Skip to main content
Select Source:

Savanna

Savanna

Grass-dominated ecosystems that contain a significant number of widely spaced trees are termed savannas. Trees may make up as little as 5 percent or as much as 30 percent of the cover of all plants in savannas, but grasses and grasslike plants form a continuous ground cover. Originally, savanna was a term used to describe primarily tropical and subtropical grasslands, which usually have more woody plants than temperate grasslands. These tropical and subtropical savannas occupy large land areas. Almost 65 percent of Africa is covered by savanna, much of the northern region of Australia has savanna vegetation and South America has extensive savannas. Worldwide, estimated land cover by savanna is nearly 20 percent.

Savannas may be a product of climatic factors, they may result from unique soil types, or they may be narrow to broad transitional zones between forests and grasslands. Fire and periods of water limitation are present in all savannas whether they occur in the tropics or in temperate zones.

Tropical and Subtropical Savannas

The extensive savannas of Africa, South America (locally known as cerrado) and Australia are primarily a result of either the climate or unique soil characteristics. Climatically derived savannas are warm all year but have distinct wet and dry (winter) seasons with annual rainfall varying widely from 30 to more than 100 centimeters of rainfall. What is critical about these climates is that during the dry season, rainfall amounts are very low. It is during these dry periods that the grasses are dormant and the trees experience water stress. Fires are also common at this time because the fine, dry fuel (dead foliage) that the grasses produce is very flammable. This allows fires, started by lightning or humans, to start easily and spread quickly. This combination of water stress and fire keeps the tree density low and distinguishes savanna from the adjacent forest.

Other savannas occur in areas where there are unique soil conditions. Although most tropical and subtropical savanna soils are poor in nutrients, some also have a hard crust or barrier at some depth in the soil. This crust separates the shallow soil layer that the grasses rely on for water, and which dries during periods of low rainfall, from the deeper soil layers that may retain moisture all year. Trees in these savannas are located where cracks in the crust occur. In these places the roots of trees can access this deep soil water. Such savannas are referred to as edaphic (related to the soil) savannas.

Savannas as Transitional Zones

Savannas in both tropical and temperate zones may occur along the edge of forests where the dominant vegetation shifts from trees to grasses. This tension zone (also called an ecotone) between forest and grassland may be relatively narrow or 50 to more than 100 kilometers wide. These savannas usually occur where annual rainfall is not quite high enough to support a closed forest and where fire is common. In North America, the aspen parkland of Canada is an example of a temperate savanna and in the United States there are the oak savannas that extend from Minnesota to Texas. Historically, the region occupied by oak savanna moved eastward in periods of aridity and with frequent fire. In contrast, with fire suppression these savannas may be converted to closed canopy forest. Much of the original extent of North American savanna was found on deep fertile soils, but greater than 99 percent has been lost because the land was so valuable for row crop agriculture.

Savannas and Biodiversity

Savannas contain a mixture of forest and grassland species, as well as some species unique to this ecosystem type. Because of this they are important zones of high biodiversity for both plants and animals. In North America, oak trees embedded in tallgrass prairie vegetation are joined by species specifically adapted to partial shade and frequent fire. In Africa and Australia, thorny acacia, eucalyptus, and baobab trees are scattered among the grasses. Savanna grasses are well adapted to fire because their buds are protected below ground. Like the grasses, some mature savanna tree species are resistant to fire, particularly compared to other forest species. Many savanna trees (such as the oaks) have thick insulating bark that protects the inner growing layers of the tree from fire. Others, such as the baobab tree in Africa, can store tremendous amounts of water in their bark and trunk, protecting them from both fire and drought. Other savanna trees are capable of resprouting vigorously after fire. Despite these adaptations, frequent fire decreases the density of trees in most savannas, with tree seedlings especially susceptible to fire.

