The savannas are tropical to subtropical climate ecosystems in which grasses abound and there are few trees and shrubs. They are part of the so-called grasslands next to the meadows, differing from these by climate and species composition. The rainfall, fertility and permeability of soils is what determines the presence of savanna instead of tropical forest.
Savannas are distributed throughout much of tropical and subtropical America, from southern North America to South America. We find them in vast areas of sub-Saharan Africa, from the Atlantic to the Indian Oceans.
Similarly, there are savannas in the foothills of the Himalayas, in the north and east of Australia and in Hawaii. These plant formations have a simple structure with a herbaceous cover dominated by grasses and some scattered trees.
Savannas develop in variable soil conditions from sandy loam to clay. Among the factors that affect the ecology of these ecosystems are fires (natural and man-made) and herbivory.
Characteristics of the savanna
The geographical delimitation of the savannas is framed in the intertropical zone, conditioned by climatic and edaphic factors (soils). The savannas develop in low tropical areas, with high average temperatures and low total rainfall.
Savannas have a simple structure, where trees only appear sparsely and are even absent in large areas. The dominant stratum is the herbaceous cover, mainly composed of grasses, with some subshrubs and shrubs.
The grass cover can have a height from 0.20 to 3 m. while in wooded savannas the trees have heights between 5 and 15 m.
Although in the savannas the soils are variable, in most cases they are loamy-sandy, clay-sandy to clayey. In well-drained savannas entisol and oxisol soils predominate; while in poorly drained savannas there are mainly vertisols and alfisols.
There are also regional peculiarities such as the volcanic ash soils of the Serengeti in Tanzania.
Fires are a characteristic component of the savannahs, being both natural and human-caused. The grasses that dominate the savanna have developed adaptations that allow them to survive burning.
These periodic burns allow the renewal of biomass to the extent that it promotes the emergence of new grass shoots.
Savannas, like all herbaceous biomes in the world, have developed a process of coevolution between herbivores and herbs. Herbivores have specialized to reduce competition and some consume mainly grass while others browse the leaves of scattered trees.
The human being has caused great negative impacts on the savannas, especially with agriculture, farming and hunting. In some cases it has expanded the limits of the ecosystem by deforesting bordering forests that are transformed into secondary savannas.
In others, the limits of the natural savannah are reduced by dedicating extensions to the cultivation of cereals or the raising of cattle.
Loss of species
Hunting has been the main cause of the decline in large populations of herbivores in the savannas. For example, the intensification of hunting with the arrival of Europeans in Africa, substantially reduced the fauna in the Guinean and Sahelian savannas.
Location: geographical distribution
Savannas exist in different regions of the Earth:
We find savannas in America from southern North America to northern South America in Colombia and Venezuela. The most representative being the Colombian-Venezuelan plains and the Guyanese savannas that limit the Amazon and the Guiana jungle to the south.
Then there is the Cerrado, stretching through central Brazil, northeastern Paraguay, and eastern Bolivia. There is also an extensive savanna from Rio Grande do Sul (Brazil), all of Uruguay and even part of Entre Ríos (Argentina).
In Africa the savanna extends in a wide strip below the Sahara desert, from the Atlantic to the Indian Ocean, in what is known as the Sahel. To the south are savannas up to the edge of the Congo jungles and another area that includes the wooded savannas of Zimbabwe.
In the Indomalaya region are the Terai-Duar savannas, in the foothills of the Himalayas. This tall grass savannah spans Bhutan, India, and Nepal.
Savannas are found in this region of the world in the north and east of Australia as well as shrubby savannas in Hawaii.
Types of savanna
The types of savanna can be classified in different ways:
The World Wildlife Foundation o World Wildlife Fund(WWF), identifies up to 50 savanna ecoregions worldwide. Each ecoregion represents a type of savanna defined by some combination of species composition, climate, and soils.
By prominent biotypes
The biotype is the general morphological expression of the plant, of which four basic forms are recognized: grass, subshrub, shrub and tree. In the savanna the predominant biotype is grass, although there are savannas with scattered trees or with shrubs and subshrubs.
In this sense, we speak of non-wooded savannas, bush savannas and wooded savannas. For example, the non-wooded savannas of the Gran Sabana in Venezuelan Guiana.
