Canopy soils

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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. [1] 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. [2] 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.

Contents

Development

Numerous factors are involved in evaluating the characteristics of a developing canopy soil. The types of plant material that accumulate on canopy soils can strongly influence the conditions that develop, including pH, moisture content, nutrient content, and nutrient availability for the soil. [3] The age of the canopy is also important to its development. Older canopies can accumulate more material and create a deeper soil. Within the soil, the organic material will further decompose in an older canopy soil, and will have less fibrous material than a younger canopy soil. Perhaps more intuitively, the height at which organic material begins to accumulate can also significantly impact the development of canopy soils. Canopy soils higher in a forest's canopy will be more exposed to the elements, resulting in a higher exposure to sunlight and wind, which could result in extreme shifts in available soil moisture.

Most epiphytes have very shallow root systems, mainly used to attach them to their host tree. Thus moisture-dependent epiphytes in shallow root systems are more sensitive to changes in moisture content, and at risk of desiccation. In contrast, canopy soils that form lower in the canopy are more likely to be sheltered from more extreme swings in light exposure and moisture content. Additionally, lower canopy soils also have a greater chance of accumulating organic matter that falls from higher neighboring trees, or from the higher regions of the tree housing the canopy soil. This allows these lower canopy soils to accumulate more organic matter and nutrients, which allows them to be more productive.

The organisms that inhabit a soil significantly influence the development and the turnover time of nutrients, and the same is true for canopy soils. Macro-organisms such as mites and maggots can consume organic material and break it down in their digestive tracts, aiding in the mixing and formation of soil. Microorganisms such as bacteria and fungi essentially serve the same purpose, but use different degradation pathways. The presence of these organisms is critical in maintaining the nutrient cycles within the soil, and make available the necessary nutrients for the growth of epiphytes and the micro-ecosystem. The microorganism community found in canopy soils has been found to be distinct, but similar to the communities found in the soil of the forest floor. [4] Generally, bacterial communities from fallen epiphytic material are quickly replaced by forest floor bacterial communities, although not completely. Also, when limbs of a host tree containing canopy soils have been severed from the host, a shift in the bacterial community within the soil can be measured. This indicates that the communities contained in the canopy have some reliance on the host tree.

Classification

Canopy soils are classified as histosols , which are composed primarily of organic material. Although they vary in depth, canopy soils commonly have a hemic layer at the very top, consisting mostly of undecomposed sphagnum moss. Their nature and history makes the soils somewhat simple, and nearly always lacking in any kind of mineral component.

Distribution and evolution

Vascular epiphytes represent in total about 9% of all vascular plants in the world, but are much more common in tropical areas. [5] This under-representation of vascular epiphyte diversity is still being disputed, but likely pertains to a few abiotic factors including cooler temperatures, moisture availability, and glacial history. The distributions of epiphytes when pertaining to the Northern and Southern hemispheres is extremely asymmetric. [6] The temperate zones in the southern hemisphere have a much greater abundance of vascular epiphytes than in the northern hemisphere, and they persist further into more polar latitudes. This suggests that abiotic factors such as temperature are far less influential than the glacial history of the region. During the Last Glacial Maximum, [7] about 27,000 years ago, much of the area now occupied by temperate rainforests in the northern hemisphere was covered by extensive ice sheets that removed all life. In contrast, temperate rainforests in the southern hemisphere remained largely ice-free. This strongly favoured ecosystems in the southern hemisphere, and allowed many more species of obligate, vascular epiphytes to evolve and occupy a particular niche. The intimate relationship that vascular epiphytes have with the formation of canopy soils means that the distributions of canopy soils follow a parallel distribution pattern, as it is the pattern of growth and decay of epiphytic growth that promotes the formation of canopy soils.

