Tropical Rainforest Ecosystem (AQA GCSE Geography)
Revision Note
Written by: Bridgette Barrett
Reviewed by: Jenna Quinn
Characteristics of a Tropical Rainforest
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
Characteristics | Equatorial Climate |
|---|---|
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 7oC |
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 & 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
Adaptations of Plants and Animals in a Tropical Rainforest
Plants | Animals |
|---|---|
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 | Sloth: Algae grow in the fur of the sloth helping to camouflage it |
Buttress roots: These large roots above the ground which help to support the very tall trees because the roots below the surface are shallow | 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 |
Lianas: Vines which use the tall trees as support to reach the sunlight | Primates: They have prehensile tails to help them climb trees |
Epiphytes: These are plants which grow on trunks and branches of trees getting nutrients from air, rain or debris accumulating around the plant | Geckos: They have large, flattened toe pads with sticky scales which allow them to grip the smooth tree trunks |
Straight, smooth trunks: To reduce the number of epiphytes using the tree | Stick Insects: Their stick and leave shapes help them to be camouflaged |
Worked Example
Study figure 1, a diagram showing the structure of the tropical rainforest.
Using figure 1, which part of the rainforest matches the following description?
'An almost continuous layer of branches and leaves between 15 and 30 meters high'
[1 mark]
A. Emergent layer
B. Upper Canopy
C. Lower Canopy
D. Understory
Answer:
B. Upper Canopy (none of the other layers are almost continuous)
Examiner Tips and Tricks
You may be asked to describe the rainforest vegetation characteristics. As well as adaption features remember to include information about the different layers and heights of each layer.
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 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
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