This data currently only refers to the Ukraine.
  13. *Unclassified forest data – Forest data showing forest extent only with no further information about their type.

Those marked * have been created as a result of data holdings which do not specify the forest type, hence 26 categories are quoted, not 28 shown here.[34]

Tropical forest types[edit]

The Fatu Hiva rainforest in Polynesia.
  1. Lowland evergreen broadleaf rain forest – Natural forests with > 30% canopy cover, below 1,200 m (3,937 ft) altitude that display little or no seasonality, the canopy being >75% evergreen broadleaf.
  2. Lower montane forest – Natural forests with > 30% canopy cover, between 1200–1800 m altitude, with any seasonality regime and leaf type mixture.
  3. Upper montane forest – Natural forests with > 30% canopy cover, above 1,800 m (5,906 ft) altitude, with any seasonality regime and leaf type mixture.
  4. Freshwater swamp forest – Natural forests with > 30% canopy cover, below 1,200 m (3,937 ft) altitude, composed of trees with any mixture of leaf type and seasonality, but in which the predominant environmental characteristic is a waterlogged soil.
  5. Semi-evergreen moist broadleaf forest – Natural forests with > 30% canopy cover, below 1,200 m (3,937 ft) altitude in which between 50–75% of the canopy is evergreen, > 75% are broadleaves, and the trees display seasonality of flowering and fruiting.
  6. Mixed broadleaf/needleleaf forest – Natural forests with > 30% canopy cover, below 1,200 m (3,937 ft) altitude, in which the canopy is composed of a more or less even mixture of needleleaf and broadleaf crowns (between 50:50% and 25:75%).
  7. Needleleaf forest – Natural forest with > 30% canopy cover, below 1,200 m (3,937 ft) altitude, in which the canopy is predominantly (> 75%) needleleaf.
  8. Mangroves – Natural forests with > 30% canopy cover, composed of species of mangrove tree, generally along coasts in or near brackish or seawater.
  9. Deciduous/semi-deciduous broadleaf forest – Natural forests with > 30% canopy cover, below 1,200 m (3,937 ft) altitude in which between 50–100% of the canopy is deciduous and broadleaves predominate (> 75% of canopy cover).
  10. Sclerophyllous dry forest – Natural forests with > 30% canopy cover, below 1,200 m (3,937 ft) altitude, in which the canopy is mainly composed of sclerophyllous broadleaves and is > 75% evergreen.
  11. Thorn forest – Natural forests with > 30% canopy cover, below 1,200 m (3,937 ft) altitude, in which the canopy is mainly composed of deciduous trees with thorns and succulent phanerophytes with thorns may be frequent.
  12. Sparse trees and parkland – Natural forests in which the tree canopy cover is between 10–30%, such as in the savannah regions of the world. Trees of any type (e.g., needleleaf, broadleaf, palms).
  13. Disturbed natural forest – Any forest type above that has in its interior significant areas of disturbance by people, including clearing, felling for wood extraction, anthropogenic fires, road construction, etc.
  14. Exotic species plantation – Intensively managed forests with > 30% canopy cover, which have been planted by people with species not naturally occurring in that country.
  15. Native species plantation – Intensively managed forests with > 30% canopy cover, which have been planted by people with species that occur naturally in that country.

Forest loss and management[edit]

Main articles: Forestry, Logging and Deforestation
Coastal Douglas fir woodland in northwest Oregon
Redwood tree in northern California redwood forest, where many redwood trees are managed for preservation and longevity, rather than being harvested for wood production

The scientific study of forest species and their interaction with the environment is referred to as forest ecology, while the management of forests is often referred to as forestry. Forest management has changed considerably over the last few centuries, with rapid changes from the 1980s onwards culminating in a practice now referred to as sustainable forest management. Forest ecologists concentrate on forest patterns and processes, usually with the aim of elucidating cause-and-effect relationships. Foresters who practice sustainable forest management focus on the integration of ecological, social, and economic values, often in consultation with local communities and other stakeholders.

Anthropogenic factors that can affect forests include logging, urban sprawl, human-caused forest fires, acid rain, invasive species, and the slash and burn practices of swidden agriculture or shifting cultivation. The loss and re-growth of forest leads to a distinction between two broad types of forest, primary or old-growth forest and secondary forest. There are also many natural factors that can cause changes in forests over time including forest fires, insects, diseases, weather, competition between species, etc. In 1997, the World Resources Institute recorded that only 20% of the world's original forests remained in large intact tracts of undisturbed forest.[35] More than 75% of these intact forests lie in three countries—the Boreal forests of Russia and Canada and the rainforest of Brazil.