Savannas support a diverse array of herbivores , especially so in the African savannas. Grassland grazers such as zebras and wildebeest are found with herbivores that feed on trees, such as giraffes and elephants. Elephants have been termed a keystone species of African savannas for the role they play in determining the density of trees. When elephant populations are low, acacia trees and shrubs may become so dense that the grasses are shaded out and grassland species disappear. Conversely, if elephant populations are too high, the trees may disappear along with those species that depend on woody plants for food and shelter. Another group of organisms that is particularly notable in tropical savannas for their diversity and numbers, if not their individual size, are the termites. Conspicuous above-ground termite mounds are present in Australian and African savannas, but most termites live underground without building mounds. Termites fill a very important role as one of the major decomposers in savannas. As much as 90 percent of the grass biomass that is decomposed in some savannas can be attributed to termites. Thus, these organisms are valuable for making nutrients available to plants.

Savanna Management and Conservation

Most of the larger savannas in tropical and subtropical regions are grazed by livestock. Fire is used as a management tool to keep the density of trees low and stimulate the productivity of the grasses. Savannas can produce abundant plant biomass for grazers in regions with high rainfall, but savannas in the driest regions and with the most nutrient-poor soils can support only a modest number of livestock. In Africa, human-induced shifts in the populations of large native herbivores (elephants) have altered the density of trees in some savannas, and conservation programs for these species must also take into account their effect on other species as well as the savanna vegetation.

Interest in conserving and restoring savanna ecosystems is also great in North America, where the greatest proportion of the original savanna ecosystems has been lost. Controlled fire and even mechanical removal of woody species is typically used in areas where dense shrubs and tree seedlings have displaced the grasses.

see also Biome; Fabaceae; Grasses; Grasslands.

Alan K. Knapp

Bibliography

Archibold, O. W. Ecology of World Vegetation. New York: Chapman & Hall, 1995.

Barbour, Michael G., Jack H. Burk, Wanna D. Pitts, Frank S. Gilliam, and Mark W. Schwartz. Terrestrial Plant Ecology. Menlo Park, CA: Addison Wesley Longman, Inc., 1998.

Cole, M. M. The Savannas: Biogeography and Geobotany. New York: Academic Press, 1986.

Daubenmire, Rexford. Plant Geography. New York: Academic Press, 1978.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Savanna." Plant Sciences. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Savanna." Plant Sciences. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/news-wires-white-papers-and-books/savanna

"Savanna." Plant Sciences. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/news-wires-white-papers-and-books/savanna

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

savanna

savanna or savannah (both: səvăn´ə), tropical or subtropical grassland lying on the margin of the trade wind belts. The climate of a savanna is characterized by a rainy period during the summer when the area is covered by grasses, and by a dry winter when the grasses wither. Savannas near the equatorial belt, e.g., in Nigeria, support clumps of trees. The most extensive savannas—all important pasture lands—are in Africa; others include the llanos and the campos of South America.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"savanna." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"savanna." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/savanna

"savanna." The Columbia Encyclopedia, 6th ed.. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/savanna

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

savannah

savannah An extensive tropical vegetation dominated by grasses with varying admixtures of tall bushes and/or trees in open formation. Savannah occurs in diverse tropical environments, although most experience a dry season. Much savannah is no doubt climatic climax, although extensive tracts are anthropogenic fire climaxes and others are edaphically controlled; it is generally difficult to distinguish one type from the other.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"savannah." A Dictionary of Ecology. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"savannah." A Dictionary of Ecology. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/savannah

"savannah." A Dictionary of Ecology. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/savannah

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

savannah

savannah An extensive tropical vegetation dominated by grasses with varying admixtures of tall bushes and/or trees in open formation. Savannah occurs in diverse tropical environments, although most experience a dry season. Much savannah is no doubt climatic climax, although extensive tracts are anthropogenic fire climaxes, and it is generally difficult to distinguish one type from the other.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"savannah." A Dictionary of Plant Sciences. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"savannah." A Dictionary of Plant Sciences. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/savannah-0

