Editing Forest (section)

== Ecology<span class="anchor" id="Distribution"></span> ==
{{Main|Forest ecology}}
[[File:Hellyer Gorge, Tasmania.jpg|thumb|[[Temperate rainforest]] in Tasmania's [[Hellyer Gorge]]]]

Forests account for 75% of the [[gross primary productivity]] of the Earth's [[biosphere]], and contain 80% of the Earth's plant biomass.<ref name="yude" /> [[Biomass (ecology)|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. 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.<ref name=":0">{{Cite book |title=Global Forest Resources Assessment 2020 – Key findings |publisher=[[Food and Agriculture Organization]] |year=2020 |isbn=978-92-5-132581-0 |location=Rome |doi=10.4060/ca8753en |s2cid=130116768}}</ref>

Forest ecosystems broadly differ based on [[climate]]; latitudes 10° north and south of the [[equator]] are mostly covered in [[tropical rainforest]], and the latitudes between [[53rd parallel north|53°N]] and [[67th parallel north|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. The trees that form the principal structural and defining component of a forest may be of a great variety of species (as in [[tropical rainforest]]s and [[temperate deciduous forest]]s), or relatively few species over large areas (e.g., [[taiga]] and arid [[montane]] coniferous forests). The biodiversity of forests also encompasses [[shrubs]], herbaceous plants, [[moss]]es, [[fern]]s, [[lichen]]s, [[fungi]], and a variety of [[animal]]s.

Trees rising up to {{convert|35|meters|ft}} in height add a vertical dimension to the area of land that can support plant and animal species, opening up numerous [[ecological niche]]s for [[arboreal locomotion|arboreal]] animal species, [[epiphyte]]s, and various species that thrive under the regulated microclimate created under the canopy.<ref>{{cite web |last1=Cannon |first1=Charles |last2=Schlesinger |first2=William H. |title=Arboreal Dimensions of Biodiversity |date=2 August 2021 |url=https://blogs.nicholas.duke.edu/citizenscientist/arboreal-dimensions-of-biodiversity/}}</ref> Forests have intricate three-dimensional structures that increase in complexity with lower levels of disturbance and greater variety of tree species.<ref>{{cite web |title=Forests of the world in 3-D: Research team analyses complexity of forest structure |url=https://phys.org/news/2021-02-forests-world-d-team-analyses.html |website=phys.org |publisher=University of Gottingen}}</ref>

The biodiversity of forests varies considerably according to factors such as forest type, geography, climate, and soils – in addition to human use.<ref name=":1">{{Cite book |url=https://doi.org/10.4060/ca8985en |title=The State of the World's Forests 2020. Forests, biodiversity and people – In brief |publisher=[[Food and Agriculture Organization|FAO]] & UNEP |year=2020 |isbn=978-92-5-132707-4 |location=Rome |doi=10.4060/ca8985en |s2cid=241416114}}</ref> 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.<ref name=":1" /> 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.<ref name=":1" /> Northern Africa, southern Australia, coastal Brazil, Madagascar, and South Africa are also identified as areas with striking losses in biodiversity intactness.<ref name=":1" />

=== Components ===
[[File:Brussels Zonienwoud.jpg|thumb|Even, dense [[Old growth forest|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]].]]

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]]s, [[shrub]]s, [[vine]]s, [[grass]]es and other herbaceous (non-woody) plants, [[moss]]es, [[algae]], [[fungi]], [[insect]]s, [[mammal]]s, [[bird]]s, [[reptile]]s, [[amphibian]]s, and microorganisms living on the plants and animals and in the soil, connected by [[mycorrhizal network]]s.<ref>{{cite news|url=https://www.npr.org/sections/health-shots/2021/05/04/993430007/trees-talk-to-each-other-mother-tree-ecologist-hears-lessons-for-people-too|title=Trees Talk To Each Other. 'Mother Tree' Ecologist Hears Lessons For People, Too|date=4 May 2021|first=Dave|last=Davies|publisher=NPR|work=Fresh Air}}</ref>

===Layers===
[[File:Spiny Forest Ifaty Madagascar.jpg|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.<ref>{{cite web |last1=Franklin |first1=Brooke |title=This Fall, Leave the Leaves! |url=https://www.usda.gov/media/blog/2022/10/17/fall-leave-leaves |website=usda.gov}}</ref> The [[Fungi|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]], [[amphibian]]s, [[spider]]s, and [[millipede]]s. 
* '''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.<ref>{{Cite book|title = The Living World|publisher = D.A.V. College Managing Committee}}</ref>

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 ===
[[File:La foresta sopra la vista del lago di Ridracoli.jpg|thumb|[[Foreste Casentinesi, Monte Falterona, Campigna National Park|Casentinesi Forests]], Italy]]

