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 forming open habitats with plenty of sunlight and limited shade (se ...

grassland A grassland is an area where the vegetation is dominated by grasses ( Poaceae). However, sedge ( Cyperaceae) and rush ( Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur na ...

(i.e. grassy woodland)

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

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 grapes 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 layer consisting primarily of grasses. According to '' Britannica'', there exists four savanna forms; ''savanna woodland'' where trees and shrubs form a light canopy, ''tree savanna'' with scattered trees and shrubs, ''shrub savanna'' with distributed shrubs, and ''grass savanna'' where trees and shrubs are mostly nonexistent.Smith, Jeremy M.B.. "savanna".

Encyclopedia Britannica An encyclopedia (American English) or encyclopædia (British English) is a reference work or compendium providing summaries of knowledge either general or special to a particular field or discipline. Encyclopedias are divided into articl ...

, 5 Sep. 2016, https://www.britannica.com/science/savanna/Environment. Accessed 17 September 2022. 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 ecoregion of tropical savanna in eastern Brazil, particularly in the states of Goiás, Mato Grosso do Sul, Mato Grosso, Tocantins, Minas Gerais, and the Federal District. The core areas of the Cerrado biome are the ...

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 to 3300 trees per

hectare The hectare (; SI symbol: ha) is a non-SI 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 hectares in one square kilometre. An acre is ...

(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, stream, pond, lake, marshland, estuary, canal Canals or artificial waterways are waterways or engineered chann ...

, 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 biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...

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 United Nations' ...

and desert or

, though they're mostly a transition between desert to forest. Savanna covers approximately 20% of the Earth's land area. Unlike the

prairie Prairies are ecosystems considered part of the temperate grasslands, savannas, and shrublands biome by ecologists, based on similar temperate climates, moderate rainfall, and a composition of grasses, herbs, and shrubs, rather than trees, as the ...

s in North America and steppes in

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelago ...

, which would feature cold winters, savannahs are mostly located in areas having warm to hot climates, such as those in Africa, Australia, Thailand, South America and India.

Etymology

The word derives from the

Spanish Spanish might refer to: * Items from or related to Spain: **Spaniards are a nation and ethnic group indigenous to Spain **Spanish language, spoken in Spain and many Latin American countries **Spanish cuisine Other places * Spanish, Ontario, Can ...

''sabana'', which is itself a loanword from

Taíno The Taíno were a historic indigenous people of the Caribbean whose culture has been continued today by Taíno descendant communities and Taíno revivalist communities. At the time of European contact in the late 15th century, they were the pri ...

, which means "treeless grassland" in the

West Indies The West Indies is a subregion of North America, surrounded by the North Atlantic Ocean and the Caribbean Sea that includes 13 independent island countries and 18 dependencies and other territories in three major archipelagos: the Greate ...

. The letter ''b'' in Spanish, when positioned in the middle of a word, is pronounced almost like an English ''v;'' hence the change of

grapheme In linguistics, a grapheme is the smallest functional unit of a writing system. The word ''grapheme'' is derived and the suffix ''-eme'' by analogy with ''phoneme'' and other names of emic units. The study of graphemes is called '' graphemi ...

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 first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a co ...

'', "savannah", ''n.'' Oxford University Press (Oxford), 2012. This was equivalent in the

orthography An orthography is a set of conventions for writing a language, including norms of spelling, hyphenation, capitalization, word breaks, emphasis, and punctuation. Most transnational languages in the modern period have a writing system, and ...

of the times to ''zavana'' (see history of V). Peter Martyr reported it as the local name for the plain around Comagre, the court of the cacique Carlos in present-day

Panama Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Co ...

. 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. Guna Yala is home to the indigenous people known as the Gunas. Its capital is Gaigirgordub. It is bounded on the north by the Car ...

coast opposite Ustupo or on Point Mosquitos. These areas are now either given over to

modern Modern may refer to: History * Modern history ** Early Modern period ** Late Modern period *** 18th century *** 19th century *** 20th century ** Contemporary history * Moderns, a faction of Freemasonry that existed in the 18th century Phil ...

cropland Agricultural land is typically land ''devoted to'' agriculture, the systematic and controlled use of other forms of lifeparticularly the rearing of livestock and production of cropsto produce food for humans. It is generally synonymous with bot ...

jungle A jungle is land covered with dense forest and tangled vegetation, usually in tropical climates. Application of the term has varied greatly during the past recent century. Etymology The word ''jungle'' originates from the Sanskrit word ''ja� ...

