Poaceae or Gramineae is a large and nearly ubiquitous family of monocotyledonous flowering plants known as grasses referred to collectively as grass. Poaceae includes the cereal grasses and the grasses of natural grassland and cultivated lawns and pasture. Grasses have stems that are hollow except at the nodes and narrow alternate leaves borne in two ranks; the lower part of each leaf encloses the stem. With around 780 genera and around 12,000 species, Poaceae are the fifth-largest plant family, following the Asteraceae, Orchidaceae and Rubiaceae. Grasslands such as savannah and prairie where grasses are dominant are estimated to constitute 40.5% of the land area of the Earth, excluding Greenland and Antarctica. Grasses are an important part of the vegetation in many other habitats, including wetlands and tundra; the Poaceae are the most economically important plant family, providing staple foods from domesticated cereal crops such as maize, rice and millet as well as forage, building materials and fuel.
Though they are called "grasses", seagrasses and sedges fall outside this family. The rushes and sedges are related to the Poaceae, being members of the order Poales, but the seagrasses are members of order Alismatales; the name Poaceae was given by John Hendley Barnhart in 1895, based on the tribe Poeae described in 1814 by Robert Brown, the type genus Poa described in 1753 by Carl Linnaeus. The term is derived from the Ancient Greek πόα. Grasses include some of the most versatile plant life-forms, they became widespread toward the end of the Cretaceous period, fossilized dinosaur dung have been found containing phytoliths of a variety that include grasses that are related to modern rice and bamboo. Grasses have adapted to conditions in lush rain forests, dry deserts, cold mountains and intertidal habitats, are the most widespread plant type. A cladogram shows subfamilies and approximate species numbers in brackets: Before 2005, fossil findings indicated that grasses evolved around 55 million years ago.
Recent findings of grass-like phytoliths in Cretaceous dinosaur coprolites have pushed this date back to 66 million years ago. In 2011, revised dating of the origins of the rice tribe Oryzeae suggested a date as early as 107 to 129 Mya. Wu, You & Li described grass microfossils extracted from a specimen of the hadrosauroid dinosaur Equijubus normani from the Early Cretaceous Zhonggou Formation; the authors noted that India became separated from Antarctica, therefore all other continents at the beginning of late Aptian, so the presence of grasses in both India and China during the Cretaceous indicates that the ancestor of Indian grasses must have existed before late Aptian. Wu, You & Li considered the Barremian origin for grasses to be probableThe relationships among the three subfamilies Bambusoideae and Pooideae in the BOP clade have been resolved: Bambusoideae and Pooideae are more related to each other than to Oryzoideae; this separation occurred within the short time span of about 4 million years.
According to Lester Charles King the spread of grasses in the Late Cenozoic would have changed patterns of hillslope evolution favouring slopes that are convex upslope and concave downslope and lacking a free face were common. King argued that this was the result of more acting surface wash caused by carpets of grass which in turn would have resulted in more soil creep. Grasses may be annual or perennial herbs with the following characteristics: The stems of grasses, called culms, are cylindrical and are hollow, plugged at the nodes, where the leaves are attached. Grass leaves are nearly always alternate and distichous, have parallel veins; each leaf is differentiated into a lower sheath hugging a blade with entire margins. The leaf blades of many grasses are hardened with silica phytoliths, which discourage grazing animals. A membranous appendage or fringe of hairs called the ligule lies at the junction between sheath and blade, preventing water or insects from penetrating into the sheath. Flowers of Poaceae are characteristically arranged in each having one or more florets.
The spikelets are further grouped into spikes. The part of the spikelet that bears the florets is called the rachilla. A spikelet consists of two bracts at called glumes, followed by one or more florets. A floret consists of the flower surrounded by two bracts, one external—the lemma—and one internal—the palea; the flowers are hermaphroditic—maize being an important exception—and anemophilous or wind-pollinated, although insects play a role. The perianth is reduced to two scales, called lodicules, that expand and contract to spread the lemma and palea; this complex structure can be seen in the image on the right. The fruit of grasses is a caryopsis. A tiller is a leafy shoot other than the first shoot produced from the seed. Grass blades grow at the base of the blade and not from elongated stem tips; this low growth point evolved in response to grazing animals and allows grasses to be grazed or mown without severe damage to the plant. Three general classifications of growth habit present in g
A wetland is a distinct ecosystem, inundated by water, either permanently or seasonally, where oxygen-free processes prevail. The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants, adapted to the unique hydric soil. Wetlands play a number of functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines, support of plants and animals. Wetlands are considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. Whether any individual wetland performs these functions, the degree to which it performs them, depends on characteristics of that wetland and the lands and waters near it. Methods for assessing these functions, wetland ecological health, general wetland condition have been developed in many regions and have contributed to wetland conservation by raising public awareness of the functions and the ecosystem services some wetlands provide.
