savanna
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A savanna or savannah is a mixed
woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest A forest is an area of land dominated by trees. Hundreds of de ...

woodland
-
grassland Grasslands are areas where the vegetation Vegetation is an assemblage of plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things t ...

grassland
ecosystem An ecosystem is a community (ecology), community of living organisms in conjunction with the nonliving components of their environment, interacting as a system. These Biotic component, biotic and abiotic components are linked together through ...
characterised by the trees being sufficiently widely spaced so that the
canopy Canopy may refer to: Plants * Canopy (biology), aboveground portion of plant community or crop (including forests) * Canopy (grape), aboveground portion of grapevine Religion and ceremonies * Baldachin or canopy of state, typically placed over an ...
does not close. The open canopy allows sufficient light to reach the ground to support an unbroken
herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground, including many perennials, and nearly all annuals and biennial Biennial means (an event) lasting for two years or occurring every two years. The related te ...
layer consisting primarily of grasses. Savannas maintain an open canopy despite a high tree density. It is often believed that savannas feature widely spaced, scattered trees. However, in many savannas, tree densities are higher and trees are more regularly spaced than in forests.Manoel Cláudio da Silva Jánior, Christopher William Fagg, Maria Cristina Felfili, Paulo Ernane Nogueira, Alba Valéria Rezende, and Jeanine Maria Felfili 2006 “Chapter 4. Phytogeography of Cerrado Sensu Stricto and Land System Zoning in Central Brazil” in “Neotropical Savannas and Seasonally Dry Forests: Plant Diversity, Biogeography, and Conservation” R. Toby Pennington, James A. Ratter (eds) 2006 CRC PressAbdullahi Jibrin 2013 “A Study of Variation in Physiognomic Characteristics of Guinea Savanna Vegetation” Environment and Natural Resources Research 3:2Erika L. Geiger, Sybil G. Gotsch, Gabriel Damasco, M. Haridasan, Augusto C. Franco & William A. Hoffmann 2011 “Distinct roles of savanna and forest tree species in regeneration under fire suppression in a Brazilian savanna” Journal of Vegetation Science 22Scholz, Fabian G.; Bucci, Sandra J.; Goldstein, Guillermo; Meinzer, Frederick C.; Franco, Augusto C.; Salazar, Ana. 2008 “Plant- and stand-level variation in biophysical and physiological traits along tree density gradients in the Cerrado”, Brazilian Journal of Plant Physiology The South American savanna types ''
cerrado The ''Cerrado'' (, ) is a vast Tropics, tropical savanna ecoregion of Brazil, particularly in the states of Goiás, Mato Grosso do Sul, Mato Grosso, Tocantins, Minas Gerais and the Federal District (Brazil), Federal District. The core areas of the ...

cerrado
sensu stricto'' and ''cerrado dense'' typically have densities of trees similar to or higher than that found in South American tropical forests, with savanna ranging from 800–3300 trees per
hectare The hectare (; SI symbol: ha) is a Non-SI units mentioned in the SI, non-SI metric system, metric unit of area equal to a square with 100-metre sides (1 hm2), or 10,000 m2, and is primarily used in the measurement of land. There are 100 h ...

hectare
(trees/ha) and adjacent forests with 800–2000 trees/ha. Similarly Guinean savanna has 129 trees/ha, compared to 103 for
riparian forest A riparian forest or riparian woodland is a forested or wooded area of land adjacent to a body of water such as a river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In so ...
, while Eastern Australian sclerophyll forests have average tree densities of approximately 100 per hectare, comparable to savannas in the same region. Savannas are also characterised by seasonal water availability, with the majority of rainfall confined to one season; they are associated with several types of
biome A biome is a collection of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared ...
s, and are frequently in a transitional zone between
forest A forest is an area of land dominated by 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 Food and Agricult ...

forest
and
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or
grassland Grasslands are areas where the vegetation Vegetation is an assemblage of plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things t ...

grassland
. Savanna covers approximately 20% of the Earth's land area.