Canada has about 4,020,000 square kilometres (1,550,000 sq mi) of forest land. More than 90% of forest land is publicly owned and about 50% of the total forest area is allocated for harvesting. These allocated areas are managed using the principles of sustainable forest management, which includes extensive consultation with local stakeholders. About eight percent of Canada’s forest is legally protected from resource development (Global Forest Watch Canada)[36] (Natural Resources Canada).[37] Much more forest land—about 40 percent of the total forest land base—is subject to varying degrees of protection through processes such as integrated land use planning or defined management areas such as certified forests (Natural Resources Canada).[37]

These maps represent only virgin forest lost. Some regrowth has occurred but not to the age, size, or extent of 1620, due to population increases and food cultivation. From William B. Greeley's, The Relation of Geography to Timber Supply, Economic Geography, 1925, vol. 1, p. 1–11. Source of "Today" map: compiled by George Draffan from roadless area map in The Big Outside: A Descriptive Inventory of the Big Wilderness Areas of the United States, by Dave Foreman and Howie Wolke (Harmony Books, 1992).'

By December 2006, over 1,237,000 square kilometers of forest land in Canada (about half the global total) had been certified as being sustainably managed (Canadian Sustainable Forestry Certification Coalition).[38] Clearcutting, first used in the latter half of the 20th century, is less expensive, but devastating to the environment, and companies are required by law to ensure that harvested areas are adequately regenerated. Most Canadian provinces have regulations limiting the size of clearcuts, although some older clearcuts can range upwards of 110 square kilometres (27,000 acres) in size which were cut over several years. China instituted a ban on logging, beginning in 1998, due to the erosion and flooding that it caused.[39]

In 2010, the Food and Agriculture Organization of the United Nations[40] reported that world deforestation, mainly the conversion of tropical forests to agricultural land, had decreased over the past ten years but still continues at an alarmingly high rate in many countries. Globally, around 13 million hectares of forests were converted to other uses or lost through natural causes each year between 2000 and 2010 as compared to around 16 million hectares per year during the 1990s. The study covered 233 countries and areas. Brazil and Indonesia, which had the highest loss of forests in the 1990s, have significantly reduced their deforestation rates. In addition, ambitious tree planting programmes in countries such as China, India, the United States and Viet Nam - combined with natural expansion of forests in some regions - have added more than seven million hectares of new forests annually. As a result the net loss of forest area was reduced to 5.2 million hectares per year between 2000 and 2010, down from 8.3 million hectares annually in the 1990s.

In the United States, most forests have historically been affected by humans to some degree, though in recent years improved forestry practices has helped regulate or moderate large scale or severe impacts. However, the United States Forest Service estimates a net loss of about 2 million hectares (4,942,000 acres) between 1997 and 2020; this estimate includes conversion of forest land to other uses, including urban and suburban development, as well as afforestation and natural reversion of abandoned crop and pasture land to forest. However, in many areas of the United States, the area of forest is stable or increasing, particularly in many northern states. The opposite problem from flooding has plagued national forests, with loggers complaining that a lack of thinning and proper forest management has resulted in large forest fires.[41]

Old-growth forest contains mainly natural patterns of biodiversity in established seral patterns, and they contain mainly species native to the region and habitat. The natural formations and processes have not been affected by humans with a frequency or intensity to change the natural structure and components of the habitat. Secondary forest contains significant elements of species which were originally from other regions or habitats.

Smaller areas of woodland in cities may be managed as Urban forestry, sometimes within public parks. These are often created for human benefits; Attention Restoration Theory argues that spending time in nature reduces stress and improves health, while forest schools and kindergartens help young people to develop social as well as scientific skills in forests. These typically need to be close to where the children live, for practical logistics.

Forest land area[edit]

Forest Land Area[42]
2008 2009 2010
('000 km2) ('000 mi2) ('000 km2) ('000 mi2) ('000 km2) ('000 mi2)
Australia 1,511 583 1,502 580 1,493 576
Brazil 5,239 2,023 5,217 2,014 5,195 2,006
Canada 3,101 1,197 3,101 1,197 3,101 1,197
China 2,013 777 2,041 788 2,069 799
European Union 1,559 602 1,564 604 1,569 606
Germany 111 43 111 43 111 43
India 681 263 683 264 684 264
Indonesia 958 370 951 367 944 364
Japan 250 97 250 97 250 97
Russia 8,090 3,120 8,090 3,120 8,091 3,124
United States 3,033 1,171 3,036 1,172 3,040 1,170
World total 40,318 15,567 40,261 15,545 40,204 15,523

See also[edit]

References[edit]

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