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A forest is an area of land dominated by
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only wood plants with se ...

tree
s. 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 The Food and Agriculture Organization of the United Nations (FAO)french: Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is a list of specialized ...
(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 2020'' (FRA 2020) found that forests covered , or approximately 31 percent of the world's land area in 2020. Forests are the predominant terrestrial
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

ecosystem
of Earth, and are distributed around the globe. More than half of the world's forests are found in only five countries (Brazil, Canada, China, the Russian Federation, and the United States of America). The largest share of forests (45 percent) are in the
tropical latitudes
tropical latitudes
, followed by those in the
boreal Boreal, meaning "(far) northern" in Latin and Greek language, Greek, may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a c ...
,
temperate In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use ...
, and
subtropic The subtropical zones or subtropics are geographic Geography (from Greek: , ''geographia'', literally "earth description") is a field of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic ent ...
domains. Forests account for 75% of the
gross primary production In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Topics of interest include the bi ...
of the Earth's
biosphere The biosphere (from βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all s. It can also be termed the zo ...
, and contain 80% of the Earth's plant biomass. Net primary production is estimated at 21.9
gigatonne The tonne ( or ; symbol: t) is a metric unit of mass equal to 1,000 kilogram The kilogram (also kilogramme) is the base unit of mass in the International System of Units (SI), the current metric system, having the unit symbol kg. I ...
s of biomass per year for
tropical forest The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is ...

tropical forest
s, 8.1 for
temperate forest A temperate forest is a forest found between the tropical The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in ...
s, and 2.6 for
boreal forest Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic Turkic may refer to: * anything related to the country of Turkey * Turkic languages, a language family of at least thirty-five documented languages ** Turkic alphabets (di ...
s. Forests at different latitudes and elevations, and with different precipitation and
evapotranspiration Evapotranspiration (ET) is the sum of water evaporation and transpiration from a surface area to the Atmosphere of Earth, atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and ...

evapotranspiration
form distinctly different
biome A biome is a collection of flora, plants and fauna, animals that have common characteristics for the natural environment, environment they exist in. They can be found over a range of continents. Biomes are distinct biological community (ecology ...
s: around the North Pole,
tropical moist forests Tropical and subtropical moist forest (TSMF), also known as tropical moist forest, is a tropical The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphe ...
and
tropical dry forests The tropical and subtropical dry forest is a habitat (ecology), habitat type defined by the World Wide Fund for Nature and is located at tropical and subtropical latitudes. Though these forests occur in climates that are warm year-round, and may ...
around the
Equator The Equator is a , about in circumference, that divides into the and hemispheres. It is an located at 0 degrees , halfway between the and poles. In , as applied in , the equator of a rotating (such as a ) is the parallel (circle of l ...

Equator
, and
temperate forest A temperate forest is a forest found between the tropical The tropics are the region of Earth surrounding the Equator. They are delimited in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in ...
s at the
middle latitudes The middle latitudes (also called the mid-latitudes, sometimes midlatitudes, or moderate latitudes) are a spatial region on Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29 ...
. Areas at higher elevations tend to support forests similar to those at higher latitudes, and the amount of precipitation also affects forest composition. Almost half the 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. Human society and forests influence each other in both positive and negative ways. Forests provide
ecosystem services Ecosystem services are the many and varied benefits to humans provided by the natural environment and from healthy . Such ecosystems include, for example, s, s, s and s. These ecosystems, functioning in healthy relationship, offer such things ...
to humans and serve as tourist attractions. Forests can also affect people's health. Human activities, including unsustainable use of forest resources, can negatively affect forest ecosystems.


