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Encyclopedia > Savanna
Typical subcoastal Eucalyptus/Melaleuca savanna in Northern Australia demonstrating the high tree density and regular spacing characteristic of many savannas.
Typical subcoastal Eucalyptus/Melaleuca savanna in Northern Australia demonstrating the high tree density and regular spacing characteristic of many savannas.

A savanna or savannah is a grassland ecosystem with scattered trees or shrubs. In savannas trees are small or widely spaced so that the canopy does not close. It is often believed that savannas are characterized by widely spaced, scattered trees, however in many savanna communities tree densities are higher and trees are more regularly spaced than in forest communities. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.[1] Savannas are also characterised by seasonal water availability, with the majority of rainfall being confined to one season of the year. Savannas can be associated with several types of biomes. Savannas are frequently seen as a transitional zone, occurring between forest and desert or prairie. is the 126th day of the year (127th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance to the Gregorian calendar. ... Look up savannah in Wiktionary, the free dictionary. ... Image File history File linksMetadata Download high-resolution version (1024x531, 450 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Savanna Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Image File history File linksMetadata Download high-resolution version (1024x531, 450 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Savanna Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Ngorongoro redirects here. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The Konza tallgrass prairie in the Flint Hills of northeastern Kansas. ... A coral reef near the Hawaiian islands is an example of a complex marine ecosystem. ... Overview of C4 carbon fixation C4 carbon fixation is one of three methods, along with C3 and CAM photosynthesis, used by land plants to fix carbon dioxide (binding the gaseous molecules to dissolved compounds inside the plant) for sugar production through photosynthesis. ... A biome is a climate and geographical area of ecologically similar communities of plants, animals, and soil organisms, often referred to as ecosystems. ... This article is about a community of trees. ... This article is about arid terrain. ... For other uses, see Prairie (disambiguation). ...


Although the term savanna is believed to have originally come from a Native American word describing "land which is without trees but with much grass either tall or short" (Oviedo y Valdes, 1535), by the late 1800s it was used to mean "land with both grass and trees". It now refers to land with grass and either scattered trees or an open canopy of trees. Indigenous languages of the Americas (or Amerindian Languages) are spoken by indigenous peoples from the southern tip of South America to Alaska and Greenland, encompassing the land masses which constitute the Americas. ... Gonzalo Fernandez de Oviedo y Valdes (August, 1478-1557), Spanish historian, was born at Madrid. ... The canopy is the habitat found at the uppermost level of a forest, especially rainforest. ...

Contents

Threats to savannas

Changes in fire management

Savannas are subject to regular fires and the ecosystem appears to be the result of human use of fire. For example Native Americans created subtropical savannas by periodic burning in some areas of the US southeastern coast where fire-resistant Longleaf Pine was the dominant species.[2] Aboriginal burning appears to have been responsible for the widespread occurrence of savanna in tropical Australia and New Guinea[3] and savannas in India are a creation of human fire use.[4] The maquis shrub savannas of the Mediterranean region were likewise created and maintained by anthropogenic fire.[5] This article is about the people indigenous to the United States. ... ... Maquis (French) or macchia (Italian; plural macchie) is a shrubland biota in Mediterranean countries, typically consisting of densely-growing evergreen shrubs such as sage, juniper and myrtle. ...


These fires are usually confined to the herbaceous layer and do little long term damage to mature trees. However, these fires do serve to 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 vegetation[6] and may have maintained and modified savanna flora.[7][8] It has been suggested by many authors[9][6] 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.[6][10] It has been suggested by many authors[9][11] 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.[12] 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.[13]


Grazing and browsing animals

The closed forests 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.[14] In contrast the open structure of savannas allows the growth of a herbaceous layer and are commonly used for grazing domestic livestock.[15] 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.[16]


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.[17] In addition to this effect the removal of fuel reduces both the intensity and the frequency of fires which may control woody plant species.[18] 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.[19] 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.[6] In addition to this cattle and horses are implicated in the spread of the seeds of weed species such as Prickly Acacia (Acacia nilotica) and Stylo (Stylosanthes spp.).[20] These 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.[21] 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 soil can lead to severe degradation. Alteration in soil structure and nutrient levels affects the establishment, growth and survival of plant species and in turn can lead to a change in woodland structure and composition.


Tree clearing

Large areas of savanna 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.[6] 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. A hectare (symbol ha) is a unit of area, equal to 10 000 square metres, commonly used for measuring land area. ...


