Equatorial Tropical Forest (SQA National 5 Geography): Revision Note

Equatorial climate

Equatorial tropical forest distribution

• Tropical rainforests are located in a band between 15° north and 15° south of the equator within the equatorial climate zone

• They cover 6% of the Earth’s surface and are found mostly in the following regions

  • South America        

    • The Amazon is the largest remaining rainforest on Earth

    • It is usually associated with Brazil, but covers parts of several neighbouring 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

  • South East Asia

    • Including Malaysia, Indonesia, Thailand, the Philippines and Papua New Guinea

Equatorial Climate

• Temperatures are high all year round

  • Between 26–28°C

• Precipitation is high all year round

  • Over 2000 mm per year

• Humidity is high

  • Usually over 75–80%

• There are no seasons

  • It is hot and wet all year round

Tropical rainforest ecosystem

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

• The wet and warm climate means there is a continual growing season

• Rapid nutrient cycling increases plant growth 

• The structure of the tropical rainforest, with multiple layers, increases biodiversity

• Each layer has a different level of light, temperature and humidity, with different food sources

• This creates lots of distinct habitats which support a wide variety of plant and animal species 

Structure of the tropical rainforest

• The tropical rainforest has five distinct layers

  • Ground layer (0m)

    • Darkest layer with very little sunlight

    • Humid and damp

    • Covered with a thick layer of leaf litter, which decays rapidly

    • Insects and animals such as tapirs and jaguars are found here

  • Shrub layer (3–4m)

    • Quite dark with little sunlight

    • Low-growing plants and shrubs

    • Insects and small animals like snakes and mice are found here

  • Under canopy (15m)

    • Most light is blocked by the canopy layer

    • Due to a lack of light, trees tend to be relatively small and young

    • Vines grow around trees to try to reach more light

    • Animals like frogs and monkeys are found here

  • Canopy (30m)

    • Lots of sunlight

    • Thick layer of mature trees

    • Many animals, such as toucans, sloths and orangutans, live here

  • Emergents (45–55m)

    • Full sunlight and strong winds

    • Tallest trees rise above the canopy layer

    • Animals like eagles, bats and butterflies are found here

• Plants and animals within the tropical rainforest are very well adapted to the climate conditions and the light available

Plant adaptations

• Waxy leaves with drip tips

  • Ensure that rainwater runs off the leaf and does not remain, which would encourage mould growth or break the leaf

• Buttress roots

  • Large roots above the ground help to support very tall trees because the roots below the surface are shallow

• Lianas

  • Vines which climb up tall trees to reach sunlight

• Epiphytes

  • Plants that 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 on 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

The nutrient cycle

• The nutrient cycle in the tropical rainforest is rapid

  • Trees and plants lose their leaves all year round

    • This moves nutrients from the biomass store to the litter store

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

    • This moves nutrients from the litter store to the soil store

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

    • This moves nutrients from the soil store to the biomass store

  • This means that the soil in the tropical rainforest is not very fertile because nutrients in the soil are used by plants to grow