Savanna
From Wikipedia, the free encyclopedia
A savanna is a grassland with widely spaced trees, and occurs in several types of biomes. In savannas, grasses and trees are co-dominant vegetation types, with trees and grasses often alternating in dominance over time. The herbaceous layer is usually a mixture of grasses and herbs with trees and shrubs scattered individually or in small clumps. Savannas are frequently seen as a transitional zone, occurring between forest or woodland regions and grassland or desert regions.
Savannas are targets of regular fires. Most savannas experience fire at least twice a decade and annual fires are common in many savanna types. 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. Browsing animals such as elephants, antelope and deer also play an important role in suppressing tree growth in savannas.
Savannas appear 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.[1] Aboriginal burning appears to have been responsible for the widespread occurrence of savanna in tropical Australia and New Guinea[2] and savannas in India are a creation of human fire use.[3] With the removal or lateration of traditional burning regimes many savannas are being replaced by forest and shrub thickets with little herbaceous layer.[4]
Although the term savanna is believed to have originally come from an Amerindian 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. Savannah, Georgia is named after such an area.
Savanna ecoregions are of several different types:
- Tropical and subtropical savannas are classified with tropical and subtropical grasslands and shrublands as the tropical and subtropical grasslands, savannas, and shrublands biome. The savannas of Africa, including the Serengeti, famous for its wildlife, are typical of this type.
- Temperate savannas are mid-latitude savannas with wetter summers and drier winters. They are classified with temperate savannas and shrublands as the temperate grasslands, savannas, and shrublands biome.
- 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. The oak tree savannas of California, part of the California chaparral and woodlands ecoregion, fall into this category.
- Flooded savannas are savannas that are flooded seasonally or year-round. They are classified with flooded savannas as the flooded grasslands and savannas biome, which occurs mostly in the tropics and subtropics.
- Montane savannas are high-altitude savannas, located in a few spots around the world's high mountain regions, part of the montane grasslands and shrublands biome. The highland savannas of the Angolan scarp savanna and woodlands ecoregion are an example.
[edit] See also
- Coastal plain
- Coastal prairie
- Field
- Flooded grasslands and savannas
- Flood-meadow
- Grassland
- Meadow
- Pasture
- Plain
- Prairie
- Rangeland
- Steppe
- Water-meadow
- Wet meadow
- Veld
[edit] References
- ^ http://www.learnpress.org/editions/cede_longleaf/1 URL accessed August 5, 2006.
- ^ Flannery, T. (1994) "The future eaters" Reed Books Melbourne.
- ^ 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.
- ^ 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.