Wetlands occur on every continent. The main wetland types are swamp, marsh and fen. Many peatlands are wetlands; the water in wetlands is either brackish, or saltwater. Wetlands can be non-tidal; the largest wetlands include the Amazon River basin, the West Siberian Plain, the Pantanal in South America, the Sundarbans in the Ganges-Brahmaputra delta. The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth. Constructed wetlands are used to treat municipal and industrial wastewater as well as stormwater runoff, they may play a role in water-sensitive urban design. A patch of land that develops pools of water after a rain storm would not be considered a "wetland" though the land is wet. Wetlands have unique characteristics: they are distinguished from other water bodies or landforms based on their water level and on the types of plants that live within them. Wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants.
A more concise definition is a community composed of hydric soil and hydrophytes. Wetlands have been described as ecotones, providing a transition between dry land and water bodies. Mitsch and Gosselink write that wetlands exist "...at the interface between terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet dependent on both."In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions. A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota rooted plants, to adapt to flooding." There are four main kinds of wetlands – marsh, swamp and fen. Some experts recognize wet meadows and aquatic ecosystems as additional wetland types; the largest wetlands in the world include the swamp forests of the Amazon and the peatlands of Siberia. Under the Ramsar international wetland conservation treaty, wetlands are defined as follows: Article 1.1: "...wetlands are areas of marsh, peatland or water, whether natural or artificial, permanent or temporary, with water, static or flowing, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."
Article 2.1: " may incorporate riparian and coastal zones adjacent to the wetlands, islands or bodies of marine water deeper than six metres at low tide lying within the wetlands." Although the general definition given above applies around the world, each county and region tends to have its own definition for legal purposes. In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, that under normal circumstances do support, a prevalence of vegetation adapted for life in saturated soil conditions. Wetlands include swamps, marshes and similar areas"; this definition has been used in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and New York, have separate definitions that may differ from the federal government's. In the United States Code, the term wetland is defined "as land that has a predominance of hydric soils, is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation adapted for life in saturated soil conditions and under normal circumstances supports a prevalence of such vegetation."
Related to this legal definitions, the term "normal circumstances" are conditions expected to occur during the wet portion of the growing season under normal climatic conditions, in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Wetlands can be dry during the dry season and abnormally dry periods during the wet season, but under normal environmental conditions the soils in a wetland will be saturated to the surface or inundated such that the soils become anaerobic, those conditions will persist through the wet portion of the growing season; the most important factor producing wetlands is flooding. The duration of flooding or prolonged soil saturation by groundwater determines whether the resulting wetland has aquatic, marsh or swamp vegetation
An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy is incorporated into plant tissue. By feeding on plants and on one-another, animals play an important role in the movement of matter and energy through the system, they influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be used by plants and other microbes. Ecosystems are controlled by internal factors. External factors such as climate, the parent material which forms the soil and topography, control the overall structure of an ecosystem, but are not themselves influenced by the ecosystem. Ecosystems are dynamic entities—they are subject to periodic disturbances and are in the process of recovering from some past disturbance.
Ecosystems in similar environments that are located in different parts of the world can end up doing things differently because they have different pools of species present. Internal factors not only control ecosystem processes but are controlled by them and are subject to feedback loops. Resource inputs are controlled by external processes like climate and parent material. Resource availability within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Although humans operate within ecosystems, their cumulative effects are large enough to influence external factors like climate. Biodiversity affects ecosystem functioning, as do the processes of disturbance and succession. Ecosystems provide a variety of services upon which people depend; the term ecosystem was first used in 1935 in a publication by British ecologist Arthur Tansley. Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment.
