Changing Ecosystems » Tropical Rainforest Global Distribution

What you'll learn this session

Study time: 30 minutes

The global distribution of tropical rainforests
Factors affecting where rainforests are located
Key characteristics of major tropical rainforest regions
The importance of the equatorial climate for rainforest development
Current threats to rainforest distribution
How to interpret rainforest distribution maps

Tropical Rainforest Global Distribution

Tropical rainforests are one of Earth's most spectacular and important ecosystems. They cover just 6% of the Earth's land surface but are home to over 50% of the world's plant and animal species! Let's explore where these amazing forests are found and why they grow where they do.

Key Definitions:

Tropical rainforest: Dense, moisture-loving forests found near the equator with high biodiversity, year-round warmth and heavy rainfall.
Equatorial climate: Hot and wet conditions found near the equator with little seasonal variation in temperature.
Biodiversity: The variety of plant and animal life in a particular habitat or ecosystem.

🌎 Global Distribution Pattern

Tropical rainforests are found in a band around the equator between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S). This region is known as the tropics. The largest rainforest areas are found in:

South America: The Amazon Basin (Brazil, Peru, Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname, French Guiana)
Central Africa: The Congo Basin (Democratic Republic of Congo, Republic of Congo, Gabon, Cameroon, Central African Republic)
Southeast Asia: Indonesia (particularly Sumatra and Borneo), Malaysia, Papua New Guinea, Philippines and parts of mainland Southeast Asia

🌞 Climate Requirements

Tropical rainforests thrive under specific climate conditions:

Temperature: Average monthly temperatures above 18°C year-round
Rainfall: At least 2,000mm annually, often much higher
Seasonality: Minimal seasonal variation in temperature
Humidity: Consistently high (80-90%)

These conditions occur primarily near the equator where the sun's rays hit the Earth most directly throughout the year.

Major Tropical Rainforest Regions

The Amazon Rainforest

The Amazon is the world's largest tropical rainforest, covering approximately 5.5 million square kilometres across nine South American countries. It represents over half of the planet's remaining rainforests and is unmatched in terms of biodiversity.

🌱 Size & Scale

The Amazon Basin is roughly the size of the continental United States. Brazil contains about 60% of the Amazon rainforest, with Peru having the second-largest portion.

🌩 Climate Factors

The Amazon receives 2,000-3,000mm of rainfall annually. The ITCZ (Intertropical Convergence Zone) passes over twice yearly, creating two wet seasons in many parts.

🗺 Geographical Features

The Amazon River system with over 1,100 tributaries helps distribute moisture throughout the basin, supporting rainforest growth even at some distance from the equator.

The Congo Rainforest

The Congo Basin contains the world's second-largest tropical rainforest, spanning about 3.7 million square kilometres across six Central African countries. It's home to endangered species like gorillas, chimpanzees and forest elephants.

🌏 Location Factors

The Congo rainforest straddles the equator, with the Congo River (the world's deepest river) and its tributaries creating a vast wetland ecosystem. The Democratic Republic of Congo contains about 60% of the Congo rainforest.

🌲 Unique Features

Parts of the Congo Basin include 'swamp forests' that are seasonally flooded. The region has remained relatively intact compared to other rainforest regions due to political instability limiting development, though this is changing rapidly.

Southeast Asian Rainforests

The rainforests of Southeast Asia are scattered across islands and mainland areas, making them more fragmented than the Amazon or Congo. They're known for unique wildlife like orangutans, tigers and the world's largest flower, the Rafflesia.

🏜 Island Distribution

Major rainforest areas are found on Borneo (shared by Indonesia, Malaysia and Brunei), Sumatra (Indonesia), New Guinea (shared by Indonesia and Papua New Guinea) and parts of the Philippines, Thailand, Cambodia, Vietnam and Myanmar.

🌊 Monsoon Influence

Southeast Asian rainforests are influenced by monsoon systems, with some areas experiencing more seasonal rainfall patterns than equatorial South America or Central Africa. The maritime location means high humidity year-round.

