Canopy (biology)

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The canopy of a forest in Sabah, Malaysia JigsawCanopy.jpg
The canopy of a forest in Sabah, Malaysia
Canopy of tropical evergreen forest, Andaman Islands Havelock Island, Canopy of tropical moist evergreen forest, Andaman Islands.jpg
Canopy of tropical evergreen forest, Andaman Islands
Canopy layers of primary tropical forest, Thailand Khao Sok primary tropical rainforest, southern Thailand.jpg
Canopy layers of primary tropical forest, Thailand
Macrocystis pyrifera - giant kelp - forming the canopy of a kelp forest Giantkelp2 300.jpg
Macrocystis pyrifera – giant kelp – forming the canopy of a kelp forest
Bamboo canopy in the Western Ghats of India Bamboo Canopy.jpg
Bamboo canopy in the Western Ghats of India
Urban canopy of Atlanta, Georgia Atlanta Skyline, May 2013.jpg
Urban canopy of Atlanta, Georgia

In biology, the canopy is the aboveground portion of a plant cropping or crop, formed by the collection of individual plant crowns. [1] [2] [3] In forest ecology, canopy refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms (epiphytes, lianas, arboreal animals, etc.). [4] The communities that inhabit the canopy layer are thought to be involved in maintaining forest diversity, resilience, and functioning. [5] Shade trees normally have a dense canopy that blocks light from lower growing plants.

Contents

Observation

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 broadened the scope of canopy study. [6]

Structure

A monkey-ladder vine canopy over a road Monkey Ladder Vine canopy.jpg
A monkey-ladder vine 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. [7]

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. [8] 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. [9] 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. [10]

Ecology

Forest canopies have unique structural and ecological complexities and are important components of the overall forest ecosystem. They are involved in critical functions such as rainfall interception, light absorption, nutrient & energy cycling, gas exchange, as well as providing habitats for a diverse range of wildlife. [11] 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. [11]

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. [12] Forest canopies are arguably considered some of the most species-rich environments on the planet. [13] It is believed that the communities found within the canopy layer play an important role in the functioning of the forest, as well as maintaining diversity and ecological resilience. [12]

Climate regulation

Forest canopies contribute to forest microclimate by controlling and buffering variations in climatic conditions. Forest canopies intercept rain and snowfall, thereby buffering the effects of precipitation on the local climate. [14] Forest canopies also buffer the effects of temperature within forests by creating vertical light gradients. [15] Variations in forest microclimate are also driven by the structure and physiology of canopy trees and epiphytes. This produces feedback loops where forest microclimate both determines and is determined by the species identity, growth traits and forest stand composition of canopy trees. [14]

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 which reduce the increase of atmospheric CO2 caused by human activity. The destruction of forest canopies would lead to the release of carbon dioxide which would result in an increased concentration of atmospheric CO2. This would then contribute to the greenhouse effect, thereby causing the planet to become warmer. [16]

Canopy interception

This section is an excerpt from Canopy interception.[ edit ]

Canopy interception is the rainfall that is intercepted by the canopy of a tree and successively evaporates from the leaves. Precipitation that is not intercepted will fall as throughfall or stemflow on the forest floor.

Many methods exist to measure canopy interception. The most often used method is by measuring rainfall above the canopy and subtract throughfall and stem flow [17] ). However, the problem with this method is that the canopy is not homogeneous, which causes difficulty in obtaining representative throughfall data.

A method employed to avoid this problem is covering forest floor with plastic sheets and collecting the throughfall. [18] [19] [20] The disadvantage of this method is that it is not suitable for long periods, because in the end the trees will dry from water shortage, and the method is also not applicable for snow events.

The method by Hancock and Crowther [21] avoided these problems by making use of the cantilever effect of branches. If leaves on a branch hold water, it becomes more heavy and will bend. By measuring the displacement, it is possible to determine the amount of intercepted water. this method was refined in 2005 by making use of strain gauges. [22] However, the disadvantages of these methods are that only information about one single branch is obtained and it would be quite laborious to measure an entire tree or forest.

See also

Related Research Articles

<span class="mw-page-title-main">Forest</span> Dense collection of trees covering a relatively large area

A forest is an ecosystem characterized by a dense community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' Food and Agriculture Organization (FAO) defines a forest as, "Land spanning more than 0.5 hectares with trees higher than 5 meters and a canopy cover of more than 10 percent, or trees able to reach these thresholds in situ. It does not include land that is predominantly under agricultural or urban use." Using this definition, Global Forest Resources Assessment 2020 found that forests covered 4.06 billion hectares, or approximately 31 percent of the world's land area in 2020.