The presence of certain types of epiphytes could be considered ecosystem engineers, as they can form new canopy soils within an upper story in forest. For example, Fascicularia bicolor is a species of epiphyte in South American temperate rainforests, and belongs to a group known as trash basket epiphytes. These form extensive mats that capture falling organic matter and accumulate it, promoting the formation of canopy soils. These mats regulate the temperature and humidity of the surrounding canopy, and alter the species diversity of epiphytic growth, which should classify them as an ecosystem engineer. [8]

Related Research Articles

<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">Epiphyte</span> Non-parasitic surface organism that grows upon another plant but is not nourished by it

An epiphyte is a plant or plant-like organism that grows on the surface of another plant and derives its moisture and nutrients from the air, rain, water or from debris accumulating around it. The plants on which epiphytes grow are called phorophytes. Epiphytes take part in nutrient cycles and add to both the diversity and biomass of the ecosystem in which they occur, like any other organism. They are an important source of food for many species. Typically, the older parts of a plant will have more epiphytes growing on them. Epiphytes differ from parasites in that they grow on other plants for physical support and do not necessarily affect the host negatively. An organism that grows on another organism that is not a plant may be called an epibiont. Epiphytes are usually found in the temperate zone or in the tropics. Epiphyte species make good houseplants due to their minimal water and soil requirements. Epiphytes provide a rich and diverse habitat for other organisms including animals, fungi, bacteria, and myxomycetes.

<span class="mw-page-title-main">Tasmanian temperate rainforests</span> Terrestrial ecoregion in Tasmania, Australia

The Tasmanian temperate rain forests are a temperate broadleaf and mixed forests ecoregion in western Tasmania. The ecoregion is part of the Australasian realm, which includes Tasmania and Australia, New Zealand, New Guinea, New Caledonia, and adjacent islands.

<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 with high rainfall 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. True rainforests usually occur in tropical rainforest climates where there is no dry season – all months have an average precipitation of at least 60 mm. Seasonal tropical forests with tropical monsoon or savanna climates are sometimes included in the broader definition.

<span class="mw-page-title-main">Old-growth forest</span> Forest that has developed over a long period of time without disturbance

An old-growth forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Nations defines primary forests as naturally regenerated forests of native tree species where there are no clearly visible indications of human activity and the ecological processes are not significantly disturbed. One-third of the world's forests are primary forests. Old-growth features include diverse tree-related structures that provide diverse wildlife habitats that increases the biodiversity of the forested ecosystem. Virgin or first-growth forests are old-growth forests that have never been logged. The concept of diverse tree structure includes multi-layered canopies and canopy gaps, greatly varying tree heights and diameters, and diverse tree species and classes and sizes of woody debris.

<span class="mw-page-title-main">Sundaland heath forests</span> WWF ecoregion

The Sundaland heath forests, also known as Kerangas forest, is a type of tropical moist forest found on the island of Borneo, which is divided between Brunei, Indonesia, and Malaysia, as well as on the Indonesian islands of Belitung and Bangka, which lie to the west of Borneo.

<span class="mw-page-title-main">Forest ecology</span> Study of interactions between the biota and environment in forests.

Forest ecology is the scientific study of the interrelated patterns, processes, flora, fauna and ecosystems in forests. The management of forests is known as forestry, silviculture, and forest management. A forest ecosystem is a natural woodland unit consisting of all plants, animals, and micro-organisms in that area functioning together with all of the non-living physical (abiotic) factors of the environment.

<span class="mw-page-title-main">Canopy (biology)</span> Aboveground portion of a plant community or crop

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

<i>Myrmecodia</i> Genus of epiphytes

Myrmecodia is a genus of epiphytic myrmecophytes, native to Southeast Asia and present in Indochina, Malaysia, the Southwest Pacific, the Philippines, and extending south to Fiji and Cape York in Queensland, Australia. It is one of five ant-plant genera in the family Rubiaceae, the others being Anthorrhiza, Hydnophytum, Myrmephytum, and Squamellaria.

<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">Hemiepiphyte</span>

A hemiepiphyte is a plant that spends part of its life cycle as an epiphyte. The seeds of primary hemiepiphytes germinate in the canopy and initially live epiphytically. They send roots downward, and these roots eventually make contact with the ground. Secondary hemiepiphytes are root-climbers that begin as rooted vines growing upward from the forest floor, but later break their connection to the ground. When this happens, they may send down long roots to the ground.

<span class="mw-page-title-main">Forest floor</span> Part of the forest ecosystem

The forest floor, also called detritus or duff, is the part of a forest ecosystem that mediates between the living, aboveground portion of the forest and the mineral soil, principally composed of dead and decaying plant matter such as rotting wood and shed leaves. In some countries, like Canada, forest floor refers to L, F and H organic horizons. It hosts a wide variety of decomposers and predators, including invertebrates, fungi, algae, bacteria, and archaea.

