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examBoard: Cambridge
examType: IGCSE
lessonTitle: Tropical Rainforest Structure
Tropical rainforests are incredibly complex ecosystems found near the equator where temperatures are warm and rainfall is abundant. They're like nature's skyscrapers, with distinct layers that create homes for millions of plant and animal species. In fact, though they cover less than 7% of Earth's land surface, they contain over 50% of the world's plant and animal species!
Key Definitions:
Tropical rainforests are found in a belt around the equator, primarily between the Tropic of Cancer (23.5°N) and the Tropic of Capricorn (23.5°S). Major rainforests include the Amazon in South America, the Congo Basin in Central Africa and the Southeast Asian rainforests across Indonesia, Malaysia and Papua New Guinea.
The Amazon Rainforest alone produces about 20% of the world's oxygen, which is why it's often called "the lungs of the planet." It's home to 1 in 10 known species on Earth!
Tropical rainforests have a unique vertical structure with several distinct layers. Each layer has its own microclimate and specialized plants and animals that have adapted to the specific conditions.
Tropical rainforests typically experience:
Layers form in the rainforest because:
Height: 45-55m
Giant trees that poke above the main canopy, exposed to strong sunlight, wind and rain.
Adaptations: Umbrella-shaped crowns, buttress roots for support, drip-tips on leaves to shed water.
Wildlife: Eagles, bats, butterflies, monkeys
Height: 30-45m
Dense layer of overlapping trees forming a roof over the forest. Receives 90% of the sunlight.
Adaptations: Broad, waxy leaves to shed water, shallow roots to quickly absorb nutrients.
Wildlife: Most rainforest animals live here - monkeys, sloths, birds, insects
Height: 5-30m
Shaded environment beneath the canopy with smaller trees and shrubs. Only 5% of sunlight reaches here.
Adaptations: Large leaves to capture limited light, ability to grow in shade.
Wildlife: Jaguars, snakes, frogs, insects
Height: 1-5m
Dark, humid layer with small shrubs, ferns and young trees waiting for a gap in the canopy.
Adaptations: Shade tolerance, ability to grow quickly when light becomes available.
Wildlife: Insects, reptiles, amphibians
Height: 0-1m
Dark layer (less than 2% of sunlight) with decomposing leaves, fruits and branches. Nutrient recycling happens here.
Adaptations: Decomposers break down material quickly in the warm, moist conditions.
Wildlife: Insects, worms, fungi, bacteria, large mammals like tapirs
Plants in the rainforest have evolved special features to help them survive in this challenging environment:
The Amazon Rainforest spans nine countries in South America, with 60% in Brazil. It contains:
The forest structure creates countless microhabitats. For example, a single hectare may contain over 480 tree species and one tree might host up to 40 different ant species!
The layered structure of the rainforest creates a complex web of relationships between species:
Many rainforest plants rely on specific animals for pollination. For example, some orchids can only be pollinated by one species of bee or butterfly. The plant provides nectar and in return, the pollinator transfers pollen as it moves from flower to flower.
Fruit-eating animals like monkeys, birds and bats spread seeds throughout the forest. Some seeds even need to pass through an animal's digestive system before they can germinate. This relationship helps plants reproduce and ensures animals have food.
As you move from the forest floor to the emergent layer, conditions change dramatically:
These microclimates create specialized niches for different species, contributing to the incredible biodiversity of tropical rainforests.
Understanding the structure of tropical rainforests helps us appreciate:
Human activities are disrupting the delicate structure of rainforests through:
When the structure is damaged, the entire ecosystem suffers as the specialized habitats for countless species are lost.
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