On the other hand, the bush savannas of northwestern Tanzania or the wooded miombo savannas of the central Zambezi from Tanzania to Angola.
By water regime
Another criterion for classifying savannas is the water regime; thus there are floodable and non-floodable savannas. For example, in the Colombian-Venezuelan plains there are savannas associated with the course of large rivers that flood in the rainy season.
In this case we speak of seasonal savannas, hyperstational savannas and semi-seasonal savannas given by the duration of the dry and rainy seasons. The seasonal savannas alternate a rainy season of 6-8 months with a dry season of 4-6 months, have well-drained soils and do not flood.
The hyperstational savannas have poorly drained soils and are periodically flooded; with a dry season of 3 to 4 months. These savannas actually have four seasons: the dry season, the rainy season, the flooding season and the rainy season.
For their part, semi-seasonal savannas are similar to hyperstational ones, but with a dry season that lasts only a few weeks.
By floristic criteria
A criterion that is also used to define the types of savannas is the presence of characteristic species due to their abundance or representativeness. Thus, for example, in the Colombian-Venezuelan region they speak of savannas ofTrachipogon (not floodable) and sheets of Paspalum fasciculatum (floodable).
Savannas thrive in warm tropical and subtropical climates with variable rainfall. In the savannas there are two seasons: a dry period and a rainy or humid period; the duration of one and the other being variable.
In northern South America, the dry period lasts from 3 to 5 months and the rainy one from 7 to 9 months. However, in the Australian savannas the relationship is reversed, with 5 months of rains and 7 months of drought.
During the dry period, sporadic rainfall does not contribute more than 100 mm. While in the rainy period the rains are intense and long-lasting. The amount of water supplied varies depending on the region, even locally, and can range from 600 to 3,000 mm.
The average annual temperature is around 27 ºC although it is variable in the extension of the biome.
In the Australian savannas, temperatures are high throughout the year with maximums of 25 to 35 ºC. In the Serengeti (Africa) the average maximum temperatures vary from 24 to 27 ºC, and the minimum from 15 to 21 ºC.
Flora of the savanna
The dominant family in the savannas is Poaceae, with an enormous diversity of genera and species. Among the few subshrubs, shrubs and trees legumes (Leguminosae or Fabaceae) abound.
– American species
In the savannas of southern North America, species such as Tridens texanus, Tridens muticus, Trichachne hitchcockii, Aristida roemeriana and Bouteloua radicosa.
On the other hand, in the savannas of the Colombian-Venezuelan plains, species of the genera Trachypogon and Paspalum. Other genres represented areAxonopus, Andropogon, Leptocoryphium, Sporobolus and Aristida.
Further south, the Cerrado is the largest savanna region in South America and one of the most biologically rich in the world. Here are species likeGymnopogon foliosus, Country panicum, Saccharum asperum,and many others.
Trees and shrubs
A representative tree of the American savanna is the chaparro (Byrsonima crassifolia and Byrsonima coccolobifolia). There are also savannas where the “arboreal” element is palms, for example the plains palm savannasCopernicia tectorum) In Venezuela.
In the plains, the formation of tree islands in the middle of the savannah is common, associated with conditions of the water table and fertility. These islands are called “matas” and are made up of species of trees and shrubs.
Among the common species in the plain “bushes” are oil (Copaifera officinalis), the carob tree (Hymenaea courbaril) and cane fistula (Cassia grandis).
– African species
In the African savannas, short and medium grasslands predominate with species of grasses of the genera Sporobolus, Chloris, Digitaria, Eragrostis, Cynodon, Panicum, Pennisetum, among others. Although there are also taller species such asHyparrhenia rufa up to 3 m.
In the savannas near the Sahara desert there are typical species of this desert such as Panicum turgidum and Aristida sieberana. Wooded savannas of tall grasses also develop where the dominant species is elephant grass (Pennisetum purpureum).
Trees and shrubs
Among the trees of the savannas of Africa, the most characteristic species are those of the genus Acacia (legumes). Legumes are rich in protein, being highly sought after by species that browse (consume tree leaves), such as giraffes.
One of the savanna ecoregions of Africa is the Sahelian acacia savannas, which form a continuous band from the Atlantic Ocean to the Red Sea. Also this ecoregion includes the Sahara desert to the north.