<span class="mw-page-title-main">Rainforest</span> Type of forest with high rainfall

Rainforests are forests characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforests can be generally classified as tropical rainforests or temperate rainforests, but other types have been described.

<span class="mw-page-title-main">Understory</span> Layer of plant life growing above the shrub layer and below the canopy

In forestry and ecology, understory, or understorey, also known as underbrush or undergrowth, includes plant life growing beneath the forest canopy without penetrating it to any great extent, but above the forest floor. Only a small percentage of light penetrates the canopy so understory vegetation is generally shade-tolerant. The understory typically consists of trees stunted through lack of light, other small trees with low light requirements, saplings, shrubs, vines and undergrowth. Small trees such as holly and dogwood are understory specialists.

<span class="mw-page-title-main">Tropical and subtropical moist broadleaf forests</span> Habitat type defined by the World Wide Fund for Nature

Tropical and subtropical moist broadleaf forests (TSMF), also known as tropical moist forest, is a subtropical and tropical forest habitat type defined by the World Wide Fund for Nature.

<span class="mw-page-title-main">Temperate rainforest</span> Forests in the temperate zone

Temperate rainforests are rainforests with coniferous or broadleaf forests that occur in the temperate zone and receive heavy rain.

<span class="mw-page-title-main">Tropical rainforest</span> Forest in areas with heavy rainfall in the tropics

Tropical rainforests are dense and warm rainforests that occur in tropical rainforest climate where there is no dry season – all months have an average precipitation of at least 60 mm. True rainforests are typically found between 10 degrees north and south of the equator ; they are a subset of the tropical forest biome that occurs roughly within the 28-degree latitudes. Tropical rainforests are a type of tropical moist broadleaf forest, that includes the more extensive seasonal tropical forests.

Canopy research is the field of scientific research based upon data collected in the canopy of trees.

<span class="mw-page-title-main">Forest dynamics</span> Biotic and abiotic ecosystem influences

Forest dynamics describes the underlying physical and biological forces that shape and change a forest ecosystem. The continuous state of change in forests can be summarized with two basic elements: disturbance and succession.

Articles on forestry topics include:.

<span class="mw-page-title-main">Treefall gap</span> Ecological feature

A treefall gap is a distinguishable hole in the canopy of a forest with vertical sides extending through all levels down to an average height of 2 m (6.6 ft) above ground. These holes occur as result of a fallen tree or large limb. The ecologist who developed this definition used two meters because he believed that "a regrowth height of 2 m was sufficient" for a gap to be considered closed, but not all scientists agree. For example, Runkle believed that regrowth should be 10–20 m (33–66 ft) above the ground. Alternatively, a treefall gap is "the smallest gap [that must] be readily distinguishable amid the complexity of forest structure."

<span class="mw-page-title-main">Canopy interception</span> Rainfall that is intercepted by the canopy of a tree

Canopy interception is the rainfall that is intercepted by the canopy of a tree and successively evaporates from the leaves. Precipitation that is not intercepted will fall as throughfall or stemflow on the forest floor.

<span class="mw-page-title-main">Stemflow</span>

In hydrology, stemflow is the flow of intercepted water down the trunk or stem of a plant. Stemflow, along with throughfall, is responsible for the transferral of precipitation and nutrients from the canopy to the soil. In tropical rainforests, where this kind of flow can be substantial, erosion gullies can form at the base of the trunk. However, in more temperate climates stemflow levels are low and have little erosional power.

<span class="mw-page-title-main">Nalini Nadkarni</span> American ecologist

Nalini Nadkarni (1954) is an American forest ecologist who pioneered the study of Costa Rican rain forest canopies. Using mountain climbing equipment to make her ascent, Nadkarni first took an inventory of the canopy in 1981, followed by two more inventories in 1984. She is also known with a characteristic nickname, «the queen of the forest canopy».

<span class="mw-page-title-main">Forest floor interception</span>

Forest floor interception is the part of the (net) precipitation or throughfall that is temporarily stored in the top layer of the forest floor and successively evaporated within a few hours or days during and after the rainfall event. The forest floor can consist of bare soil, short vegetation or litter. This throughfall is especially rich in nutrients which makes its redistribution into the soil is an important factor for the ecology and water demand of surrounding vegetation. As a hydrological process it is crucial for water resource management and climate change.

Monodominance is an ecological condition in which more than 60% of the tree canopy comprises a single species of tree. Monodominant forests are quite common under conditions of extra-tropical climate types. Although monodominance is studied across different regions, most research focuses on the many prominent species in tropical forests. Connel and Lowman, originally called it single-dominance. Conventional explanations of biodiversity in tropical forests in the decades prior to Connel and Lowman's work either ignored monodominance entirely or predicted that it would not exist.

