Prepare for the Tropical Rainforest unit of GCSE Geography with Beyond’s series of “revise” blogs, which delve into the key areas of the topic. This blog explores the Physical Characteristics of Tropical Rainforests. 

Physical Characteristics of Tropical Rainforests

Climate 

• Hot (20-28°C).
• Sun is overhead all year round so there is no seasonal variation.
• Wet (2000mm per year).
• Convectional rainfall every day.

Water 

• The roots of plants take up water from the ground.
• Rain is intercepted as it falls – much of it at the canopy level, this will evaporate as it heats up to form convectional rainfall.

Soils 

• Rain washes away nutrients from soil.
• Soil is not very fertile. 
• Humus layer of rotting leaf-fall is very thin (heat speeds up decomposition).

Plants 

• Most trees are evergreen.
• Continual growing season.
• Five layers: forest floor, shrub later, under-canopy, canopy (30m) and emergent.
• Epiphytes (plants that feed off other plants and take moisture from the air) e.g. ferns.
• Absorb CO₂ and release oxygen.

Animals 

• Many species of animals live in the tropical rainforest.
• Food is plentiful and grows all year.
• Hundreds of different types of monkeys, snakes and birds.
• Thousands of insect species live in the tropical rainforest.

Issues Relating to Biodiversity

• Tropical rainforest ecosystems contain more species than any other ecosystem. Brazil’s rainforests are thought to contain 59,851 species!
• Tropical rainforests cover less than 2% of the planet, but contain an estimated 50% of all life on earth’s land masses.
• Habitat loss is the main cause of extinction. Deforestation (at a rate of about 300,000km² a year) has been caused by commercial logging, mineral extraction, commercial farming and subsistence farming.
• Many organisms have adapted and evolved to depend on a few species for survival. They may only be found in a very specific area. If something changes, that species will quickly become extinct e.g. golden poison frog.
• Sumatran orangutans exist only on the Indonesian island of Sumatra. Over the last 75 years, their population has diminished by 80 per cent due to human encroachment of their forest habitat, especially for timber and agriculture.

Summary

• Tropical rainforest ecosystems contain more species than any other ecosystem.
• Many organisms have adapted and evolved to depend on a few species for survival.
• Habitat loss is the main cause of extinction. 

Global Distribution of Tropical Rainforests

• Most of the world’s tropical rainforests lie between the Tropic of Cancer and the Tropic of Capricorn.
• Tropical rainforests are found on either side of the equator in South America, Central Africa, South East Asia and Northern Australia.
• The world’s largest tropical rainforest (the Amazon) is found in South America.

How Plants and Animals Adapt to Tropical Rainforests

Plants adapt to cope with the high temperature, rainfall and competition for light.

Trees: 

• Grow tall in search of light. Most trees grow to 30m and form the canopy, where most photosynthesis takes place;
• Have large buttress roots to support the trunk and to absorb nutrients from the thin leaf layer;
• Have thin bark because they do not need to be kept warm;
• Have smooth bark so water can run off easily;
• Have thick, waxy leaves which repel water;
• Have leaves with drip-tips so water can run off easily so leaves do not get too heavy.

Animals:

• Adapt to find food and escape predators.
• Many animals live in the canopy their entire lives as this is where most fruits and flowers are. 
• Some have strong limbs for climbing and leaping e.g. howler monkeys.
• Some have suction-cups for climbing e.g. red-eyed frogs.
• Some have flaps of skin for gliding between branches e.g. flying squirrels.
• Some are camouflaged to hide from predators e.g. leaf toad.
• Many animals have adapted by learning to eat a food eaten by no other animal, e.g. toucans have a long, large bill to reach fruit on branches that are too small to support the bird’s weight. The bill also is used to cut the fruit from the tree.
• Many animals are only active at night (nocturnal) when it is cooler e.g. sloths. 
• Many can swim, allowing them to cross rivers or escape a flood e.g. jaguars.
• Some animals increase their sense of hearing, smell and even taste to help escape from predators in the dark of the forest floor e.g. carpet python.

Structure of a Tropical Rainforest

Emergent Layer (50m)

• Tallest trees

Canopy (30m)

• Engine of the rainforest
• Captures most sunlight

Understorey (20m)

• Younger trees

Shrub Layer (2-5m)

• Ferns, bushes etc.

Forest Floor (0m)

• Dark and quiet
• Decomposition.
• Sometimes flooded.

Case Study: The Amazon Rainforest 

Causes of Deforestation in the Amazon

• Ranching
• Logging
• Small-scale farming
• Large-scale farming, e.g. Brazil is the world’s second largest soya bean producer.
• Road building opens up the rainforest to further development.
• Dam building to produce HEP, e.g. Belo Monte dam complex is under construction and will be the world’s fourth largest HEP dam complex.
• Mining, e.g. the Carajas complex in Brazil is the world’s  largest iron ore mine. It produces 109 million tonnes of iron ore a year.

Economic Impacts

• Farming significantly contributes to the economy, e.g. ranching earns Brazil over $6.9 billion a year.
• Logging contributes to the economy, however, it is estimated that 80% of Brazilian hardwood is from illegal logging.
• Mining provides many jobs, e.g. the Carajas complex provides upto 3000 jobs.
• Indigeneous people lose their traditional farming and hunting lands.

Environmental Impacts

• Deforestation of the Amazon could release 100 billion tonnes of carbon, resulting in increased atmospheric CO₂ and global warming.
• Deforestation means there are fewer trees to absorb CO₂ from the atmosphere, resulting in global warming.
• Mining releases dangerous toxins into the soil and rivers.
• 80 per cent of land animals live in tropical rainforest ecosystems, so deforestation will reduce earth’s biodiversity.
• Removing tree cover will leave soil exposed to heavy rainfall causing soil erosion. Soya bean farming alone is responsible for the loss of 55 million tonnes of topsoil each year in Brazil.
• Deforestation could affect the water cycle, causing changes to weather patterns

Characteristics of Tropical Rainforests revision material from Beyond

This Characteristics of Tropical Rainforests blog is our first-ever GCSE Geography revision blog! Keep checking in to find more content and, in the meantime, you can find English, Maths and Science revision here!