Forests are classified differently and to different degrees of specificity. One such classification is in terms of the [[biome]]s 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, [[conifer]]ous (needle-leaved) trees, or mixed.
* [[Boreal forest]]s occupy the [[subarctic]] zone and are generally evergreen and coniferous.
* [[Temperate]] zones support both broadleaf deciduous forests (e.g., [[Temperate broadleaf and mixed forests|temperate deciduous forest]]) and evergreen coniferous forests (e.g., [[temperate coniferous forests]] and [[temperate rainforest]]s). Warm temperate zones support broadleaf evergreen forests, including [[laurel forest]]s.
* Tropical and [[subtropical]] forests include [[Tropical and subtropical moist broadleaf forests|tropical and subtropical moist forests]], [[Tropical and subtropical dry broadleaf 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 [[Ecological succession|developmental stage]] (e.g. [[old growth]] vs. [[Secondary forest|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 [[Forest inventory|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.<ref>{{cite web |last1=Amos |first1=Jonathan |title=Earth's trees number 'three trillion' |url=https://www.bbc.co.uk/news/science-environment-34134366 |publisher=BBC |access-date=3 September 2015 |date=3 September 2015 |url-status=live |archive-url=https://web.archive.org/web/20150903082255/http://www.bbc.co.uk/news/science-environment-34134366 |archive-date=3 September 2015}}</ref>

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.<ref name="Chazdon">{{cite journal|last=Chazdon|first=Robin L.|author-link=Robin Chazdon|year=2008|title=Beyond deforestation: restoring forests and ecosystem services on degraded lands|url=http://lerf.eco.br/img/publicacoes/2008_2411%20Beyond%20Deforestation%20Restoring%20Forests%20and%20Ecosystem%20Services%20on%20Degraded%20Lands.pdf|url-status=live|journal=Science|volume=320|issue=5882|pages=1458–60|bibcode=2008Sci...320.1458C|doi=10.1126/science.1155365|pmid=18556551|archive-url=https://web.archive.org/web/20161021132745/http://lerf.eco.br/img/publicacoes/2008_2411%20Beyond%20Deforestation%20Restoring%20Forests%20and%20Ecosystem%20Services%20on%20Degraded%20Lands.pdf|archive-date=21 October 2016|s2cid=206511664}}</ref>

Different global forest classification systems have been proposed, but none has gained universal acceptance.<ref name=wcmc>{{cite book |last1=Jenkins |first1=Martin D. |last2=Groombridge |first2=Brian |title=World Atlas of Biodiversity: Earth's Living Resources in the 21st Century |publisher=[[World Conservation Monitoring Centre]], [[United Nations Environment Programme]] |url=https://books.google.com/books?id=_kHeAXV5-XwC&q=UNESCO+forest+and+woodland+subformations&pg=RA3-PA81 |isbn=978-0-520-23668-4 |year=2002}}</ref> [[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.<ref name=wcmc/> Each category is described in a separate section below.

==== Temperate needleleaf<span class="anchor" id="Coniferous forests"></span> ====
[[Temperate coniferous forest|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, [[pine]]s ''Pinus'', [[spruce]]s ''Picea'', [[larch]]es ''Larix'', [[fir]]s ''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.<ref name=wcmc/>

====Temperate broadleaf and mixed====
[[File:Namdapha2.jpg|thumb|upright|Broadleaf forest in [[Bhutan]]]]

[[Temperate broadleaf and mixed forest]]s 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 [[rainforest]]s 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.<ref name=wcmc/>

==== Tropical moist ====
There are many different types of [[Tropical and subtropical moist broadleaf forests|tropical moist forests]], with lowland evergreen broad-leaf [[tropical rainforest]]s: for example [[Várzea forest|várzea]] and [[Cantão#Natural Communities|igapó]] forests and the terra firme forests of the [[Amazon Basin]]; the [[peat swamp forest]]s; [[dipterocarp]] forests of [[Southeast Asia]]; and the [[high forest]]s of the [[Congo Basin]]. [[Seasonal tropical forest]]s, perhaps the best description for the colloquial term "[[jungle]]", typically range from the rainforest zone 10 degrees north or south of the [[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.<ref>{{cite book|first1=S|last1=Chape|first2=M|last2=Spalding|first3=M|last3=Jenkins|url=https://books.google.com/books?id=HuaGXdMTTmcC&q=Tropical+moist+forests+include+many+different+forest+types&pg=PA53|title=The world's protected areas: status, values and prospects in the 21st century|publisher=Univ de Castilla La Mancha|year=2008|isbn=978-0-520-24660-7}}</ref>

==== 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. 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]]". [[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]]s develop.<ref name=wcmc/>

==== Sparse trees and savanna ====
Sparse trees and [[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]]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]], open [[lichen]] woodland, and forest tundra. A savanna is a mixed [[woodland]]–[[grassland]] [[ecosystem]] characterized by the trees being sufficiently widely spaced so that the 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.<ref name=wcmc/>

==== 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]]. Some are managed in ways that enhance their biodiversity protection functions and can provide ecosystem services such as nutrient capital maintenance, [[Drainage basin|watershed]] and soil structure protection and carbon storage.<ref name=Chazdon/><ref name=wcmc/>