<span class="mw-page-title-main">Stratification (vegetation)</span> Vertical layering of a habitat

Stratification in the field of ecology refers to the vertical layering of a habitat; the arrangement of vegetation in layers. It classifies the layers of vegetation largely according to the different heights to which their plants grow. The individual layers are inhabited by different animal and plant communities (stratozones).

<span class="mw-page-title-main">Light gap</span> Ecological terminology

In ecology, a light gap is a break in forest canopy or similar barrier that allows young plants to grow where they would be otherwise inhibited by the lack of light reaching the seedbed. Light gaps form predominantly when a tree falls, and thus produces an opening in the forest canopy. Light gaps are important for maintaining diversity in species-rich ecosystems.

A canopy root, also known as an arboreal root, is a type of root that grows out of a tree branch underneath an epiphytic mat. These adventitious roots form in response to moist, dark, nutrient-rich conditions that are found in “canopy soils”. Canopy roots have been found in species of maple, poplar, alder, myrtle, beech, and spruce, among many others. They are structurally similar to roots found on the forest floor and likely serve a similar purpose for water and nutrient uptake, though their specific functions are still being studied.

Canopy soils, also known as arboreal soils, exist in areas of the forest canopy where branches, crevices, or some other physical feature on a tree can accumulate organic matter, such as leaves or fine branches. Eventually, this organic matter weathers into some semblance of a soil, and can reach depths of 30 cm in some temperate rainforests. Epiphytes can take root in this thin soil, which accelerates the development of the soil by adding organic material and physically breaking up material with their root system. Common epiphytes in the canopy soils in temperate rainforests include mosses, ferns, and lichens. Epiphytes on trees in the temperate zone are often ubiquitous and can cover entire trees. Some host trees house up to 6.5 tons dry weight of epiphytic biomass, which can equate to more than 4x of its own foliar mass. This massive presence means their dynamics need to be better understood in order to fully understand forest dynamics. The nutrients that become stored within canopy soils can then be utilized by the epiphytes that grow in them, and even the tree that the canopy soil is accumulating in through the growth of canopy roots. This storage allows nutrients to be more closely cycled through an ecosystem, and prevents nutrients from being washed out of the system.

<span class="mw-page-title-main">Tropical Wet Forests (US and Mexico)</span>

The Tropical Wet Forests are a Level I ecoregion of North America designated by the Commission for Environmental Cooperation (CEC) in its North American Environmental Atlas. As the CEC consists only of Mexico, the United States, and Canada, the defined ecoregion does not extend outside these countries to Central America nor the Caribbean.