Etymology

The word derives from the
Spanish Spanish may refer to: * Items from or related to Spain , * gl, Reino de España, * oc, Reiaume d'Espanha, , , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = , national_an ...

Spanish
''sabana'', which is itself a loanword from
Taíno The Taíno were an indigenous people of the Caribbean. At the time of European contact in the late fifteenth century, they were the principal inhabitants of most of Cuba Cuba ( , ), officially the Republic of Cuba ( es, República de Cub ...
. Letter ''b'' in Spanish is pronounced almost like an English ''v'', when positioned in the middle of a word, hence the change of
grapheme In linguistics Linguistics is the science, scientific study of language. It encompasses the analysis of every aspect of language, as well as the methods for studying and modeling them. The traditional areas of linguistic analysis include ...

grapheme
when transcribed into English. The word originally entered English as the ''Zauana'' in a description of the ''ilands of the kinges of Spayne'' from 1555.''
Oxford English Dictionary The ''Oxford English Dictionary'' (''OED'') is the principal historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a comprehensive res ...
'', "savannah", ''n.'' Oxford University Press (Oxford), 2012.
This was equivalent in the
orthography An orthography is a set of conventions for writing Writing is a medium of human communication that involves the representation of a language with written symbols. Writing systems are not themselves human languages (with the debatable excep ...
of the times to ''zavana'' (see
history of V V, or v, is the twenty-second and fifth-to-last letter in the modern English alphabet and the ISO basic Latin alphabet. Its name in English is ''vee'' (pronounced ), plural ''vees''. History The letter V comes from the Semitic letter ' ...
). Peter Martyr reported it as the local name for the plain around Comagre, the court of the
cacique A ''cacique'' (Iberian ; Latin American ; ; feminine form: ''cacica'') translates to "king" or "prince" of an indigenous group, derived from the Taíno language, Taíno word ''kasike'' for the pre-Columbian tribal chiefs in the Bahamas, the Grea ...
Carlos in present-day
Panama Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country This is a list of countries located on more than one continent A continent is one of several ...

Panama
. The accounts are inexact, but this is usually placed in present-day Madugandí or at points on the nearby
Guna Yala Guna Yala, formerly known as San Blas, is a '' comarca indígena'' (indigenous province) in northeast Panama (Official Gazette of Panama). Guna Yala is home to the indigenous people known as the Gunas. Its capital is El Porvenir. It is bounded ...
coast opposite
Ustupo Ustupo is a town A town is a human settlement. Towns are generally larger than villages and smaller than city, cities, though the criteria to distinguish between them vary considerably in different parts of the world. Origin and use ...
or on
Point Mosquitos Point Mosquitos ( es, Punta Mosquitos, links=no or ''Mosquito'') is a point Point or points may refer to: Places * Point, Lewis, a peninsula in the Outer Hebrides, Scotland * Point, Texas, a city in Rains County, Texas, United States * Point, th ...
. These areas are now either given over to
modern Modern may refer to: History *Modern history Human history, also known as world history, is the description of humanity's past. It is informed by archaeology Archaeology or archeology is the study of human activity through the recov ...
or
jungle , Malaysia File:Puerto Rico El Yunque 1.jpg, El Yunque National Forest is the only tropical rainforest in the U.S. National Forest Service A jungle is land covered with dense tropical forest, forest and tangled vegetation, usually in tropical ...

jungle
.


Distribution

Many grassy landscapes and mixed communities of trees, shrubs, and grasses were described as savanna before the middle of the 19th century, when the concept of a tropical savanna climate became established. The
Köppen climate classification The Köppen climate classification is one of the most widely used climate classification 350px, Leslie Holdridge's Life Zone Classification system is essentially a climate classification scheme. Climate classification is a way of categorizing th ...
system was strongly influenced by effects of temperature and precipitation upon tree growth, and his oversimplified assumptions resulted in a tropical savanna classification concept which resulted in it being considered as a "climatic climax" formation. The common usage meaning to describe vegetation now conflicts with a simplified yet widespread climatic concept meaning. The divergence has sometimes caused areas such as extensive savannas north and south of the Congo and
Amazon River The Amazon River (, ; es, Río Amazonas, pt, Rio Amazonas) in South America is the List of rivers by discharge, largest river by Discharge (hydrology), discharge volume of water in the world, and the disputed List of rivers by length, longest ...