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 systems. It was first published by German-Russian climatologist Wladimir Köppen (1846–1940) in 1884, with several later modifications by Köppen, notabl ...

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 Rivers to be excluded from mapped savanna categories. In different parts of North America, the word "savanna" has been used interchangeably with " barrens", "

", "

glade Glade may refer to: Computing * Glade Interface Designer, a GUI designer for GTK+ and GNOME Geography *Glade (geography), open area in woodland, synonym for "clearing" **Glade skiing, skiing amongst trees ;Places in the United States * Glade, Kan ...

", "grassland" and " oak opening". 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 weather in the tropics is dominated by the tropical rain belt, which moves from the northern to the southern tropics and back over the course of the year. The te ...

wildfire A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identi ...

s. In the

Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...

, e.g. in

Belize Belize (; bzj, Bileez) is a Caribbean and Central American country on the northeastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a wate ...

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

, savanna vegetation is similar from

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

and to the Caribbean. The distinction between woodland and savanna is vague and therefore the two can be combined into a single biome as both woodlands and savannas feature open-canopied trees with crowns not usually interlinking (mostly forming 25-60% cover).WOODLAND SAVANNA
Wrangle - WORLD RANGELAND LEARNING EXPERIENCE. 2022 Arizona Board of Regents. Retrieved 17 September 2022. 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. The annual rainfall ranges from to per year, with the precipitation being more common in six or eight months of the year, followed by a period of drought. Savannas may at times be classified as forests. In

climatic geomorphology Climatic geomorphology is the study of the role of climate in shaping landforms and the earth-surface processes. An approach used in climatic geomorphology is to study relict landforms to infer ancient climates. Being often concerned about past cl ...

it has been noted that many savannas occur in areas of

pediplain In geology and geomorphology a pediplain (from the Latin ''pes'', genitive case ''pedis'', meaning "foot") is an extensive plain formed by the coalescence of pediments. The processes through which pediplains forms is known as pediplanation. Th ...

s and

inselberg An inselberg or monadnock () is an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain. In Southern Africa a similar formation of granite is known as a koppie, a ...

s. It has been posited that

river incision River incision is the narrow erosion caused by a river or stream that is far from its base level. River incision is common after tectonic uplift of the landscape. Incision by multiple rivers result in a dissected landscape, for example a dissected ...

is not prominent but that rivers in savanna landscapes erode more by lateral migration. Flooding and associated sheet wash have been prosposed as dominant erosion processes in savanna plains.

Ecology

The savannas of tropical America comprises broadleaved trees such as

Curatella ''Curatella americana'', commonly known as the wild cashew tree, sambaı́ba, and the sandpaper tree, is a species of tree in the family Dilleniaceae. It is the sole accepted species in genus ''Curatella''. Description ''Curatella americana'' is ...

Byrsonima ''Byrsonima'' is one of about 75 genera in the Malpighiaceae, a family of flowering plants in the order Malpighiales. In particular in American English, they are known as locustberries (which also may refer specifically to '' Byrsonima coccolob ...

, and

Bowdichia ''Bowdichia'' is a genus of flowering plants in the legume family, Fabaceae. It belongs to the subfamily Faboideae The Faboideae are a subfamily of the flowering plant family Fabaceae or Leguminosae. An acceptable alternative name for the s ...

, with grasses such as Leersia and

Paspalum ''Paspalum'' is a genus of plants in the grass family. The group is widespread across much of Asia, Africa, Australia, and the Americas. Commonly known as paspalum, bahiagrasses, crowngrasses or dallis grasses, many of the species are tall pere ...