He refined the term, describing it as "The whole system... including not only the organism-complex, but the whole complex of physical factors forming what we call the environment". Tansley regarded ecosystems not as natural units, but as "mental isolates". Tansley defined the spatial extent of ecosystems using the term ecotope. G. Evelyn Hutchinson, a limnologist, a contemporary of Tansley's, combined Charles Elton's ideas about trophic ecology with those of Russian geochemist Vladimir Vernadsky; as a result, he suggested. This would, in turn, limit the abundance of animals. Raymond Lindeman took these ideas further to suggest that the flow of energy through a lake was the primary driver of the ecosystem. Hutchinson's students, brothers Howard T. Odum and Eugene P. Odum, further developed a "systems approach" to the study of ecosystems; this allowed them to study the flow of material through ecological systems. Ecosystems are controlled both by internal factors. External factors called state factors, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem.
The most important of these is climate. Climate determines the biome. Rainfall patterns and seasonal temperatures influence photosynthesis and thereby determine the amount of water and energy available to the ecosystem. Parent material determines the nature of the soil in an ecosystem, influences the supply of mineral nutrients. Topography controls ecosystem processes by affecting things like microclimate, soil development and the movement of water through a system. For example, ecosystems can be quite different if situated in a small depression on the landscape, versus one present on an adjacent steep hillside. Other external factors that play an important role in ecosystem functioning include time and potential biota; the set of organisms that can be present in an area can significantly affect ecosystems. Ecosystems in similar environments that are located in different parts of the world can end up doing things differently because they have different pools of species present; the introduction of non-native species can cause substantial shifts in ecosystem function.
Unlike external factors, internal factors in ecosystems not only control ecosystem processes but are controlled by them. They are subject to feedback loops. While the resource inputs are controlled by external processes like climate and parent material, the availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading. Other factors like disturbance, succession or the types of species present are internal factors. Primary production is the production of organic matter from inorganic carbon sources; this occurs through photosynthesis. The energy incorporated through this process supports life on earth, while the carbon makes up much of the organic matter in living and dead biomass, soil carbon and fossil fuels, it drives the carbon cycle, which influences global climate via the greenhouse effect. Through the process of photosynthesis, plants capture energy from light and use it to combine carbon dioxide and water to produce carbohydrates and oxygen.
The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production. About half of the GPP is consumed in plant respiration; the remainder, that portion of GPP, not used up by respirati
Bracken is a genus of large, coarse ferns in the family Dennstaedtiaceae. Ferns are vascular plants that have alternating generations, large plants that produce spores and small plants that produce sex cells. Brackens are noted for their large divided leaves, they are found on all continents except Antarctica and in all environments except deserts, though their typical habitat is moorland. The genus has the widest distribution of any fern in the world. In the past, the genus was treated as having only one species, Pteridium aquilinum, but the recent trend is to subdivide it into about ten species. Like other ferns, brackens do not have seeds or fruits, but the immature fronds, known as fiddleheads, are sometimes eaten, although some are thought to be carcinogenic; the word bracken is of Old Norse origin, related to Swedish bräken and Danish bregne, both meaning fern. Evolutionarily, bracken may be considered one of the most successful ferns. Bracken, like heather, is found in moorland environments, is referred to by local populations in the north of England as'Moorland Scrub'.
It is one of the oldest ferns, with fossil records over 55 million years old having been found. The plant sends up large, triangular fronds from a wide-creeping underground rootstock, may form dense thickets; this rootstock may travel a metre or more underground between fronds. The fronds may grow up to 2.5 m long or longer with support, but are in the range of 0.6–2 m high. In cold environments, bracken is deciduous and, as it requires well-drained soil, is found growing on the sides of hills. Fern spores are contained in structures found on the underside of the leaf called sori; the linear, leaf-edge pattern of these in bracken is different from that in most other ferns, where the sori are circular and occur towards the centre of the leaf. Pteridium aquilinum is the most common species with a cosmopolitan distribution, occurring in temperate and subtropical regions throughout much of the world, it is a prolific and abundant plant in the moorlands of Great Britain, where it is limited to altitudes of below 600 metres.