"savannah." A Dictionary of Plant Sciences. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/savannah-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

savanna

savanna Plain with coarse grass and scattered tree growth, particularly the wide plains of tropical and subtropical regions. An extensive example is the savanna of the East African tableland.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"savanna." World Encyclopedia. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"savanna." World Encyclopedia. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/savanna-0

"savanna." World Encyclopedia. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/savanna-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

savanna

sa·van·na / səˈvanə/ (also sa·van·nah) • n. a grassy plain in tropical and subtropical regions, with few trees.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"savanna." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"savanna." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/savanna

"savanna." The Oxford Pocket Dictionary of Current English. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/savanna

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

savanna

savanna See grassland.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"savanna." A Dictionary of Biology. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"savanna." A Dictionary of Biology. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/savanna

"savanna." A Dictionary of Biology. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/savanna

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Savanna

Savanna


A savanna is a dry grassland with scattered trees. Most ecologists agree that a characteristic savanna has an open or sparse canopy with 1025% tree cover, a dominant ground cover of annual and perennial grasses, and less than 20 in (50 cm) of rainfall per year. Greatly varied environments, from open deciduous forests and parklands, to dry, thorny scrub, to nearly pure grasslands , can be considered savannas. At their margins these communities merge, more or less gradually, with drier prairies or with denser, taller forests. Savannas occur at both tropical and temperate latitudes and on all continents except Antarctica . Most often savannas occupy relatively level, or sometimes rolling, terrain. Characteristic savanna soils are dry, well-developed ultisols, oxisols, and alfisols, usually basic and sometimes lateritic. These soils develop under savannas' strongly seasonal rainfall regimes, with extended dry periods that can last up to 10 months. Under natural conditions an abundance of insect, bird, reptile, and mammal species populate the land.

Savanna shrubs and trees have leathery, sometimes thorny, and often small leaves that resist drought , heat, and intense sunshine normally found in this environment . Savanna grasses are likewise thin and tough, frequently growing in clumps, with seasonal stalks rising from longerlived underground roots. Many of these plants have oily or resinous leaves that burn intensely and quickly in a fire. Extensive root systems allow most savanna plants to exploit moisture and nutrients in a large volume of soil . Most savanna trees stand less than 32 ft (10 m) tall; some have a wide spreading canopy while others have a narrower, more vertical shape. Characteristic trees of African and South American savannas include acacias and miombo (Brachystegia spp.). Australian savannas share the African baobab, but are dominated by eucalyptus species. Oaks characterize many European savannas, while in North America oaks, pines, and aspens are common savanna trees.

Because of their extensive and often nutritious grass cover, savannas support extensive populations of large herbivores. Giraffes, zebras , impalas, kudus, and other charismatic residents of African savannas are especially well-known. Savanna herbivores in other regions include North American bison and elk and Australian kangaroos and wallabies. Carnivoreslions, cheetahs, and jackals in Africa, tigers in Asia, wolves and pumas in the Americashistorically preyed upon these huge herds of grazers. Large running birds, such as the African ostrich and the Australian emu, inhabit savanna environments, as do a plethora of smaller animal species. In the past century or two many of the world's native savanna species, especially the large carnivores, have disappeared with the expansion of human settlement. Today ranchers and their livestock take the place of many native grazers and carnivores.

Savannas owe their existence to a great variety of convergent environmental conditions, including temperature and precipitation regimes, soil conditions, fire frequency, and fauna . Grazing and browsing activity can influence the balance of trees to grasses. Fires, common and useful for some savannas but rare and harmful in others, are an influential factor in these dry environments. Precipitation must be sufficient to allow some tree growth, but where rainfall is high some other factors, such as grazing, fire, or soil drainage needs to limit tree growth. Human activity also influences the occurrence of these lightly-treed grasslands. In some regions recent expansion of ranches, villages, or agriculture have visibly extended savanna conditions. Elsewhere centuries or millennia of human occupation make natural and anthropogenic conditions difficult to distinguish. Because savannas are well suited to human needs, people have occupied some savannas for tens of thousands of years. In such cases people appear to be an environmental factor, along with climate , soils, and grazing animals, that help savannas persist.

