Moist savannah

Climate diagram of Lagos in Nigeria

The savannah is depending on the approach an ecological zone , a Zonobiom or vegetation zone of the tropics . Together with the dry and thorn-bush savannah, it forms the transition between the tropical rainforest and the arid trade wind zone . The moist savannah has 7 to 9.5 rainy, humid months (tropical rainforest 9.5 to 12 humid months) and a pronounced dry season . In the humid savannah, like in the tropical rainforest, there is a daytime climate .

In addition to the wet savannah, there are also the dry savannah and the thorn bush savannah as further types of savannah .

distribution

The wet savannah occurs in the transition area between the arid trade wind zone and the tropical rainforest climate. It is part of the humid tropics and not the tropical dry areas. They are mainly found in Africa and Southeast Asia , but also in Australia and South America . Overall, the wet savannah covers 9.4% of the earth. It is one of the largest and most animal-rich areas on earth after the tropical rainforest.

Rainy season

The rainy season occurs after the zenith of the sun in the moist savannah, as more water evaporates during the zenith. Furthermore, the intertropical convergence shifts with the zenith. Thus, the wet savannahs have 7–9.5 humid months and the annual rainfall averages 1000–1500 mm.

Sertao in Rio Grande do Norte, northeastern Brazil

vegetation

The vegetation is adapted to the dry and rainy seasons . In the wet savannas mainly grasses grow, such as B. elephant grass , which can be up to 6 meters high. The grasses absorb near-surface precipitation in the rainy season and dry up in the dry season because they have no protection against evaporation. Woody plants occur only in the slightly closed moist savannah forest or on rivers in gallery forests . Thanks to their deep root system, they can maintain their water balance even in the dry season. In addition, the trees shed their leaves in the dry season to save water. The wood stocks were pushed back by human slash and burn .

Floors

The typical soils of the tropical rainforest are also represented in the wet savannah . Long-term weathering forms the clay mineral kaolinite , which has only a low cation exchange capacity and can store few nutrients. The most important soil type is called Ferralsol (according to the international soil classification system World Reference Base for Soil Resources (WRB)). Plinthosols also occur in small areas . These are soils with high concentrations of iron oxide, which form characteristic patterns through redox processes . Oxide-rich horizons can harden and are then called laterite . Laterite horizons are a physical barrier to root growth.

In addition to these typical rainforest soils, soils with clay shift ( lessivation ) are also widespread. In more humid areas, the strongly acidic and nutrient-poor acrisols dominate and in drier regions the base-rich lixisols . Both are also dominated by kaolinite , but contain less humus than Ferralsole. Lixisols are somewhat better equipped with nutrients, but they are very prone to erosion. Vertisoles can sometimes be found in the lowlands . These are soils with clay minerals that swell and shrink, including smectite in particular . Although they are well supplied with nutrients, roots can tear when the clay minerals shrink, which is why fewer trees and more grasses grow on vertisoles. When dry, these soils are rock-hard, and when wet they melt.

Clearing and agriculture increases the risk of soil erosion . The danger of erosion is highest after the dry season, because then the grasses are mostly dried up and the dried out soil has a wetting resistance.

literature

• Wilfried Büttner: Moist savannah . In: People and Space. Developing countries . ISBN 3-464-08018-8 , pp. 20-21.

Individual evidence

1. ↑ ^{a b c} W. Zech, P. Schad, G. Hintermaier-Erhard: Soils of the world . 2nd Edition. Springer Spectrum, Heidelberg 2014, ISBN 978-3-642-36574-4 .