canopy (biology)

{{Short description|Aboveground portion of a plant community or crop}}

{{Redirect|Overstory|the architectural feature|Clerestory|the novel by Richard Powers|The Overstory}}

File:Havelock Island, Canopy of tropical moist evergreen forest, Andaman Islands.jpg]]

File:Khao Sok primary tropical rainforest, southern Thailand.jpg

File:Giantkelp2_300.jpg – giant kelp – forming the canopy of a kelp forest]]

File:Bamboo Canopy.jpg canopy in the Western Ghats of India ]]

File: Atlanta Skyline, May 2013.jpg, Georgia ]]

In biology, the canopy is the aboveground portion of a plant cropping or crop, formed by the collection of individual plant crowns.{{Cite book|last1=Campbell|first1=G.S.|title=Plant Canopies: Their Growth, Form and Function|last2=Norman|first2=J.M.|publisher=Cambridge University Press|year=1989|isbn=978-0-521-39563-2|editor-last=Russell|editor-first=Graham|pages=1–19|chapter=The description and measurement of plant canopy structure|doi=10.1017/CBO9780511752308.002|lccn=87032902|editor-last2=Marshall|editor-first2=Bruce|editor-last3=Jarvis|editor-first3=Paul G.|editor-link3=Paul Gordon Jarvis}}{{Cite journal|last=Moffett|first=Mark W.|author-link=Mark W. Moffett|date=December 2000|title=What's "Up"? A Critical Look at the Basic Terms of Canopy Biology|journal=Biotropica|volume=32|issue=4|pages=569–596|doi=10.1646/0006-3606(2000)032[0569:WSUACL]2.0.CO;2|s2cid=45947367 }}{{Cite book|last1=Hay|first1=Robert K.M.|title=The Physiology of Crop Yield|last2=Porter|first2=John R.|publisher=Blackwell Publishing|year=2006|isbn=978-1-4051-0859-1|edition=Second|lccn=2006005216}} In forest ecology, the canopy is the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms (epiphytes, lianas, arboreal animals, etc.).{{Cite book|last=Parker|first=Geoffrey G.|title=Forest Canopies|publisher=Academic Press|year=1995|isbn=978-0124576506|editor-last=Lowman|editor-first=Margaret D.|editor-link=Margaret D. Lowman|edition=First|pages=73–106|chapter=Structure and microclimate of forest canopies|lccn=94041251|editor-last2=Nadkarni|editor-first2=Nalini M.|editor-link2=Nalini Nadkarni}} The communities that inhabit the canopy layer are thought to be involved in maintaining forest diversity, resilience, and functioning.{{Cite journal|last=Nadkarni|first=Nalini M.|date=February 1994|title=Diversity of Species and Interactions in the Upper Tree Canopy of Forest Ecosystems|url=https://academic.oup.com/icb/article/34/1/70/111781|journal=American Zoologist|volume=34|issue=1|pages=70–78|doi=10.1093/icb/34.1.70 |via=Oxford Academic|doi-access=free}} Shade trees normally have a dense canopy that blocks light from lower growing plants.

Early observations of canopies were made from the ground using binoculars or by examining fallen material. Researchers would sometimes erroneously rely on extrapolation by using more reachable samples taken from the understory. In some cases, they would use unconventional methods such as chairs suspended on vines or hot-air dirigibles, among others. Modern technology, including adapted mountaineering gear, has made canopy observation significantly easier and more accurate, allowed for longer and more collaborative work, and broaddened the scope of canopy study.{{Cite journal|last1=Lowman|first1=Margaret D.|author-link=Margaret D. Lowman|last2=Wittman|first2=Philip K.|date=1996|title=Forest Canopies: Methods, Hypotheses, and Future Directions|url=https://outonalimb-forestcanopies.com/PDFs/papers/0056.pdf|url-status=live|journal=Annual Review of Ecology, Evolution, and Systematics|volume=27|pages=55–81|doi=10.1146/annurev.ecolsys.27.1.55|jstor=2097229|archive-url=https://web.archive.org/web/20190207214156/https://outonalimb-forestcanopies.com/PDFs/papers/0056.pdf|archive-date=7 February 2019}}

Structure

File:Monkey Ladder Vine canopy.jpg canopy over a road]]

Canopy structure is the organization or spatial arrangement (three-dimensional geometry) of a plant canopy. Leaf area index, leaf area per unit ground area, is a key measure used to understand and compare plant canopies. The canopy is taller than the understory layer. The canopy holds 90% of the animals in the rainforest. Canopies can cover vast distances and appear to be unbroken when observed from an airplane. However, despite overlapping tree branches, rainforest canopy trees rarely touch each other. Rather, they are usually separated by a few feet.{{Cite web|title=The Rainforest Canopy|url=https://rainforests.mongabay.com/0401.htm|last=Butler|first=Rhett|date=30 July 2012|website=Mongabay|url-status=live|archive-url=https://web.archive.org/web/20200505223821/https://rainforests.mongabay.com/0401.htm|archive-date=5 May 2020}}

Dominant and co-dominant canopy trees form the uneven canopy layer. Canopy trees are able to photosynthesize relatively rapidly with abundant light, so it supports the majority of primary productivity in forests. The canopy layer provides protection from strong winds and storms while also intercepting sunlight and precipitation, leading to a relatively sparsely vegetated understory layer.

