The Savanna biome is part of a larger grassland biome and is mainly made up of flat grassland vegetation. Except for Antarctica, the grassland biome is present in all continents and spans over 20% of the earth’s surface.
Despite these different features, the two biomes have a common thing: grass that sustains the ecosystem, thus the name ‘grassland.’ The Savanna biome is characterized by dominant ground cover by grass species and scattered trees and shrubs.
The Savanna biome is Tropical grassland. It is located between the two tropics, the Tropic of Cancer to the north and the Tropic of Capricorn to the south. The area between the tropics is what is known as the tropical grasslands.
The biome covers over half of Africa, most of South America, and portions of Asia such as India. For instance, in Africa, the biome is mostly in the Eastern part, including Kenya and Tanzania.
Acacia savannas are mostly spread in the region. These biomes have provided habitat for various wild animals, leading to the establishment of animal game parks and reserves. Notable ones are the Maasai Mara in Kenya and the Serengeti in Tanzania. These two are home to one of the most unique animal migrations in the world.
The climate of this biome varies with the pre-existing season. There are two distinct seasons consisting of a wet and a dry season.
The wet season comes during summer, while the dry season comes during winter. The climate during the dry season is disastrous to animal and plant life since most plants wither and dry up, leading to no food for the animals.
Most of the rain in the Savanna biome is from the wet season. With the warmth of the Savanna, there is more rainfall. Also, there is the sprouting of healthy plants due to adequate water. Rivers flow, and ponds of water fill with water.
The two seasons of the biome are the key to determining precipitation in the ecosystem. There are two major rainy seasons per annum.
The dry season experiences lower rainfall of about 4 inches per annum for a period of 4 months spanning from October to January. On the other hand, the wet season, with an average of 25 inches, provides a lot of rainfall for the biome.
This results in the presence of constant precipitation regardless of the intensity and, consequently, adequate water for plant life and animal life all year long.
Despite the presence of two dominant seasons, there are other predisposing factors preventing equal rainfall all over the Tropical grasslands.
A case in point is the distance from the Equator. Areas around the Equator, characterized by equal days and nights, receive more rainfall due to the high amount of solar heating relative to other areas far from the equator.
The climate of the Savanna is gradually changing for the worse. Human interference with the original grasslands has led to a lot of destruction of the ecosystem and the reduction of forest cover due to deforestation. In some areas, it has led to desertification, thus changing the climate of the place.
Overgrazing and artificial fires have also contributed to a lot of harm to the Savanna biome. Nonetheless, these fires do not always negate the soil or plant life. For sure, they destroy habitats and scorch both animal and plant life, but they also help regenerate grass every year. Also, they regulate plant life and animal population to ensure balance in the ecosystem.
The Savanna biome has an average temperature of 25oC. It goes as high as 30oC during the summer and as low as 20oC in winter. Because of the slight temperature changes within the ranges of just between 20oC and 30oC in the Savanna biome, it is easy for the animals and plants to adapt.
Though there are only two seasons in the biome, the dry season can be further divided into two due to the range in temperatures.
The first one is the cold, dry season. It is characterized by high mid-day temperatures of about 29oC but experiences lower temperatures of about 21oC at night.
The second dry season is the warm, dry season, which experiences day temperatures of 32oC to 38oC. This is caused by the nature of the rays of the sun, which are close to vertical, thus the high temperatures.
The soil in the savannah is not very fertile and only has a thin layer of humus made up of decomposed plant and animal matter. It is porous, which means the water drains away very quickly. Soils tend to be red due to high iron content.
The hummus gives the plants nutrients. The nutrients in the soil are found near the surface as they come from decayed organic matter (vegetation) from the previous growing season. This organic matter decays rapidly due to the high temperatures.
There are four layers of soil in savanna grassland:
- Hardpan of laterite
- Red clays and re-deposited silica
Plant roots cannot penetrate the hardpan layer, which restricts vegetation growth.
There are generally 6 types of soils in the savannahs around the world.
- Lithosols – These are not very fertile and consist mostly of stones and gravel.
