thumb|upright=1.4|The [[Amazon rainforest alongside the Solimões River, a tropical rainforest. These forests are the most biodiverse and productive ecosystems in the world.]]

thumb|upright=1.4|Proportion and distribution of global forest area by climatic domain, 2020

A forest is an ecosystem characterized by a dense community of 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. The United Nations' Food and Agriculture Organization (FAO) defines a forest as, "Land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 percent, or trees able to reach these thresholds in situ. It does not include land that is predominantly under agricultural or urban use." Using this definition, Global Forest Resources Assessment 2025 found that forests covered , or approximately 31 percent of the world's land area in 2025.

Forests are the largest terrestrial ecosystems of Earth by area, and are found around the globe. 45 percent of forest land is in the tropical latitudes. The next largest share of forests are found in subarctic climates, followed by temperate, and subtropical zones.

Forests account for 75% of the gross primary production of the Earth's biosphere, and contain 80% of the Earth's plant biomass. Net primary production is estimated at 21.9 gigatonnes of biomass per year for tropical forests, 8.1 for temperate forests, and 2.6 for boreal forests. These biomes include boreal forests in subarctic climates, tropical moist forests and tropical dry forests around the Equator, and temperate forests at the middle latitudes. Forests form in areas of the Earth with high rainfall, while drier conditions produce a transition to savanna. However, in areas with intermediate rainfall levels, forest transitions to savanna rapidly when the percentage of land that is covered by trees drops below 40 to 45 percent. Research conducted in the Amazon rainforest shows that trees can alter rainfall rates across a region, releasing water from their leaves in anticipation of seasonal rains to trigger the wet season early. Because of this, seasonal rainfall in the Amazon begins two to three months earlier than the climate would otherwise allow. Deforestation in the Amazon and anthropogenic climate change hold the potential to interfere with this process, causing the forest to pass a threshold where it transitions into savanna.

Deforestation threatens many forest ecosystems. Deforestation occurs when humans remove trees from a forested area by cutting or burning, either to harvest timber or to make way for farming. Most deforestation today occurs in tropical forests. The vast majority of this deforestation is because of the production of four commodities: wood, beef, soy, and palm oil. Over the past 2,000 years, the area of land covered by forest in Europe has been reduced from 80% to 34%. Large areas of forest have also been cleared in China and in the eastern United States, in which only 0.1% of land was left undisturbed. Almost half of Earth's forest area (49 percent) is relatively intact, while 9 percent is found in fragments with little or no connectivity. Tropical rainforests and boreal coniferous forests are the least fragmented, whereas subtropical dry forests and temperate oceanic forests are among the most fragmented. Roughly 80 percent of the world's forest area is found in patches larger than . The remaining 20 percent is located in more than 34 million patches around the world – the vast majority less than in size. Forests provide ecosystem services to humans and serve as tourist attractions. Forests can also affect people's health.<!--Specific statements supported by refs in "Relationship to human society" section--> Human activities, including unsustainable use of forest resources, can negatively affect forest ecosystems.<!--See same section for refs-->

Definitions

thumb|Boreal forest in [[Finland ]]

Although the word forest is commonly used, there is no universally recognised precise definition, with more than 800 definitions of forest used around the world. or was legally designated as a forest regardless of vegetation type.

There are three broad categories of definitions of forest in use: administrative, land use, and land cover. which excludes woodlands and savannas, which have a lower canopy cover. Other definitions consider savannas to be a type of forest, and include all areas with tree canopies over 10%.]]

The word forest derives from the Old French forest (also forès), denoting "forest, vast expanse covered by trees"; forest was first introduced into English as the word denoting wild land set aside for hunting without necessarily having trees on the land. Possibly a borrowing, probably via Frankish or Old High German, of the Medieval Latin , denoting "open wood", Carolingian scribes first used foresta in the capitularies of Charlemagne, specifically to denote the royal hunting grounds of the king. The word was not endemic to the Romance languages, e.g., native words for forest in the Romance languages derived from the Latin silva, which denoted "forest" and "wood(land)" (cf. the English sylva and sylvan; the Italian, Spanish, and Portuguese selva; the Romanian silvă; the Old French selve). Cognates of forest in Romance languages—e.g., the Italian foresta, Spanish and Portuguese floresta, etc.—are all ultimately derivations of the French word.

The precise origin of Medieval Latin is obscure. Some authorities claim the word derives from the Late Latin phrase forestam silvam, denoting "the outer wood"; others claim the word is a Latinisation of the Frankish *forhist, denoting "forest, wooded country", and was assimilated to forestam silvam, pursuant to the common practice of Frankish scribes. The Old High German forst denoting "forest"; Middle Low German vorst denoting "forest"; Old English fyrhþ denoting "forest, woodland, game preserve, hunting ground" (English frith); and Old Norse fýri, denoting "coniferous forest"; all of which derive from the Proto-Germanic *furhísa-, *furhíþija-, denoting "a fir-wood, coniferous forest", from the Proto-Indo-European *perk<sup>w</sup>u-, denoting "a coniferous or mountain forest, wooded height" all attest to the Frankish *forhist.