See also Deforestation

[Mary Ann Cunningham ]


RESOURCES

BOOKS

Cole, M. M. The Savannas: Biogeography and Geobotany. London: Academic Press, 1986.

Danserreau, P. Biogeography: An Ecological Perspective. New York: Ronald Press Company, 1957.

de Laubenfels, D. J. Mapping the World's Vegetation. Syracuse, NY: Syracuse University Press, 1975.

White, R. O. Grasslands of the Monsoon. New York: Praeger, 1968.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Savanna." Environmental Encyclopedia. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Savanna." Environmental Encyclopedia. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/savanna

"Savanna." Environmental Encyclopedia. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/savanna

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Savanna

Savanna

The water economy

The faunas of the savannas

Resources

A savanna is a plant community characterized by a continuous grassy layer, often with scattered trees or shrubs, that is subject to regular, severe drought and occasional bush fires. A savanna is also the flat, open landscape in which such plant communities thrive. The word savanna comes from the Taino word zabana, which was used to describe a grassy, treeless plain. (Taino was the language of a now extinct Native American group that lived in the Greater Antilles and Bahamas.) The word entered the English, French, and Spanish languages almost simultaneously, between 1529 and 1555, as a result of Spanish exploration of the Caribbean.

Savannas occur in a broad band around the globe, occupying much of the land in the tropics and semi-tropics that is not a rain forest or a desert. Savanna grasslands occur predominantly in South America, Africa, Madagascar, the Indian subcontinent, and northern Australia. Over time, the original meaning of savanna as a treeless, grassy plain has been lost, and the scientific definition has becoming increasingly broad. Thus, the term now encompasses the treeless grasslands of Florida; the grasslands with palm trees in the Orinoco basin in Venezuela; the open pampas, semi-enclosed cerrados, and thorny, brushy caatingas of Brazil; the woodlands (miombo ) and park like grasslands (veldt ) of southern Africa; and various grasslands in Asia that resulted from cutting of forests over the centuries. Overall, savanna accounts for 20% of the land cover on Earth, and some savanna is to be found on every continent.

Savannas still defy adequate classification, although several complex schemes have been developed that take into account soil types, distance between plants, average height of the woody layer in relation to the herbaceous (grassy) layer, and similar quantifiable factors. A useful four-part descriptive classification divides savannas according to the increasing proportion of trees and shrubs: grassy savannas, open savannas, closed savannas, and woodland. Even in the most heavily wooded savannas, however, where trees may reach 40% of the cover, the primary flow of energy and nutrients is still through the grassy layer.

The water economy

Waterits availability, its timing, its distributionis the primary factor shaping the dynamics of the savanna ecosystem. The savanna experiences recurrent episodes of drought lasting 4-8 months out of the year. During the xeropause, or dry spell, plant activitiesgrowing, dying, decomposingcontinue, but at vastly reduced rates. Studies have shown that resistance to drought is more important to savanna vegetation than resistance to fire. The plants that thrive in the savannas employ many strategies to exploit available water and to survive the xeropause. The mechanisms of survival endow the savanna with its characteristic appearance.

The common savanna grasses grow in tussock form; from protected underground growing points the seasonal grasses grow in a bunch 12 in (30 cm) high or higher. A dense root system allows the individual plant to survive the annual drought, when the aerial (above-ground) grasses die. Typical savanna grasses are the sedges (Latin family name, Cyperaceae), the true grasses (Gramineae), and the bunch grasses (for example, the genera Andropogon and Stipa ). The grasses are chiefly of the C4 group; that is, they follow the C4 pathway of photosynthesis, which benefits from high

light intensity (such as is found in the tropics), high temperatures, and high evaporation rates. The dominance of C4 grasses is a useful way to demarcate savannas from temperate grasslands, where the grasses are predominantly of the C3 group.

