Tropical Rainforest Biodiversity (OCR GCSE Geography)

Distribution of the Equatorial Climate

Distribution of the equatorial climate

• The tropical rainforest (TRF) biome is mainly found in a band between 15° north and 15° south of the equator within the equatorial climate zone
• Covering only 6% of the Earth's surface, the main areas of tropical rainforest ecosystem are in the following countries:
  • Amazon which is the largest remaining rainforest on Earth usually associated with Brazil but covers parts of seven other countries
  • Central America including parts of Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama
  • Central Africa including Cameroon, the Central African Republic, the Republic of Congo, the Democratic Republic of Congo (DRC), Equatorial Guinea and Gabon
  • Indo-Malaysia, including Malaysia, Indonesia and a number of other countries in South-East Asia

Tropical rainforest climate characteristics

 Characteristics of Tropical Rainforests

Climate Graph for Iquitos, Peru

Climate graph for Iquitos, Peru

Structure of the tropical rainforest 

• The tropical rainforest has five distinct layers:
  • Ground layer (0m)
  • Shrub layer (3-4m)
  • Under canopy (15m)
  • Canopy (30m)
  • Emergents (45-55m)

Diagram of Tropical Rainforest Structure

Typical structure of a tropical rainforest 

• All parts of the tropical rainforest ecosystem are interdependent
  • A change in one part affects others
  • Deforestation leads to the loss of habitats and reduction in biodiversity
  • Loss of trees also impacts the nutrient cycle

Nutrient cycle

• Tropical rainforests have a continual growing season with high rainfall and temperatures all year round
• The nutrient cycle is rapid
  • Trees and plants lose their leaves all year round
  • The high level of moisture and high temperatures leads to rapid decomposition and recycling of nutrients
  • Plants grow quickly which leads to a rapid uptake of nutrients from the soil
• Most of the nutrients are stored in the biomass
• Few nutrients are stored in the soil and the litter

Nutrient Cycle Within a Tropical Rainforest 

Tropical rainforest nutrient cycle

• The result of this rapid nutrient cycle is that the soil in the tropical rainforest is not very fertile

Soil

• Soil is an important factor in the development of vegetation within the rainforest ecosystem
• The climatic conditions of rainforests, result in deep soils
• The soils rely on the rainforest to maintain fertility
• Nutrients leach away quickly when the forest is felled and the layer of humus is no longer being replaced
• Soils are some of the least fertile in the world because:
  • Heavy rain causes rapid leaching of nutrients
  • The layer of topsoil and organic matter is thin
  • The soil is acidic due to the leaching of nutrients 
  • Rapid plant growth means that any nutrients are rapidly taken up by the plants
  • There is a lack of weathered rock due to the depth of the soil

Soil Profile of a Tropical Rainforest

Soil profile of a tropical rainforest

Water cycle 

• Precipitation is intercepted by the rainforest canopy 
  • This protects the soil from erosion
• Water on the trees and plants evaporates rapidly due to the high temperatures
  • This leads to cloud formation and high levels of precipitation

• Tropical rainforests have some of the highest levels of biodiversity of any ecosystem
  • The wet and warm climate means there is year-round growth 
  • Wide variety of plants provides a range of habitats and food 
  • Rapid nutrient cycling increases plant growth
  • Lack of human activity has in the past meant that plants and animals are undisturbed 
• Threats to the rainforest biodiversity are increasing mainly due to human activity and include:
  • Agriculture, particularly large scale slash and burn 
  • Mining
  • Hydroelectric power
  • Logging
  • Road building and settlements
  • Wildfires (although natural, increasing frequency and severity is linked to climate change)
• The interdependence of the rainforest components means that when one element is affected it then impacts all the other components
• A decline in one species (especially if it is a keystone species) can lead to a decline in other species 
  • The Zam tree produces seed which are food for agouti and who disperse the seeds 
  • The agouti is hunted for meat reducing their populations this means fewer seeds are dispersed
  • Fewer new Zam trees will germinate and so there is less food for leaf cutter ants which in turn means less food for the tree frogs and the snakes which prey on the frogs
  • The Zam tree is pollinated by a particular species of butterfly. Without the flowers the numbers of the butterfly species will decline - this also affects the beetles which lay their eggs in the butterfly faeces
• Plant and animal species may become extinct - this may happen to some before they are even discovered
• Important medicinal plants may become extinct
• Indigenous communities may be forced to abandon their traditional lifestyle due to the lack of food to hunt and gather