Uses of forest in English to denote any uninhabited and unenclosed area are presently considered archaic.

These hunting forests did not necessarily contain any trees. Because that often included significant areas of woodland, "forest" eventually came to connote woodland in general, regardless of tree density. By the beginning of the fourteenth century, English texts used the word in all three of its senses: common, legal, and archaic. Other English words used to denote "an area with a high density of trees" are firth, frith, holt, weald, wold, wood, and woodland. Unlike forest, these are all derived from Old English and were not borrowed from another language. Some present classifications reserve woodland for denoting a locale with more open space between trees, and distinguish kinds of woodlands as open forests and closed forests, premised on their crown covers. Finally, sylva (plural sylvae or, less classically, sylvas) is a peculiar English spelling of the Latin silva, denoting a "woodland", and has precedent in English, including its plural forms. While its use as a synonym of forest, and as a Latinate word denoting a woodland, may be admitted; in a specific technical sense it is restricted to denoting the species of trees that comprise the woodlands of a region, as in its sense in the subject of silviculture. The resorting to sylva in English indicates more precisely the denotation that the use of forest intends.

Evolutionary history

The first known forests on Earth arose in the Middle Devonian (approximately 390 million years ago), with the evolution of cladoxylopsid plants like Calamophyton. Appeared in the Late Devonian, Archaeopteris was both tree-like and fern-like plant, growing to in height or more. It quickly spread throughout the world, from the equator to subpolar latitudes. Global forest biomass in 2025 is estimated at 709 gigatonnes, which is an average of 171 tonnes per ha. The forest carbon stock, including all carbon pools, is estimated at 714 gigatonnes, or 172 tonnes per ha. 46% of the forest carbon stock is in soil, 44% is in living (above ground and below ground) biomass and 10% is in litter and deadwood. Forests have intricate three-dimensional structures that increase in complexity with lower levels of disturbance and greater variety of tree species.

The biodiversity of forests varies considerably according to factors such as forest type, geography, climate, and soils – in addition to human use. Most forest habitats in temperate regions support relatively few animal and plant species, and species that tend to have large geographical distributions, while the montane forests of Africa, South America, Southeast Asia, and lowland forests of Australia, coastal Brazil, the Caribbean islands, Central America, and insular Southeast Asia have many species with small geographical distributions.

Layers

thumb|Spiny forest at Ifaty, [[Madagascar, featuring various Adansonia (baobab) species, Alluaudia procera (Madagascar ocotillo) and other vegetation]]

The main layers of all forest types are the forest floor, the understory, and the canopy. The emergent layer, above the canopy, exists in tropical rainforests. Each layer has a different set of plants and animals, depending upon the availability of sunlight, moisture, and food.

  • The Forest floor is covered in dead plant material such as fallen leaves and decomposing logs, which detritivores break down into new soil. The layer of decaying leaves that covers the soil is necessary for many insects to overwinter and for amphibians, birds, and other animals to shelter and forage for food. Leaf litter also keeps the soil moist, stops erosion, and protects roots against extreme heat and cold. The fungal mycelium that helps form the mycorrhizal network transmits nutrients from decaying material to trees and other plants. The forest floor supports a variety of plants, ferns, grasses, and tree seedlings, as well as animals such as ants, amphibians, spiders, and millipedes.
  • Understory is made up of bushes, shrubs, and young trees that are adapted to living in the shade of the canopy.
  • Canopy is formed by the mass of intertwined branches, twigs, and leaves of mature trees. The crowns of the dominant trees receive most of the sunlight. This is the most productive part of the trees, where maximum food is produced. The canopy forms a shady, protective "umbrella" over the rest of the forest.
  • Emergent layer exists in a tropical rain forest and is composed of a few scattered trees that tower over the canopy.

In botany and countries like Germany and Poland, a different classification of forest vegetation is often used: tree, shrub, herb, and moss layers (see stratification (vegetation)).

Types

Forests are classified differently and to different degrees of specificity. One such classification is in terms of the biomes 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 occupy the subarctic zone and are generally evergreen and coniferous.
  • Temperate zones support both broadleaf deciduous forests (e.g., temperate deciduous forest) and evergreen coniferous forests (e.g., temperate coniferous forests and temperate rainforests). Warm temperate zones support broadleaf evergreen forests, including laurel forests.
  • Tropical and subtropical forests include tropical and subtropical moist forests, tropical and subtropical dry forests, and tropical and subtropical coniferous forests.
  • Forests are classified according to physiognomy based on their overall physical structure or developmental stage (e.g. old growth vs. second growth).
  • Forests can also be classified more specifically based on the climate and the dominant tree species present, resulting in numerous different forest types (e.g., Ponderosa pine/Douglas fir forest).