- Lateritic – these soils have an iron content, which makes the soil look reddish. It is also not very fertile.
- Cracking clays – This soil can hold much water but dries out and cracks easily. It isn’t easy to cultivate because heavy machinery is needed to dig the soil.
- Red yellow earths – Red earth is dry, and yellow earth is not very fertile.
- Saline and alluvial – This is the soil found near waterways and estuaries. It is the most fertile of the soil types in the savannah.
- Deep sands – This is very sandy soil and hardly fertile at all. They are nearer to the desert biome.
Plantlife in the Savanna is vastly adapted to cope with the climate. There are a variety of plant species in this biome, both tree and grass species.
Trees and grasses grow in the biome. These grasses grow to heights of as low as 80cm to as high as 350cm. There are also serious environmental weeds amongst the woody plant species.
- Prickly Acacia (Acacia nilotica)
- Rubbervine (Cryptostegiagrandiflora)
- Mesquite (Prosopis spp.)
- Lantana (Lantana camara and L. montevidensis)
- Prickly Pear (Opuntia spp.)
- Rhodes grass
- Red oat grass
- Buffel grass (Cenchrusciliaris)
- Giant rat’s tail grass (Sporoboluspyramidalis)
- Parthenium (Partheniumhysterophorus)
- Stylos (Stylosanthes spp.)
- other legumes
- White sage
- Spotted cactus
In as much as the Savanna biome is grassland, there are areas in the biome with open patches devoid of grass.
The grasses take on a brown desert-like color during the dry season, probably due to low photosynthesis. All the same, when seasons change and it is humid again, they turn green.
Plus, there are a few vast spaces that favor the scattered growth of shrubs.
The trees grow to an average height of 6m. Plants in this biome have developed long taproots constituting a hydrophilic root system that can extend deeper into the soil in search of water.
These trees have large tree trunks to store excess water when there is adequate water in the biome to prepare for the dry seasons. Their barks are hardened and thick and are prone to wildfires in the forests. Wildfires easily spread in the Savanna biome due to the vast presence of grass.
The leaves of the plants are deciduous and fall during the winter season. Since leafy plants are at risk of losing a lot of water to the atmosphere through transpiration, they shed their leaves once a season to conserve water.
The Savanna biome is one of the most diverse biomes in terms of animals. It’s not only aided by the vastness of the tropical grassland but also the varying changes in the climate. This biome supports one of the world’s most renowned species of animals.
- Bat-eared foxes
Most of these animals are found in the African Savanna. The South American Savanna has fewer mammals but has more bird species. Also, it is only in the Australian Savanna that hosts mammals such as the kangaroos. Overall, the Savanna biome is home to thousands of insect species that attract birds for feeding and nesting.
The carnivore population grows exponentially during the rainy season. The reason being, the rainy season leads to more grass growth in the Savanna leading to more reproduction of the herbivores.
As keystone species, carnivores such as lions and cheetahs have to be present in the ecosystem in order to strike a balance in the biome. They prevent incidences of overgrazing that can arise due to the overpopulation of prey species like the gazelles and zebras.
In spite of a large number of animals in the biome, there is always enough food for all, especially for the herbivores. Each of these animals has developed uniquely different feeding habits that reduce competition for food.
For instance, giraffes feed on the top vegetation on trees that other animals such as the zebra cannot reach. Elephants feed on leaves from shorter trees. Zebras feed on shrubs and tall grasses, while wildebeests and gazelles feed on medium and short grasses, respectively. It is for this reason that these groups of animal species can be found in the same area, feeding without competing for food.
The dry season leads to loss of water through evaporation and transpiration. Consequently, there is inadequate drinking water for animals, and the soils are dry and cracked due to extensive loss of water. With no means of plant growth, herbivores start reducing in number. Carnivores may increase slightly due to abundant food.
Due to the fluctuation in climatic levels, animals migrate in search of food. They may migrate to very far places to search for water and pasture. The migration varies among animals. There are some that migrate only to come later when the rainy season is back while others migrate never to return. Again, there are those that move during the rainy season.