Definition

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. 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, 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 Land use involves the management and modification of natural environment or wilderness Wilderness or wildlands (usually in the plural), are natural environments on Earth that have not been significantly modified by human activity or any nonur ...
, and land cover. Administrative definitions are based primarily upon the legal designations of land, and commonly bear little relationship to its vegetation: land that is legally designated as a forest is defined as such even if no trees are growing on it. Land-use definitions are based on the primary purpose that the land serves. For example, a forest may be 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 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 In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only wood plants with secondary ...
(canopy cover) or the section of land that is occupied by the cross-section of tree trunks (basal area). Under such land-cover definitions, an area of land can only be known as forest if it is growing trees. Areas that fail to meet the land-cover definition may be still included while immature trees are present that are expected to meet the definition at maturity. Under land-use definitions, there is considerable variation on where the cutoff points are between a forest,
woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see d ...

woodland
, and
savanna A savanna or savannah is a mixed woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ' woods), a low-density forming open s with plenty of sunlight and li ...

savanna
. Under some definitions, to be considered a forest requires very high levels of tree canopy cover, from 60% to 100%, 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%. Some areas covered with trees are legally defined as agricultural areas, e.g.
Norway spruce ''Picea abies'', the Norway spruce or European spruce, is a species of native to , and . It has s that typically hang downwards, and the largest cones of any , 9–17 cm long. It is very closely related to the (''Picea obovata''), which replac ...
plantations, under Austrian forest law, when the trees are being grown as Christmas trees and are below a certain height.


Etymology

The word ''
forest A forest is an area of land dominated by tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a ...
'' derives from the
Old French Old French (, , ; Modern French French ( or ) is a Romance language The Romance languages, less commonly Latin or Neo-Latin languages, are the modern languages that evolved from Vulgar Latin Vulgar Latin, also known as Popular o ...
''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 Frankish may refer to: * Franks The Franks ( la, Franci or ) were a group of Germanic peoples The historical Germanic peoples (from lat, Germani) are a category of ancient northern European tribes, first mentioned by Graeco-Roman author ...
or
Old High German Old High German (OHG, german: Althochdeutsch, German abbr. ) is the earliest stage of the German language, conventionally covering the period from around 750 to 1050. There is no standardised or supra-regional form of German at this period, and ...
, of the
Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share ...
, denoting "open wood",
Carolingian The Carolingian dynasty (known variously as the Carlovingians, Carolingus, Carolings, Karolinger or Karlings) was a Frankish Frankish may refer to: * Franks The Franks ( la, Franci or ) were a group of Germanic peoples The historic ...
scribes first used ''foresta'' in the capitularies of
Charlemagne Charlemagne ( , ) or Charles the Great ( la, Carolus Magnus; 2 April 748 – 28 January 814) was King of the Franks The Franks—Germanic-speaking peoples that invaded the Western Roman Empire in the 5th century—were first led by i ...

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 Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with") is "an appa ...

Latin
''silva'', which denoted "forest" and "wood(land)" (
cf. The abbreviation ''cf.'' (short for the la, confer/conferatur, both meaning 'compare') is used in writing to refer the reader to other material to make a comparison with the topic being discussed. Style guides recommend that ''cf.'' be used only ...
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 Late Latin ( la, Latinitas serior) is the scholarly name for the written Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, kn ...
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 Middle Low German or Middle Saxon (autonym: ''Sassisch'', i.e. "Saxon", Standard German, Standard High German: ', Dutch language, Modern Dutch: ') is a developmental stage of Low German. It developed from the Old Saxon language in the Middle ...
''vorst'' denoting "forest";
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language English is a West Germanic language of the Indo-European language family The Indo-European languages are a language family A language ...
''fyrhþ'' denoting "forest, woodland, game preserve, hunting ground" (English ''
frith Frith is an Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval ...
''); and
Old Norse Old Norse, Old Nordic, or Old Scandinavian is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia Scandinavia; : ''Skades ...
''fýri'', denoting "coniferous forest"; all of which derive from the
Proto-Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed Reconstruction may refer to: Politics, history, and sociology *Reconstruction (law), the transfer of a company's (or several companies') business to a new ...
*''furhísa-'', *''furhíþija-'', denoting "a fir-wood, ''coniferous'' forest", from the
Proto-Indo-European Proto-Indo-European (PIE) is the theorized common ancestor of the Indo-European language family The Indo-European languages are a language family A language is a structured system of communication used by humans, including speech ( ...
*''perkwu-'', 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. The Norman rulers of England introduced the word as a legal term, as seen in Latin texts such as the ''
Magna Carta (Medieval Latin for "Great Charter of Freedoms"), commonly called (also ''Magna Charta''; "Great Charter"), is a Royal charter, royal charter of rights agreed to by King John of England at Runnymede, near Windsor, Berkshire, Windsor, on ...