Factors Affecting Rainforest Distribution

Several key factors determine where tropical rainforests can develop:

🌞 Solar Radiation

The equatorial region receives consistent, direct sunlight year-round, providing the energy needed for high plant productivity. The sun is directly overhead twice yearly at the equator, creating ideal growing conditions.

🌩 Rainfall Patterns

The ITCZ (where trade winds converge) brings heavy rainfall to equatorial regions. Rising warm air creates a low-pressure zone that draws in moisture-laden air, resulting in almost daily rainfall in many rainforest areas.

🌎 Continental Position

Rainforests tend to develop on the eastern sides of continents in the tropics, where warm ocean currents and prevailing winds bring moisture inland. Western continental edges often have drier conditions due to cold ocean currents.

🗻 Topography

Mountains can create 'rain shadow' effects, blocking moisture from reaching inland areas. However, mountains can also force air to rise, cool and release moisture, creating localized rainforest conditions. The Andes play a crucial role in Amazon rainfall patterns.

🌁 Ocean Currents

Warm ocean currents increase evaporation and moisture in the atmosphere. The warm waters of the western Pacific contribute to the high rainfall in Southeast Asian rainforests, while the Atlantic influences rainfall patterns in the Amazon.

Case Study Focus: The Amazon Rainforest Distribution

The Amazon rainforest extends from approximately 10°N to 20°S latitude, stretching beyond the typical equatorial zone. This unusual reach is possible because of several geographical factors:

The Amazon River system distributes moisture throughout the basin
The Andes Mountains block westerly winds, trapping moisture in the basin
The 'flying rivers' phenomenon - trees release water vapor through transpiration, creating atmospheric rivers that carry moisture inland
The Atlantic Ocean provides a constant source of moisture carried inland by trade winds

These factors allow rainforest conditions to extend much further from the equator than in other parts of the world, creating the planet's largest continuous rainforest ecosystem.

Current Changes in Rainforest Distribution

Tropical rainforest distribution is changing rapidly due to human activities and climate change:

🔨 Deforestation

Approximately 17% of the Amazon has been lost in the past 50 years, with similar losses in Southeast Asia. The Congo Basin has historically been better preserved but is now experiencing accelerating deforestation. Major causes include:

Agricultural expansion (especially soy and cattle in the Amazon)
Palm oil plantations (particularly in Indonesia and Malaysia)
Logging (both legal and illegal)
Mining operations
Infrastructure development

🌡 Climate Change

Changing climate patterns are affecting rainforest distribution:

Parts of the Amazon are experiencing longer dry seasons
Increasing temperatures are stressing rainforest ecosystems
Changing rainfall patterns may shift where rainforests can grow
More frequent and severe El Niño events cause drought in some rainforest regions

Scientists warn that the Amazon may be approaching a 'tipping point' where deforestation and climate change could convert parts of the rainforest to savanna.

Interpreting Rainforest Distribution Maps

When studying maps of tropical rainforest distribution, look for these patterns:

The concentration of rainforests between the Tropics of Cancer and Capricorn
The highest density of rainforests near the equator
The relationship between rainforest locations and major river systems
The influence of mountain ranges on rainforest distribution
The fragmentation patterns in Southeast Asia compared to the more continuous forests of the Amazon and Congo
Areas of recent deforestation, often appearing as patchy or fragmented forest at the edges of major rainforest blocks

Understanding these patterns helps explain why rainforests grow where they do and how human activities are changing their distribution.

Key Takeaways: Tropical Rainforest Distribution

Tropical rainforests are concentrated in three main regions: the Amazon Basin, the Congo Basin and Southeast Asia
They require consistent warmth, high rainfall and high humidity to develop
Their distribution is primarily determined by the equatorial climate but is also influenced by continental position, ocean currents and topography
Human activities, especially deforestation for agriculture, are rapidly changing rainforest distribution
Climate change is beginning to affect where rainforests can grow and may cause significant shifts in their distribution in the coming decades

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