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.
Tropical rainforests are found in the equatorial zone in Central America, South America, Africa, Asia and Australia (see map above).
Tropical rainforests have warm temperatures and high humidity. Humidity is the proportion of water vapour in the air. Tropical rainforests typically receive between 1.5 m to 4 m of rainfall each year. That’s a lot of moisture! This consistently warm and humid climate makes tropical rainforests a great habitat for plants and animals. Rainforests are one of the most biodiverse biomes on Earth. Biodiversity is a measure of the number of living things. As many as half of the Earth’s terrestrial species are found in this one biome!
Plants & Animals
For plants in tropical rainforests, it’s all about competition. These forests are very dense. This means that the trees stand close to each other. Their branches and leaves overlap greatly, creating what is known as a tree canopy. This canopy prevents much of the sunlight from getting to the forest floor. Only 2% of the Sun’s rays pass through! Some plants have adapted to the small amount of light they receive by growing tall while others have adapted by growing over top, covering other plants.
Animals in the rainforest are also very diverse. Most animals live in the trees. There they can find everything they need, so they rarely come down to the floor of the forest. Insects make up most of the living creatures in the tropical rainforest. Many amphibians and insects are poisonous to their potential predators. This is because they absorb harmful chemicals called toxins from plants, usually by eating them. You can tell when a species has adapted in this way because it has very brightly colored markings that warn predators not to eat it. Poison dart frogs are a good example of this.
On the other end of the colour spectrum, mammals such as big cats and monkeys camouflage into their surroundings. Jaguars, tigers and boars move quietly along the forest floor in search of food. Monkeys, lemurs and sloths use the abundant branches to their advantage. They stay away from predators by finding food high up above in the trees.
Human Impacts & Conservation
Local human populations in tropical rainforests harvest fruit, wood and medicinal plants as well as hunt animals. The biggest threat to tropical rainforests is deforestation. Deforestation is the cutting down of trees. Humans cut down the trees for wood. They also often burn the land where the trees had been to prepare the soil for farming. Brazil and Indonesia have lost over 46% of their rainforest area. In many places, such as deforested areas, the soil damage makes it difficult for rainforests to regrow, and the lost biodiversity is irreplaceable.
Many of the plants found in rainforests are being used to make medicine, including anti-cancer drugs, along with beauty products and foods. An example of deforestation that has put many species of plants and animals at serious risk is in Malaysia. Thousands of acres of forest have been cut down to accommodate oil palm plantations. Palm oil from palm trees is used in many products, from soap and shampoo to chocolate bars. One endangered species that suffers from deforestation in this area is the orang-utan (meaning ‘man of the forest in Malay’).
For many years, individuals, environmental organizations and other stakeholders have pressured governments to protect tropical rainforests. There has been success in many places, but deforestation is still a major problem. One way to prevent further destruction is to develop and encourage sustainable farming methods in regions that have already been cleared in order to discourage further deforestation. Farmers can be taught new farming methods that require less land and less water. They can also be encouraged to maintain the forests themselves. Projects are also underway in many regions to replant trees in cleared areas.
It is important for tropical rainforests to be preserved so that they can mitigate (make less severe) climate change, because they act as ‘carbon sinks.’ Similar to how we take in oxygen when we breathe, plants take in carbon dioxide and release oxygen, when they make their food (through the process of photosynthesis). By taking in carbon dioxide from our atmosphere, the rainforest helps to slow down the effects of climate change.