Savanna

  • Desert climate
  • Savannah climate
  • Tundra
  • Eisklima

As Savannah (via Spanish sabana from a Caribbean language borrowed ) a tropical or subtropical vegetation type is generally referred to, consists of a closed herbaceous layer and a more open woodland layer. The demarcation of steppes, grasslands and dry forests is handled differently. Also, Savannah is a collective term for the vegetation zone between the tropical rainforest and the desert. Savannah or savana / sabana means as much as " vast plain ". The Savannah makes depending on your perspective from 13 to 18 percent of the total land surface of the earth. The large spread between these figures is due to the fact that boundaries are fluid in nature as a rule, and can extend over hundreds of kilometers. Therefore, artificial boundaries are required to calculate the percentage. These boundaries differ from author to author from each other.

The term savannah

Although the terms " savanna " and " steppe " was introduced to describe certain types of vegetation, the name from the 1970s by geographers has been used more for certain climates. Carl Troll first proposed to call in the tropics all hygrophilic plant communities as savannas, no matter what it is for vegetation. However, since hygrophilous and xerophilic relative and elusive concepts, Eckhart John Hunter has given the concept of a savannah climatic sense, which had nothing to do with the zonal vegetation.

Ecology

The Savannah is a landscape zone of the tropics, by their open vegetation ( grassland ) and related relative periodically trees is characterized. They occur in the transition zone between the arid trade wind zone and the tropical rain forest climate. Accordingly, the vegetation zone of savannas is between the vegetation zones desert and tropical forest. Savannas are deciduous dry barren plant communities due to the summer rainy season.

Factors of development dynamics

The vegetation dominant factor is the seasonal water shortage here. Typical values ​​are between 500 and 1500 mm of annual precipitation ( ie 500 to 1500 liters of water per m² ). The vegetation shows a distinct period of activity in the summer. Productivity increases with the length of the rainy season from 7 tonnes per hectare per year in desert regions close to up to 20 tonnes per hectare per year in the equatorial part - evergreen forests.

Important tree species of the savannah, the genus Acacia, with around 900 species worldwide. The dry barren Baobab has to protect against water loss weichholzigen a very thick trunk with a circumference of sometimes more than 20 m. Such individuals are able to save up to 100,000 liters of water. In some areas there are also tree-shaped leaf succulents, such as Aloe dichotoma. In wetter, more closed forests, such as the Miombowäldern Central Africa one finds the important woody family of Caesalpiniaceae. This includes for example the Mopanebaum ( Colophospermum mopane ).

Fire plays an important role in the ecosystem of savannah. They lead to the death of young trees and favor grasses. Through the fires of dead plant parts are removed and nutrients to the circulation returned ( remineralization ).

In the savanna there is, as in all other climates animal species that have adapted to the vegetation of this habitat, and on the other hand, species that hit the adapted species as prey or consume as carrion. Among the large herbivores ( plant eaters ) of the savannas include, for example, wildebeest, gazelle, zebra, elephant, kangaroo, and giraffe. Among the most important carnivores (meat eaters ) include, for example, cheetah, lion or puma. But by far the most common herbivorous species come from the tribe of insects, especially ants and termites.

The competition structure between grasses and trees is also influenced by these large herbivores: elephants break off branches of trees to get to the leaves, peel the bark and hit enter or trees around for other reasons. By the death of the tree layer of the forest stand will be thinned, which improves the growing conditions for grasses that are grazed by buffalo, zebras and gazelles. In particularly intensive grazing, in turn, improve the conditions for the emergence of young trees. In particular, the spine reinforced and thus stifled resistant acacia can then spread.

For this reason, the ecological balance is heavily impacted by human activities. Here overgrazing and destruction of the sward by kicking deserve particular mention, which contribute to erosion feed. In addition, the firewood and the pollarding comes to animal feed production. These activities will be boosted by the increase in population. An erosion of the fertile soil layer is forced, degradation put an ( desertification ).

Types of savannas

There are three different types of savannas: dry, wet and thorn shrub savannah.

Features of adaptation to drought, for example, leaf fall during the dry season, reduced tree growth and increased stature water-storing plants.

Location and distribution

Savannas are particularly widespread in Africa, especially the Serengeti is known. However, they also occur in India, Australia and in the northern part of South America. In Africa, a savanna belt draws a semicircle across the continent, starting in the Sudan and Sahel zone of West Africa through the East African savannah to the South African Veld.

Savannas are distinguished as tropical and subtropical vegetation type of the arid grasslands ( steppes ) of the temperate latitudes, such as the steppes of Eastern Europe and Central Asia, the prairies in North America and the pampas in South America.

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