Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants. In West Africa, savannah vegetation is about the most important types of vegetation. In Nigeria, over 80% of the vegetation is one type of savannah or another.
Characteristics of Grassland
- The savanna vegetation is typified by tall grasses and scattered trees and shrubs. The species of grasses in the sudan and sahel savannah are annuals which often have cylindrical leaves to reduce transportation. During the dry season, the leaves of the grass turn yellow and die but the roots remain dormant. The grasses are deciduous.
- Savannah trees have thick barks which protect them from the effect of fire. Most of the trees are deciduous, they shed their leaves in dry season to reduce loss of water by transpiration and because of annual fire. The trees have long roots (e.g. acacia) to search to search for ground water.
- Savannah vegetation is usually not as luxuriant as the forest vegetation. This is because the trees are fewer, smaller in structure and scattered within the savannah habitat.
- The annual burning and fire in the savanna reduce the quality of the humus in the soil, while the ash retains some minerals salts which are washed into the soil during rains.
- Rainfall is usually moderate (1000 -1500 min per year) distributed over 6 to 8 months of the year. The dry season is longer in the savanna than the forest region.
- Savannah soil is usually sandy, shallow of relative lower fertility than the forest soils.
Dry seasons bush fires and livestock grazing are common in the tropical savannah
Types of Grasslands
The two main types of grassland are tropical and temperate savanna. Tropical savannas occur in West and East Africa, Southern Africa, north of the tropic of Capricorn, part of Brazil, north and east of Australian Desert and part of Indian deccan Plateau. About 80% of the vegetation of Nigeria is savanna type.
The different types of savanna vegetation in West Africa include – the Guinea savanna, the Sudan savanna and the Sahel savanna.
Temperate grassland includes the Steppe of Asia, Prairies of North America, Pampas of Argentina, Veldt of South Africa and Downs of Murray Darling Basin of grasslands are almost treeless. Among the trees of temperate grassland are poplars, willows and alders.
Distribution of Plants and Animals in Grasslands
Grass is the dominant vegetation of the savanna. These shrubs and herbs are scattered in the savanna while grasses cover the soil within them. In the guinea savanna are broad leaved trees, while further north in the sudan and sahel savanna the trees are more scattered and shorter. There are thorny trees with narrow leaves- to reduce transpiration and withstand the prolonged drought.
Palms which cannot withstand the drought are restricted to the wettest area or along the rivers.
Tropical savanna is the home of wild animals. The animals population include herbivores like caterpillars, grasshoppers and birds which feed on grass seeds, grazing animals like cows, goats, sheep and wild herbivores like antelope, deer, elephant, giraffe and okapi.
Carnivores include lion tiger, leopard panter, jacka; and cheetah. Along the rivers and marshy lakes are several species of reptiles such as alligators, crocodiles, giant and monitor lizards; and mammals such as hippopotamus and rhinoceros. There are also numerous species of birds, butterflies, moth and other insects.
Some Adaptation of Grassland Communities
Adaptations of Savanna Animals
The main adaptations of savanna animals include the following:
- Adaptation for drought which include burrowing into the ground by animals such as the rats and building of well ventilated terminals by termites.
- Adaptations such as sharp claw and teeth of the carnivores for catching their prey; and fast movement to catch them.
- Sharp vision, sharp hearing and fast movement of prey to escape from the predators and living together in groups or herd to ensure protection for their members.
Adaptations of Savanna Plants
The main adaptations of the savanna plants include the following:
- Adaptation of savanna plants for drought include shedding of leaves, possession of tiny leaves with highly reduced surface area, possession of thick cuticle over the leaf surface and reduction in the number of stomata on the leaves. Many plants possess underground stem through which tides them over the drought period.
- Adaptation of savanna plants for annual fire include: the thick and cropy barts of the woody plants, possession of fire-restricted twigs; rapid regeneration shortly after fires by suckering and coppicing, possession of various methods of regeneration vegetative after fires by herbs. This is by the use of organs such as bulbs, tubers, corms and rhizomes, which are buried below. The plants also produce numerous seeds which can remain buried in the soil and sprout quickly during the rains.