Tropical Grasslands of the World
What are Savannas?
Most dictionaries simply define a savanna as a plane that is characterized by scattered grass and trees that are located in areas with seasonal rainfall, and specifically tropical and subtropical regions. However, these definitions do not nearly begin the extensive factors that contribute to these regions. Geographically, savannas cover half of Africa, large areas of Australia, India, and South America. In fact, about 46% of the land in Africa can be classified under this specific biome type. Savannas are often a result of humans burning down grasslands and then planting crops. Since they are found in lower latitudes, savannas tend to have a very raining season and a very dry season, which detests the misconception that savannas are only dry.
The land that is classified as tropical grasslands is essentially nonexistent in places such as North America, Europe, and Antartica because these locations are far from the equator. The most predominant and well defined savannas are found in stretches of Africa, Australia, and South America.
Blow is a world map depicting the areas that are roughly considered to be savannas (shown by yellow coloring).
Savanna in Africa stretches from the tropical forests to the deserts. Red oat grass dominates on the dryer, well drained areas such as Kenya. Dominant grass nearby Uganda is lemon grass. The most common trees found are Baobabs.
South American Savanna
Depending on the amount of moisture, savanna spreads through areas of grassland to woodland. The largest savanna in the continent is located in the Cerrado area of Brazil where dominant grasses include species of Andropogon and Aristida. These grasses are special because they are drought-tolerant and fire resistant.
Although not commonly assumed, 65% of Australia consists of savanna. The northern regions receive months of rain which helps to produce Eucalyptus trees.
South American Savanna
Essential Abiotic Factors
Savannas are classified neither as a rainforest or desert. They are not classified as a rainforest because there is only 15 to 25 inches of rain per year, and it is not a dessert because it is not dry enough. In the winter savannas are still slightly dry and cool. In the summer, savannas are humid and can reach extremely high temperatures. The average temperature can be around 70 degrees fahrenheit.
During the winter, the soil on savannas can dry out due to no rainfall and can become infertile. This means that all grass and shrubs will die. In the summer that is the opposite, since the soil receives plenty of sunlight and a decent amount of water it is very fertile. This benefits both animals and the grass because the animals eat the grass (grazing) for their food and the grass reproduces due to the nutrients left behind from the animals.
Varied Vegetation & Plant Adaptation
Because of the inconsistent climate and seasons for savannas, vegetation varies immensely. During the rainy season, plants and grass grow very tall, but there are many floods. In contrast, during the very hot and dry season, plants will typically die because of the lack of precipitation. Tree growth is controlled not only by the rainfall, but also by the soil type. Areas of hardpan soil do not allow for tree roots to penetrate, except through certain cracks. These cracks evidently determine the tree distribution throughout the biome. Trees also have extensive root systems that help to absorb as much water as possible. Many plants are pyrophytic so that they can survive fires, many of which are caused by farmers deliberately so that they can create more open land. Specific plants that are found primarily in savannas includes bermuda grass, senegal gum, gum trees, and candelabra trees.
A variety of animals migrate to coincide with the seasonal flush of growth. That applies specifically to mammals in Africa and birds in Australia. Many animals burrow to avoid from being eaten from their predator. One example is birds, savannas are ideal for birds of prey. Birds can use their long-range vision for prey and can set up their nest on the long branches. There are big niche separations in African ungulates. One example is browsers and grazers who both have multiple differences. The proportion of grass in which each species consumes is different, for grazers it is a great amount unlike others.
About the Authors
Emmet Weinman is enrolled at Morristown High School and is graduating in 2017. He has one younger sibling who attends Frelinghuysen Middle School. Emmet has taken three courses in the science department over his high school career (Physics, Chemistry, Biology).
T. (2010, November 28). ABIOTIC FACTORS. Retrieved May 17, 2016, from https://tropicalgrassland.wordpress.com/abiotic-factors/
U. (2016). Savanna. Retrieved May 17, 2016, from http://www.pugetsound.edu/academics/academic-resources/slater-museum/biodiversity-resources/world-biomes/characteristics-of-bioclimatic/savanna/
Dowd, M. (2016). What Types of Vegetation Dominate the Savanna Biome? Retrieved May 17, 2016, from http://education.seattlepi.com/types-vegetation-dominate-savanna-biome-6243.html