The primary water recruitment strategy of savanna tree species is to maintain an extensive root system. The root system may extend deep underground, sometimes reaching the water table, or it may be a shallow, lateral system designed to harvest water over a broad area. The leaves of the trees are often tough and fibrous; they may be leathery, sandpapery, or hairyall features that enable them to husband water. Most leaves are lost during the dry period. Thorns, which may represent leaves that have been reduced through evolution to save water, are common on African savanna tree and shrub species. Many savanna tree types are unfamiliar to North Americans. The more familiar ones are Eucalyptus, Acacia, and Adansonia, the last of which includes the storied baobab tree. Seeds grow within thick casings that allow them to survive until the first rainfall before germinating. And in the midst of this thorny, corky, leathery protection, delicate, showy flowers bloom briefly on grasses and shrubs.

Having survived the dry season, savanna plants next must survive the rainy season, which is not simply a respite from drought but a completely different life episode. For many savanna grasses, the entire reproductive cycle must be accomplished during the rainy season. As the new leaves, which serve photosynthesis, and new flowers are borne in close succession, the energy needs of the grasses zoom upward. These energy-consuming activities must then be reined in and shut down to a semidormant state in preparation for the next dry period. This general pattern has shown some partitioning, with precocious species blooming even before the start of the rainy season, early and intermediate bloomers blooming serially during the rainy season, and late bloomers blooming at the end of the rainy season or after the start of the dry season. The temporal niching strategies of similar species may take advantage of different nutrient availability, or may be driven by some other, unknown factor. For each species, however, the cycle of growth and dormancy is driven by water availability, not by genetics.

In contrast to the grasses, savanna trees may conduct the entirety of their reproductive cycle during the dry season. Such a strategy would maximize the amount of foliage available for photosynthesis during the rainy season.

Besides water, other primary factors that affect the savanna ecosystem are fire and soil type. Fire triggers the growth of seeds, protected in seed beds underground during the dry season. Fire also limits the growth of trees, maintaining the distinction between savanna and forest. In particular, juvenile trees that have not reached a certain height are susceptible to fire; the lack of young trees contributes to the open appearance of a savanna. Some fires result from lightning strikes, but the majority are set by humans as part of hunting or agricultural pursuits. Fire improves soil by adding the nutrients calcium, magnesium, and potassium, which occur in the ashes, to the soil. The timing of fireearly or late in the dry seasonis critical, however, and the ideal time seems to differ for different plant associations.

Soil determines whether the deep roots will grow to their potential length. Different soils have different moisture-holding and drainage capacities. The soils underlying savannas cover a wide range of types, and it is thought that at least some of these soils are inhospitable to tree growth, thereby maintaining the characteristic physiognomy of the savanna. Soil type and bedrock geology have a major controlling influence over the plant communities that will grow in them. Depending on their structure, degree of porosity, and so forth, the major soil types may determine whether a savanna is classified as moist or arid, independent of the amount of rainfall. There is usually a noticeable disconformity in soil type at the boundary between forest and savanna, and again at the boundary between savanna and desert.

The faunas of the savannas

The wild animals most commonly associated with savannas are herbivores, browsers of grass, palatable shrubs, and tree leaves, and the carnivores that prey on them. The greatest species richness occurs on the African savannas, where climatic changes over geological time have favored the evolution and branching of many different animal species. Indeed, it is probable that the first bipedal humans walked upright on African savannas. The best-known species of African herbivores include the elephant, rhinoceros, zebra, 78 species of antelopes and buffalo, hippopotamus, pig, oryx, gemsbock, impala, waterbuck, kudu, eland, and hartebeest. On the Serengeti plains in Tanzania and elsewhere in Africa the proximity of different types of savanna vegetation, affording browse at different times

KEY TERMS

Primary consumer An organism that consumes primary producers as food; the latter are organismschiefly green plantsthat convert simple organic substances to more complex ones that can be used as food.

Xeropause A period of low biological activity in plants as a consequence of insufficient water.

of the year, has led to the great annual migrations of wild game.