The number of trees in the world, according to a 2015 estimate, is 3 trillion, of which 1.4 trillion are in the tropics or sub-tropics, 0.6 trillion in the temperate zones, and 0.7 trillion in the coniferous boreal forests. The 2015 estimate is about eight times higher than previous estimates, and is based on tree densities measured on over 400,000 plots. It remains subject to a wide margin of error, not least because the samples are mainly from Europe and North America.

Forests can also be classified according to the amount of human alteration. Old-growth forest contains mainly natural patterns of biodiversity in established seral patterns, and they contain mainly species native to the region and habitat. In contrast, secondary forest is forest regrowing following timber harvest and may contain species originally from other regions or habitats.

Different global forest classification systems have been proposed, but none has gained universal acceptance. 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.

Tropical dry

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. Under some conditions, such as 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 or herbivory are recurrent phenomena, savannas develop. More than half (54%) of the world’s forests is in only five countries (in descending order by area).; Russia, Brazil, Canada, the United States of America and China. Seven countries and areas; the Falkland Islands, Gibraltar, Holy See, Monaco, Nauru, Svalbard and Jan Mayen Islands, and Tokelau reported having no forest at all, and forest accounts for less than 10% of the total land area in another 49 countries and areas.

  • Acting as a carbon sink. Therefore, they are necessary to mitigate climate change.
  • Aiding in regulating climate. For example, research from 2017 shows that forests induce rainfall. If the forest is cut, it can lead to drought, and in the tropics to occupational heat stress of outdoor workers.
  • Purifying water.
  • Mitigating natural hazards such as floods.
  • Serving as a genetic reserve.
  • Serving as a source of lumber and as recreational areas.
  • Serving as a source of woodlands and trees for millions of people dependent almost entirely on forests for subsistence for their essential fuelwood, food, and fodder needs.

The main ecosystem services can be summarized in the next table:

{| class="wikitable"

|+ Main ecosystem services of the 3 main types of forest

|-

! Type of forest !! Carbon stored !! Biodiversity !! Other

|-

| Primary Boreal Forests || 1,042 billion tonnes of carbon, more than currently found in the atmosphere, 2 times more than all human caused emissions since the year 1870. || Biodiversity services given by Canada forest alone are estimated as 703 billion dollars per year. Important for almost half of the birds in North America. || Contain 60% of world surface freshwater.

|-

| Primary Temperate Forests || 119 billion tonnes (like all CO2 emitted by humans in 2005–2017) || Old growth forest has very high biodiversity. Some species link terrestrial ecosystems to marine. || Some trees can live 1,000 years providing many services to humans. Help to protect people from floods and droughts.

|-

| Primary Tropical Forests || 471 billion tonnes (more than all CO2 emissions from fossil fuel industry from the year 1750) || Contain about two thirds of all species of terrestrial animals and plants. || Creates clouds, rainfall.

|}

Some researchers state that forests do not only provide benefits, but can in certain cases also incur costs to humans. Forests may impose an economic burden, diminish the enjoyment of natural areas, reduce the food-producing capacity of grazing land and cultivated land, reduce biodiversity, reduce available water for humans and wildlife, harbour dangerous or destructive wildlife, and act as reservoirs of human and livestock disease.

An important consideration regarding carbon sequestration is that forests can turn from a carbon sink to a carbon source if plant diversity, density or forest area decreases, as has been observed in different tropical forests The typical tropical forest may become a carbon source by the 2060s. An assessment of European forests found early signs of carbon sink saturation, after decades of increasing strength. The Intergovernmental Panel on Climate Change (IPCC) concluded that a combination of measures aimed at increasing forest carbon stocks, andsustainable timber offtake will generate the largest carbon sequestration benefit.

Forest-dependent people

The term forest-dependent people is used to describe any of a wide variety of livelihoods that are dependent on access to forests, products harvested from forests, or ecosystem services provided by forests, including those of Indigenous peoples dependent on forests. In India, approximately 22 percent of the population belongs to forest-dependent communities, which live in close proximity to forests and practice agroforestry as a principal part of their livelihood. People of Ghana who rely on timber and bushmeat harvested from forests and Indigenous peoples of the Amazon rainforest are also examples of forest-dependent people.