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.[22] Since stock carrying capacity is strongly correlated with herbage yield there can be major financial benefits from the removal of trees.[23] The removal of trees also assists grazing management. For example in sheep grazing regions of dense tree and shrub cover harbours predators, leading to increased stock losses[24] while woody plant cover hinders mustering in both sheep and cattle areas.[25]


A number of techniques have been employed to clear or kill woody plants in savanna. Early pastoralists used felling and ringbarking, the removal of a ring of bark and sapwood, as a means of clearing land[26]). In the 1950’s 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 1980’s also saw the release of soil-applied arboricides, notably tebuthiuron, that could be utilised without cutting and injecting each individual tree.


In many ways ‘artificial’ clearing, particularly pulling, mimics the effects of fire and, in savannas adapted to regeneration after fire as most Queensland savannas are, there is a similar response to that after fire.[27] Tree clearing in many savanna communities, although causing a dramatic reduction in basal area and canopy cover, often leaves a high percentage of woody plants alive either as seedlings too small to be affected or as plants capable of re-sprouting from lignotubers and broken stumps. A population of woody plants equal to half or more of the original number often remains following pulling of eucalypt communities, even if all the trees over 5 metres are uprooted completely.


Exotic plant species

A number of exotic plants species have been introduced to the savannas around the world. Amongst the woody plant species are serious environmental weeds such as Prickly Acacia (Acacia nilotica), Rubbervine (Cryptostegia grandiflora), Mesquite (Prosopis spp.), Lantana (Lantana camara and 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 rats tail grass (Sporobolus pyramidalis) parthenium (Parthenium hysterophorous) and stylos (Stylosanthes spp.) and other legumes. These introductions have the potential to significantly alter the structure and composition of savannas worldwide, and have already done so in many areas through a numbers of processes including altering the fire regime, increasing grazing pressure, competing with native vegetation and occupying previously vacant ecological niches.[27][28]


Climate change

There exists the possibility that human induced climate change in the form of the greenhouse effect may result in an alteration of the structure and function of savannas. Some authors[29] have suggested that savannas and grasslands may become even more susceptible to woody plant encroachment as a result of greenhouse induced climate change. A recent case described involved 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.[30]


Savanna ecoregions

Savanna ecoregions are of several different types: An ecoregion is a relatively large area of land or water that contains a geographically distinct assemblage of natural communities. ...

Equatorial savanna in the East Province of Cameroon
Equatorial savanna in the East Province of Cameroon

Guinean savanna in the East Province of Cameroon. ... The East Province (French Province de lEst) occupies the southeastern portion of the Republic of Cameroon. ... Tropical and subtropical grasslands, savannas, and shrublands are a grassland biome located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes. ... A zebra and wildebeests during migration The Serengeti ecosystem is located in north-western Tanzania and extends to south-western Kenya between latitudes 1 and 3 S and longitudes 34 and 36 E. It spans some 30,000 km. ... A restored Illinois grassland ecosystem at Morton Arboretum. ...  Areas with Mediterranean climate A Mediterranean climate is one that resembles the climate of the lands in the Mediterranean Basin, which includes over half of the area with this climate type world-wide. ... A Mediterranean forest. ... This article is about oaks (Quercus desert-oak is unrelated, and instead belongs to the genus Allocasuarina. ... This article is about the U.S. state. ... The California chaparral and woodlands is a terrestrial ecoregion of central and southern California (United States) and northwestern Baja California (Mexico), located on the west coast of North America. ... Flooded grasslands and savannas are a biome, generally located at subtropical and tropical latitudes, where flooding is very frequent. ... Montane grasslands and shrublands is a biome defined by the World Wildlife Fund. ...

External links

  • The Savanna

See also

Wikimedia Commons has media related to:
Savanna

A coastal plain is an area of flat, low-lying land adjacent to a seacoast and separated from the interior by other features. ... Coastal prairie may refer to either: The California coastal prairie, a plant community found along the coasts of California and Oregon The Western Gulf coastal grasslands of Louisiana, Texas, and Tamaulipas This is a disambiguation page: a list of articles associated with the same title. ... A green field or paddock In agriculture, a field refers generally to an area of land enclosed or otherwise and used for agricultural purposes such as: Cultivating crops Usage as a paddock or generally an enclosure of livestock Land left to lie fallow or as arable land See also Pasture... Flooded grasslands and savannas are a biome, generally located at subtropical and tropical latitudes, where flooding is very frequent. ... Flood-meadow near Hohenau an der March A flood-meadow (or floodmeadow) is an area of grassland or pasture beside a river, subject to seasonal flooding. ... The Konza tallgrass prairie in the Flint Hills of northeastern Kansas. ... A meadow is a habitat of rolling or flat terrain where grasses predominate. ... Pastureland Pasture is land with lush herbaceous vegetation cover used for grazing of ungulates as part of a farm or ranch. ... In geography, a plain is a large area of land with relatively low relief. ... For other uses, see Prairie (disambiguation). ... Rangeland refers to a large, mostly unimproved section of land that is predominantly used for livestock grazing. ... This article is about the ecological zone type. ... A water-meadow (or watermeadow) is an area of grassland or pasture beside a river, subject to controlled seasonal flooding. ... A wet meadow is a semi-wetland meadow which is saturated with water throughout much of the year. ... south american veldt The term Veld, or Veldt, refers primarily to the wide open rural spaces of South Africa or southern Africa and in particular to certain flatter areas or districts covered in grass or low scrub. ...