Magna Carta
'', to denote uncultivated land that was legally designated for hunting by feudal
nobility Nobility is a social class normally ranked immediately below Royal family, royalty and found in some societies that have a formal aristocracy (class), aristocracy. Nobility has often been an Estates of the realm, estate of the realm that p ...
(see
Royal Forest A royal forest, occasionally "Kingswood" (), is an area of land with different definitions in England England is a that is part of the . It shares land borders with to its west and to its north. The lies northwest of England and the ...
). These hunting forests did not necessarily contain any trees. However, because hunting forests 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 A synonym is a word, morpheme A morpheme is the smallest meaningful lexical item in a language. A morpheme is not a word. The difference between a morpheme and a word is that a morpheme bound and free morphemes, sometimes does not stand alone ...
of ''forest'', and as a
Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation with") is "an appa ...

Latin
ate 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 Silviculture is the practice of controlling the growth, composition/structure, and quality of forest A forest is an area of land dominated by s. Hundreds of definitions of forest are used throughout the world, incorporating factors such a ...
. 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
Late Devonian The Devonian ( ) is a period (geology), geologic period and system of the Paleozoic, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, ...
(approximately 380
million years ago One million (1,000,000), or one thousand thousand, is the natural number In mathematics, the natural numbers are those used for counting (as in "there are ''six'' coins on the table") and total order, ordering (as in "this is the ''third'' l ...
), with the evolution of ''
Archaeopteris ''Archaeopteris'' is an extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life ...

Archaeopteris
'', which was a plant that was both tree-like and fern-like, growing to in height. It quickly spread throughout the world, from the equator to subpolar latitudes; and it formed the first forest by being the first species known to cast shade due to its fronds and by forming soil from its roots. ''Archaeopteris'' was deciduous, dropping its fronds onto the forest floor, the shade, soil, and forest duff from the dropped fronds creating the first forest. The shed organic matter altered the freshwater environment, slowing its flow and providing food. This promoted freshwater fish.


Ecology

Forests account for 75% of the gross primary productivity of the Earth's
biosphere The biosphere (from βίος ''bíos'' "life" and σφαῖρα ''sphaira'' "sphere"), also known as the ecosphere (from Greek οἶκος ''oîkos'' "environment" and σφαῖρα), is the worldwide sum of all s. It can also be termed the zo ...
, and contain 80% of the Earth's plant biomass. The world's forests contain about 606 gigatonnes of living biomass (above- and below-ground) and 59 gigatonnes of dead wood. The total biomass has decreased slightly since 1990, but biomass per unit area has increased. Forest ecosystems can be found in all regions capable of sustaining tree growth, at altitudes up to the
tree line The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually cold temperatures, extreme snowpa ...

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 The Equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the N ...

equator
are mostly covered in
tropical rainforest Tropical rainforests are rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape ...

tropical rainforest
, and the latitudes between 53°N and 67°N have
boreal forest Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic Turkic may refer to: * anything related to the country of Turkey * Turkic languages, a language family of at least thirty-five documented languages ** Turkic alphabets (di ...
. As a general rule, forests dominated by
angiosperms Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greec ...
(''broadleaf forests'') are more species-rich than those dominated by
gymnosperms The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also ...
(''conifer'', ''montane'', or ''needleleaf forests''), although exceptions exist. Forests sometimes contain many tree species within a small area (as in
tropical rainforest Tropical rainforests are rainforest Rainforests are characterized by a closed and continuous tree canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape ...

tropical rainforest
s and
temperate deciduous forest#REDIRECT Temperate deciduous forestTemperate deciduous or temperate broad-leaf forests are a variety of temperate forest 'dominated' by trees that lose their leaves each year. They are found in areas with warm moist summers and cool winters. The s ...
s), or relatively few species over large areas (e.g.,
taiga Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic Turkic may refer to: * anything related to the country of Turkey * Turkic languages, a language family of at least thirty-five documented languages ** Turkic alphabets (di ...

