The Trockensavanne is depending on the approach an ecological zone , a Zonobiom or vegetation zone of the tropics . The dry savannah has five to seven arid months . Every year, between 500 and 1000 mm of precipitation falls in a pronounced rainy season . In the dry savannah, like in the tropical rainforest, there is a daytime climate .
In addition to the dry savannah, there is the moist savannah and thorn bush savannah , see savannah . According to Schultz, the dry and wet savannas together form the eco-zone of the summer-humid tropics . The dry savannahs form the transition area to the tropical / subtropical dry areas .
The dry savannah lies between the wet savannah and the thorn bush savannah and is part of the humid tropics , as it has 5.5 to 7 arid and 4.5 to 7 humid months . It is very pronounced in Africa ( Sahel zone and eastern Africa), on the Indian subcontinent and in northern Australia. The dry savannah is less pronounced in Central and South America. All dry savannahs together make up about 3% of the land area.
The vegetation in the dry savannah is adapted to the dry season. For example, African baobab trees store water in the trunk and the umbrella acacias form a large crown with which they protect the soil from drying out. Most of the vegetation consists of knee-high grasses and solitary trees. Gallery forests can be found along rivers because the trees there have year-round access to water.
Because of the lack of water, chemical weathering is slow. Therefore, underdeveloped soils can be found on young land surfaces. According to the international soil classification system World Reference Base for Soil Resources (WRB), these are: Leptosols (soils in which rock occurs at shallow depths or which are very skeletal ), Arenosols (very sandy soils) and Regosols (less developed, low-skeletal, clayey or silty soils). However, more weathered soils can be found on old land surfaces. These include Cambisole , Luvisole and Lixisole .
In the long dry season, rising water movement prevails . If groundwater is to be found at a shallow depth , it rises with the ions dissolved in it close to the soil surface, which can result in salt soils ( Solontschake ). Usually, however, only the rainwater rises again and evaporates. But because the seepage water flow only reaches a small depth, secondary carbonates can precipitate in the subsoil , which can lead to the formation of calcisols .
Due to the low biomass production and the resulting low amount of litter , the soils are poor in humus and therefore also poor in nutrients . However, the low nutrient leaching and the relatively high pH values and the associated relatively high proportions of calcium , magnesium and potassium are favorable for land use . In contrast, there is a severe deficiency of phosphorus in many places.
Despite the short rainy season, there is a high risk of soil erosion due to the heavy rain . This is especially true for soils that are silty in the topsoil, i.e. for many Luvisols and Lixisols.
The wet and dry savannas are usually the most densely populated regions in the tropics. Before the onset of modern global warming predominantly falling in the summer rain ranged mostly from to traditional shifting cultivation (mostly as a hoe to cultivate without mechanical or animal aid) different in small fields quite a large variety of crops ( maize , sorghum , millet , beans types , Sweet potatoes , cassava in subsistence farming - and partly for the market cotton and peanuts . In addition, rice in irrigated farming , especially in Southeast Asia). Above all in Africa, agropastoralism prevails , since in addition to agriculture , livestock (mainly cattle and goats in Africa and water buffalo in South and Southeast Asia) are kept. Depending on the food supply, the lifestyle is more or less sedentary to semi-nomadic . On the fringes of the arid regions of Africa, there is sometimes an exchange with the mobile livestock owners there and the last fully nomadic tribes. They supply the villages in the dry savannah with salt , meat and camel milk .
- Wilfried Büttner: Dry and thorn savannah. In: Man and Space Developing Countries. ISBN 3-464-08018-8 , p. 22 f.