Tree

==Distribution==
{{further |Forest}}
[[File:Daintree Rainforest 4.jpg|thumb|upright|left|The [[Daintree Rainforest]]]]

The number of trees in the world, according to a 2015 estimate, is 3.04 trillion, of which 1.39 trillion (46%) are in the tropics or [[Subtropics|sub-tropics]], 0.61 trillion (20%) in the [[Temperate climate|temperate zones]], and 0.74 trillion (24%) in the [[Forest|coniferous]] [[Taiga|boreal forests]]. The 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. The estimate suggests that about 15 billion trees are cut down annually and about 5 billion are planted. In the 12,000 years since the start of human agriculture, the number of trees worldwide has decreased by 46%.<ref name=Crowther>{{Cite journal |title=Mapping tree density at a global scale |journal=Nature |date=2 September 2015 |issn=1476-4687 |volume=advance online publication |issue=7568 |pages=201–205 |doi=10.1038/nature14967 |pmid=26331545 |first1=T. W. |last1=Crowther |first2=H. B. |last2=Glick |first3=K. R. |last3=Covey |first4=C. |last4=Bettigole |first5=D. S. |last5=Maynard |first6=S. M. |last6=Thomas |first7=J. R. |last7=Smith |first8=G. |last8=Hintler |first9=M. C. |last9=Duguid |bibcode=2015Natur.525..201C |s2cid=4464317 |url=https://resolver.sub.uni-goettingen.de/purl?gro-2/35970 |access-date=29 November 2023 |archive-date=1 January 2024 |archive-url=https://web.archive.org/web/20240101151145/https://publications.goettingen-research-online.de/handle/2/35970 |url-status=live }}</ref><ref>{{cite web |url=https://www.npr.org/sections/goatsandsoda/2015/09/02/436919052/tree-counter-is-astonished-by-how-many-trees-there-are |title=Tree Counter Is Astonished By How Many Trees There Are |publisher=National Public Radio |date=2 September 2015 |first=Nell |last=Greenfieldboyce |author-link=Nell Greenfieldboyce |access-date=4 April 2018 |archive-date=8 March 2018 |archive-url=https://web.archive.org/web/20180308193905/https://www.npr.org/sections/goatsandsoda/2015/09/02/436919052/tree-counter-is-astonished-by-how-many-trees-there-are |url-status=live }}</ref><ref>{{Cite news |last1=Amos |first1=Jonathan |title=Earth's trees number 'three trillion' |journal=BBC News |url=https://www.bbc.co.uk/news/science-environment-34134366 |access-date=3 September 2015 |date=3 September 2015 |archive-date=19 July 2019 |archive-url=https://web.archive.org/web/20190719204607/https://www.bbc.co.uk/news/science-environment-34134366 |url-status=live }}</ref><ref>{{Cite journal |title=Global count reaches 3 trillion trees |journal=Nature |url=http://www.nature.com/news/global-count-reaches-3-trillion-trees-1.18287 |access-date=3 September 2015 |doi=10.1038/nature.2015.18287 |year=2015 |last1=Ehrenberg |first1=Rachel |s2cid=189415504 |archive-date=21 December 2019 |archive-url=https://web.archive.org/web/20191221053821/http://www.nature.com/news/global-count-reaches-3-trillion-trees-1.18287 |url-status=live }}</ref> There are approximately 64,100 known tree species in the world. With 43% of all tree species, South America has the highest biodiversity, followed by Eurasia (22%), Africa (16%), North America (15%), and Oceania (11%).<ref>{{Cite web |last=Pappas |first=Stephanie |title=Thousands of Tree Species Remain Unknown to Science |url=https://www.scientificamerican.com/article/thousands-of-tree-species-remain-unknown-to-science/ |access-date=18 January 2023 |website=[[Scientific American]] |date=May 2022 |archive-date=17 January 2023 |archive-url=https://web.archive.org/web/20230117172407/https://www.scientificamerican.com/article/thousands-of-tree-species-remain-unknown-to-science/ |url-status=live }}</ref>

In suitable environments, such as the [[Daintree Rainforest]] in [[Queensland]], or the mixed [[Podocarpus|podocarp]] and [[Temperate broadleaf and mixed forest|broadleaf forest]] of [[Ulva Island, New Zealand]], forest is the more-or-less stable [[climax community|climatic climax community]] at the end of a plant succession, where open areas such as grassland are colonised by taller plants, which in turn give way to trees that eventually form a forest canopy.<ref>{{cite web |title=Climax Community |url=http://www.eoearth.org/view/article/171226/ |archive-url=https://web.archive.org/web/20140906133528/http://www.eoearth.org/view/article/171226/ |archive-date=6 September 2014 |publisher=Encyclopedia of Earth |access-date=28 June 2014 |url-status=dead }}</ref><ref>{{cite web |title=Physical Environments Biosphere Vegetation Succession Moorlands |publisher=Macaulay Institute |url=http://www.macaulay.ac.uk/soilquality/Moorland%20Succession.pdf |access-date=28 June 2014 |archive-date=6 September 2014 |archive-url=https://web.archive.org/web/20140906154403/http://www.macaulay.ac.uk/soilquality/Moorland%20Succession.pdf |url-status=live }}</ref>

[[File:New snow, Swabian Alps (2019).jpg|thumb|Conifers in the [[Swabian Jura|Swabian alps]]]]