It does not like poorly drained fen. It has been observed growing in soils from pH 2.8 to 8.6. Exposure to cold or high pH inhibits its growth, it causes such a problem of invading pastureland that at one time the British government had an eradication programme. Special filters have been used on some British water supplies to filter out the bracken spores. NBN distribution map for the United Kingdom Bracken is a characteristic moorland plant in the UK which over the last decades has out-competed characteristic ground-cover plants such as moor grasses, cowberry and heathers and now covers a considerable part of upland moorland. Once valued and gathered for use in animal bedding, tanning and glass making and as a fertiliser, bracken is now seen as a pernicious and opportunistic plant, taking over from the plants traditionally associated with open moorland and reducing easy access by humans, it is toxic to cattle, sheep and horses and is linked to cancers in humans. It can harbour high levels of sheep ticks.
Grazing provided some control by stock trampling, but this has ceased since the 2007 foot-and-mouth disease outbreak reduced commercial livestock production. Global climatic changes have suited bracken well and contributed to its rapid increase in land coverage. Bracken is a well-adapted pioneer plant which can colonise land with the potential to extend its area by as much as 1–3% per year; this ability to expand is at the expense of other plants and wildlife, can cause major problems for land users and managers. It colonises ground with an open vegetation structure but is slow to colonise healthy, well managed heather stands. Bracken presents a threat to biodiversity. Many species occur only on upland moorland, tied to features unique to the habitat; the loss and degradation of such areas due to the dominance of bracken has caused many species to become rare and isolated. Species Woodland fungi such as Mycena epipterygia can be found growing under the bracken canopy. Both Camarographium stephensii and Typhula quisquiliaris grow from dead bracken stems.
Bracken fern is known to produce and release allelopathic chemicals, an important factor in its ability to dominate other vegetation in regrowth after fire. Its chemical emissions, shady canopy and thick litter inhibit other plant species from establishing themselves – with the occasional exception of plants which support rare butterflies. Herb and tree seedling growth may be inhibited after bracken fern is removed because active plant toxins remain in the soil. Brackens substitute the characteristics of a woodland canopy, are important for giving shade to European plants such as common bluebell and wood anemone where the woodland does not exist; these plants are intolerant to stock trampling. Dead bracken provides a warm microclimate for development of the immature stages. Climbing corydalis, wild gladiolus and chickweed wintergreen seem to benefit from the conditions found under bracken stands; the high humidity helps mosses survive underneath, including Campylopus flexuosus, Hypnum cupressiforme, Polytrichum commune, Pseudoscelopodium purum and Rhytidiadelphus squarrosus.
Brackens of the Northern Hemisphere are used as food plants by the larvae of some Lepidoptera species including dark green fritillary, dot moth, high brown fritillary, gold swift, map-winged swift, pearl-bordered fritillary, orange swift, small angle shades, small pearl-bordered fritillary. They form an i
Endemism is the ecological state of a species being unique to a defined geographic location, such as an island, country or other defined zone, or habitat type. The extreme opposite of endemism is cosmopolitan distribution. An alternative term for a species, endemic is precinctive, which applies to species that are restricted to a defined geographical area; the word endemic is from New Latin endēmicus, from Greek ενδήμος, endēmos, "native". Endēmos is formed of en meaning "in", dēmos meaning "the people"; the term "precinctive" has been suggested by some scientists, was first used in botany by MacCaughey in 1917. It is the equivalent of "endemism". Precinction was first used by Frank and McCoy. Precinctive seems to have been coined by David Sharp when describing the Hawaiian fauna in 1900: "I use the word precinctive in the sense of'confined to the area under discussion'...'precinctive forms' means those forms that are confined to the area specified." That definition excludes artificial confinement of examples by humans in far-off botanical gardens or zoological parks.
Physical and biological factors can contribute to endemism. The orange-breasted sunbird is found in the fynbos vegetation zone of southwestern South Africa; the glacier bear is found only in limited places in Southeast Alaska. Political factors can play a part if a species is protected, or hunted, in one jurisdiction but not another. There are two subcategories of endemism: neoendemism. Paleoendemism refers to species that were widespread but are now restricted to a smaller area. Neoendemism refers to species that have arisen, such as through divergence and reproductive isolation or through hybridization and polyploidy in plants. Endemic types or species are likely to develop on geographically and biologically isolated areas such as islands and remote island groups, such as Hawaii, the Galápagos Islands, Socotra. Hydrangea hirta is an example of an endemic species found in Japan. Endemics can become endangered or extinct if their restricted habitat changes, particularly—but not only—due to human actions, including the introduction of new organisms.