. Bean relative

Prosopis ''Prosopis'' is a genus of flowering plants in the family Fabaceae. It contains around 45 species of spiny trees and shrubs found in subtropical and tropical regions of the Americas, Africa, Western Asia, and South Asia. They often thrive in ari ...

is common in the Argentinian savannahs. In the East African savannas, Acacia,

Combretum ''Combretum'', the bushwillows or combretums, make up the type genus of the family Combretaceae. The genus comprises about 272 species of trees and shrubs, most of which are native to tropical and southern Africa, about 5 to Madagascar, but th ...

baobab ''Adansonia'' is a genus made up of eight species of medium-to-large deciduous trees known as baobabs ( or ). They are placed in the Malvaceae family, subfamily Bombacoideae. They are native to Madagascar, mainland Africa, and Australia.Trop ...

s, Borassus, and

Euphorbia ''Euphorbia'' is a very large and diverse genus of flowering plants, commonly called spurge, in the family Euphorbiaceae. "Euphorbia" is sometimes used in ordinary English to collectively refer to all members of Euphorbiaceae (in deference to t ...

are a common vegetation genera. Drier savannas there feature spiny shrubs and grasses, such as Andropogon,

Hyparrhenia ''Hyparrhenia'' is a genus of grasses. Many species are known commonly as thatching grass. They are mostly native to tropical Africa; some can be found in warmer areas in temperate Eurasia, Australia, and Latin America. These are annual and pere ...

, and

Themeda ''Themeda'' is a genus of plants in the grass family native to Asia, Africa, Australia, and Papuasia. There are about 18Barkworth, M. E''Themeda''.Grass Manual. Flora of North America. to 26Potdar, G. G., et al. (2003)A new species of ''Themeda'' ...

. Wetter savannas include

Brachystegia ''Brachystegia'' is a genus of tree of the subfamily Detarioideae that is native to tropical Africa. Trees of the genus are commonly known as miombo, and are dominant in the miombo woodlands of central and southern tropical Africa. The Zambezi ...

trees and

Pennisetum purpureum ''Cenchrus purpureus'', synonym ''Pennisetum purpureum'', also known as Napier grass, elephant grass or Uganda grass, is a species of perennial tropical grass native to the African grasslands. arrell, G., Simons, S. A., & Hillocks, R. J. (2002). ...

, and elephant grass type. West African savanna trees consist of

Anogeissus ''Anogeissus'' is a genus of trees in the family Combretaceae. The 10''Anogeissus''.
Fl ...

, and

Strychnos ''Strychnos'' is a genus of flowering plants, belonging to the family Loganiaceae (sometimes Strychnaceae). The genus includes about 100 accepted species of trees and lianas, and more than 200 that are as yet unresolved. The genus is widely di ...

. Indian savannas are mostly cleared, but the reserved ones feature Acacia,

Mimosa ''Mimosa'' is a genus of about 590 species of herbs and shrubs, in the mimosoid clade of the legume family Fabaceae. The generic name is derived from the Greek word (''mimos''), an "actor" or "mime", and the feminine suffix -''osa'', "resemb ...

, and

Zizyphus ''Ziziphus'' is a genus of about 40 species of spiny shrubs and small trees in the buckthorn family, Rhamnaceae, distributed in the warm-temperate, subtropical and tropical regions of the world. The leaves are alternate, entire, with three promi ...

over a grass cover comprising

Sehima ''Sehima'' is a genus of mostly Asian and African plants in the grass family.Dichanthium. The Australian savannah is abundant with sclerophyllous

evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...

vegetation, which include the

eucalyptus ''Eucalyptus'' () is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with several other genera in the tribe Eucalypteae, including '' Corymbia'', they are commonly known as e ...

, and as well as Acacia,

Bauhinia ''Bauhinia'' () is a large genus of flowering plants in the subfamily Cercidoideae and tribe Bauhinieae, in the large flowering plant family Fabaceae, with a pantropical distribution. The genus was named after the Bauhin brothers Gaspard and J ...

, Pandanus with grasses such as Heteropogon and kangaroo grass (Themeda). Animals in the African savanna generally include the giraffe, elephant, buffalo, zebra, gnu, hippopotamus, rhinoceros, and antelope, where they rely on grass and/or tree foliage to survive. In the Australian savannah, mammals in the family

Macropodidae Macropodidae is a family of marsupials that includes kangaroos, wallabies, tree-kangaroos, wallaroos, pademelons, quokkas, and several other groups. These genera are allied to the suborder Macropodiformes, containing other macropods, and ar ...

predominate, such as kangaroos and wallabies, though cattle, horses, camels, donkeys and the Asian water buffalo, among others, have been introduced by humans.

