Savanna

The Savanes constitutes a Biome semi-arid zones of planet. These écorégion S is more precisely named savannas, and the tropical and subtropical clear forests .

The savanna itself is a vegetable Formation made up mainly of Plante S herbaceous long-lived of the family of the Poacée S (Graminée S). It is more or less strewn with Arbre S or about Arbuste S. According to the density (increasing) of the woody species, one speaks about shrubby savanna, raised savanna, then clear Forêt, the transition being done in general in a progressive way.

The landscapes of savannas are mainly in Africa in the soudanien field, but also in Asia, in the central areas of the India, in South America, in particular with the Brésil and in Australia. The rivers crossing savanna are bordered of Forêts-galeries seldom exceeding a few hundred meters broad.

Savanna develops under tropical Climat characterized by the one season wet alternation and one season dries shorter, favourable with the fires.

The grasses are especially the Graminaceous ones in tufts or plates with buds on the surface of the ground. The most frequent species in African savanna are the Herbe with elephant ( Pennisetum ), the Herbe with paillottes ( Imperata ), the Andropogon … In rain season, to the maximum of their growth they can exceed 3 meters in height. Their roots often form a felting of several tens of centimetres of depth which prohibits the installation of other species, but which enables them to resist fires natural or anthropic which periodically, during the dry season, traverses savanna. The trees, almost all with null and void sheets, have a thick bark and sucker easily. Emblématique, in Africa, are the Baobab. One finds there also Acacia S, Palmier S… By evolutionary Convergence, several species of trees acquired the possibility of storing water in their trunk, during several months, to resist the Sécheresse. The herbaceous ones, it, die. Their seeds reappear with the first rains of the wet season.

The grounds of savanna are very varied: ferruginous grounds red with iron oxides and manganese; the grounds at horizon of concretion formation with an in-depth armor, which can reappear in the event of erosion and which gives the bowal ; the black grounds where the organic matter is mixed with clay where the drainage is poor (in particular in the Indian Dekkan). According to the importance of the trees one distinguishes:

  • African grassy savanna or campo limpo of Brazil
  • African raised savanna or campo cerrado Brazilian or llanos of Venezuela
  • the Brazilian cerradao or scrub

Étymolgie

The word comes from l´espagnol sabana which would be in loan of Taïno.

See too

External references

  • Site of the WWF
  • GFR " Environmental management of the ecosystems and forests tropicales" : Group Formation and of Search for AgroParisTech-ENGREF

; Video

  • Savanna in all its states " /The alive world Extracts video/Archive INA (1997)
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