Each distinct biome boasts its own exclusive flora and fauna. A noteworthy example of a grassland biome is the savanna, which is characterized by expansive, open grassy terrains with sparse tree cover. Savannas can be categorized into two types: tropical savannas and subtropical savannas. These unique ecosystems trace their origins back to the Cenozoic Era, approximately 66 million years ago, a time when rainfall patterns in tropical regions became increasingly erratic. Notably, fossil evidence indicates that the emergence of lush vegetation encircled by grasslands occurred around 20 million years ago during the Miocene Epoch.
Interestingly, early human populations first inhabited savannas, particularly on the African continent. As humans adapted to their environment, they began to manipulate and alter their surroundings in accordance with their requirements. This led to the gradual migration and dispersion of human communities to various regions worldwide, including Asia, Australia, and the Americas, expanding their presence and influence beyond the African savannas.
Overview of Savanna
The savanna biome is characterized by vast expanses of grassy terrain interspersed with scattered trees and shrubs. This distinctive natural zone is primarily situated between the two tropics, predominantly in the subequatorial climatic zone. However, it is essential to note that the term “savanna” can sometimes lack clarity, and in certain instances, the term “steppe” is utilized to describe a comparable landscape. Generally, the designation “steppe” is commonly used for grassy areas in temperate climate zones, while “savannas” typically refer to those in tropical zones. Nevertheless, the terminology can overlap, leading to the use of “tropical steppes” interchangeably with “savanna” in both scientific and popular literature.
The primary distinction between savannas and steppes lies in the abundance of tree species. Savannas tend to have a higher occurrence of trees, leading to the reference to the natural zone as “savannas and rare forests.” These small pockets of forest and shrub vegetation often exist within the grassy areas. Additionally, deciduous forests, which are common in regions experiencing distinct dry and wet seasons, are also considered part of the savanna zone.
The savanna biome serves as the habitat for some of the largest terrestrial animals on Earth. Its unique ecosystem sustains a diverse array of wildlife, making it a critical and vibrant ecological setting.
Savannas are extensive biomes prevalent in regions with predominantly subequatorial and, to a lesser extent, tropical climates around the world. They span across five continents, with the largest savannas found in Africa and South America.
In Africa, savannas are situated between equatorial forests and deserts or semi-deserts. This arc-shaped territory stretches from Senegal and Somalia, extending southward through Kenya and Tanzania, eventually reaching the Kalahari Desert in the south and the Atlantic Ocean in the west. Additionally, the western part of Madagascar’s island is also covered with savanna.
In South America, savannas occupy the areas between the equatorial forests of the Amazon and the Brazilian Atlantic forest. There is also a smaller savanna region known as “Los Llanos” in Colombia and Venezuela, situated between the Orinoco River and the Andes. Furthermore, savannas cover the dry, leeward parts of Central America, as well as the western portions of the islands of Cuba and Haiti.
In Australia, savannas are mainly found in the northern parts of the continent. In Asia, they occupy significant portions of India and Indochina, as well as certain areas of southern China and the drier regions of some Lesser Sunda Islands in Indonesia. These diverse locations showcase the wide distribution of savannas and their importance as a distinct and widespread biome across the globe.
Savannas are a defining feature of the subequatorial climate zone, to the extent that this specific climate type is occasionally referred to as “savannah.” These biomes are characterized by the presence of two distinct seasons: a dry season and a wet season, each varying in duration across different parts of the biome. Regions situated closer to equatorial forests often experience longer wet periods with higher levels of rainfall.
One notable hallmark of savannas is the pronounced contrast between the two seasons. The annual rainfall can exceed 3000 mm in several regions of South America, particularly in South Asia. Most of this precipitation falls within a concentrated period of 4 to 7 months, leading to extensive flooding. However, during the remaining months of the year, rainfall becomes exceedingly scarce, resulting in the drying up of many smaller rivers and water bodies.
This pronounced seasonality in rainfall contributes to the distinctive ecological characteristics of savannas, where vegetation and wildlife have adapted to cope with the alternating cycles of abundance and scarcity of water resources. The resulting landscape diversity and adaptive strategies of plant and animal species make savannas an ecologically fascinating and vital biome on our planet.
The savanna biome has been a significant presence on Earth since the emergence of plant and forest communities. During periods when the Earth’s climate transitioned to drier conditions, savannas dominated vast portions of the planet’s surface. However, research suggests that a substantial portion of today’s savannas was once covered by equatorial forests until approximately 7 to 8 million years ago. This understanding is supported by numerous fossil findings and climate change studies.
