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Savanna

life science Maturity 7-9 Next article →

A savanna is a complex mixed woodland-grassland biome and ecosystem. It is defined by a specific structure where trees are spaced widely enough that their canopy does not close. This open canopy is a vital feature of the landscape. Because the canopy remains open, sufficient sunlight reaches the ground to support an unbroken herbaceous layer. This layer consists primarily of various types of grasses.

Tarangire-Natpark800600
Tarangire-Natpark800600

Savannas are essential transitional zones. They often exist between forests and deserts or between forests and grasslands. They cover approximately 20% of the Earth's total land area.

There are four distinct forms of savanna based on vegetation density. The first is savanna woodland, where trees and shrubs form a light canopy. The second is tree savanna, which features scattered trees and shrubs. The third is shrub savanna, characterized by distributed shrubs. The final type is grass savanna, where trees and shrubs are mostly nonexistent.

Savanna Grasslands (199168845)
Savanna Grasslands (199168845)

While many people assume savannas always have widely spaced trees, this is not always true. In many regions, tree densities are actually higher and more regularly spaced than in forests. For example, the South American cerrado sensu stricto and cerrado dense can have densities of 800 to 3,300 trees per hectare. In comparison, adjacent forests may have only 800 to 2,000 trees per hectare.

Climate plays a fundamental role in how a savanna functions. Most savannas are located in warm to hot climates, such as in Africa, Australia, South America, and India. Unlike the North American prairies or Eurasian steppes, savannas do not typically feature cold winters. The weather is defined by seasonal water availability. Most rainfall is confined to one specific season, which is followed by a period of drought.

Upland South Africa Savanna
Upland South Africa Savanna

This cycle of wet and dry seasons creates a unique environment for plants and animals to adapt to.

The term "savanna" has a long linguistic history. It derives from the Spanish word "sabana," which is a loanword from the Taíno language. In Taíno, the word means "treeless grassland." The word first entered the English language in 1555 as "Zauana." Early historical accounts linked the name to the plains around Comagre in present-day Panama.

Australian savanna
Australian savanna

Over time, the concept of a tropical savanna climate became established in the middle of the 19th century. This helped scientists categorize these landscapes based on temperature and precipitation.

Vegetation varies significantly depending on the geographic location. In the tropical Americas, broadleaved trees like Curatella and Bowdichia are common. East African savannas are known for Acacia, baobabs, and Euphorbia.

In Australia, the savanna is abundant with sclerophyllous evergreen vegetation, including eucalyptus. These plants must survive the specific seasonal patterns of their regions. The diversity of plant life supports a wide range of animal species. In Africa, animals like giraffes, elephants, and zebras rely on the foliage and grass. In Australia, mammals in the Macropodidae family, such as kangaroos, predominate.

Fire is a critical mechanism that maintains the savanna ecosystem. Savannas are subject to regular wildfires, and many appear to be the result of human use of fire. For example, fire-stick farming is believed to have influenced the widespread occurrence of savannas in tropical Australia and New Guinea.

Bushfire Australia
Bushfire Australia

Controlled burns can be used to manage the land. These intentional fires are typically confined to the herbaceous grass layer. This prevents catastrophic wildfires that could damage mature trees. However, these fires can also suppress tree seedlings, which prevents the formation of a continuous forest canopy.

Despite their importance, savanna ecosystems face significant threats. It is estimated that less than three percent of savanna ecosystems can be classified as highly intact. Many areas are experiencing degradation due to changes in fire management. In some regions, the removal of traditional burning practices has caused savannas to be replaced by forest or shrub thickets.

Grevy's Zebra Feeding
Grevy's Zebra Feeding

Additionally, the consumption of grass by introduced grazers can reduce the amount of fuel available for natural fires. This can lead to fewer and cooler fires, which alters the natural balance of the biome.

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🖼️ Images & Media (9)
File:Tarangire-Natpark800600.jpg
Tarangire-Natpark800600.jpg
File:Savanna Grasslands (199168845).jpeg
Savanna Grasslands (199168845).jpeg
File:Australian savanna.jpg
Australian savanna.jpg
File:Bushfire Australia.jpg
Bushfire Australia.jpg
File:Grevy's Zebra Feeding.jpg
Grevy's Zebra Feeding.jpg
File:Dehesa Pigs.jpg
Dehesa Pigs.jpg
File:Upland South Africa Savanna.jpg
Upland South Africa Savanna.jpg
File:Cumberland Plain Savanna.jpg
Cumberland Plain Savanna.jpg
File:Savanna towards the south-east from the south-west of Taita Hills Game Lodge within the Taita Hills Wildlife Sanctuary in Kenya.jpg
Savanna towards the south-east from the...
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