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The Terrestrial Biomes
The terrestrial world can be divided into areas called biomes. A biome is a large area of land classified by its distinct plants and animals. The characteristics of each biome are dependent on its temperature and the amount of precipitation the area receives. The plants and animals found in each biome are adapted to the particular environment of the biome.
A biome is made up of many ecosystems. An ecosystem is the interaction of living and nonliving things in an environment. However, a biome is the specific geographic area in which ecosystems can be found.
For the purpose of this backgrounder we will identify major terrestrial biomes of the world based on the Whittaker biome classification scheme. It is interesting to note that not everyone agrees on the number and types of biomes.
Distribution of the Earth’s Major Biomes
The map below shows where each of the eight major terrestrial biomes are located in the world. Canada contains four biomes: temperate deciduous forest, grassland, boreal forest/taiga, and tundra. A biome has the same characteristics in any part of the world when it can be found. Therefore, the boreal forests of Canada look like the boreal forests of Russia. The characteristics of each biome are dependent on its climate, particularly temperature and the amount of precipitation the area receives.
Savannas are found all around the world. There are five different types of savannas:
- Tropical and subtropical savannas: found near the equator and bordered by tropical rainforests and deserts (e.g., the Serengeti in Africa)
- Temperate savannas: found in mid-latitude regions (e.g., temperate savanna of Southeast Australia)
- Mediterranean savannas: also found in mid-latitude regions, but in the Mediterranean (e.g., the Alentejo region in Portugal)
- Flooded savannas: found in the tropics (e.g., the Pantantal in South America)
- Montane savannas: found in high altitude regions (e.g., the mountains of Angola in equatorial Africa)
If you were to climb a tree in the middle of a savanna, you would see kilometres of flat land covered in tall and short grasses and spotted with low-lying shrubs and scattered trees. Savannas are usually a transitional zone between a forest and a grassland. This means that while there are still tall trees, like a forest, they are spread out and the ground is covered in grasses, like a grassland. The climate is also transitional with rotating dry periods, like a desert, and wet periods, like a rainforest. During the winter, no rain falls, and the land is very dry. In the summer, it usually rains quite a lot. This is called seasonal rainfall because it only rains in a certain season.
Plants & Animals
Due to the large amount of grass found in savannas, many types of grazing mammals can be found there. Grazing animals are animals that feed on grasses. These include zebras, wildebeests, elephants, giraffes, ostriches, gazelles, and buffalo. Herds (groups) of grazing animals are commonly seen in the African savanna. The savanna biome of sub-Saharan Africa also has the highest diversity of ungulates on Earth. Ungulates are hoofed mammals like rhinoceroses, giraffes, camels, hippopotamuses, and elephants.
Many rodents live in savannas. Rodents are a mammal group which includes mice and rats. Rodents are often found in holes leading to intricate underground homes called burrows. In their burrows, the rodents can hide from predators and keep cool.
Savannas are also home to very specialized predatory mammals and birds. The mammals, both feline (e.g., lions and cheetahs) and canine (e.g., African wild dogs), have colouring that allows them to blend into the grasslands. Raptors (birds of prey), such as vultures, eagles and goshawks, have incredible eyesight, able to spot even a well-camouflaged grassland creature from high above.
The plant-eating animals have developed ways at avoiding predators. Some animals, like the gazelle and ostrich, use speed to try and outrun predators. The giraffe uses its height to spot predators from far off and the elephant uses its size and strength to keep predators away.
Human Impacts & Conservation
Savannas are subject to natural wildfires during dry seasons, but humans often cause fires as well. Many savanna plants are adapted to thrive after fires. However, if fires happen too often, it can be damaging to the ecosystem. Savannas are also often used for farming, which is disruptive to the wildlife. This is a big problem for animals if large farms take over grazing or hunting lands. Developing farmland typically involves clearing trees, which destroys the habitats of animals and other plants that rely on those trees. Farmers also allow their domesticated livestock to graze on savannas, which can mean that there is not enough food for wildlife. This overgrazing can have negative effects on the native plants as well.
For wildlife, poaching is a major threat, especially in Africa. Poaching is the term for hunting animals illegally. Large grazers like elephants and rhinoceros are hunted for their ivory tusks and horns. This is putting these animals at risk. When animals are lost due to poaching, it can alter the entire ecosystem.
In addition to providing on-the-ground protection for animals, many countries make poaching an offense punishable by prison or heavy fines. However, a better way to stop poaching is the ongoing effort to decrease demand for illegal wildlife and wildlife parts. If no one's buying the products, there will be no need to kill these animals!
As with all biomes, climate change is a huge threat to savannas. As the average global temperature rises due to the emission of greenhouse gases, extreme weather events, such as droughts (extremely dry conditions) have become increasingly severe. Furthermore, when the landscape is altered by the human uses described above, savannas are more likely to flood and burn in an uncontrolled manner.
Sustainable farming methods can be put into place to protect the land and wildlife of savannas. This may involve growing more than one crop on a piece of land so that less space is used. Or it may mean growing native species, such as trees, on farmland instead of cutting them down. To keep grazing livestock from competing with wildlife, some farmers feed their animals in stalls rather than letting them graze out on the savanna. There are also environmental organizations and governments that are taking serious action against poaching and illegal wildlife trade.