Forest canopies are home to unique flora and fauna not found in other layers of forests. The highest terrestrial biodiversity resides in the canopies of tropical rainforests.{{Cite journal|last1=Lowman|first1=Margaret D.|author-link=Margaret D. Lowman|last2=Moffett|first2=Mark|author-link2=Mark W. Moffett|date=March 1993|title=The ecology of tropical rain forest canopies|url=https://www.canopymeg.com/PDFs/papers/0030.pdf|url-status=live|journal=Trends in Ecology & Evolution|volume=8|issue=3|pages=104–107|doi=10.1016/0169-5347(93)90061-S|pmid=21236120|archive-url=https://web.archive.org/web/20200202043829/https://www.canopymeg.com/PDFs/papers/0030.pdf|archive-date=2 February 2020}} Many rainforest animals have evolved to live solely in the canopy and never touch the ground. The canopy of a rainforest is typically about 10 m thick, and intercepts around 95% of sunlight.{{cite web|title=Light in the Rain Forest|url=http://assoc.garden.org/courseweb/course1/week4/page5a.htm|website=garden.org|access-date=23 November 2015|archive-url=https://web.archive.org/web/20151123141518/http://assoc.garden.org/courseweb/course1/week4/page5a.htm|archive-date=23 November 2015|url-status=dead}} The canopy is below the emergent layer, a sparse layer of very tall trees, typically one or two per hectare. With an abundance of water and a near ideal temperature in rainforests, light and nutrients are two factors that limit tree growth from the understory to the canopy.

In the permaculture and forest gardening community, the canopy is the highest of seven layers.{{Cite web |date=2017-03-08 |title=The Seven Layers of a Forest |url=https://www.permaculturenews.org/2017/03/08/seven-layers-forest/ |access-date=2023-09-12 |website=The Permaculture Research Institute |language=en-US}}

Ecology

Forest canopies have unique structural and ecological complexities and are important for the forest ecosystem. They are involved in critical functions such as rainfall interception, light absorption, nutrient and energy cycling, gas exchange, and providing habitat for diverse wildlife.{{Cite book|url=https://www.worldcat.org/oclc/162129566|title=Forest canopies|date=2004|publisher=Elsevier Academic Press|others=Margaret Lowman, H. Bruce Rinker|isbn=978-0-12-457553-0|edition=2nd|location=Amsterdam|oclc=162129566}} The canopy also plays a role in modifying the internal environment of the forest by acting as a buffer for incoming light, wind, and temperature fluctuations.

The forest canopy layer supports a diverse range of flora and fauna. It has been dubbed "the last biotic frontier" as it provides a habitat that has allowed for the evolution of countless species of plants, microorganisms, invertebrates (e.g., insects), and vertebrates (e.g., birds and mammals) that are unique to the upper layer of forests.{{Citation|last1=Nadkarni|first1=Nalini M.|title=Forest Canopies, Plant Diversity|date=1 January 2013|url=https://www.sciencedirect.com/science/article/pii/B9780123847195001581|encyclopedia=Encyclopedia of Biodiversity (Second Edition)|pages=516–527|editor-last=Levin|editor-first=Simon A|place=Waltham|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-384719-5.00158-1|isbn=978-0-12-384720-1|access-date=26 February 2022|last2=Merwin|first2=Mark C.|last3=Nieder|first3=Jurgen}} Forest canopies are arguably considered some of the most species-rich environments on the planet.{{Citation|last=Erwin|first=Terry L.|title=Forest Canopies, Animal Diversity|date=1 January 2013|url=https://www.sciencedirect.com/science/article/pii/B9780123847195000575|encyclopedia=Encyclopedia of Biodiversity (Second Edition)|pages=511–515|editor-last=Levin|editor-first=Simon A|place=Waltham|publisher=Academic Press|language=en|doi=10.1016/b978-0-12-384719-5.00057-5|isbn=978-0-12-384720-1|access-date=26 February 2022}} It is believed that the communities found within the canopy layer play an essential role in the functioning of the forest, as well as maintaining diversity and ecological resilience.

= Climate regulation =

Forest canopies are significantly involved in maintaining the stability of the global climate. They are responsible for at least half of the global carbon dioxide exchange between terrestrial ecosystems and the atmosphere. Forest canopies act as carbon sinks, reducing the increase of atmospheric CO₂ caused by human activity. The destruction of forest canopies would lead to the release of carbon dioxide, resulting in an increased concentration of atmospheric CO₂. This would then contribute to the greenhouse effect, thereby causing the planet to become warmer.{{Citation|last1=Didham|first1=R. K.|title=ECOLOGY {{!}} Forest Canopies|date=1 January 2004|url=https://www.sciencedirect.com/science/article/pii/B0121451607000132|encyclopedia=Encyclopedia of Forest Sciences|pages=68–80|editor-last=Burley|editor-first=Jeffery|place=Oxford|publisher=Elsevier|language=en|doi=10.1016/b0-12-145160-7/00013-2|isbn=978-0-12-145160-8|access-date=26 February 2022|last2=Fagan|first2=L. L.}}