Amazon River
s to be excluded from mapped savanna categories. "Barrens" has been used almost interchangeably with savanna in different parts of North America. Sometimes midwestern savanna were described as "grassland with trees". Different authors have defined the lower limits of savanna tree coverage as 5–10% and upper limits range as 25–80% of an area. Two factors common to all savanna environments are rainfall variations from year to year, and
dry season The dry season is a yearly period of low rainfall, especially in the tropics The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's su ...
wildfire A wildfire, bushfire, wildland fire or rural fire is an unplanned, unwanted, uncontrolled fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction P ...

wildfire
s. In the
Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to East and West. ''North'' ...

Americas
, e.g. in
Belize Belize () is a Caribbean country located on the northeastern coast of Central America. Belize borders Mexico to the north, Caribbean Sea to the east and Guatemala to the south. It has an area of and a population of 419,199 (2020). Its mainlan ...

Belize
,
Central America Central America ( es, América Central, , ''Centroamérica'' ) is a region of the Americas. It is bordered by Mexico to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. Central America consist ...

Central America
, savanna vegetation is similar from
Mexico Mexico ( es, México ; Nahuan languages: ), officially the United Mexican States (; EUM ), is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; ...

Mexico
to
South America South America is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered fr ...

South America
and to the
Caribbean The Caribbean (, ; es, Caribe; french: Caraïbes; ht, Karayib; also gcf, label=Antillean Creole, Kawayib; nl, Caraïben; Papiamento: ) is a region of the Americas that comprises the Caribbean Sea, its surrounding coasts, and its islands (some ...
. Over many large tropical areas, the dominant biome (forest, savanna or grassland) can not be predicted only by the climate, as historical events plays also a key role, for example, fire activity. In some areas, indeed, it is possible for there to be multiple stable biomes.


Threats


Changes in fire management

Savannas are subject to regular
wildfire A wildfire, bushfire, wildland fire or rural fire is an unplanned, unwanted, uncontrolled fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction P ...

wildfire
s and the ecosystem appears to be the result of human use of fire. For example,
Native Americans Native Americans may refer to: Ethnic groups * Indigenous peoples of the Americas, the pre-Columbian peoples of North and South America and their descendants * Native Americans in the United States * Indigenous peoples in Canada, the indigenous p ...
created the Pre-Columbian savannas of North America by periodically burning where fire-resistant plants were the dominant species. Pine barrens in scattered locations from New Jersey to coastal New England are remnants of these savannas. Aboriginal burning appears to have been responsible for the widespread occurrence of savanna in tropical Australia and New Guinea, and savannas in India are a result of human fire use. The Maquis shrubland, maquis shrub savannas of the Mediterranean Sea, Mediterranean region were likewise created and maintained by anthropogenic fire. These fires are usually confined to the herbaceous layer and do little long term damage to mature trees. However, these fires either kill or suppress tree seedlings, thus preventing the establishment of a continuous tree canopy which would prevent further grass growth. Prior to European settlement aboriginal land use practices, including fire, influenced vegetationWilson, B., S. Boulter, et al. (2000). Queensland's resources. Native Vegetation Management in Queensland. S. L. Boulter, B. A. Wilson, J. Westrupet eds. Brisbane, Department of Natural Resources . and may have maintained and modified savanna flora. It has been suggested by many authors that aboriginal burning created a structurally more open savanna landscape. Aboriginal burning certainly created a habitat mosaic that probably increased biodiversity and changed the structure of woodlands and geographic range of numerous woodland species. It has been suggested by many authors that with the removal or alteration of traditional burning regimes many savannas are being replaced by forest and shrub thickets with little herbaceous layer. The consumption of herbage by introduced grazers in savanna woodlands has led to a reduction in the amount of fuel available for burning and resulted in fewer and cooler fires.Pressland, A. J., J. R. Mills, et al. (1988). Landscape degradation in native pasture. Native pastures in Queensland their resources and management. W. H. Burrows, J. C. Scanlan and M. T. Rutherford. Queensland, Queensland Government Press . The introduction of exotic pasture legumes has also led to a reduction in the need to burn to produce a flush of green growth because legumes retain high nutrient levels throughout the year, and because fires can have a negative impact on legume populations which causes a reluctance to burn.


