The Living World
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Characteristics of a Tropical Rainforest

Distribution

Tropical rainforests (TRFs) have a consistent global distribution, almost universally located between 15° North and 15° South of the Equator. The biggest TRF is the Amazon, which is in South America, although there are also TRFs in Central America, Central Africa, and Indo-Malaysia.

TRFs are mainly found in this area because of the amount of rainfall and sunshine that the areas surrounding the equator receive. The equator receives the highest amount of sunlight and heat from the sun, which causes the hot air to rise. Rising air causes a drop in air pressure, which results in consistently warm, wet weather.

Climate

TRFs can only exist where there are consistent levels of heat and precipitation, which is why the conditions around 15° North and South of the Equator are perfect. The climates of TRFs are largely universal, with consistent characteristics. 

The infographic below contains information about the climatic characteristics of a TRF.

Rainforest Layers

The soil in a TRF is not very fertile. Any nutrients present in the soil, which would help flora grow, are washed out by the massive amount of rain, in a process known as leaching

This means that most of the nutrients present in the soil are there because of the decomposition of biological matter. In this case, that can mean dead animals, leaves from trees and plants, or waste from animals. To read about this in greater detail, find our page on interdependence in TRFs here.

The process leaves behind a very thin layer of fertile soil, which is quickly utilised by plant life. This leaves a fight between the trees and plants to reach sunlight.

As plants rapidly grow to reach the sunlight, to accelerate their photosynthesis, they block the light for those below. The more plants grow, the more sunlight is blocked, which means that plant life has to climb even higher. This competition and process of growth leads to a clear structure within TRFs, made up of different layers as you can see above.

  • Forest floor: Also known as the ground level, it is dark and damp, with little sunlight reaching it, but plenty of rain. Rotting leaves and dead animals make up a material called litter that covers the ground and provides nutrients for plant life. Without this decomposing litter, plants would face an extraordinary struggle for nutrition, due to the leaching effect of the rain.
  • Shrub Layer: Located a few metres above the ground, this layer consists of dense plant growth. Plants that need less sunlight, like ferns or a shrub, flourish in the wet and darker areas of the rainforest. If they grow sufficiently, many saplings (young trees) will one day join the canopy or emergent trees.
  • Under Canopy: The under canopy is mainly composed of tree trunks, stretching up to reach the main canopy or emergent levels.
  • Main Canopy: The main canopy, often simply called the canopy, is a dense blanket of leaves and trees that blocks sunlight from reaching the lower levels. Trees in the canopy grow as many leaves as they can to maximise the absorption of energy from the sun. The main canopy is around 30 metres in the air and contains about 50% of the rainforest’s wildlife.
  • Emergents: The emergents ’emerge’ above the main canopy and can be among the tallest trees in the forest, reaching heights of between 45 and 55 metres.

Key Terms

TermDefinition
EquatorAn imaginary horizontal line that is an equal distance from both poles. The equator divides the Earth into northern and southern hemispheres and sits at the parallel of latitude 0°.
DiurnalRefers to activities or patterns that occur during the daytime. It is commonly misinterpreted as the difference between the highest and lowest temperatures in a 24-hour period; however, this is actually referred to as ‘diurnal temperature variation’.
LeachingThe process by which water percolates through the soil and dissolves certain nutrients, carrying them away from the soil. This often occurs due to significant rainfall, which can deplete the soil of essential nutrients beneficial for plant growth.
LitterDead organic material that has fallen to the ground, which helps provide nutrients for the soil.
DecompositionThe process of rotting or decay of organic matter, where bacteria break down the material into simpler substances.

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