References

  1. ^ Werner, P. A., B. H. Walker, et al. (1991). "Introduction. Savanna Ecology and Management Australian Perspectives and International Comparisons." P. A. Werner ed. Blackwell Scientific Publications.
  2. ^ http://www.learnpress.org/editions/cede_longleaf/1 URL accessed August 5, 2006.
  3. ^ Flannery, T. (1994) "The future eaters" Reed Books Melbourne.
  4. ^ Saha, S. 2003. "Patterns in woody species diversity, richness and partitioning of diversity in forest communities of tropical deciduous forest biomes." Ecography 26: 80–86.
  5. ^ Pyne, Stephen J. (1997) Vestal Fire: An Environmental History, Told through Fire, of Europe and Europe's Encounter with the World. Seattle and London: University of Washington Press. ISBN 0-295-97596-2
  6. ^ a b c d e Wilson, 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.
  7. ^ Werner, P. A., B. H. Walker, et al. (1991). Introduction. Savanna Ecology and Management Australian Perspectives and International Comparisons. P. A. Werner. Oxford, Blackwell Scientific Publications.
  8. ^ Flannery, T. (1994). The future eaters. Frenchs Forest, Australia., Reed New Holland.
  9. ^ a b Lunt, I. D., N. Jones(2006). "Effects of European colonisation on indigenous ecosystems: post-settlement changes in tree stand structures in Eucalyptus–Callitris woodlands in central New South Wales, Australia." Journal of Biogeography, 33(6): 1102–1115.
  10. ^ Flannery, T. (1994). The future eaters. Frenchs Forest, Australia., Reed New Holland.
  11. ^ Archer S, (1994.) "Woody plant encroachment into southwestern grasslands and savannas: Rates, patterns and proximate causes." pp 13–68 in Vavra, Laycock and Pieper eds. "Ecological Implications of Livestock Herbivory in the West". Society For Range Management, Denver.
  12. ^ 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.
  13. ^ Dyer, R., A. Craig, et al. (1997). Fire in northern pastoral lands. Fire in the management of northern Australian pastoral lands. T. C. Grice and S. M. Slatter. St. Lucia, Australia, Tropical Grassland Society of Australia.
  14. ^ Lodge, G. M. and R. D. B. Whalley (1984). Temperate rangelands. Management of Australia’s Rangelands. G. N. Harrington and A. D. Wilson. Melbourne, CSIRO Publishing.
  15. ^ Mott, J. J., Groves, R.H. (1994). Natural and derived grasslands. Australian Vegetation. R. H. Groves. Cambridge, Cambridge University Press.
  16. ^ Winter, W. H. (1991). Australia's northern savannas: a time for change ion management philosophy. Savanna Ecology and Management Australian Perspectives and International Comparisons. P. A. Werner. Oxford, Blackwell Scientific Publications.
  17. ^ Burrows, W. H., J. C. Scanlan, et al. (1988). Plant ecological relations in open forests, woodlands and shrublands. Native pastures in Queensland their resources and management. W. H. Burrows, J. C. Scanlan and M. T. Rutherford eds. Brisbane, Department of Primary Industries.
  18. ^ Smith, G., A. Franks, et al. (2000). Impacts of domestic grazing within remnant vegetation. Native Vegetation Management in Queensland. S. L. Boulter, B. A. Wilson, J. Westrupet al. Brisbane, Department of Natural Resources.
  19. ^ Florence, R. G. (1996). Ecology and silviculture of eucalypt forests. Collingwood, CSIRO Publishing.
  20. ^ 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 eds. Queensland, Queensland Government Press.
  21. ^ Foran, B. D. (1984). Central arid woodlands. Management of Australia’s Rangelands. G. N. Harrington and A. D. Wilson. Melbourne, CSIRO Publishing.
  22. ^ Scanlan, J. and C. Chilcott (2000). Management and production aspects. Native Vegetation Management in Queensland. S. L. Boulter, B. A. Wilson, J. Westrupet al. Brisbane, Department of Natural Resources.
  23. ^ Harrington, G. N., M. H. Friedel, et al. (1984). Vegetation ecology and management. Management of Australia's Rangelands. G. N. Harrington and A. D. Wilson. Melbourne, CSIRO Publishing.
  24. ^ Harrington, G. N., D. M. D. Mills, et al. (1984). Semi-arid woodlands. Management of Australia's Rangelands. G. N. Harrington and A. D. Wilson. Melbourne, CSIRO Publishing.
