Distribution of Tropical Rainforest

Tropical Rainforest are distributed along Equator (O°). It is found between Tropics of Cancer and Capricorn (23.5°N, 23.5°S). The rainforest spanned over South America, Africa and Southeast Asia. Countries with Tropical Rainforest are Brazil, Indonesia and Congo etc.

Characteristics of the Tropical Equatorial climate

Near Equator, incoming solar radiation from sun is concentrated at the region. This leads to high temperature. With high temperature, there is convectional rain frequently leading to high rainfall. This can be observed in Singapore’s climograph below. Average temperature and rainfall is high.

The rainforest is warm all year and must stay frost-free. The average daily temperatures range from 22°C to 27°C. Rainforests receive the most rain of all of the natural vegetation in a year! A typical year sees 2,000 to 10,000 millimeters (79 to 394 inches) of rain per year.

How Tropical Rainforest Adapt to high rainfall and high temperature

Leaves often have a waxy surface with pointed drip tips at the end. This is to enable excess rainwater to run-off easily without damaging the leaves. This is important because it prevents the growth of algae, which if able to grow would block out sunlight and reduce a plants’ ability to photosynthesize. Leaves of plants in the shady, undergrowth layer are broad to maximize capture of sunlight because the continuous layer of canopy blocks out large amount of sunlight.

The tropical rainforest is known for its dense canopies of vegetation that form three different layers. The top layer or canopy contains giant trees that grow tall and reach about 40m to reach the sunlight. These trees are known as emergents. The rest of tall trees about 30m would form a continuous layer called the canopy. The branches and leaves interlock in the canopy to maximize capture of sunlight. This layer of vegetation prevents much of the sunlight from reaching the ground and blocks sunlight to the undergrowth layer.

The middle layer, or under-storey, is made up of vines, smaller trees, ferns, and palms. A large number of plants from this level are used as common houseplants. Because of the small amount of sunlight and rainfall these plants receive, they adapt easily to home environments.Lianas and vines hug trees to take advantage of nutrients and sunlight and maximise use of space. In Peru there is a vine called a stranglador which can strangle or kill its host tree.

The bottom layer or floor of the rainforest is covered with wet leaves and leaf litter. This material decomposes rapidly in the wet, warm conditions (like a compost pile) sending nutrients back into the soil. Few plants are found on the floor of the forest due to the lack of sunlight. However, the hot, moist atmosphere and all the dead plant material create the perfect conditions in which bacteria and other microorganisms can thrive.

Trees have wide roots which are above ground and thick trunks to support their tall height and big size – called buttress roots.

The roots within the soil layers are actually short and are considered shallow, about 5m-8m length. This is because the tropical equatorial climate brings heavy rainfall frequently. The roots do not need to grow deeply to absorb water in the deep soil, they just need to absorb the rainwater that infiltrates the shallow zone in soil. This is also true for nutrients. The main source is from the decay of leaves that accumulate above the soil. The decay of leaves in the humid forest generate enough nutrients to enrich the shallow zone of soil.