Tree

==Definition==
[[File:Tree secondary growth diagram.svg|thumb|Diagram of [[secondary growth]] in a [[eudicot]] or [[coniferous]] tree showing idealised vertical and horizontal sections. A new layer of wood is added in each growing season, thickening the stem, existing branches and roots.]]

Although "tree" is a term of common parlance, there is no universally recognised precise definition of what a tree is, either [[botany|botanically]] or in common language.<ref name="Knowable">{{Cite journal |last1=Ehrenberg |first1=Rachel |title=What makes a tree a tree? |url=https://knowablemagazine.org/article/living-world/2018/what-makes-tree-tree |journal=Knowable Magazine |doi=10.1146/knowable-033018-032602 |date=30 March 2018 |doi-access=free |access-date=21 June 2021 |archive-date=28 June 2021 |archive-url=https://web.archive.org/web/20210628151407/https://knowablemagazine.org/article/living-world/2018/what-makes-tree-tree |url-status=live }}</ref><ref name="as.miami.edu">{{cite web |url=http://www.as.miami.edu/qr/arboretum/what_is_a_tree.html |title=What is a tree? |year=2012 |work=Smartphone tour |publisher=University of Miami: John C. Gifford Arboretum |access-date=23 September 2014 |archive-url=https://web.archive.org/web/20140420004648/http://www.as.miami.edu/qr/arboretum/what_is_a_tree.html |archive-date=20 April 2014 |url-status=dead }}</ref> In its broadest sense, a tree is any plant with the general form of an elongated stem, or trunk, which supports the [[photosynthesis|photosynthetic]] leaves or branches at some distance above the ground.<ref>{{cite web |url=http://www.newton.dep.anl.gov/askasci/bot00/bot00761.htm |archive-url=https://web.archive.org/web/20131206131101/http://www.newton.dep.anl.gov/askasci/bot00/bot00761.htm |archive-date=6 December 2013 |title=Tree definition |last=Tokuhisa |first=Jim |publisher=Newton Ask a Scientist |access-date=18 December 2021 |url-status=dead }}</ref> Trees are also typically defined by height,<ref name="Gschwantner, Thomas 2009">{{cite journal | last=Gschwantner |first=Thomas |display-authors=etal | year=2009 | title=Common tree definitions for national forest inventories in Europe | journal=Silva Fennica | volume=43 | issue=2 | pages=303–321 | doi=10.14214/sf.463| doi-access=free }}</ref> with smaller plants from {{convert|0.5|to|10|m|ft|abbr=on}} being called [[shrub]]s,<ref name=treedictionary>{{cite web |url=http://www.treedictionary.com/ |title=Tree Biology Dictionary |last=Keslick |first=John A. |year=2004 |access-date=30 July 2012 |archive-date=19 March 2021 |archive-url=https://web.archive.org/web/20210319140326/http://www.treedictionary.com/ |url-status=live }}</ref> so the minimum height of a tree is only loosely defined.<ref name="Gschwantner, Thomas 2009"/> Large [[herbaceous]] plants such as [[papaya]] and bananas are trees in this broad sense.<ref name="as.miami.edu"/><ref>{{cite web |url=http://people.umass.edu/psoil370/Syllabus-files/Agroforestry_Principles.pdf |title=Agroforestry principles |last1=Martin |first1=Franklin |last2=Sherman |first2=Scott |year=2007 |work=Echo technical notes |access-date=22 September 2014 |archive-date=28 July 2013 |archive-url=https://web.archive.org/web/20130728035517/http://people.umass.edu/psoil370/Syllabus-files/Agroforestry_Principles.pdf |url-status=live }}</ref>