taiga
and arid
montane Montane ecosystems are found on the slopes of mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. A mountain differs from a plateau in having a limited summit area ...

montane
coniferous forests). Forests are often home to many animal and plant species, and
biomass Biomass is plant or animal material used as fuel to produce electricity Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position ...
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 In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...

detritus
. The woody component of a forest contains
lignin Lignin is a class of complex organic polymer A polymer (; Greek ''poly- Poly, from the Greek :wikt:πολύς, πολύς meaning "many" or "much", may refer to: Businesses * China Poly Group Corporation, a Chinese business group, and its s ...

lignin
, which is relatively slow to
decompose Decomposition is the process by which dead organic substance , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds com ...

decompose
compared with other organic materials such as
cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important stru ...

cellulose
or carbohydrate. 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. Areas with dense human populations and intense agricultural land use, such as Europe, parts of Bangladesh, China, India, and North America, are less intact in terms of their biodiversity. Northern Africa, southern Australia, coastal Brazil, Madagascar, and South Africa are also identified as areas with striking losses in biodiversity intactness.


Components

A forest consists of many components that can be broadly divided into two categories: biotic (living) and abiotic (non-living). The living parts include
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only wood plants with se ...

tree
s,
shrub A shrub (often called a bush) is a small- to medium-sized perennial A perennial plant or simply perennial is a plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the p ...

shrub
s,
vine A vine (Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in relation ...

vine
s,
grass Poaceae () or Gramineae () is a large and nearly ubiquitous family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain ...

grass
es and other herbaceous (non-woody) plants,
moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

moss
es,
algae Algae (; singular alga ) is an informal term for a large and diverse group of s. It is a grouping that includes species from multiple distinct s. Included organisms range from , such as '','' and the s, to forms, such as the , a large whi ...

algae
,
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
,
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s,
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s,
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s,
reptile Reptiles, as most commonly defined, are the animals in the Class (biology), class Reptilia , a paraphyletic grouping comprising all amniotes except synapsids (mammals and their extinct relatives) and Aves (birds). Living reptiles comprise turtl ...

reptile
s,
amphibian Amphibians are ectothermic, tetrapod vertebrates of the Class (biology), class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial animal, ter ...
s, and microorganisms living on the plants and animals and in the soil.


Layers

A forest is made up of many layers. 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. * Forest floor contains decomposing leaves, animal droppings, and dead trees. Decay on the forest floor forms new soil and provides nutrients to the plants. The
forest floor The forest floor, also called detritus, wikt:duff#Noun 2, duff and the O horizon, is one of the most distinctive features of a forest ecosystem. It mainly consists of shed vegetative parts, such as leaves, branches, bark, and stems, existing in ...
supports ferns, grasses, mushroom, and tree seedlings. * 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. However, in botany and in many countries (Germany, Poland, etc.), a different classification of forest vegetation is often used: tree, shrub, herb, and moss layers (see
stratification (vegetation) Stratification in the field of ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Topics o ...
).


Types

Forests are classified differently and to different degrees of specificity. One such classification is in terms of the
biome A biome is a collection of flora, plants and fauna, animals that have common characteristics for the natural environment, environment they exist in. They can be found over a range of continents. Biomes are distinct biological community (ecology ...
s in which they exist, combined with leaf longevity of the dominant species (whether they are
evergreen In botany Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "botany" comes from the Anc ...

