Tropical Rainforest Ecosystem (AQA GCSE Geography): Revision Note

Specification links

The notes on this page cover part of 3.1.2.2 Tropical rainforests on the AQA GCSE specification. (opens in a new tab)

3.1.2.2 - Key idea: Tropical rainforest ecosystems have a range of distinctive characteristics.

• The physical characteristics of a tropical rainforest.

• The interdependence of climate, water, soils, plants, animals and people.

• How plants and animals adapt to the physical conditions.

• Issues related to biodiversity.

Characteristics of a tropical rainforest

Distribution of the tropical rainforests

• 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 characteristics

Location

• Low latitudes

• Within the Tropics, 23.5^° north and south of the equator

• Amazon in South America, New Guinea, South-east Asia, and the Zaire Basin

Annual precipitation

• Over 2000mm

Temperature range

• Low range of mean monthly temperatures - 26-28^°C

• Constant high temperatures 

• Diurnal range is about 7^oC

Seasons

• No seasons—hot and wet all year round

Humidity

• High, usually over 75–80%

Soils

• Many of the soils in the rainforest are latosols

• Due to leaching and rapid uptake of nutrients by plants, the soils are not very fertile

• Nutrients are concentrated in the upper topsoil 

Biodiversity

• Tropical rainforests contain the highest biodiversity of plants and animals on Earth

• Estimates range from over 50% to 80% of the world's plant and animal species

• One 10km² area can contain up to 1,500 flowering plants, 750 species of trees, 400 species of birds and 150 species of butterflies

Humans

• Traditional communities such as the Awa in Brazil and the Huli in Papua New Guinea live in harmony with the rainforest

• Communities survive through hunting and gathering using the rainforest plants and animals in a sustainable way

• Many communities have been forced off the land by commercial activities such as mining, agriculture and logging

Interdependence in the 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

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

Plant and animal adaptations

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)

Adaptations

• The plants and animals within the tropical rainforest are very well adapted to the climate conditions

Plant adaptations

• Waxy leaves with drip tips: These ensure that rainwater runs off the leaf and does not remain which would encourage mould growth or break the leaf

• Buttress roots: These large roots above the ground which help to support the very tall trees because the roots below the surface are shallow

• Lianas: Vines which use the tall trees as support to reach the sunlight

• Epiphytes: These are plants which grow on trunks and branches of trees getting nutrients from air, rain or debris accumulating around the plant

• Straight, smooth trunks: To reduce the number of epiphytes using the tree

Animal adaptations

• Sloth: Algae grow in the fur of the sloth helping to camouflage it

• Toucan: They have a large bill to reach and cut fruit from the branches of trees. They are also strong allowing them to crack nuts open

• Primates: They have prehensile tails to help them climb trees

• Geckos: They have large, flattened toe pads with sticky scales which allow them to grip the smooth tree trunks

• Stick Insects: Their stick and leave shapes help them to be camouflaged

Biodiversity issues

• 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 which eat the ants 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