Threats

It is estimated that less than three percent of savanna ecosystems can be classified as highly intact. Reasons for savanna degradation are manifold, as outlined below.

Changes in fire management

Savannas are subject to regular

s and the ecosystem appears to be the result of human use of fire. For example, Native Americans created the

Pre-Columbian woodlands of North America Pre-Columbian woodlands of North America, consisting of a mixed woodland-grassland ecosystem, were maintained by both natural lightning fires and by Native Americans before the significant arrival of Europeans. Although decimated by widespread ...

by periodically burning where fire-resistant plants were the dominant species. Aboriginal burning appears to have been responsible for the widespread occurrence of savanna in tropical Australia and

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Australia by the wide Torr ...

, and savannas in

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...

are a result of human fire use. The maquis shrub savannas of the

Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...

region were likewise created and maintained by anthropogenic fire. These fires are usually confined to the

herbaceous layer Stratification in the field of ecology refers to the vertical layering of a habitat; the arrangement of vegetation in layers. It classifies the layers (sing. ''stratum'', pl. ''strata'') of vegetation largely according to the different heights to w ...

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 is 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 woody weed encroachment. Dehesa Pigs

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 ''Vachellia nilotica'', more commonly known as ''Acacia nilotica'', and by the vernacular names of gum arabic tree, babul, thorn mimosa, Egyptian acacia or thorny acacia, is a flowering tree in the family Fabaceae. It is native to Africa, the M ...

'') and stylo (''

Stylosanthes ''Stylosanthes'' is a genus of flowering plants in the legume family, Fabaceae and contains numerous highly important pasture and forage species. It was recently assigned to the informal monophyletic ''Pterocarpus'' clade of the Dalbergieae. The ...

'' 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

Western Sydney (Badgerys Creek) Airport site - Anton Rd

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 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 Girdling, also called ring-barking, is the complete removal of the bark (consisting of cork cambium or "phellogen", phloem, cambium and sometimes going into the xylem) from around the entire circumference of either a branch or trunk of a woody ...

, the removal of a ring of bark and 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 Tebuthiuron is a nonselective broad spectrum herbicide of the urea class. It is used in a number of herbicides manufactured by Dow AgroSciences, and is sold under several trade names, depending on the formulation. It is used to control weeds, w ...

, 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

Savanna towards the south-east from the south-west of Taita Hills Game Lodge within the Taita Hills Wildlife Sanctuary in Kenya

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 (''

''), Rubbervine (''

Cryptostegia grandiflora ''Cryptostegia grandiflora'', commonly known as rubber vine, is a woody-perennial vine that is native to south-west Madagascar. It is also a significant weed in northern Australia, sometimes regarded as the worst weed in all of Australia. It ...

''), Mesquite (''

'' spp.), Lantana (''

Lantana camara ''Lantana camara'' (common lantana) is a species of flowering plant within the verbena family ( Verbenaceae), native to the American tropics. It is a very adaptable species, which can inhabit a wide variety of ecosystems; once it has been introdu ...

'' and '' 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'' species, Buffel grass ('' Cenchrus ciliaris''), Giant rat's tail grass (''

Sporobolus pyramidalis ''Sporobolus pyramidalis'', commonly known as giant rat's tail grass, is a species of grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the ...

'')

parthenium ''Parthenium'' is a genus of North American shrubs in the tribe Heliantheae within the family Asteraceae and subfamily Asteroideae. The name ''Parthenium'' is an evolution of the Ancient Greek name παρθένιον (''parthenion''), which ref ...

('' Parthenium hysterophorus'') and stylos (''

'' 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 In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

resulting from the

greenhouse effect The greenhouse effect is a process that occurs when energy from a planet's host star goes through the planet's atmosphere and heats the planet's surface, but greenhouse gases in the atmosphere prevent some of the heat from returning directly ...