evergreen
or
deciduous In the fields of horticulture Horticulture is the art of cultivating plants in gardens to produce food and medicinal ingredients, or for comfort and ornamental purposes. Horticulturists are agriculturists who grow flowers, fruits and nuts, v ...
). Another distinction is whether the forests are composed predominantly of broadleaf trees,
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ex ...
ous (needle-leaved) trees, or mixed. *
Boreal forest Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic Turkic may refer to: * anything related to the country of Turkey * Turkic languages, a language family of at least thirty-five documented languages ** Turkic alphabets (di ...
s occupy the
subarctic The sub-Arctic zone is a region in the Northern Hemisphere immediately south of the true Arctic and covering much of Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Central Alaskan Yup'ik language, Yup'ik: ''Alaskaq''; tli, An ...
zone and are generally evergreen and coniferous. *
Temperate In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use ...
zones support both broadleaf deciduous forests (e.g.,
temperate deciduous forest#REDIRECT Temperate deciduous forestTemperate deciduous or temperate broad-leaf forests are a variety of temperate forest 'dominated' by trees that lose their leaves each year. They are found in areas with warm moist summers and cool winters. The s ...
) and evergreen coniferous forests (e.g.,
temperate coniferous forests Temperate coniferous forest is a terrestrial biome A biome is a collection of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological ...
and
temperate rainforest Temperate rainforests are conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae ...
s). Warm temperate zones support broadleaf evergreen forests, including
laurel forest Laurel forest, also called laurisilva or laurissilva, is a type of subtropical The subtropical zones or subtropics are geographical and climate zones located to the north and south of the Torrid Zone ''Torrid Zone'' is a 1940 adventure fil ...

laurel forest
s. * Tropical and
subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones located to the north and south of the tropics, Torrid Zone. Geographically part of the Geographical zone#Temperate zones, ...

subtropical
forests include tropical and subtropical moist forests, tropical and subtropical dry forests, and
tropical and subtropical coniferous forests Tropical and subtropical coniferous forests are a tropical forest habitat type defined by the World Wide Fund for Nature The World Wide Fund for Nature (WWF) is an international non-governmental organization founded in 1961 that works in th ...
. * Forests are classified according to physiognomy based on their overall physical structure or developmental stage (e.g.
old growth An old-growth forest – also termed primary forest, virgin forest, late seral forest or primeval forest – is a forest that has attained great age without significant disturbance (ecology), disturbance and thereby exhibits unique ecological ...
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 ''Pinus ponderosa'', commonly known as the ponderosa pine, bull pine, blackjack pine, western yellow-pine, or filipinus pine is a very large pine A pine is any Pinophyta, conifer in the genus ''Pinus'' () of the family (biology), family Pinac ...
/
Douglas-fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is native plant, native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. Ther ...

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. United Nations Environment Programme, UNEP-World Conservation Monitoring Centre, 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 in a separate section below.


Temperate needleleaf

Temperate needleleaf forests mostly occupy the higher latitudes of the Northern Hemisphere, as well as 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 Araucariaceae and Podocarpaceae) occur mixed with broadleaf species, and are classed as broadleaf-and-mixed forests.


Temperate broadleaf and mixed

Temperate broadleaf and mixed forests include a substantial component of trees of the Anthophyta group. 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 Basin, Mediterranean, and California; and the southern beech Nothofagus forests of Chile and New Zealand.


Tropical moist

There are many different types of Tropical and subtropical moist broadleaf forests, tropical moist forests, with lowland evergreen broad-leaf tropical rainforests: for example Várzea forest, várzea and Cantão#Natural Communities, igapó forests and the terra firma forests of the Amazon Basin; the peat swamp forests; dipterocarp forests of Southeast Asia; and the high forest (woodland), high forests of the Congo Basin. Seasonal tropical forests, perhaps the best description for the colloquial term "jungle", typically range from the rainforest zone 10 degrees north or south of the
equator The Equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the N ...

equator
, to the Tropic of Cancer and Tropic of Capricorn. Forests located on mountains are also included in this category, divided largely into upper and lower Montane ecology, montane formations, on the basis of the variation of physiognomy corresponding to changes in altitude.


Tropical dry

Tropical and subtropical dry broadleaf forests, 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". Deserts and xeric shrublands, 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,
savanna A savanna or savannah is a mixed woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ' woods), a low-density forming open s with plenty of sunlight and li ...

savanna
s develop.