Grazing and browsing animals

The closed forest types such as broadleaf forests and rainforests are usually not grazed owing to the closed structure precluding grass growth, and hence offering little opportunity for grazing. In contrast the open structure of savannas allows the growth of a herbaceous layer and are commonly used for grazing domestic livestock. As a result, much of the world's savannas have undergone change as a result of grazing by sheep, goats and cattle, ranging from changes in pasture composition to Bush encroachment, woody weed encroachment. The removal of grass by grazing affects the woody plant component of woodland systems in two major ways. Grasses compete with woody plants for water in the topsoil and removal by grazing reduces this competitive effect, potentially boosting tree growth. In addition to this effect, the removal of fuel reduces both the intensity and the frequency of fires which may control woody plant species. Grazing animals can have a more direct effect on woody plants by the browsing of palatable woody species. There is evidence that unpalatable woody plants have increased under grazing in savannas. Grazing also promotes the spread of weeds in savannas by the removal or reduction of the plants which would normally compete with potential weeds and hinder establishment. In addition to this, cattle and horses are implicated in the spread of the seeds of weed species such as prickly acacia (''Acacia nilotica'') and stylo (''Stylosanthes'' species). Alterations in savanna species composition brought about by grazing can alter ecosystem function, and are exacerbated by overgrazing and poor land management practices. Introduced grazing animals can also affect soil condition through physical compaction and break-up of the soil caused by the hooves of animals and through the erosion effects caused by the removal of protective plant cover. Such effects are most likely to occur on land subjected to repeated and heavy grazing. The effects of overstocking are often worst on soils of low fertility and in low rainfall areas below 500 mm, as most soil nutrients in these areas tend to be concentrated in the surface so any movement of soils can lead to severe degradation. Alteration in soil structure and nutrient levels affects the establishment, growth and survival of plant species and in turn can lead to a change in woodland structure and composition.


Tree clearing

Large areas of Australian and South American savannas have been cleared of trees, and this clearing is continuing today. For example, until recently 480,000 Hectare, ha of savanna were cleared annually in Australia alone primarily to improve pasture production. Substantial savanna areas have been cleared of woody vegetation and much of the area that remains today is vegetation that has been disturbed by either clearing or thinning at some point in the past. Clearing is carried out by the grazing industry in an attempt to increase the quality and quantity of feed available for stock and to improve the management of livestock. The removal of trees from savanna land removes the competition for water from the grasses present, and can lead to a two to fourfold increase in pasture production, as well as improving the quality of the feed available. Since stock carrying capacity is strongly correlated with herbage yield, there can be major financial benefits from the removal of trees, such as assisting with grazing management: regions of dense tree and shrub cover harbors predators, leading to increased stock losses, for example, while woody plant cover hinders mustering in both sheep and cattle areas. A number of techniques have been employed to clear or kill woody plants in savannas. Early pastoralists used felling and girdling, the removal of a ring of Bark (botany), bark and Wood#Heartwood and sapwood, sapwood, as a means of clearing land. In the 1950s arboricides suitable for stem injection were developed. War-surplus heavy machinery was made available, and these were used for either pushing timber, or for pulling using a chain and ball strung between two machines. These two new methods of timber control, along with the introduction and widespread adoption of several new pasture grasses and legumes promoted a resurgence in tree clearing. The 1980s also saw the release of soil-applied arboricides, notably tebuthiuron, that could be utilised without cutting and injecting each individual tree. In many ways "artificial" clearing, particularly pulling, mimics the effects of fire and, in savannas adapted to regeneration after fire as most Queensland savannas are, there is a similar response to that after fire.Scanlan, J. C. (1988). Managing tree and shrub populations. Native pastures in Queensland their resources and management. W. H. Burrows, J. C. Scanlan and M. T. Rutherford. Queensland, Queensland Government Press . Tree clearing in many savanna communities, although causing a dramatic reduction in basal area and canopy cover, often leaves a high percentage of woody plants alive either as seedlings too small to be affected or as plants capable of re-sprouting from lignotubers and broken stumps. A population of woody plants equal to half or more of the original number often remains following pulling of eucalypt communities, even if all the trees over 5 metres are uprooted completely.


