Tree

===Seeds===
{{main|Seed}}

Seeds are the primary way that trees reproduce and their seeds vary greatly in size and shape. Some of the largest seeds come from trees, but the largest tree, ''[[Sequoiadendron giganteum]]'', produces one of the smallest tree seeds.<ref name="Walker1997">{{cite book |last=Walker |first=Laurence C. |title=Forests: A Naturalist's Guide to Woodland Trees |url=https://books.google.com/books?id=LNJqY52pdSwC&pg=PA56 |year=1997 |publisher=University of Texas Press |isbn=978-0-292-79112-1 |page=56 |access-date=28 February 2016 |archive-date=4 March 2017 |archive-url=https://web.archive.org/web/20170304153834/https://books.google.com/books?id=LNJqY52pdSwC&pg=PA56 |url-status=live }}</ref> The great diversity in tree fruits and seeds reflects the many different ways that tree species have evolved to [[Seed dispersal|disperse]] their offspring.

[[File:Samara olmo frassino acero.png|thumb|left|Wind dispersed seed of elm (''[[Ulmus]]''), ash (''[[Fraxinus]]'') and maple (''[[Acer (plant)|Acer]]'')]]

For a tree seedling to grow into an adult tree it needs light. If seeds only fell straight to the ground, competition among the concentrated saplings and the shade of the parent would likely prevent it from flourishing. Many seeds such as [[birch]] are small and have papery wings to aid dispersal by the wind. [[Ash (Fraxinus)|Ash]] trees and [[maple]]s have larger seeds with blade shaped wings which spiral down to the ground when released. The [[Ceiba pentandra|kapok]] tree has cottony threads to catch the breeze.<ref name=Dispersal>{{cite web |url=http://www.vtaide.com/png/seed-dispersion.htm |title=How seeds are dispersed |last1=Meng |first1=Alan |author2=Meng, Hui |work=Interactive Assessment Worksheets |access-date=23 July 2012 |archive-date=5 August 2012 |archive-url=https://web.archive.org/web/20120805115217/http://www.vtaide.com/png/seed-dispersion.htm |url-status=live }}</ref>

The seeds of conifers, the largest group of gymnosperms, are enclosed in a cone and most species have seeds that are light and papery that can be blown considerable distances once free from the cone.<ref name="EvertEichhorn2004">{{cite book |last1=Evert |first1=Ray F. |author2=Eichhorn, Susan E. |title=Biology of Plants |url=https://books.google.com/books?id=8tz2aB1-jb4C&pg=PA422 |year=2004 |publisher=Macmillan |isbn=978-0-7167-1007-3 |page=422 |access-date=28 February 2016 |archive-date=4 March 2017 |archive-url=https://web.archive.org/web/20170304154119/https://books.google.com/books?id=8tz2aB1-jb4C&pg=PA422 |url-status=live }}</ref> Sometimes the seed remains in the cone for years waiting for a trigger event to liberate it. Fire stimulates release and germination of seeds of the [[jack pine]], and also enriches the forest floor with wood ash and removes competing vegetation.<ref>{{cite web |url=http://www.zephyrus.co.uk/firedispersal.html |title=Fire |last1=Parkin |first1=Dave |author2=Parkin, Marilyn |work=How do the seeds disperse to form new plants? |publisher=Zephyrus |access-date=23 July 2012 |archive-date=22 June 2012 |archive-url=https://web.archive.org/web/20120622181841/http://www.zephyrus.co.uk/firedispersal.html |url-status=live }}</ref> Similarly, a number of angiosperms including ''[[Acacia cyclops]]'' and ''[[Acacia mangium]]'' have seeds that germinate better after exposure to high temperatures.<ref name="BaskinBaskin2001">{{cite book |author1=Baskin, Carol C. |author2=Baskin, Jerry M. |title=Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination |url=https://books.google.com/books?id=uGJL_Ys6wlQC&pg=PA121 |year=2001 |publisher=Elsevier |isbn=978-0-12-080263-0 |pages=121, 260 |access-date=28 February 2016 |archive-date=22 December 2016 |archive-url=https://web.archive.org/web/20161222054555/https://books.google.com/books?id=uGJL_Ys6wlQC&pg=PA121 |url-status=live }}</ref>

The [[Delonix regia|flame tree]] ''Delonix regia'' does not rely on fire but shoots its seeds through the air when the two sides of its long pods crack apart explosively on drying.<ref name=Dispersal/> The miniature cone-like catkins of [[alder]] trees produce seeds that contain small droplets of oil that help disperse the seeds on the surface of water. Mangroves often grow in water and some species have [[propagule]]s, which are buoyant fruits with seeds that start germinating before becoming detached from the parent tree.<ref name="BarbourBillings1999">{{cite book |author1=Barbour, Michael G. |author2=Billings, William Dwight |title=North American Terrestrial Vegetation |url=https://books.google.com/books?id=Ra2QzAh9xdIC&pg=PA528 |year=1999 |publisher=Cambridge University Press |isbn=978-0-521-55986-7 |page=528 |access-date=28 February 2016 |archive-date=22 December 2016 |archive-url=https://web.archive.org/web/20161222052706/https://books.google.com/books?id=Ra2QzAh9xdIC&pg=PA528 |url-status=live }}</ref><ref>{{cite web |url=http://www.naturefoundationsxm.org/education/mangroves/the_white_mangrove.htm |title=The White Mangrove |publisher=Nature Foundation, St. Maarten |author=van der Neut, Marcus |work=naturefoundationsxm.org |url-status=dead |archive-url=https://web.archive.org/web/20120125214433/http://www.naturefoundationsxm.org/education/mangroves/the_white_mangrove.htm |archive-date=25 January 2012 }}</ref> These float on the water and may become lodged on emerging mudbanks and successfully take root.<ref name=Dispersal/>