There were millions of both Bermuda petrels and "Bermuda cedars" in Bermuda when it was settled at the start of the seventeenth century. By the end of the century, the petrels were thought extinct. Cedars ravaged by centuries of shipbuilding, were driven nearly to extinction in the twentieth century by the introduction of a parasite. Bermuda petrels and cedars are now rare. Principal causes of habitat degradation and loss in endemistic ecosystems include agriculture, urban growth, surface mining, mineral extraction, logging operations and slash-and-burn agriculture
In physical geography, tundra is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word тӯндар meaning "uplands", "treeless mountain tract". Tundra vegetation is composed of dwarf shrubs and grasses, lichens. Scattered trees grow in some tundra regions; the ecotone between the tundra and the forest is known as timberline. There are three regions and associated types of tundra: Arctic tundra, alpine tundra, Antarctic tundra. Arctic tundra occurs in the far Northern Hemisphere, north of the taiga belt; the word "tundra" refers only to the areas where the subsoil is permafrost, or permanently frozen soil. Permafrost tundra includes vast areas of northern Canada; the polar tundra is home to several peoples who are nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area. Arctic tundra is frozen for much of the year; the soil there is frozen from 25 to 90 cm down. Instead and sometimes rocky land can only support certain kinds of Arctic vegetation, low growing plants such as moss and lichen.
There are two main seasons and summer, in the polar tundra areas. During the winter it is cold and dark, with the average temperature around −28 °C, sometimes dipping as low as −50 °C. However, extreme cold temperatures on the tundra do not drop as low as those experienced in taiga areas further south. During the summer, temperatures rise somewhat, the top layer of seasonally-frozen soil melts, leaving the ground soggy; the tundra is covered in marshes, lakes and streams during the warm months. Daytime temperatures during the summer rise to about 12 °C but can drop to 3 °C or below freezing. Arctic tundras are sometimes the subject of habitat conservation programs. In Canada and Russia, many of these areas are protected through a national Biodiversity Action Plan. Tundra tends to be windy, with winds blowing upwards of 50–100 km/h. However, in terms of precipitation, it is desert-like, with only about 15–25 cm falling per year. Although precipitation is light, evaporation is relatively minimal. During the summer, the permafrost thaws just enough to let plants grow and reproduce, but because the ground below this is frozen, the water cannot sink any lower, so the water forms the lakes and marshes found during the summer months.
There is a natural pattern of accumulation of fuel and wildfire which varies depending on the nature of vegetation and terrain. Research in Alaska has shown fire-event return intervals that vary from 150 to 200 years, with dryer lowland areas burning more than wetter highland areas; the biodiversity of tundra is low: 1,700 species of vascular plants and only 48 species of land mammals can be found, although millions of birds migrate there each year for the marshes. There are a few fish species. There are few species with large populations. Notable animals in the Arctic tundra include reindeer, musk ox, Arctic hare, Arctic fox, snowy owl and polar bears near the ocean. Tundra is devoid of poikilotherms such as frogs or lizards. Due to the harsh climate of Arctic tundra, regions of this kind have seen little human activity though they are sometimes rich in natural resources such as petroleum, natural gas and uranium. In recent times this has begun to change in Alaska and some other parts of the world: for example, the Yamalo-Nenets Autonomous Okrug produces 90% of Russia's natural gas.
A severe threat to tundra is global warming. The melting of the permafrost in a given area on human time scales could radically change which species can survive there. Another concern is that about one third of the world's soil-bound carbon is in taiga and tundra areas; when the permafrost melts, it releases carbon in the form of carbon dioxide and methane, both of which are greenhouse gases. The effect has been observed in Alaska. In the 1970s the tundra was a carbon sink. Methane is produced when vegetation decays in wetlands; the amount of greenhouse gases which will be released under projected scenarios for global warming have not been reliably quantified by scientific studies, although a few studies were reported to be underway in 2011. It is uncertain whether the impact of increased greenhouse gases from this source will be minimal or massive. In locations where dead vegetation and peat has accumulated, there is a risk of wildfire, such as the 1,039 km2 of tundra which burned in 2007 on the north slope of the Brooks Range in Alaska.
