A savanna, also spelled savannah, is a mixed woodland-grassland biome and ecosystem characterized by trees that are sufficiently widely spaced so that the canopy does not close. It is often believed that savannas feature widely spaced, scattered trees. Savannas maintain an open canopy despite a high tree density. Savannas are also characterized by seasonal water availability, with the majority of rainfall confined to one season.
Savannas are subject to regular wildfires, and the ecosystem appears to be the result of human use of fire. Intentional controlled burns typically create fires confined to the herbaceous layer that do little long term damage to mature trees. This prevents more catastrophic wildfires that could do much more damage.
The annual rainfall ranges from 500 mm (19.69 in) to 1,270 mm (50.00 in) per year, with the precipitation being more common in six or eight months of the year, followed by a period of drought.
Savannas provide habitats for a wide array of animals, some of which foster the vegetation through grazing, browsing, pollinating, nutrient cycling, or seed dispersal.
Tropical and subtropical savannas are classified with tropical and subtropical grasslands and shrublands as the tropical and subtropical grasslands, savannas, and shrublands biome. The savannas of Africa, including the Serengeti, famous for its wildlife, are typical of this type. The Brazilian savanna (Cerrado) is also included in this category, known for its exotic and varied flora.
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Here's a look at some specific trees and their roles in the African savanna ecosystem:
Acacia Trees: The Iconic Savanna Trees
Acacia trees are without a doubt the most iconic trees in Africa. You can spot this tree within most of the Savannah area throughout the continent, most acacia usually lives only 20 to 30 years. Their long roots help stabilize the soil in areas threatened by erosion. Another name for acacia tree is thorn trees. Some have long straight thorns while others have hook-shaped ones. The main reason is that it acts as a deterrent against browsers.
The Umbrella Thorn Acacia is one of the most recognizable trees in the African Savanna. The Umbrella Thorn Acacia grow up to 20 meters high, the leaves are 2.5 centimeters long and 1 millimeter wide. The Umbrella Thorn Acacia has two types of thorns on the branches; long, straight, brown thorns and short hooked thorns grow next to each other. The Umbrella Thorn Acacia thorns grow in pairs, that one thorn hides the cluster of flowers that grow on the Acacia.
Acacia drepanolobium is a species of plants in the family Fabaceae. It fixes nitrogen. It is a photoautotroph, is a slender shrub or a tree, with short branches radiating from the main stem. The common name of the plant comes from the observation that when the wind blows over bulbous spines in which ants have made entry/exit holes, they create a whistling noise. The tree actually encourages these ants by both providing homes and food in special flower-like structures called “extra-floral nectaries”.
Umbrella Thorn Acacia
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Baobab Trees: The "Tree of Life"
The baobab can be found in the African Savanna and the Indian Savanna mostly around the equator. The baobab tree is an iconic tree of the African Savanna. The Baobab tree grows to 25 meters tall and can live up to several thousands of years. The Baobab tree is leafless for 9 months of the year. The appearance of the tree is like it was a picked out of the ground then placed upside down. The Baobab Trees bark, fruit and trunk can be used. The bark is used for cloth and rope. The leaves are for condiments and medicines, and the fruit can be eaten.
The African savanna is one of the most known savanna of the world with the East African covered with acacia trees. How to define the African Savanna is by a rolling grassland dotted with trees.
The magnificent baobab tree (Adansonia digitata) is an icon of the African continent. With bark and fruit offering over 300 life-sustaining uses, it is the root of many Indigenous remedies, traditions, and folklore. Hence its literal nickname, ‘The Tree of Life.’
European explorers claimed the trees could live for up to 5,000 years, but carbon dating indicates they may live up to 3,000 years. Known to reach up to 100 feet tall with a circumference to match, these trees are enormous, providing shelter, food, and water for various life forms. Indigenous African savanna peoples have long centered their communities around these monumental trees.
The Baobab Tree: A Lifeline for the People of Africa.
Baobab trees are fundamental to the entire dry African savanna ecosystem. They help keep soil conditions humid, aid nutrient recycling, and slow soil erosion with their massive root systems. In an arid climate, baobabs symbolize life in a landscape where little else can thrive.
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For humans, the baobab’s fruit pulp can be eaten, soaked in water to make a refreshing drink, preserved into a jam, or roasted and ground to make a coffee-like substance. The bark can be pounded to make everything from rope, mats, and baskets to paper and cloth. Leaves are also used, they can be boiled and eaten, or glue can be made from their flower’s pollen.
Baobab Alley at sunset near Morondava, Madagascar
Other Notable Trees
Jackal berry tree (Diospyros mespiliformus) is another common savanna species, and is among the tallest trees in the ecosystem, reaching a height of 80 feet. Although less common, the candelabra tree (Euphorbia ingens) is often seen near the edges of the savanna. It is an unusual tree with erect, upward-pointing branches that resemble cacti.
The sausage tree of sub-Saharan Africa is beautiful in flower, the blood-red to maroon flowers hang in long panicles. This tree can reach a height of as much as 20 meters. The large tree is spread sparsely throughout Serengeti. It produces characteristic long (up to 1 m), succulent, poisonous fruits that drop from the tree and release seeds as the pulp rots.