In savanna ecosystems the herbivores are the primary consumers; they browse available producers such as grass. The African savannas also support large populations of secondary consumersthose that eat other animals. Among them are the lion, hyena, wild dog, anteater, and bat. Reptiles, birds, and insects are also well represented on African savannas.

The savannas on other continents show highly impoverished or restricted faunas, in comparison to those of the African savannas. Some highly restricted species are the capybara, a large rodent that lives on the Brazilian campos, and the kangaroos and wallabies of Australia. The prehistoric American savannas once included mammals such as camelids, mastodons, giant ground sloths, and deer. Climatic changes in the Pleistocene that reduced available browse are believed to have contributed to the demise of these species.

Today, domestic herds, especially sheep, cattle, and goats, graze the savannas side by side with the wild herbivores. If not too numerous, they are absorbed by the savanna ecosystem, with no change to the ecosystem. In India and West Africa, however, large domestic herds that exceed the carrying capacity of the land have devastated the savannas. Areas around waterholes and population centers are especially vulnerable to overgrazing. Because most of the worlds savannas occur in developing countries, where the local economy relies on exploitation of natural resources, the careful husbandry of the savannas and the methods by which savanna grasslands are converted to farming or grazing use are likely to prove critical to the future survival of these large units of vegetation.

Resources

BOOKS

Anderson, Alan N., Garry D. Cook, and Richard J. Williams. eds. Fire in Tropical Savannas. New York: Springer Publishing, 2003.

Bassett, Thomas, Donald Crummy African Savannas: Global Narratives. Portsmouth, NH: Heinemann, May 2003.

Owens, Mark James, Cordelia Dykes Owens. Secrets of the Savanna. Boston: Houghton Mifflin, May 2006.

Packard, Stephen, Cornelia F. Mutel. eds. The Tall Grass Restoration Handbook. Island Press Washington, DC, August 2005.

Pennington, R. Toby, Gwilym P. Lewis, eds. Neotropical Savannas and Dry Forests. Boca Raton, FL: CRC Publishing, May 2006.

Scholes, R.J., B.H. Walker. An African Savanna: Synthesis of the Nylsvley Study Cambridge: Cambridge University Press, November 2004.

Marjorie Panel

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Savanna." The Gale Encyclopedia of Science. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Savanna." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/savanna-0

"Savanna." The Gale Encyclopedia of Science. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/savanna-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Savanna

Savanna

A savanna is a plant community characterized by a continuous grassy layer, often with scattered trees or shrubs, that is subject to regular, severe drought and occasional bush fires. A savanna is also the flat, open landscape in which such plant communities thrive. The word savanna comes from the Taino word zabana, which was used to describe a grassy, treeless plain. (Taino was the language of a now extinct Native American group that lived in the Greater Antilles and Bahamas.) The word entered the English, French, and Spanish languages almost simultaneously, between 1529 and 1555, as a result of Spanish exploration of the Caribbean.

Savannas occur in a broad band around the globe, occupying much of the land in the tropics and semitropics that is not a rain forest or a desert . Savanna grasslands occur predominantly in South America , Africa , Madagascar, the Indian subcontinent, and northern Australia . Over time, the original meaning of savanna as a treeless, grassy plain has been lost, and the scientific definition has becoming increasingly broad. Thus, the term now encompasses the treeless grasslands of Florida; the grasslands with palm trees in the Orinoco basin in Venezuela; the open pampas, semi-enclosed cerrados, and thorny, brushy caatingas of Brazil; the woodlands (miombo) and park like grasslands (veldt) of southern Africa; and various grasslands in Asia that resulted from cutting of forests over the centuries. Overall, savanna accounts for 20% of the land cover on Earth , and some savanna is to be found on every continent .

Savannas still defy adequate classification, although several complex schemes have been developed that take into account soil types, distance between plants, average height of the woody layer in relation to the herbaceous (grassy) layer, and similar quantifiable factors. A useful four-part descriptive classification divides savannas according to the increasing proportion of trees and shrubs: grassy savannas, open savannas, closed savannas, and woodland. Even in the most heavily wooded savannas, however, where trees may reach 40% of the cover, the primary flow of energy and nutrients is still through the grassy layer.