A commonly applied narrower definition is that a tree has a woody trunk formed by [[secondary growth]], meaning that the trunk thickens each year by growing outwards, in addition to the primary upwards growth from the [[apical meristem|growing tip]].<ref name="Gschwantner, Thomas 2009"/><ref>{{cite web |url=http://warnell.forestry.uga.edu/SERVICE/LIBRARY/index.php3?docID=171 |title=Secondary Growth Anatomy and Tree Rings |last=Coder |first=Kim D. |publisher=Warnell School of Forest Resources, University of Georgia |date=August 1999 |access-date=23 September 2014 |url-status=dead |archive-url=https://web.archive.org/web/20140908112429/http://warnell.forestry.uga.edu/SERVICE/LIBRARY/index.php3?docID=171 |archive-date=8 September 2014 }}</ref> Under such a definition, herbaceous plants such as [[Arecaceae|palms]], bananas and papayas are not considered trees regardless of their height, growth form or stem girth. Certain [[Monocotyledon|monocots]] may be considered trees under a slightly looser definition;<ref>{{cite journal | last=Gyde |first=Lund H. | year=1999 | title=A forest by any other name&nbsp;… | journal=Environmental Science & Policy | volume=2 | issue=2| pages=125–133 | doi=10.1016/s1462-9011(98)00046-x}}</ref> while the [[Yucca brevifolia|Joshua tree]], bamboos and palms do not have secondary growth and never produce true wood with growth rings,<ref name="botany.wisc.edu">{{cite web |url=http://www.botany.wisc.edu/courses/botany_400/Lecture/0pdf/25MonocotOrigin.pdf |title=Diversity and evolution of monocots |publisher=University of Wisconsin |access-date=22 September 2014 |archive-date=22 October 2016 |archive-url=https://web.archive.org/web/20161022091304/http://www.botany.wisc.edu/courses/botany_400/Lecture/0pdf/25MonocotOrigin.pdf |url-status=live }}</ref><ref name="RoddStackhouse2008">{{cite book |first1=Tony |last1=Rodd |first2=Jennifer |last2=Stackhouse |title=Trees: A Visual Guide |url=https://books.google.com/books?id=Mpsc2hsYk1YC&pg=PA112 |year=2008 |publisher=University of California Press |isbn=978-0-520-25650-7 |page=112 |access-date=28 February 2016 |archive-date=4 March 2017 |archive-url=https://web.archive.org/web/20170304154820/https://books.google.com/books?id=Mpsc2hsYk1YC&pg=PA112 |url-status=live }}</ref> they may produce "pseudo-wood" by [[lignin|lignifying]] cells formed by primary growth.<ref>{{cite web |url=http://www.bio.miami.edu/dana/dox/stem.html |title=Monocot stems |work=The stem |publisher=University of Miami |access-date=22 September 2014 |archive-date=19 March 2021 |archive-url=https://web.archive.org/web/20210319140404/http://www.bio.miami.edu/dana/dox/stem.html |url-status=live }}</ref> Tree species in the genus [[Dracaena (plant)|''Dracaena'']], despite also being monocots, do have secondary growth caused by meristem in their trunk, but it is different from the thickening meristem found in dicotyledonous trees.<ref name="Jura-Morawiec2015">{{cite journal |last=Jura-Morawiec |first=Joanna |title=Formation of amphivasal vascular bundles in ''Dracaena draco'' stem in relation to rate of cambial activity |journal=Trees |volume=29 |issue=5 |year=2015 |pages=1493–1499 |issn=0931-1890 |doi=10.1007/s00468-015-1230-3|bibcode=2015Trees..29.1493J |doi-access=free }}</ref>

Aside from structural definitions, trees are commonly defined by use; for instance, as those plants which yield lumber.<ref name="fao.org">{{cite web |url=http://www.fao.org/docrep/006/t7540e/T7540E04.htm |title=Community forestry rapid appraisal of tree and land tenure |publisher=Food and Agriculture Organisation |access-date=1 October 2014 |archive-date=17 July 2018 |archive-url=https://web.archive.org/web/20180717100135/http://www.fao.org/docrep/006/t7540e/T7540E04.htm |url-status=live }}</ref>