At the end of the early Miocene epoch, the Earth’s climate was considerably wetter compared to the present day. Many areas in South America, Africa, and Australia that now house savannas were once lush and moist equatorial forests. The transformation of these regions into savannas began as a result of planetary climate changes during this period.
Average temperatures declined, certain ocean currents shifted direction, and precipitation became scarcer. Notably, the uplifted mountain ranges of the Ruwenzori and the East African Rift played a significant role in the emergence of the African savanna. They hindered the inflow of moist and warm air masses from the Atlantic Ocean and, combined with global climate changes, resulted in more frequent droughts in the forest belt from Senegal to East Africa. Over time, the forests were gradually replaced by savannas.
This particular transformation is of great interest to researchers, particularly in Africa, as it is believed to have played a crucial role in the development of early humans in the newly formed savanna regions of East Africa. Many of the earliest human species, such as Sahelanthropus tchadensis, Australopithecus, Orrorin tugenensis, Paranthropos, and Homo sapiens, have been discovered in these areas through the recovery of skeletons and fossils.
During the last glacial period, the climate became even drier, leading to significant changes and challenges for the fauna inhabiting these regions. This period witnessed one of the most substantial extinctions of megafauna in history, with many of the largest terrestrial mammals and birds disappearing from the landscape. For example, South America experienced the extinction of large predatory birds, while Africa lost species like deinotheriums and saber-toothed tigers. However, the heaviest losses were observed in Australia and South America, where all animals weighing over 1 ton vanished.
These historical climatic shifts and ecological changes have profoundly influenced the development and adaptation of plant and animal life in the savanna biome, shaping it into the diverse and dynamic ecosystem it is today.
Savannas are characterized by steppe landscapes where grasses and shrubs are the predominant components of the vegetation cover. Trees are scarce and typically widely spaced apart, creating an open and grassy terrain. However, there are exceptions, particularly in moist savannas, where individual forest formations are more prevalent. These forested areas often appear as isolated islands amid the typical savanna landscape. Nevertheless, closer to the equatorial forest zone, these forested regions merge into a continuous forest mass.
In the savanna-forest transitional areas, which experience higher annual rainfall (above 1400 mm) and shorter dry seasons, the vegetation displays greater variety and richness. These regions harbor the greatest biodiversity within the savanna biome. Most of the tree species found in these areas are broad-leaved and evergreen, contributing to the lush and verdant character of the landscape. In some moist savannas, evergreen trees are also present, enhancing the overall diversity.
While coniferous species are generally rare in savannas, South America is an exception, where species like araucarias can be found.
Several iconic tree species define the character of savannas, including the baobabs, eucalyptus, bottle tree, and traveler’s tree, among others. Acacias are particularly typical of savannas and can sometimes form extensive forests.
By contrast, grasses and shrubs predominate in dry savannas. Some grass species, such as elephant grass, can grow to heights of over 2 meters, contributing to the distinct appearance of these regions.
Overall, the vegetation composition in savannas varies significantly depending on factors such as rainfall, temperature, and the duration of the dry season. This diversity in vegetation contributes to the unique and dynamic nature of savanna ecosystems and their vital role in supporting diverse wildlife and ecological processes.
Savannas indeed boast the most extensive diversity of large mammals on Earth, with African savannas, in particular, being renowned for hosting the largest terrestrial animals on the planet. While many representatives of the “megafauna” once inhabited South America and Australia, climatic changes around 10,000 to 2 million years ago led to the extinction of many of these large species in those regions. However, a remarkable variety of large mammals continue to live in African savannas, including the well-known “Big Five”—the African elephant, rhinoceros, Cape buffalo, lion, and leopard—a term that the Scottish hunter and naturalist John Hunter coined in his book.
The diversity of large mammals in savannas extends to South Asia as well, where a wide variety of notable animals such as kangaroos, anteaters, antelopes, and gazelles can be found.
Savannas are also teeming with rich avian diversity, with some bird species forming awe-inspiring flocks. Particularly noteworthy is the abundance of birdlife in South America and Australia, where numerous species of parrots, toucans, and other birds thrive, many of which are rarely seen in other biomes.
The combination of vast grasslands and scattered trees in savannas provides ample space and resources for these large mammals and birds to thrive. The ecological diversity of savannas plays a crucial role in supporting such a wide range of plant and animal species, making them one of the most ecologically significant biomes on Earth.