The water economy

Water—its availability, its timing, its distribution—is the primary factor shaping the dynamics of the savanna ecosystem . The savanna experiences recurrent episodes of drought lasting 4-8 months out of the year. During the xeropause, or "dry spell," plant activities—growing, dying, decomposing—continue, but at vastly reduced rates. Studies have shown that resistance to drought is more important to savanna vegetation than resistance to fire. The plants that thrive in the savannas employ many strategies to exploit available water and to survive the xeropause. The mechanisms of survival endow the savanna with its characteristic appearance.

The common savanna grasses grow in tussock form; from protected underground growing points the seasonal grasses grow in a bunch 12 in (30 cm) high or higher. A dense root system allows the individual plant to survive the annual drought, when the aerial (aboveground) grasses die. Typical savanna grasses are the sedges (Latin family name, Cyperaceae), the true grasses (Gramineae), and the bunch grasses (for example, the genera Andropogon and Stipa). The grasses are chiefly of the C4 group; that is, they follow the C4 pathway of photosynthesis , which benefits from high light intensity (such as is found in the tropics), high temperatures, and high evaporation rates. The dominance of C4 grasses is a useful way to demarcate savannas from temperate grasslands, where the grasses are predominantly of the C3 group.

The primary water recruitment strategy of savanna tree species is to maintain an extensive root system. The root system may extend deep underground, sometimes reaching the water table, or it may be a shallow, lateral system designed to harvest water over a broad area. The leaves of the trees are often tough and fibrous; they may be leathery, sandpapery, or hairy—all features that enable them to husband water. Most leaves are lost during the dry period. Thorns, which may represent leaves that have been reduced through evolution to save water, are common on African savanna tree and shrub species. Many savanna tree types are unfamiliar to North Americans. The more familiar ones are Eucalyptus, Acacia, and Adansonia, the last of which includes the storied baobab tree. Seeds grow within thick casings that allow them to survive until the first rainfall before germinating. And in the midst of this thorny, corky, leathery protection, delicate, showy flowers bloom briefly on grasses and shrubs.

Having survived the dry season, savanna plants next must survive the rainy season, which is not simply a respite from drought but a completely different life episode. For many savanna grasses, the entire reproductive cycle must be accomplished during the rainy season. As the new leaves, which serve photosynthesis, and new flowers are borne in close succession , the energy needs of the grasses zoom upward. These energy-consuming activities must then be reined in and shut down to a semidormant state in preparation for the next dry period. This general pattern has shown some partitioning, with precocious species blooming even before the start of the rainy season, early and intermediate bloomers blooming serially during the rainy season, and late bloomers blooming at the end of the rainy season or after the start of the dry season. The temporal niching strategies of similar species may take advantage of different nutrient availability, or may be driven by some other, unknown factor. For each species, however, the cycle of growth and dormancy is driven by water availability, not by genetics .

In contrast to the grasses, savanna trees may conduct the entirety of their reproductive cycle during the dry season. Such a strategy would maximize the amount of foliage available for photosynthesis during the rainy season.

Besides water, other primary factors that affect the savanna ecosystem are fire and soil type. Fire triggers the growth of seeds, protected in seed beds underground during the dry season. Fire also limits the growth of trees, maintaining the distinction between savanna and forest. In particular, juvenile trees that have not reached a certain height are susceptible to fire; the lack of young trees contributes to the open appearance of a savanna. Some fires result from lightning strikes, but the majority are set by humans as part of hunting or agricultural pursuits. Fire improves soil by adding the nutrients calcium , magnesium , and potassium, which occur in the ashes, to the soil. The timing of fire—early or late in the dry season—is critical, however, and the ideal time seems to differ for different plant associations.