  25. ^ Harrington, G. N., A. D. Wilson, et al. (1984). Management of Rangeland Ecosystems. Management of Australia's Rangelands. G. N. Harrington and A. D. Wilson. Melbourne, CSIRO Publishing.
  26. ^ Partridge, I. (1999). Managing grazing in northern Australia. Brisbane, Department of Primary Industries.
  27. ^ a b 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.
  28. ^ Tothill, J. C. and C. Gillies (1992). The pasture lands of northern Australia. Brisbane, Tropical Grassland Society of Australia.
  29. ^ Archer, S. (1991). Development and stability of grass/woody mosaics in a subtropical savanna parkland, Texas, USA. Savanna Ecology and Management Australian Perspectives and International Comparisons. P. A. Werner. Oxford, Blackwell Scientific Publications.
  30. ^ llen, C. D. and D. D. Breshears (1998). "Drought-induced shift of a forest–woodland ecotone: Rapid landscape response to climate variation." Proceedings of The National Academy of Sciences 95: 14839–14842.
Stephen J. Pyne is a professor in the School of Life Sciences at Arizona State University, specializing in the history of ecology, the history of exploration, and the history of fire. ... A biome is a climate and geographical area of ecologically similar communities of plants, animals, and soil organisms, often referred to as ecosystems. ... Tropic wet forests in the World Tropical and subtropical moist broadleaf forests, also known as tropical wet forests, are a tropical and subtropical forest biome. ... Trinidad and Tobago dry forest on Chacachacare showing the dry-season deciduous nature of the vegetation The tropical and subtropical dry broadleaf forest biome, also known as tropical dry forest, is located at tropical and subtropical latitudes. ... Tropical and subtropical coniferous forests are a biome located at tropical and subtropical latitudes. ... Temperate mixed forest in Yunnan, southwest China. ... Pine forests are an example of a temperate coniferous forests Temperate coniferous forests are a terrestrial biome found in temperate regions of the world with warm summers and cool winters and adequate rainfall to sustain a forest. ... A Mediterranean forest. ... For other uses, see Taiga (disambiguation). ... Above and below water view at the edge of the mangal. ... Tropical and subtropical grasslands, savannas, and shrublands are a grassland biome located in semi-arid to semi-humid climate regions of subtropical and tropical latitudes. ... A restored Illinois grassland ecosystem at Morton Arboretum. ... Flooded grasslands and savannas are a biome, generally located at subtropical and tropical latitudes, where flooding is very frequent. ... Montane grasslands and shrublands is a biome defined by the World Wildlife Fund. ... In isolation, Hawaiis Silverswords have adapted to xeric microclimates within volcanic craters, trapping and channeling dew and protecting leaves with reflective hairs. ... For other uses, see Tundra (disambiguation). ...

  Results from FactBites:
 
Savanna Animal Printouts - EnchantedLearning.com (677 words)
Savannas are located in the dry tropics and the subtropics, often bordering a rainforest.
The animals that live in savannas have adapted to a great deal of variability in the food supply throughout the year; there are times of plenty (during and after the wet season) and times of almost no food or water (during the dry season).
Savannas are located in Africa, Madagascar (an island off the east coast of Africa), Australia, South America, India, and the Myanmar-Thailand region of Southeast Asia.
Savanna - Wikipedia, the free encyclopedia (625 words)
Savannas are frequently seen as a transitional zone, occurring between forest or woodland regions and grassland or desert regions.
Tropical and subtropical savannas are classified with tropical and subtropical grasslands and shrublands as the tropical and subtropical grasslands, savannas, and shrublands biome.
Mediterranean savannas are mid-latitude savannas in Mediterranean climate regions, with mild, rainy winters and hot, dry summers, part of the Mediterranean forests, woodlands, and shrub biome.
  More results at FactBites »

 
 

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