Indigenous peoples

Forests are fundamental to the culture and livelihood of indigenous people groups that live in and depend on forests, many of which have been removed from and denied access to the lands on which they lived as part of global colonialism. Indigenous lands contain 36% or more of intact forest worldwide, host more biodiversity, and experience less deforestation. Indigenous activists have argued that degradation of forests and indigenous peoples' marginalization and land dispossession are interconnected. Other concerns among indigenous peoples include lack of Indigenous involvement in forest management and loss of knowledge related for the forest ecosystem. Since 2002, the amount of land that is legally owned by or designated for indigenous peoples has broadly increased, but land acquisition in lower-income countries by multinational corporations, often with little or no consultation of indigenous peoples, has also increased. Research in the Amazon rainforest suggests that indigenous methods of agroforestry form reservoirs of biodiversity. In the U.S. state of Wisconsin, forests managed by indigenous people have more plant diversity, fewer invasive species, higher tree regeneration rates, and higher volume of trees.

Management

thumb|World production of selected forest products

Forest management has changed considerably over the last few centuries, with rapid changes from the 1980s onward, 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.

alt=Priest River winds through mountains with a checkerboard design of trees to its east|thumb|[[Priest River (Idaho)|Priest River winding through Whitetail Butte with lots of forestry to the east—these lot patterns have existed since the mid-19th century. The white patches reflect areas with younger, smaller trees, where winter snow cover shows up brightly to the astronauts. Dark green-brown squares are parcels]]

Humans have generally decreased the amount of forest worldwide. 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 forests lead 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. More than 75% of these intact forests lie in three countries: the boreal forests of Russia and Canada, and the rainforest of Brazil.

According to Food and Agriculture Organization's (FAO) Global Forest Resources Assessment 2020, an estimated of forest have been lost worldwide through deforestation since 1990, but the rate of forest loss has declined substantially. In the most recent five-year period (2015–2020), the annual rate of deforestation was estimated at , down from annually in 2010–2015. According to the Special Report on Global Warming of 1.5&nbsp;°C of the Intergovernmental Panel on Climate Change, to avoid temperature rise by more than 1.5 degrees above pre-industrial levels, there will need to be an increase in global forest cover equal to the land area of Canada () by 2050. In addition, ambitious tree-planting programmes in countries such as China, India, the United States, and Vietnam – combined with natural expansion of forests in some regions – have added more than of new forests annually. As a result, the net loss of forest area was reduced to per year between 2000 and 2010, down from annually in the 1990s. In 2015, a study for Nature Climate Change showed that the trend has recently been reversed, leading to an "overall gain" in global biomass and forests. This gain is due especially to reforestation in China and Russia. New forests are not equivalent to old growth forests in terms of species diversity, resilience, and carbon capture. On 7 September 2015, the FAO released a new study stating that over the last 25 years the global deforestation rate has decreased by 50% due to improved management of forests and greater government protection.

thumb|Proportion of forest in legally established protected areas, by region, 2025

In 2025 the area of forest in legally established protected areas worldwide was estimated at 813 million ha, which is around 20% of the total forest area. Of the six regions, Asia has the largest share of forests in protected areas, at 26 %. The area of forest in protected areas has increased by 251 million ha globally since 1990. In 2020 there was an estimated of forest in protected areas worldwide. Of the six major world regions, South America was the highest share of forests in protected areas, at 31 percent. The area of such areas globally had increased by since 1990, but the rate of annual increase slowed in 2010–2020. 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. 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 new clear-cuts, although some older ones grew to over several years.

The Canadian Forest Service is the government department which looks after Forests in Canada.

Latvia

thumb|Latvian [[Pine Forest in Ķegums Municipality ]]

Latvia has about of forest land, which equates to about 50.5% of Latvia's total area of of forest land (46% of total forest land) is publicly owned and of forest land (54% of the total) is in private hands. Latvia's forests have been steadily increasing over the years, which is in contrast to many other nations, mostly due to the forestation of land not used for agriculture. In 1935, there were only of forest; today this has increased by more than 150%. Birch is the most common tree at 28.2%, followed by pine (26.9%), spruce (18.3%), grey alder (9.7%), aspen (8.0%), black alder (5.7%), oak/ash (1.2%), with other hardwood trees making up the rest (2.0%).

United States

In the United States, most forests have historically been affected by humans to some degree, though in recent years improved forestry practices have helped regulate or moderate large-scale impacts. The United States Forest Service estimated a net loss of about 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. 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.

See also

Sources

References

  • Forests in danger
  • Intact Forests with maps and reports (archived 8 September 2015)
  • Global Forest Resources Assessment 2005 by the Food and Agriculture Organization
  • (archived 24 January 2008)
  • Forest area is land under natural or planted stands of trees of at least 5 meters in situ, whether productive or not, and excludes tree stands in agricultural production systems
  • Forest area (sq. km) data from the World Bank's World Development Indicators, made available by Google