Soil determines whether the deep roots will grow to their potential length. Different soils have different moisture-holding and drainage capacities. The soils underlying savannas cover a wide range of types, and it is thought that at least some of these soils are inhospitable to tree growth, thereby maintaining the characteristic physiognomy of the savanna. Soil type and bedrock geology have a major controlling influence over the plant communities that will grow in them. Depending on their structure, degree of porosity, and so forth, the major soil types may determine whether a savanna is classified as moist or arid, independent of the amount of rainfall. There is usually a noticeable disconformity in soil type at the boundary between forest and savanna, and again at the boundary between savanna and desert.


The faunas of the savannas

The wild animals most commonly associated with savannas are herbivores, browsers of grass, palatable shrubs, and tree leaves, and the carnivores that prey on them. The greatest species richness occurs on the African savannas, where climatic changes over geological time have favored the evolution and branching of many different animal species. Indeed, it is probable that the first bipedal humans walked upright on African savannas. The best-known species of African herbivores include the elephant , rhinoceros , zebra, 78 species of antelopes and buffalo, hippopotamus, pig, oryx , gemsbock, impala, waterbuck , kudu, eland , and hartebeest. On the Serengeti plains in Tanzania and elsewhere in Africa the proximity of different types of savanna vegetation, affording browse at different times of the year, has led to the great annual migrations of wild game.

In savanna ecosystems the herbivores are the primary consumers; they browse available producers such as grass. The African savannas also support large populations of secondary consumers—those that eat other animals. Among them are the lion, hyena , wild dog, anteater, and bat. Reptiles , birds , and insects are also well represented on African savannas.

The savannas on other continents show highly impoverished or restricted faunas, in comparison to those of the African savannas. Some highly restricted species are the capybara, a large rodent that lives on the Brazilian campos, and the kangaroos and wallabies of Australia. The prehistoric American savannas once included mammals such as camelids, mastodons, giant ground sloths , and deer . Climatic changes in the Pleistocene that reduced available browse are believed to have contributed to the demise of these species.

Today, domestic herds, especially sheep , cattle, and goats , graze the savannas side by side with the wild herbivores. If not too numerous, they are absorbed by the savanna ecosystem, with no change to the ecosystem. In India and West Africa, however, large domestic herds that exceed the carrying capacity of the land have devastated the savannas. Areas around waterholes and population centers are especially vulnerable to overgrazing. Because most of the world's savannas occur in developing countries, where the local economy relies on exploitation of natural resources, the careful husbandry of the savannas and the methods by which savanna grasslands are converted to farming or grazing use are likely to prove critical to the future survival of these large units of vegetation.


Resources

books

Bourlière, François. "Mammals as Secondary Consumers in Savanna Ecosystems." In Tropical Savannas. Ecosystems of the World. Edited by David W. Goodall. Amsterdam: Elsevier, 1983.

Bourlière, François, and Hadley, M. "Present-Day Savannas: An Overview." In Tropical Savannas. Ecosystems of the World. Edited by David W. Goodall. Amsterdam: Elsevier, 983.

Cole, Monica M. The Savannas: Biogeography and Geobotany. London: Academic Press, 1986.

Hancock P.L. and B.J. Skinner, eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Sarmiento, Guillermo. The Ecology of Neotropical Savannas:. Cambridge: Harvard University Press, 1984.

Walker, Brian H., ed. Determinants of Tropical Savannas. Oxford: IRL Press, 1987.


Marjorie Panel

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Primary consumer

—An organism that consumes primary producers as food; the latter are organisms—chiefly green plants—that convert simple organic substances to more complex ones that can be used as food.

Xeropause

—A period of low biological activity in plants as a consequence of insufficient water.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Savanna." The Gale Encyclopedia of Science. . Encyclopedia.com. 14 Nov. 2018 <https://www.encyclopedia.com>.

"Savanna." The Gale Encyclopedia of Science. . Encyclopedia.com. (November 14, 2018). https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/savanna

"Savanna." The Gale Encyclopedia of Science. . Retrieved November 14, 2018 from Encyclopedia.com: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/savanna

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.