Strangler fig is one of the most common hemiepiphyte. Is the towering strangler fig tree which starts life as a tiny seed in the canopy named for their pattern of growth upon host trees. Strangler figs are ecologically important in some tropical forests. The hollow centers of strangler figs are full of spaces that provide shelter and breeding sites for bats, birds, and other animals. This tree is native in Africa, specifically Tanzania where is common in kopjes and along rivers in Serengeti.
Phoenix reclinata is growing in a range of habitats, often seasonally water-log, such as along watercourses in high rainfall areas, in riverine forest and even in rainforest areas. Phoenix reclinata can reach up to 12 m but is most often between 3 and 6 m. Flowers and fruits: fruits are up to 1-2.5 cm long, ovoid and reddish-brown to scarlet when ripe.
Salvadora persica L, also known as Arak (in Arabic) and Peelu (in Urdu), is the most common traditional source of tooth or chewing stick (miswak). The fresh leaves are sometimes useful as salad and are also useful in traditional medicine for cough, asthma, scurvy, rheumatism, piles, and other diseases.
Euphorbia candelabrum is a succulent tree with branches that are persistent from around 3 metres upwards, almost erect, rebranching to form a large, broadly rounded crown. It’s one of the more poisonous spurges. The bark has a rough feel and is grey to black in color. The tree has a combination of one straight thorn with a small hooked thorn alongside. The thorns are thin and grow in pairs. The flowers form in clusters of old wood. The flowers themselves are creamy, white, balls. The pods are a distinctive pale, gold brown color and are curled and twisted. In extremely arid conditions, it may occur as a small, wiry bush. It grows up to 21 m (69 ft) in height. The tree carries leaves that grow approximately. 2.5 cm (1 in) in length with between 4 and 10 pairs of pinnae, each with up to 15 pairs of leaflets. Flowers are small and white, highly aromatic, and occur in tight clusters.
The yellow fever Tree is a low elevation medium to tall tree growing along or in water. The beauty of this tree comes from the clusters of 10 yellow ball flowers. Pieces of the magnificent, smooth, greenish-yellow bark flake off as the tree matures, giving an interesting, colorful pattern to the trunk. Leaflets are 2.5-6.5 mm × 0.75-1.75 mm. Petiolar glands are usually present at the base of the upper pinnae pairs. The common name comes from the misunderstanding of early settlers who thought the tree was the carrier of the malaria fever.
Other Plant Life in the Savanna
Shrubs generally occur within the savanna near sources of water and along the slopes of hills. Sickle bush (Dichrostachys cinerea) is one of the most common shrubs in the savanna, found along brackish waterways and in roadside ditches. Several species of raisin bush (Grewia spp.) are also commonly found near seasonal and permanent watersheds in the savanna. White raisin bush (Grewia bicolor) is identifiable by its large, hairy leaves and yellow, star-shaped flowers. Sandpaper raisin (Grewia flavescens) superficially resembles other members of the genus, although its fruit ripens later in the year, from March until July. Buffalo thorn (Ziziphus mucronata) is a large shrub known for its distinctive zig-zag-shaped twigs and shiny, light-green leaves.
By far the most abundant type of plant in the savanna, grasses define the ecosystem and represent nearly 75 species. Common finger grass (Digitaria eriantha) is the African savanna's most important forage grass. Animals rely on the long-lived foliage through the dry season when most other types of grass become unpalatable. Eleven species of lovegrass (Eragrostis spp.) are also commonly found throughout the savanna. Of those, saw-tooth lovegrass (Eragrostis superba) and heart seed lovegrass (E. capensis) are the most abundant. Bluestem grass (Bothriochloa spp.) is found in the warmer areas of the savanna, and include three common species: purple plume grass (Bothriochloa bladhii), pinhole grass (B. insculpta) and stinking grass (B.)
Threats and Conservation
Human induced climate change resulting from the greenhouse effect may result in an alteration of the structure and function of savannas. Some authors have suggested that savannas and grasslands may become even more susceptible to woody plant encroachment as a result of greenhouse induced climate change.
However, due to climate change, nine of thirteen of Africa’s oldest and largest baobab trees have died in the past decade. Scientists speculate that warming temperatures have killed the trees directly or made them weaker and more susceptible to drought, diseases, fire, or wind.
Only with the integration of ecological, social, and economic studies involving local communities can we restore Africa’s climate and ecosystem over the long term and ensure that the baobab tree will continue to live and thrive for thousands of years to come.
The removal of grass by grazing affects the woody plant component of woodland systems in two major ways. Grasses compete with woody plants for water in the topsoil and removal by grazing reduces this competitive effect, potentially boosting tree growth. In addition to this effect, the removal of fuel reduces both the intensity and the frequency of fires which may control woody plant species.
Large areas of Australian and South American savannas have been cleared of trees, and this clearing continues today. Clearing is carried out by the grazing industry in an attempt to increase the quality and quantity of feed available for stock and to improve the management of livestock.
A number of exotic plants species have been introduced to savannas around the world. Amongst the woody plant species are serious environmental weeds such as prickly acacia (Acacia nilotica), Rubbervine (Cryptostegia grandiflora), Mesquite (Prosopis spp.), Lantana (Lantana camara and L. montevidensis) and Prickly Pear (Opuntia spp.).
The African savanna's trees are integral to its ecosystem, offering sustenance, shelter, and crucial ecological services. Protecting them is vital for the savanna's health and the well-being of its inhabitants.
