Characteristics of the Tropical Rainforest (Cambridge (CIE) IGCSE Geography) : Revision Note

Global distribution of 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 ecosystems are in the following countries:

  • Amazon

    • The largest remaining rainforest on Earth is 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 several other countries in South-East Asia

Characteristics of equatorial climates

Equatorial climate distribution

Equatorial climate 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 2,000 mm

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%

Prevailing winds

• Winds blow into the equatorial region from high-pressure areas to the north and south. 

• The winds from the north blow from the northeast, and the winds from the south blow from the southeast

• The winds are known as the trade winds

Factors influencing the equatorial climate

• There are a range of factors that influence the climate, including:

  • The midday sun is almost directly overhead all year, meaning there is maximum insolation

  • Low pressure all year leads to rising air, condensation, cloud formation, and high precipitation levels

  • Dense vegetation cover leads to high levels of evaporation and transpiration 

  • The warm air stores large amounts of water vapour until the temperatures start to cool in the late afternoon, which then leads to heavy, daily convectional rainfall

The tropical rainforest ecosystem

Biodiversity

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

Structure of the tropical rainforest 

• The TRF has five distinct layers:

  • ground layer (0 m)

  • shrub layer (3-4 m)

  • under canopy (15 m)

  • canopy (30 m)

  • emergents (45-55 m)

Interrelationships in the tropical rainforest

Nutrient cycle

• The TRFs have a continual growing season with high rainfall and high temperatures all year round

• The nutrient cycle in the TRF is rapid

  • Trees and plants lose their leaves all year round

  • The high level of moisture and high temperatures lead to rapid decomposition

  • Plants grow quickly, which leads to the rapid uptake of nutrients from the soil

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

• This is because the nutrients are quickly used by the plants

Food web

• As with all ecosystems, the TRF has a complex food web, which includes:

  • producers

  • primary consumers

  • secondary consumers

  • tertiary consumers

Adaptations

• The plants and animals within the TRF 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 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

  • Plants which grow on trunks and branches of trees and get 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

  • Has a large bill to reach and cut fruit from the branches of trees

• Primates

  • Have prehensile tails to help them climb trees

• Gecko

  • Have large, flattened toe pads with sticky scales which allow them to grip the smooth tree trunks

• Stick insects

  • Their stick and leaf shapes help them to be camouflaged