Regional Differences of Savannas
Owing to the unique attributes of flora and fauna on every continent and biogeographic ecozone, a categorization of savannas into four distinct types can be delineated on a regional basis.
The savanna stretches in a vast arc from Senegal, extending through Ethiopia and Kenya, and further south through Tanzania to South Africa, reaching the western Atlantic coast. It encompasses the equatorial forest zone in Africa, making it the most extensive savanna on the planet.
The vegetation varies greatly across different regions of the African savanna. The savanna takes on a typical steppe appearance along its borders with the Sahel and Kalahari deserts, where grasses and dry shrublands predominate. In the Kalahari, this zone often overlaps with the desert biome. Areas near the equatorial forest boundary are covered by seasonal broad-leaved forests. These are sometimes considered separate zones or included as part of the tropical rainforest.
The mountainous regions and vast plateaus that dominate the East African savannas’ landscape are extremely diverse. The vegetation consists of individual forest formations, most commonly acacia woodlands, separated by grassy spaces. Some of these mountains, such as Kilimanjaro, Kenya, Ruwenzori, and Ngorongoro, act as significant barriers to moist oceanic air masses from the east. As a result, subequatorial deciduous forests that transition into mountain equatorial forests are present in windward and mountainous regions, while the inland plateaus are dry and have a semi-desert landscape.
The extensive grasslands in the savanna are characterized by very tall grasses, with elephant grass being a prominent species, reaching heights of over 2 meters.
The African savanna is home to the largest diversity of large mammals in the world. It hosts the largest terrestrial animals, such as African elephants, white and black rhinoceroses, Cape buffalo, lions, leopards, hyenas, and others. In regions with more trees and forest formations, the variety of bird species is enormous. Weaverbirds are particularly characteristic of the African landscape, forming immense flocks and building their unique nests hanging from the tree branches. Reptiles found here include monitor lizards, various snake species, and chameleons. The diversity of insects is vast, with the tsetse fly being one of the most well-known and dangerous inhabitants, as it transmits sleeping sickness.
South American Savanna
The savanna region of South America encompasses the Brazilian Plateau, extending from the Atlantic coast and Marajo Island in the Amazon River delta to the northern regions of Argentina and Uruguay. Notably, the Brazilian Plateau hosts a unique and globally significant ecosystem known as the “cerrado.” This particular area stands out for possessing the highest biodiversity among savannas worldwide and can even compete with equatorial forests in terms of species diversity. Moreover, it serves as a hotspot for endemic species.
The Cerrado exhibits a diverse landscape characterized predominantly by savanna-woodland features. In contrast to most other savannas found globally, it showcases more substantial forest formations and denser tree populations. The cerrado is home to various species of palms, acacias, and uncommon flora, such as the bottle tree and araucaria.
In terms of fauna, the cerrado boasts an impressive array of wildlife, particularly bird species, totaling 1,700, surpassing the combined count of other savannas. The abundance of parrots, including the majestic hyacinth macaw, considered the largest parrot species globally, contributes to the remarkable avian diversity found here. Additionally, the cerrado provides a habitat for several large animals, such as the giant anteater, deer, peccaries, pumas, and jaguars, as many of the megafauna disappeared during the last ice age.
Another notable feature in South America is the Pantanal wetland, renowned for its vast biodiversity and rivaling the Cerrado in terms of biological richness. Alongside the aforementioned species, the Pantanal is also a habitat for crocodiles, caimans, piranhas, and numerous other wildlife species.
The Australian savanna covers the northern and partially central parts of Australia, and it is characterized by its unique features. On the Arnhem Land peninsula in the northwestern part of Australia, a wide variety of savanna landscapes can be observed. Here, both wet and flooded savannas, typical of the Kakadu National Park’s landscape, and drier landscapes dominated by low, thorny shrubs or semi-deserts can be found. Eucalyptus trees are a distinctive feature of the Australian savannas, and in the wetter regions, they form small forest formations.
Among the animals, the impressive diversity of parrots is notable, which is not typical for savannas in other parts of the world. Parrots usually inhabit rainforests, and the species found in savannas are relatively rare. However, Australia makes an exception. Numerous species of cockatoos, budgerigars, and others can be found here. Besides them, typical of the Australian savanna are the large and sluggish kookaburra, the lyrebird, and the emu, which is the largest bird in Australia. Among the mammals, kangaroos are the most common, with the large gray kangaroo being typical for the zone. In the wetter regions dominated by eucalyptus, you can also find koalas. The savannas are also home to Australian endemics such as the echidna, the thorny devil lizard, and others.