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 woody plant encroachment as a result of 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

A savanna can simply be distinguished by the open savannah, where grass prevails and trees are rare; and the wooded savannah, where the trees are densest, bordering an open woodland or forest. Specific savanna ecoregions of several different types include: * Tropical savannas are classified with tropical and subtropical grasslands and shrublands as the

tropical and subtropical grasslands, savannas, and shrublands Tropical and subtropical grasslands, savannas, and shrublands is a terrestrial biome defined by the World Wide Fund for Nature. The biome is dominated by grass and/or shrubs located in semi-arid to semi-humid climate regions of subtropical and t ...

biome. The savannas of Africa, including the

Serengeti The Serengeti ( ) ecosystem is a Geography of Africa, geographical region in Africa, spanning northern Tanzania. The protected area within the region includes approximately of land, including the Serengeti National Park and several game res ...

, famous for its wildlife, are typical of this type. The Brazilian savanna (

Cerrado The ''Cerrado'' (, ) is a vast ecoregion of tropical savanna in eastern Brazil, particularly in the states of Goiás, Mato Grosso do Sul, Mato Grosso, Tocantins, Minas Gerais, and the Federal District. The core areas of the Cerrado biome are the ...

) is also included in this category, known for its exotic and varied flora. Other examples include the

Kimberley tropical savanna The Kimberley tropical savanna is a tropical and subtropical grasslands, savannas, and shrublands ecoregion in northwestern Australia, covering portions of Western Australia and the Northern Territory south of the Timor Sea. Geography The ec ...

, Central Zambezian miombo woodlands, Guinean forest–savanna mosaic,

Cape York Peninsula tropical savanna The Cape York Peninsula tropical savanna is a tropical grasslands, savannas, and shrublands ecoregion in northern Australia. It occupies the Cape York Peninsula in Queensland, mainland Australia's northernmost point. It is coterminous with t ...

, Somali Acacia–Commiphora bushlands and thickets, Terai–Duar savanna and grasslands and the

Victoria Basin forest–savanna mosaic The Victoria Basin forest–grassland mosaic is an ecoregion that lies mostly in Uganda and extends into neighboring countries. The ecoregion is centered north and west of Lake Victoria, with an outlier on the border of Ethiopia and South Sudan.Bu ...

. * Subtropical and 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 Temperate grasslands, savannas, and shrublands is a terrestrial biome defined by the World Wide Fund for Nature. The predominant vegetation in this biome consists of grass and/or shrubs. The climate is temperate and ranges from semi-arid to sem ...

biome, that for example cover much of the plains of southeastern Australia, northern India, Southern Africa, southeastern Argentina and Uruguay. Examples of subtropical and temperate savannas include the

Southeast Australia temperate savanna The Southeast Australia temperate savanna ecoregion is a large area of grassland dotted with eucalyptus trees running north–south across central New South Wales, Australia. In Australia, the region is known as, or corresponds to, the Grey Box ...

Argentine Espinal The Espinal (NT0801) is an ecoregion of dry, thorny forest, savanna and steppe in Argentina. It has been extensively modified by large scale cattle ranching, but remnants of the original flora remain. It is threatened by the advance of the irriga ...

Pampas The Pampas (from the qu, pampa, meaning "plain") are fertile South American low grasslands that cover more than and include the Argentine provinces of Buenos Aires, La Pampa, Santa Fe, Entre Ríos, and Córdoba; all of Uruguay; and Brazi ...

Cumberland Plain Woodland The Cumberland Plain Woodland, or Western Sydney woodland,

Southern Cone Mesopotamian savanna The Southern Cone Mesopotamian savanna, also known as the Argentine Mesopotamian grasslands, is a flooded grassland ecoregion of Argentina and southern Paraguay. Setting The ecoregion covers an area of , lying west of the Uruguay River in Argent ...

New England Peppermint Grassy Woodland The New England Peppermint Grassy Woodland is a grassy-woodland community primarily situated in the New England and Northern Tablelands regions in northern New South Wales, Australia. Named after the Eucalyptus nova-anglica, it is listed as a ...

and the

Uruguayan savanna The Uruguayan savanna, also known as the Brazilian-Uruguayan savanna, is a subtropical grassland and savanna ecoregion which includes all of Uruguay and southernmost Brazil, along with portions of Argentina along the Uruguay River, In Brazil, th ...

