The Tropical Rainforest

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The Tropical Rainforest

Tropical Rainforests are the world's most productive ecosystems in terms of NPP and biomass. They are complex ecosystems with variations in climate, temperatures, and vegetation, within individual forests.

Temperatures are often thought to be permanently high, but they are highest on the forest edge where vegetation is more limited. The climate changes on a daily basis within the forest, and the idea of the forest being difficult to penetrate is only true at the edges where the sunlight allows rapid growth of vegetation.

Their development relies on:

Insolation and temperatures High temps. Allow all year growth of vegetation.
Moisture Varies throughout the year, and true TRFs are said to have rainfall in excess of 2000mm and a dry season of no longer than 2 months.
Nutrients Scarce, but are rapidly recycled and transferred. Phosphorus and nitrogen are the nutrients needed most.

Structure

The nature of a forest in terms of its ecology is due to the amount of energy from the sun that reaches plants and animals. Several vertical layers are found, with distinctive plant and animal species.

The Tropical Rainforest

Layer: Characteristics:
Top (Euphatic) Most productive (NPP, animal life and biomass). Tress over 25m. 25% of available energy absorbed.
Middle (Oligotrophic) Trees are 10 - 25m.
Bottom Smaller trees and some young saplings between 5 and 10m in height.
Shrub Smaller seedlings and some pygmy trees of 5 to 10m.
Herb Tree seedlings, and ferns in existence.
Top Root Roots that penetrate to a depth of 5cm (majority).
Middle root Fewer roots to a depth of 5 - 50cm.
Bottom root Minimal numbers of roots in this layer, below 50cm.

The Tropical Rainforest

  • Small annual temperature range (2 - 4 degrees).
  • Regular insolation, result of location near equator.
  • Daily temperature range in excess of annual range (8 - 10 degrees), with daytime temperatures up to 32 degrees.
  • High levels of convectional rainfall, often with a minimum in July/August/September.
  • Extremely high humidity levels.
  • Light winds.
  • Quick evapotranspiration.
  • Year long growing season (but not all plants in the forest grow all year).

  • Decay of leaf litter is rapid, and nutrient recycling.
  • Photosynthesis occurs all year.
  • Extremely large variety of vegetation, trees appear to be evergreen but are deciduous.
  • Vegetation adapts to the climate. For example, buttress roots to support tall trees, drip tips to help remove excess moisture.
  • Tallest trees can be over 50m high and are known as emergence.
  • Where forests are near the coast Mangrove swamps may be found.

May appear to be fertile but the tropical latosols are not. The humus layer is extremely thin, as is the amount of litter. Leaching occurs as a result of the high precipitation and is increased greatly by deforestation. Minerals such as Calcium and magnesium are lost. Bedrock is weathered quickly. The characteristic red colour of the soil is due to iron and aluminium accumulating.

Click on the arrows to move the diagram up and down:

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If the rainforest is undisturbed the nutrient cycle acts effectively to help maintain the large and varied vegetation found within them, as mentioned in the previous section on nutrient cycling.

Once the cycle is disturbed the fragile ecosystem is quickly upset as shown in the diagrams below:

The Tropical Rainforest
The Tropical Rainforest

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