The Tropical Rainforest – a large scale ecosystem

Tropical rainforests have distinct characteristics that support a wide variety of different species. This means that they have a high biodiversity. The biotic, or living components of the ecosystem, and the abiotic, or non-living components of the ecosystem depend on one another - a change in one leads to a change in the other.

Tropical rainforests are mostly found in South America, central Africa, and south Asia.

Climate

  • Very wet with over 2,000 mm of rainfall per year.
  • Very warm with an average daily temperature of 28°C. The temperature never drops below 20°C and rarely exceeds 35°C.
  • The atmosphere is hot and humid.
  • The climate is consistent all year round. There are no seasons.

Soil

  • Most of the soil is not very fertile.
  • A thin layer of fertile soil is found at the surface where the dead leaves decompose.
  • It is red in colour because it is rich in iron.
  • Due to heavy rainfall the nutrients are quickly washed out of the soil.

Plants and animals

  • The warm and very wet climate provides perfect conditions for plant growth.
  • The wide range of plant species supports many different animals, birds and insects.
  • Species have adapted to the conditions of the rainforest, eg trees and plants have shallow-reaching roots to absorb nutrients from the fertile top layer of soil

Structure of a tropical rainforest

A tropical rainforest is made up of the following layers.

  • Ground level - contains less vegetation due to the dark, damp conditions, a thick layer of decomposing leaves and buttress roots of trees.
  • Shrub level - dense and dark with small plants.
  • Under canopy - contains younger trees and saplings competing for light in dark conditions.
  • Main canopy - the 'roof' of the forest. Contains tall trees, climbing plants like vines and lianas. 50 per cent of rainforest life is found here.
  • Emergents - contains the tallest trees emerging out of canopy.
Emergents at the top receive most light. Beneath is the canopy, then the under canopy, and lastly the shrub level, receiving the least light.

Processes within a rainforest ecosystem

Rainforests house a complex set of processes, among which is the way in which energy is transferred through the ecosystem. The main energy source in an ecosystem is sunlight. This is absorbed by plants, called ‘producers’. This energy is then passed on to the animals through the plants they eat, these animals are called ‘primary consumers’. Often these primary consumers are eaten by larger animals called ‘secondary consumers’, who are then eaten by ‘tertiary consumers’, the largest animal. Throughout this process energy continues to be passed on. This is called a food chain.

A typical rainforest food web divided into its four stages.

A complex food chain is called a rainforest food web – this means that some animals and plants are consumed by more than one other organism. Water and nutrients are also passed through the ecosystem.

The rainforest nutrient cycle: trees shed leaves all year round, decaying vegetation decomposes rapidly, nutrients enter the soil, shallow roots take up the nutrients, and trees grow rapidly.The rainforest nutrient cycle

Rainforest water cycle

Plant roots take up water from the ground. Rain is intercepted as it falls due to the rainforest canopy. As the rainforest heats up, the water evaporates and transfers back into the atmosphere. Clouds form to make the next day's rain. This is convectional rainfall.