References

  1. ↑ Campbell, G.S.; Norman, J.M. (1989). "The description and measurement of plant canopy structure". In Russell, Graham; Marshall, Bruce; Jarvis, Paul G. (eds.). Plant Canopies: Their Growth, Form and Function. Cambridge University Press. pp. 1–19. doi:10.1017/CBO9780511752308.002. ISBN   978-0-521-39563-2. LCCN   87032902.
  2. ↑ Moffett, Mark W. (December 2000). "What's "Up"? A Critical Look at the Basic Terms of Canopy Biology". Biotropica . 32 (4): 569–596. doi:10.1646/0006-3606(2000)032[0569:WSUACL]2.0.CO;2. S2CID   45947367.
  3. ↑ Hay, Robert K.M.; Porter, John R. (2006). The Physiology of Crop Yield (Second ed.). Blackwell Publishing. ISBN   978-1-4051-0859-1. LCCN   2006005216.
  4. ↑ Parker, Geoffrey G. (1995). "Structure and microclimate of forest canopies". In Lowman, Margaret D.; Nadkarni, Nalini M. (eds.). Forest Canopies (First ed.). Academic Press. pp. 73–106. ISBN   978-0124576506. LCCN   94041251.
  5. ↑ Nadkarni, Nalini M. (February 1994). "Diversity of Species and Interactions in the Upper Tree Canopy of Forest Ecosystems". American Zoologist. 34 (1): 70–78. doi: 10.1093/icb/34.1.70 – via Oxford Academic.
  6. ↑ Lowman, Margaret D.; Wittman, Philip K. (1996). "Forest Canopies: Methods, Hypotheses, and Future Directions" (PDF). Annual Review of Ecology, Evolution, and Systematics . 27: 55–81. doi:10.1146/annurev.ecolsys.27.1.55. JSTOR   2097229. Archived (PDF) from the original on 7 February 2019.
  7. ↑ Butler, Rhett (30 July 2012). "The Rainforest Canopy". Mongabay . Archived from the original on 5 May 2020.
  8. ↑ Lowman, Margaret D.; Moffett, Mark (March 1993). "The ecology of tropical rain forest canopies" (PDF). Trends in Ecology & Evolution . 8 (3): 104–107. doi:10.1016/0169-5347(93)90061-S. PMID   21236120. Archived (PDF) from the original on 2 February 2020.
  9. ↑ "Light in the Rain Forest". garden.org. Archived from the original on 23 November 2015. Retrieved 23 November 2015.
  10. ↑ "The Seven Layers of a Forest". The Permaculture Research Institute. 8 March 2017. Retrieved 12 September 2023.
  11. 1 2 Forest canopies. Margaret Lowman, H. Bruce Rinker (2nd ed.). Amsterdam: Elsevier Academic Press. 2004. ISBN   978-0-12-457553-0. OCLC   162129566.{{cite book}}: CS1 maint: others (link)
  12. 1 2 Nadkarni, Nalini M.; Merwin, Mark C.; Nieder, Jurgen (1 January 2013), "Forest Canopies, Plant Diversity", in Levin, Simon A (ed.), Encyclopedia of Biodiversity (Second Edition), Waltham: Academic Press, pp. 516–527, doi:10.1016/b978-0-12-384719-5.00158-1, ISBN   978-0-12-384720-1 , retrieved 26 February 2022
  13. ↑ Erwin, Terry L. (1 January 2013), "Forest Canopies, Animal Diversity", in Levin, Simon A (ed.), Encyclopedia of Biodiversity (Second Edition), Waltham: Academic Press, pp. 511–515, doi:10.1016/b978-0-12-384719-5.00057-5, ISBN   978-0-12-384720-1 , retrieved 26 February 2022
  14. 1 2 Nakamura, Akihiro; Kitching, Roger L.; Cao, Min; Creedy, Thomas J.; Fayle, Tom M.; Freiberg, Martin; Hewitt, C. N.; Itioka, Takao; Koh, Lian Pin; Ma, Keping; Malhi, Yadvinder (1 June 2017). "Forests and Their Canopies: Achievements and Horizons in Canopy Science". Trends in Ecology & Evolution. 32 (6): 438–451. doi: 10.1016/j.tree.2017.02.020 . hdl: 2440/114347 . ISSN   0169-5347. PMID   28359572.
  15. ↑ Pfeifer, Marion; Gonsamo, Alemu; Woodgate, William; Cayuela, Luis; Marshall, Andrew R.; Ledo, Alicia; Paine, Timothy C. E.; Marchant, Rob; Burt, Andrew; Calders, Kim; Courtney-Mustaphi, Colin (8 January 2018). "Tropical forest canopies and their relationships with climate and disturbance: results from a global dataset of consistent field-based measurements". Forest Ecosystems. 5 (1): 7. doi: 10.1186/s40663-017-0118-7 . hdl: 2164/9969 . ISSN   2197-5620. S2CID   31219827.
  16. ↑ Didham, R. K.; Fagan, L. L. (1 January 2004), "ECOLOGY | Forest Canopies", in Burley, Jeffery (ed.), Encyclopedia of Forest Sciences, Oxford: Elsevier, pp. 68–80, doi:10.1016/b0-12-145160-7/00013-2, ISBN   978-0-12-145160-8 , retrieved 26 February 2022
  17. ↑ Helvey, J. D., Patric, J. H., 1965. Canopy and litter interception of rainfall by hardwoods of Eastern United States. Water Resources Research 1 (2), 193–206.
  18. ↑ Shuttleworth, W. J., Gash, J. H. C., Lloyd, C. R., Moore, C. J., Roberts, J. M., et.al, 1984. Eddy correlation measurements of energy partition for Amazonian forest. Quarterly Journal of the Royal Meteorological Society 110, 1143–1162.
  19. ↑ Calder, I. R., 1986. A stochastic model of rainfall interception. Journal of Hydrology 89, 65–71.
  20. ↑ Calder, I. R., 1990. Evaporation in the uplands. John Wiley & Sons.
  21. ↑ Hancock, N. H., Crowther, J. M., 1979. A technique for the direct measurement of water storage on a forest canopy. Journal of Hydrology 41, 105–122.
  22. ↑ Huang, Y. S., Chen, S. S., Lin, T. P., 2005. Continuous monitoring of water loading of trees and canopy rainfall interception using the strain gauge method. Journal of Hydrology 311, 1–7.

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