Common tree species in this ecoregion include Acacia tortilis, Acacia laeta, Commiphora africana, Balanites aegyptiaca and Boscia senegalensis. While to the south of the sahel there are shrubby savannas with a predominance of shrubs ofCombretum and Terminalia.
Likewise, you can find the teak wooded savannas (Baikiaea plurijuga) of the Zambezi (Zimbabwe).
– Indo-Malay species
In the Indo-Malay savannas there are tall grasses with the species of grasses Saccharum spontaneum, Saccharum benghalensis, Arundo donax, Narenga porphyracoma, among other. Low grass savannahs are also found with species such asImperata cylindrica, Andropogonspp. andAristida ascensionis.
– Australian species
In the Australian savannas there are grasses of the genera Sorghum, Chrysopogon, Aristida, among others. There are also low grass savannas such as those dominated by the species ofDichanthium spp.
Trees and shrubs
In the case of the Australian savannas, legumes (Acacia spp., Bauhinia spp., Albizia spp.) and myrtaceae (Eucalyptusspp.). There are also species of the generaMacropteranthesand Terminalia of the Combretaceae family.
Savannas are home to a large number of animal species, in some cases such as those in Africa with large populations. The abundance of grasses allows the development of large herds of herbivores that attract large predators.
– American species
In the savannas of the Colombian-Venezuelan plains the most prominent animal is the capybara or chigüire (Hydrochoerus hydrochaeris). This mammal is considered the largest rodent in the world and lives in the lagoons of the savannas.
Another inhabitant of the savannas is the plains deer or caramerudo deer (Odocoileus virginianus apurensis).
The savannas of America are very rich in birds, including the jabirú (Jabiru mycteria) and the red corocora or scarlet ibis (Eudocimus ruber). Among the birds of prey are the chimachimá or caricare (Milvago chimachima) and the red busardo or red hawk (Busarellus nigricollis).
Among the predators of the capybara are large carnivores that inhabit the savannah. Among them is the jaguar or yaguar (Panthera onca), the largest feline in America.
In the water the green anaconda (Eunectes murinus) and the Orinoco caiman (Crocodylus intermedius). The latter were abundant in the past, but hunting for their skin and meat brought them to the brink of extinction.
The Orinoco caiman is one of the largest crocodiles in the world, reaching up to 7 m in length. For its part, the anaconda is the largest snake in the world, reaching up to 10 m in length.
In the rivers and lagoons of the plains there is an abundance of the spectacled caiman or baba (Caiman crocodilus) relatively small in size (1-2.5 m). Also inhabits an ant predator, known giant anteater or palm bear (Myrmecophaga tridactyla).
– African species
Among the herbivores of the African savannas, the wildebeest (Connochaetes gnou and C. taurinus) and zebras (Equus quagga, E. zebra and E. grevyi). Other grass eaters are gazelles (Gazella spp.) and the savanna elephant (Loxodonta africana).
There are browsers like the giraffe (Giraffa camelopardalis), which consume the leaves of Acacia. Among the omnivores is the wild pig or string (Hylochoerus meinertzhageni) that consumes herbs, roots, but can also be a scavenger.
The emblematic animal of the savannas of Africa is the lion (Panthera leo). Also, there are other felines such as the leopard (Panthera pardus pardus) and cheetah (Acinonyx jubatus).
Other carnivores are hyenas (Crocuta crocuta) and spotted wild dogs (Lycaon pictus), which hunt in packs. Additionally there is the Nile crocodile (Crocodylus niloticus), which stalks the herds of wildebeest and zebra on their migrations.
– Asian species
The savannas at the foot of the Himalayas are home to the largest number of tigers, rhinos, and ungulates in Asia.
These plant formations constitute the habitat of the Asian elephant (Elephas maximus).
Among the ungulates are the nilgó or blue bull (Boselaphus tragocamelus) and the water buffalo (Bubalus arnee).
The hispid hare (Caprolagus hispidus) is threatened while the dwarf wild boar (Porcula salvania) is critically endangered.
In these savannas lives the one-horned rhinoceros (Rhinoceros unicornis) and the Asian tiger (Panthera tigris) which is the second largest feline in the world.