In [[temperateness|cool temperate]] regions, conifers often predominate; a widely distributed climax community in the far north of the northern hemisphere is moist [[taiga]] or northern coniferous forest (also called boreal forest).<ref>{{cite web |last=Nelson |first=Rob |title=The Taiga |url=http://www.thewildclassroom.com/biomes/taiga.html |access-date=28 June 2014 |archive-date=6 May 2017 |archive-url=https://web.archive.org/web/20170506045042/http://www.thewildclassroom.com/biomes/taiga.html |url-status=dead }}</ref><ref>{{cite web |url=http://dendro.cnre.vt.edu/forsite/ncfbiome.htm |title=Northern Coniferous Forest Biome |access-date=28 June 2014 |work=The Forest Community |publisher=FORSite |quote=The diversity of tree species in the boreal forest is quite low, with black spruce (''Picea mariana''), larch or tamarack (''Larix laricina''), and white spruce (''P. glauca'') the most common species. The former two species generally occupy wet sites with poorly drained mineral or organic soils, while white spruce is the climatic climax species on sites that are drier and higher in nutrient content. Balsam fir (''Abies balsamea'') is a dominant tree species in the eastern half of the biome. |archive-date=30 October 2014 |archive-url=https://web.archive.org/web/20141030070027/http://dendro.cnre.vt.edu/forsite/ncfbiome.htm |url-status=live }}</ref> Taiga is the world's largest land [[biome]], forming 29% of the world's forest cover.<ref>{{cite web |url=http://www.wilds.mb.ca/taiga/tbsfaq.html |title=Taiga Biological Station: FAQ |publisher=Taiga Biological Station |date=23 March 2010 |access-date=21 February 2011 |archive-date=13 December 2018 |archive-url=https://web.archive.org/web/20181213075347/http://www.wilds.mb.ca/taiga/tbsfaq.html |url-status=live }}</ref> The long cold winter of the far north is unsuitable for plant growth and trees must grow rapidly in the short summer season when the temperature rises and the days are long. Light is very limited under their dense cover and there may be little plant life on the forest floor, although fungi may abound.<ref>{{cite web |url=http://www.ucmp.berkeley.edu/exhibits/biomes/forests.php/#boreal |title=The forest biome: Boreal forest |publisher=University of California Museum of Paleontology |access-date=28 July 2012 |archive-date=9 August 2012 |archive-url=https://web.archive.org/web/20120809060726/http://www.ucmp.berkeley.edu/exhibits/biomes/forests.php#boreal |url-status=live }}</ref> Similar woodland is found on mountains where the altitude causes the average temperature to be lower thus reducing the length of the growing season.<ref>{{cite web |url=https://plantecology.unibas.ch/treeline_elevation/index.shtml |title=High elevation treeline research |last=Körner |first=Christian |publisher=University of Basel: Institute of Botany |access-date=28 July 2012 |archive-date=23 October 2016 |archive-url=https://web.archive.org/web/20161023055635/https://plantecology.unibas.ch/treeline_elevation/index.shtml |url-status=live }}</ref>

Where rainfall is relatively evenly spread across the seasons in temperate regions, [[temperate broadleaf and mixed forest]] typified by species like oak, beech, birch and maple is found.<ref>{{cite web |url=http://wwf.panda.org/about_our_earth/ecoregions/about/habitat_types/selecting_terrestrial_ecoregions/habitat04.cfm |title=Temperate Broadleaf and Mixed Forest Ecoregions |publisher=WWF |access-date=10 September 2014 |url-status=dead |archive-url=https://web.archive.org/web/20141006121415/http://wwf.panda.org/about_our_earth/ecoregions/about/habitat_types/selecting_terrestrial_ecoregions/habitat04.cfm |archive-date=6 October 2014}}</ref> Temperate forest is also found in the southern hemisphere, as for example in the Eastern Australia<!--sic, this is the usual form--> temperate forest, characterised by ''[[Eucalyptus]]'' forest and open acacia woodland.<ref>{{cite web |url=http://wwf.panda.org/about_our_earth/ecoregions/easternaustralia_temperate_forests.cfm |title=Eastern Australia Temperate Forest |publisher=WWF |access-date=10 September 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140910215824/http://wwf.panda.org/about_our_earth/ecoregions/easternaustralia_temperate_forests.cfm |archive-date=10 September 2014}}</ref>

In tropical regions with a [[monsoon climate|monsoon]] or monsoon-like climate, where a drier part of the year alternates with a wet period as in the [[Amazon rainforest]], different species of broad-leaved trees dominate the forest, some of them being deciduous.<ref>{{cite web |url=http://www.marietta.edu/~biol/biomes/troprain.htm |title=The tropical rain forest |work=Biomes of the World |publisher=Marietta College |access-date=28 July 2012 |archive-date=23 May 2011 |archive-url=https://web.archive.org/web/20110523222037/http://www.marietta.edu/~biol/biomes/troprain.htm |url-status=live }}</ref> In tropical regions with a drier [[savanna climate]] and insufficient rainfall to support dense forests, the canopy is not closed, and plenty of sunshine reaches the ground which is covered with grass and scrub. ''[[Acacia]]'' and [[baobab]] are well adapted to living in such areas.<ref>{{cite encyclopedia |url=http://www.britannica.com/EBchecked/topic/242157/grass-savanna |title=Grass savanna |encyclopedia=Encyclopædia Britannica |access-date=28 July 2012 |archive-date=20 November 2012 |archive-url=https://web.archive.org/web/20121120171336/http://www.britannica.com/EBchecked/topic/242157/grass-savanna |url-status=live }}</ref>