<span class="mw-page-title-main">Plant litter</span> Dead plant material that has fallen to the ground

Plant litter is dead plant material that have fallen to the ground. This detritus or dead organic material and its constituent nutrients are added to the top layer of soil, commonly known as the litter layer or O horizon. Litter is an important factor in ecosystem dynamics, as it is indicative of ecological productivity and may be useful in predicting regional nutrient cycling and soil fertility.

<i>Igapó</i> Flooded Amazon forests in Brazil

Igapó is a word used in Brazil for blackwater-flooded forests in the Amazon biome. These forests and similar swamp forests are seasonally inundated with freshwater. They typically occur along the lower reaches of rivers and around freshwater lakes. Freshwater swamp forests are found in a range of climate zones, from boreal through temperate and subtropical to tropical. In the Amazon Basin of Brazil, a seasonally whitewater-flooded forest is known as a várzea, which is similar to igapó in many regards; the key difference between the two habitats is in the type of water that floods the forest.

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).

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.

<i>Antitrichia curtipendula</i> Species of moss

Antitrichia curtipendula is a species of feather-moss found predominantly in western North America and the western coast of Europe.

An ant garden is a mutualistic interaction between certain species of arboreal ants and various epiphytic plants. It is a structure made in the tree canopy by the ants that is filled with debris and other organic matter in which epiphytes grow. The ants benefit from this arrangement by having a stable framework on which to build their nest while the plants benefit by obtaining nutrients from the soil and from the moisture retained there.

Saprotrophic bacteria are bacteria that are typically soil-dwelling and utilize saprotrophic nutrition as their primary energy source. They are often associated with soil fungi that also use saprotrophic nutrition and both are classified as saprotrophs.

References

  1. ↑ Tejo Haristoy, Camila; Zabowski, Darlene; Nadkarni, Nalini (May 30, 2014). "Canopy Soils of Sitka Spruce and Bigleaf Maple in the Queets River Watershed, Washington". Soil Science Society of America Journal. 78 (S1): 118–124. Bibcode:2014SSASJ..78S.118H. doi:10.2136/sssaj2013.07.0300nafsc.
  2. ↑ Nadkarni, Nalini (1984). "Biomass and mineral capital of epiphytes in an Acer macrophyllum community of a temperate moist coniferous forest, Olympic Peninsula, Washington State". Canadian Journal of Botany. 62 (11): 2223–2228. doi:10.1139/b84-302.
  3. ↑ "Search | Soil Science Society of America".
  4. ↑ Dangerfield, Cody R.; Nadkarni, Nalini M.; Brazelton, William (September 6, 2017). "Canopy soil bacterial communities altered by severing host tree limbs". PeerJ. 5: e3773. doi: 10.7717/peerj.3773 . PMC   5591635 . PMID   28894646.
  5. ↑ Hoeber, Vincent; Weichgrebe, Tizian; Zotz, Gerhard (June 1, 2019). "Accidental epiphytism in the Harz Mountains, Central Europe". Journal of Vegetation Science. 30 (4): 765–775. Bibcode:2019JVegS..30..765H. doi:10.1111/jvs.12776. S2CID   191192192.
  6. ↑ Zotz, Gerhard (March 15, 2004). "Vascular epiphytes in the temperate zones–a review" (PDF). Plant Ecology. 176 (2): 173–183. doi:10.1007/s11258-004-0066-5. S2CID   38353313.
  7. ↑ Clark, Peter U.; Dyke, Arthur S.; Shakun, Jeremy D.; Carlson, Anders E.; Clark, Jorie; Wohlfarth, Barbara; Mitrovica, Jerry X.; Hostetler, Steven W.; McCabe, A. Marshall (2009). "The Last Glacial Maximum". Science. 325 (5941): 710–714. Bibcode:2009Sci...325..710C. doi:10.1126/science.1172873. PMID   19661421. S2CID   1324559. Archived from the original on 2019-12-09. Retrieved 2019-12-05.
  8. ↑ Ortega-Solísac, Gabriel; Diaz, Ivan; Mellado-Mansilla, Daniela; Telloc, Francisco; Moreno, Ricardo; Tejo, Camila (September 15, 2017). "Ecosystem engineering by Fascicularia bicolor in the canopy of the South-American temperate rainforest". Forest Ecology and Management. 400: 417–428. Bibcode:2017ForEM.400..417O. doi:10.1016/j.foreco.2017.06.020.
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