Savannah is a natural area dominated by herbaceous vegetation on red lateritic soils. This zonal natural complex (PC) is distributed between humid forests and semi-deserts. More than 40% of the area of Africa is occupied by vast expanses of savannah. Soils of a reddish color are formed under tall grass vegetation with a predominance of cereals, rare specimens of trees and thickets of shrubs.
Tropical forest-steppe
Savannahs, except for Africa, are common in Australia and the Hindustan Peninsula. This type of PC includes campos and llanos on the mainland of South America. The savannah is often compared with the forest-steppe of the temperate zone of Eurasia. There are some similarities, but there are more differences. The main features that characterize the savannas:
- soils with low humus content;
- herbaceous xeromorphic vegetation;
- umbrella-shaped trees and shrubs;
- rich and diverse fauna (unlike the steppes, itpreserved).
Kampos - savannah in the Brazilian Highlands - formed by different types of plant communities. Serrados is distinguished by the presence of low-growing trees and shrubs. Limpos forms a tall grassy steppe. Llanos on both sides of the Orinoco River in South America are covered with dense grass and individual groups of trees (palm trees).
African savannas. Soils and climate
The tropical forest-steppe zone occupies about 40% of the territory on the hot continent. In the Northern Hemisphere, savannahs reach semi-deserts at a latitude of 16–18°, coming close to Lake Chad and the sands of the Sahara. The boundary of this zonal PC in the south is the Southern Tropic. Savannas occupy flat spaces and rise to a considerable height within the East African Plateau.
The prevailing types of climate are subequatorial and tropical. Two seasons are clearly distinguishable during the year - wet and dry. The rainy period is reduced when moving from the equator to the tropics from 7–9 to 3–4 months. In January, when the wet season begins in the Northern Hemisphere, the dry season begins in the Southern. The total amount of moisture reaches 800–1200 mm/year. Moisture coefficient - less than 1 (not enough precipitation). Some areas suffer from poor moisture intake (Kmoisture below 0.5–0.3).
What kind of soil in the savannah is formed in such climatic conditions? During the rainy season, nutrients are intensively washed out by water into the lower horizons. When the dry period sets in, the opposite phenomenon is observed - soil solutionsrising.
Vegetation type and climate
After receiving moisture, the tropical forest-steppe in Africa comes to life. Yellow-brown shades of dry stems are replaced by emerald greens. Leaves grow on those trees and shrubs that shed their leaves during a drought, grasses rapidly stretch, sometimes reaching 3 m in height. The soil, plant and animal world of the African savannas is formed under the influence of climate. Temperature conditions and humidity depend on the geographical location of the site.
Closer to the border of the equatorial forests, the rainy season lasts about 9 months. Tall-grass savanna is formed here; groups of trees and shrubs are more numerous. There are mimosa and palm trees that form gallery forests along the river valleys. The most interesting representative of the plant world of the savannah is the baobab. The tree trunk often reaches 45 m in girth.
As you move away from the equator and approach the tropics, the rainy season is reduced, typical savannahs develop. The territory bordering on semi-deserts receives moisture 3 months a year. Vegetation, which is formed in arid conditions, belongs to the desert type of savannah. At 50 ° C, it differs little from the desert. North African peoples call these natural areas "sahel", the inhabitants of South Africa - "bush".
What soils prevail in the savannah
The soil of the tropical forest-steppe is red-brown in color, which is given to it by iron compounds. This type is characterized by lowhumus content - from 1.5 to 3%. The middle part of the profile contains clays; the lower part shows an illuvial-carbonate soil horizon. The above features are typical for East Africa, the northern part of the Australian continent and certain regions of South America.
What kind of soil will form in the savanna depends on the type of moisture. With a sufficiently long dry period, humus accumulates due to the gradual decomposition of vegetation. More fertile soils in the dry savannas of Africa and the steppes of South America. With regular moisture, a granular structure or shell (hard crust) forms on the surface of the earth.
Soil types
Within the same natural zone, a different amount of precipitation falls, dry periods differ in duration. Features of the relief and climatic conditions leave their mark on the type of vegetation of the savannah. Soils are formed by the interaction of all elements of the natural complex. For example, plant residues in the zone of moist forests do not have time to decompose, nutrients are washed out by heavy rainfall.
Compared to the red-yellow ferrallitic soils of the forests of the equatorial belt, more humus accumulates in the savannas. Due to the dry period, there is a slow decomposition of plant residues and the formation of humus. Intermediate type - red ferralitic substrates of variable-humid forests. Under the grass savannahs, lateritic and red-brown soils are mainly located. Chernozems are formed under the dry type of this natural zone. As they approach the desert areas, they are replaced by reddish-brown soils. The soil acquires a bright brownish or brick-red color due to the accumulation of iron ions.
Savannah wildlife
The tropical forest-steppe fauna is amazingly rich and diverse. There are representatives of all groups of the animal world. Spiders, scorpions, snakes, elephants, hippos, rhinoceroses, wild boars find food in the savannah, shelter from the heat of the day or rain. Earthen cones of termite structures rise everywhere, enlivening the flat surface of the savannah. The soils are inhabited by spiders and small rodents, rustles are constantly heard in the grass - snakes and other reptiles scurry about. Large predators - lions, tigers - deftly hide in tall grass to attack the victim unexpectedly.
Ostriches behave cautiously: high growth and a long neck allow a massive bird to notice danger in time and hide its head. Most of the inhabitants of the savanna flee from predators by flight. Ungulate herbivorous animals overcome considerable distances: zebras, gazelles, antelopes, buffaloes. Giraffes gracefully nibble on the delicate foliage of the tallest trees, and clumsy hippos toss and turn in the grass on the banks of the lakes.
Savanna and woodland agriculture
Significant areas of the tropical forest-steppe of Australia and South America are occupied by pastures and the cultivation of cotton, corn, and peanuts. In the agriculture of India and Africa, savannahs and light forests are also used. Red-brown soils are fertile when moistened and properly cultivated. The low culture of agriculture and the lack of land reclamation led to the development of erosion processes. The Sahel zone in Africa is the territory of modern desertification caused by a combination of natural and anthropogenic factors.
Savanna soil conservation issues
The nature of Africa is changing under the influence of man: forests are being cut down, the savanna is plowed up. Vegetation and animals are negatively affected by the anthropogenic factor. The number of predators and ungulates is declining, and the population of primates is under threat. Disturbance of the vegetation cover during plowing of the savannah or deforestation leads to the rapid destruction of the soil. Downpours erode the upper fertile layer, revealing a dense mass of clay and iron compounds. It is cemented under the influence of high air temperatures. Such phenomena occur in areas of intensive agriculture and grazing. The red-brown soils of the savannas need protection and restoration in vast areas in the developing countries of Africa and Latin America.