Such events may both contribute to global warming. Antarctic tundra occurs on Antarctica and on several Antarctic and subantarctic islands, including South Georgia and the South Sandwich Islands and the Kerguelen Islands. Most of Antarctica is too cold and dry to support vegetation, most of the continent is covered by ice fields. However, some portions of the continent the Antarctic Peninsula, have areas of rocky soil that support plant life; the flora presently consists of around 300–400 lichens, 100 mosses, 25 liverworts, aro
Peat known as turf, is an accumulation of decayed vegetation or organic matter. It is unique to natural areas called peatlands, mires, moors, or muskegs; the peatland ecosystem is the most efficient carbon sink on the planet, because peatland plants capture CO2 released from the peat, maintaining an equilibrium. In natural peatlands, the "annual rate of biomass production is greater than the rate of decomposition", but it takes "thousands of years for peatlands to develop the deposits of 1.5 to 2.3 m, the average depth of the boreal peatlands". Sphagnum moss called peat moss, is one of the most common components in peat, although many other plants can contribute; the biological features of Sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed'habitat manipulation'. Soils consisting of peat are known as histosols. Peat forms in wetland conditions, where flooding obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition. Peatlands bogs, are the primary source of peat, although less-common wetlands including fens and peat swamp forests deposit peat.
Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss, ericaceous shrubs, sedges. Because organic matter accumulates over thousands of years, peat deposits provide records of past vegetation and climate by preserving plant remains, such as pollen; this allows humans to reconstruct past environments and study changes in human land use. Peat is harvested as an important source of fuel in certain parts of the world. By volume, there are about 4 trillion cubic metres of peat in the world, covering a total of around 2% of the global land area, containing about 8 billion terajoules of energy. Over time, the formation of peat is the first step in the geological formation of other fossil fuels such as coal low-grade coal such as lignite. Depending on the agency, peat is not regarded as a renewable source of energy, due to its extraction rate in industrialized countries far exceeding its slow regrowth rate of 1 mm per year, as it is reported that peat regrowth takes place only in 30-40% of peatlands.
Because of this, the UNFCCC, another organization affiliated with the United Nations classified peat as a fossil fuel. However, the Intergovernmental Panel on Climate Change has begun to classify peat as a "slowly renewable" fuel; this is the classification used by many in the peat industry. At 106 g CO2/MJ, the carbon dioxide emission intensity of peat is higher than that of coal and natural gas. Peat forms when plant material does not decay in acidic and anaerobic conditions, it is composed of wetland vegetation: principally bog plants including mosses and shrubs. As it accumulates, the peat holds water; this creates wetter conditions that allow the area of wetland to expand. Peatland features can include ponds and raised bogs. Most modern peat bogs formed 12,000 years ago in high latitudes after the glaciers retreated at the end of the last ice age. Peat accumulates at the rate of about a millimetre per year. Peat material is either hemic, or sapric. Fibric peats are the least consist of intact fibre.
Hemic peats are decomposed and sapric are the most decomposed. Phragmites peat are composed of reed grass, Phragmites australis, other grasses, it is denser than many other types of peat. Engineers may describe a soil as peat which has a high percentage of organic material; this soil is problematic because it exhibits poor consolidation properties – it cannot be compacted to serve as a stable foundation to support loads, such as roads or buildings. In a cited article and Clarke defined peatlands or mires as...the most widespread of all wetland types in the world, representing 50 to 70% of global wetlands. They cover over 3 % of the land and freshwater surface of the planet. In these ecosystems are found one third of the world’s soil carbon and 10% of global freshwater resources; these ecosystems are characterized by the unique ability to accumulate and store dead organic matter from Sphagnum and many other non-moss species, as peat, under conditions of permanent water saturation. Peatlands are adapted to the extreme conditions of high water and low oxygen content, of toxic elements and low availability of plant nutrients.
Their water chemistry varies from alkaline to acidic. Peatlands occur on all continents, from the tropical to boreal and Arctic zones from sea level to high alpine conditions. Peatlands are areas of land with formed layers of peat, they can cover around 4 million square kilometres. In Europe, peatlands extend to about 515,000 km2. About 60% of the world's wetlands are made of peat. Peat deposits are found in many places around the world, including northern Europe and North America; the North American peat deposits are principally found in the Northern United States. Some of the world's largest peatlands include the West Siberian Lowland, the Hudson Bay Lowlands, the Mackenzie River Valley. There is less peat in part because there is less land; that said, the vast Magellanic Moorland in South America is an extensive peat-dominated landscape. Peat can be found in New Zealand