– Australian species
The fauna of the Australian savannas is not very diverse compared to the other regions of the biome. There is an important diversity of reptiles, including theCtenotus rimacola.
Similarly, there are small marsupials like the kangaroo hare (Lagorchestes conspicillatus), the rabipelado kangaroo (Onychogalea unguifera) and the bronze quota (Dasyurus spartacus).
Several economic activities can occur in the savannas:
The soils of the savannas are variable in fertility and water availability, with wide areas useful for agriculture. Sorghum and millet are grown in parts of Africa, while soy, corn, sunflower and sesame are grown in America.
Savannas are ecosystems linked to grazing, making them ideal for extensive livestock rearing. A large part of the savannahs of the Colombian-Venezuelan plains have traditionally been dedicated to this activity.
Likewise, dual-purpose cattle and sheep mainly for wool in the savannas of Uruguay.
There are protected savannahs such as national parks or fauna reserves and in these areas the main activity is tourism. For example, the national parks of Africa where the famous photographic safaris take place.
A historical activity in the savannas has been hunting, leading to the extinction of many species. In the acacia savannahs of the Sahel the immense herds of ungulates were drastically reduced by hunting by European settlers.
Today, even in protected areas hunting continues. For example, an estimated 200,000 animals are killed within the Serengeti National Park annually in poaching.
Examples of savannas in the world
– Serengeti National Park (Tanzania)
Its 13,000 km² extend through the volcanic savannas of the Serengeti in northern Tanzania, near the border with Kenya. It was created in 1951 and shelters acacia wooded savannas in flat plains and rolling areas.
The dominant tree species is acacia (Acaciaspp.) of mimosoid legumes. For its part, the predominant plant group is the short and intermediate grasslands of grasses.
Among the dominant species are Sporobolus spp., Pennisetum mezianum, Eragrostis tenuifolia, Andropogon greenwayi and Panicum coloratum. Also foundCynodon dactylon, Chloris gayana and Digitaria macroblephara.
It is home to a huge amount of fauna, both in species diversity and population size. Here live elephants, wildebeest, giraffes, lions, hyenas, gazelles, rhinos, among others.
It is also inhabited by the black rhinoceros (Diceros bicornis) and the Kaffir buffalo (Syncerus caffer).
This region is famous for the migrations of huge herds such as the blue wildebeest (Connochaetes taurinus) that reach up to 1.3 million. For their part, Thomson’s gazelles (Gazella thomsoni) displace up to 400,000 individuals and Burchell’s zebras (Equus burchelli) 200,000.
These animals make a long journey between this area and the ecoregion of the forests of Acacia–Commiphora of the South every year.
It is the land of the Maasai, an ethnic group that traditionally practices livestock and agriculture. However, as part of the park’s creation, these natives were transferred to the Ngorongoro Highlands.
For the rest, tourism is a highly developed activity that generates high income for the country. However, there are also illegal activities such as poaching that seriously affects the ecosystem.
– Santos Luzardo National Park (Venezuela)
Its 5,844 km² extend between the Cinaruco and Capanaparo rivers until the confluence of both with the Orinoco river. It was created in 1988 and is located in the Apure state in southern Venezuela, close to the border with Colombia.
It is a representative area of the flooded savannas of the Colombian-Venezuelan plains, with flat relief, except for some granite elevations.
Grass Paspalum fasciculatum(Chigüirera straw) is the most abundant in these savannas. Other species of the shoals (lower parts) areImperata contracts (viper) and Leersia hexandra (lambedora straw).
Then in the highest parts (benches) there is Andropogon sealanus, Sporobolus indicus (tupuquén), Paspalum plicatulum (gamelotillo), among others. There are some bushes (Ex .:Cassia tetraphylla) and trees (Ex .: Bowdichia virgilioides , the American cork oak).
The capybara or chigüire, the jaguar and the caramerudo deer inhabit these lands. In the rivers are the Orinoco caiman, the anaconda and the piranhas. As well as the giant otter (Pteronura brasiliensis), the arrau turtle (Podocnemis expansa) and the pink dolphin or boto (Inia geoffrensis).
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World Wild Life (Viewed 4 Sep 2019). Taken from:worldwildlife.org/biomes/tropical-and-subtropical-grasslands-savannas-and-shrublands