. * Mediterranean savannas are mid-latitude savannas in

Mediterranean climate A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...

regions, with mild, rainy winters and hot, dry summers, part of the Mediterranean forests, woodlands, and scrub biome. The

oak tree An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...

savannas of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

, part of the California chaparral and woodlands ecoregion, fall into this category, including the

Temperate Grassland of South Australia The Iron-grass Natural Temperate Grassland of South Australia is a temperate grassland in the southeast of South Australia that stretches from Orroroo in the north, to Strathalbyn in the south, just straddling the eastern fringes of Adelaide' ...

, which features eucalyptuses. Parts of the

Middle East steppe The Middle East steppe ecoregion (WWF ID: PA0812) stretches in an arc from southern Jordan across Syria and Iraq to the western border of Iran. The upper plains of the Tigris and Euphrates Rivers dominate most of the ecoregion. The terrain is mo ...

and the Eastern Mediterranean conifer–sclerophyllous–broadleaf forests may also feature savannah-like landscapes. * Flooded savannas are savannas that are flooded seasonally or year-round. They are classified with flooded savannas as the

flooded grasslands and savannas Flooded grasslands and savannas is a terrestrial biome of the WWF biogeographical system, consisting of large expanses or complexes of flooded grasslands. These areas support numerous plants and animals adapted to the unique hydrologic regimes ...

biome, which occurs mostly in the tropics and subtropics. Examples include the

Everglades The Everglades is a natural region of tropical wetlands in the southern portion of the U.S. state of Florida, comprising the southern half of a large drainage basin within the Neotropical realm. The system begins near Orlando with the Kissim ...

, Mesopotamian Marshes,

Pantanal The Pantanal () is a natural region encompassing the world's largest tropical wetland area, and the world's largest flooded grasslands. It is located mostly within the Brazilian state of Mato Grosso do Sul, but it extends into Mato Grosso and ...

, Nile Delta flooded savanna, Lake Chad flooded savanna,

Zambezian flooded grasslands The Zambezian flooded grasslands is an ecoregion of southern and eastern Africa that is rich in wildlife. Setting The Zambezian flooded grasslands can be found on seasonally- or permanently-flooded lowlands in the basin of the Zambezi and neighb ...

, and the Sudd. *

Montane Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...

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 Montane grasslands and shrublands is a biome defined by the World Wildlife Fund. The biome includes high elevation grasslands and shrublands around the world. The term "montane" in the name of the biome refers to "high elevation", rather than th ...

biome. The

Bogotá savanna The Bogotá savanna is a montane savanna, located in the southwestern part of the Altiplano Cundiboyacense in the center of Colombia. The Bogotá savanna has an extent of and an average altitude of . The savanna is situated in the Eastern Ran ...

, located at an average altitude of on the

Altiplano Cundiboyacense The Altiplano Cundiboyacense () is a high plateau located in the Eastern Cordillera of the Colombian Andes covering parts of the departments of Cundinamarca and Boyacá. The altiplano corresponds to the ancient territory of the Muisca. The Alt ...

Eastern Ranges The Eastern Ranges is an Australian rules football team in the NAB League, the Victorian statewide under-18s competition. The club is a founding member of the competition (1992) and has produced several players for the Australian Football Leag ...

of the

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

, is an example of a montane savanna. The savannas of the

Angolan Scarp savanna and woodlands The Angolan Scarp savanna and woodlands is an ecoregion located on the coast of Angola, an area with a variety of habitats and rich in wildlife including many endemic birds and animals. Geography This ecoregion consists of the strip of land that ...

ecoregion are a lower altitude example, up to .Angolan Scarp savanna and woodlands
/ref> Other examples include the Al Hajar montane woodlands and the southern part of the Eastern Anatolian montane steppe.

References

External links

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

Etymology

Distribution

Ecology

Threats

Changes in fire management

Grazing and browsing animals

Tree clearing

Exotic plant species

Climate change

Savanna ecoregions

See also

References

External links