[[File:Gebarsten bolster van een paardenkastanje (Aesculus) 20-09-2020 (d.j.b.) 01.jpg|thumb|Cracked [[Thorns, spines, and prickles|thorny]] skin of a [[Aesculus tree]] seed|upright]]
Other seeds, such as apple pips and plum stones, have fleshy receptacles and smaller fruits like [[Crataegus|hawthorns]] have seeds enclosed in edible tissue; animals including mammals and birds eat the fruits and either discard the seeds, or swallow them so they pass through the gut to be deposited in the animal's droppings well away from the parent tree. The germination of some seeds is improved when they are processed in this way.<ref>{{cite web |url=http://www.webpages.uidaho.edu/range556/appl_behave/projects/seed_dispersal.html |title=Seed Dispersal by Animals: Behavior Matters |author=Yang, Suann |work=BEHAVE: Behavioral Education for Human, Animal, Vegetation and Ecosystem Management |access-date=23 July 2012 |archive-date=9 December 2013 |archive-url=https://web.archive.org/web/20131209043548/http://www.webpages.uidaho.edu/range556/appl_behave/projects/seed_dispersal.html |url-status=live }}</ref> [[Nut (fruit)|Nuts]] may be gathered by animals such as squirrels that [[hoarding (animal behavior)|cache]] any not immediately consumed.<ref name="LeveySilva2002">{{cite book |author1=Levey, Douglas J. |author2=Silva, Wesley R. |author3=Galetti, Mauro |title=Seed Dispersal and Frugivory: Ecology, Evolution and Conservation |url=https://books.google.com/books?id=sU7213gPmDMC&pg=PA206 |year=2002 |publisher=CABI |isbn=978-0-85199-525-0 |page=206 |access-date=28 February 2016 |archive-date=4 March 2017 |archive-url=https://web.archive.org/web/20170304160055/https://books.google.com/books?id=sU7213gPmDMC&pg=PA206 |url-status=live }}</ref> Many of these caches are never revisited, the nut-casing softens with rain and frost, and the seed germinates in the spring.<ref>{{cite journal |author1=Ruxton, Graeme D. |author1-link=Graeme Ruxton |author2=Schaefer, H. Martin |year=2012 |title=The conservation physiology of seed dispersal | journal=Philosophical Transactions of the Royal Society | volume=367 | issue=1596 | pages=1708–1718 | doi=10.1098/rstb.2012.0001 |pmid=22566677 |pmc=3350653 |doi-access=free}}</ref> Pine cones may similarly be hoarded by [[red squirrel]]s, and [[grizzly bear]]s may help to disperse the seed by raiding squirrel caches.<ref>{{cite web |url=http://www.webpages.uidaho.edu/range556/Appl_BEHAVE/projects/whitebark_pine.html |title=Whitebark Pine Seeds, Red Squirrels, and Grizzly Bears: An Interconnected Relationship |author=Sager, Kim |work=BEHAVE: Behavioral Education for Human, Animal, Vegetation and Ecosystem Management |access-date=23 July 2012 |archive-date=9 December 2013 |archive-url=https://web.archive.org/web/20131209043552/http://www.webpages.uidaho.edu/range556/Appl_BEHAVE/projects/whitebark_pine.html |url-status=live }}</ref>

The single extant species of Ginkgophyta (''Ginkgo biloba'') has fleshy seeds produced at the ends of short branches on female trees,<ref>{{cite web |url=http://faculty.unlv.edu/landau/gymnosperms.htm |title=Gymnosperms |work=unlv.edu |access-date=27 September 2012 |archive-date=9 October 2012 |archive-url=https://web.archive.org/web/20121009024559/http://faculty.unlv.edu/landau/gymnosperms.htm |url-status=live }}</ref> and ''[[Gnetum]]'', a tropical and subtropical group of gymnosperms produce seeds at the tip of a shoot axis.<ref name="BhatnagarMoitra1996">{{cite book |author1=Bhatnagar, S. P. |author2=Moitra, Alok |title=Gymnosperms |url=https://books.google.com/books?id=4dvyNckni8wC&pg=PA371 |year=1996 |publisher=New Age International |isbn=978-81-224-0792-1 |page=371 |access-date=28 February 2016 |archive-date=4 March 2017 |archive-url=https://web.archive.org/web/20170304152805/https://books.google.com/books?id=4dvyNckni8wC&pg=PA371 |url-status=live }}</ref>