Sparse trees and savanna

Sparse trees and
savanna A savanna or savannah is a mixed woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ' woods), a low-density forming open s with plenty of sunlight and li ...

savanna
are forests with sparse tree-Canopy (biology), canopy cover. They occur principally in areas of transition from forested to non-forested landscapes. The two major zones in which these
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

ecosystem
s occur are in the boreal ecosystem, boreal region and in the seasonally dry tropics. At high latitudes, north of the main zone of boreal forestland, growing conditions are not adequate to maintain a continuously closed forest cover, so tree cover is both sparse and discontinuous. This vegetation is variously called open
taiga Taiga (; rus, тайга́, p=tɐjˈɡa; relates to Mongolic and Turkic Turkic may refer to: * anything related to the country of Turkey * Turkic languages, a language family of at least thirty-five documented languages ** Turkic alphabets (di ...

taiga
, open lichen woodland, and forest tundra. A savanna is a mixed
woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see d ...

woodland
–grassland
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

ecosystem
characterized by the trees being sufficiently widely spaced so that the Canopy (forest), canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer that consists primarily of grasses. Savannas maintain an open canopy despite a high tree density.


Forest plantations

Forest plantations are generally intended for the production of timber and pulpwood. Commonly mono-specific, planted with even spacing between the trees, and intensively managed, these forests are generally important as habitat for native biodiversity. However, they can be managed in ways that enhance their biodiversity protection functions and they can provide ecosystem services such as maintaining nutrient capital, protecting Drainage basin, watersheds and soil structure, and storing carbon.


Forest area

The net loss of forest area has decreased substantially since 1990, but the world is not on track to meet the target of the United Nations Strategic Plan for Forests to increase forest area by 3 percent by 2030. While deforestation is taking place in some areas, new forests are being established through natural expansion or deliberate efforts in other areas. As a result, the net loss of forest area is less than the rate of deforestation; and it, too, is decreasing: from per year in the 1990s to per year during 2010–2020. In absolute terms, the global forest area decreased by between 1990 and 2020, which is an area about the size of Libya.


Societal significance

Forests provide a diversity of
ecosystem services Ecosystem services are the many and varied benefits to humans provided by the natural environment and from healthy . Such ecosystems include, for example, s, s, s and s. These ecosystems, functioning in healthy relationship, offer such things ...
including: * Converting carbon dioxide into oxygen and biomass. A full-grown tree produces about of net oxygen per year. * Acting as a carbon sink. Therefore, they are necessary to Climate change mitigation, mitigate climate change. According to the Special Report on Global Warming of 1.5 °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 the year 2050. * 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. 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.


Forest management

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 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 Stakeholder engagement, consultation with local communities and other stakeholders. 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, Forest pathology#Animals, insects, Forest pathology, 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 of Russia and Canada, and the rainforest of Brazil. According to
Food and Agriculture Organization The Food and Agriculture Organization of the United Nations (FAO)french: Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is a list of specialized ...
'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. China instituted a ban on logging, beginning in 1998, due to the erosion and flooding that it caused. 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. However, new forests are not completely 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 forest management, management of forests and greater government protection. There is an estimated of forest in protected areas worldwide. Of the six major world regions, South America has the highest share of forests in protected areas, at 31 percent. The area of such areas globally has increased by since 1990, but the rate of annual increase slowed in 2010–2020. Smaller areas of
woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the ''plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunlight and limited shade (see d ...

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 School (education), forest schools and Forest kindergarten, 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.


Canada

Canada has about 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 include extensive consultation with local stakeholders. About eight percent of Canada's forest is legally protected from resource development. 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. By December 2006, over of forest land in Canada (about half the global total) had been certified as being sustainably managed. 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 clear-cuts, although some older clear-cuts can range upwards of in size, which was cut over several years. The Canadian Forest Service is the government department which looks after Forests in Canada.


Latvia

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. However, the United States Forest Service estimates 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. 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.


Largest forests in the world


See also


Sources


References


External links


Forests in danger

Intact Forests
with maps and reports

by the
Food and Agriculture Organization The Food and Agriculture Organization of the United Nations (FAO)french: Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is a list of specialized ...

CoolForests.org – Conservation Cools the Planet

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 * * * {{Authority control Forests, Habitats Trees Ecosystems