Exotic plant species

A number of exotic plants species have been introduced to the savannas around the world. Amongst the woody plant species are serious environmental weeds such as Prickly Acacia (''Acacia nilotica''), Rubbervine (''Cryptostegia grandiflora''), Mesquite (''Prosopis'' spp.), Lantana (''Lantana camara'' and ''Lantana montevidensis, L. montevidensis'') and Prickly Pear (''Opuntia'' spp.) A range of herbaceous species have also been introduced to these woodlands, either deliberately or accidentally including Rhodes grass and other ''Chloris (plant), Chloris'' species, Buffel grass (''Cenchrus ciliaris''), Giant rat's tail grass (''Sporobolus pyramidalis'') parthenium (''Parthenium hysterophorus'') and stylos (''Stylosanthes'' spp.) and other legumes. These introductions have the potential to significantly alter the structure and composition of savannas worldwide, and have already done so in many areas through a number of processes including altering the fire regime, increasing grazing pressure, competing with native vegetation and occupying previously vacant ecological niches. Other plant species include: white sage, spotted cactus, cotton seed, rosemary.


Climate change

Human induced climate change resulting from the greenhouse effect may result in an alteration of the structure and function of savannas. Some authors have suggested that savannas and grasslands may become even more susceptible to Bush encroachment, woody plant encroachment as a result of Global warming, greenhouse induced climate change. However, a recent case described a savanna increasing its range at the expense of forest in response to climate variation, and potential exists for similar rapid, dramatic shifts in vegetation distribution as a result of global climate change, particularly at ecotones such as savannas so often represent.


Savanna ecoregions

Savanna ecoregions are of several different types: * Tropical and subtropical savannas are classified with tropical and subtropical grasslands and shrublands as the tropical and subtropical grasslands, savannas, and shrublands biome. The savannas of Africa, including the Serengeti, famous for its wildlife, are typical of this type. The Brazilian savanna (Cerrado) is also included in this category, known for its Cerrado#Flora, exotic and varied flora. * Temperate savannas are mid-latitude savannas with wetter summers and drier winters. They are classified with temperate savannas and shrublands as the temperate grasslands, savannas, and shrublands biome, that for example cover much of the Great Plains of the United States. (See areas such as the Central forest-grasslands transition.) * Mediterranean savannas are mid-latitude savannas in Mediterranean climate regions, with mild, rainy winters and hot, dry summers, part of the Mediterranean forests, woodlands, and scrub biome. The oak tree savannas of California, part of the California chaparral and woodlands ecoregion, fall into this category. * Flooded savannas are savannas that are flooded seasonally or year-round. They are classified with flooded savannas as the flooded grasslands and savannas biome, which occurs mostly in the tropics and subtropics. * Montane savannas are mid- to high-altitude savannas, located in a few spots around the world's high mountain regions, part of the montane grasslands and shrublands biome. The Bogotá savanna, located at an average altitude of on the Altiplano Cundiboyacense, Cordillera Oriental (Colombia), Eastern Ranges of the Andes, is an example of a montane savanna. The savannas of the Angolan Scarp savanna and woodlands ecoregion are a lower altitude example, up to .Angolan Scarp savanna and woodlands
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See also

*Pampas *Pasture *Prairie *Rangeland *Steppe *Veld


References


External links


The Savanna
* * {{Authority control Ecosystems Grasslands Temperate grasslands, savannas, and shrublands Tropical and subtropical grasslands, savannas, and shrublands