Characteristics of Tropical Rainforests

Climate of Tropical Rainforests

Tropical rainforests are located between 20° North and South of the equator. This climate zone is known as the equatorial climate, characterised by consistently hot and wet conditions throughout the year. Temperatures range from 27°C to 30°C, and precipitation averages 2000–3000mm annually. The climate is perfect for a range of plant species to thrive.

Interdependence of Biotic and Abiotic Characteristics

Abiotic characteristics (non-living components, such as rocks, soils, water and atmosphere) interact closely with biotic characteristics (living components, such as plants, animals and humans).

• Soils and vegetation: Plants use nutrients in the soil to grow. The hot, wet climate allows rapid decomposition, quickly returning nutrients to the soil, which plants then absorb.
• Climate and plants: The high rainfall and constant warmth encourage year-round plant growth, providing food and shelter for animals and people.
• Water and animals: Rivers and rainfall provide fresh water for both wildlife and human communities.
• Humans: Indigenous people rely on the rainforest for food, medicine, and building materials. They practise subsistence farming, hunting, and fishing, showing the close link between human life and the rainforest ecosystem.
• This shows how plants, animals, soils, climate, water, and people are all interdependent. If one part of the system is disturbed (e.g. deforestation), the whole balance can be upset.

Nutrient Cycling in the Rainforest

In the tropical rainforest, most of the nutrients are stored in biomass (the living things in an ecosystem, such as plants and animals).

• Nutrients are recycled very quickly in this biome. The hot, wet climate is perfect for decomposers, which break down dead material in the litter layer (fallen leaves, dead plants, and animals lying on the soil surface). Once broken down, the nutrients are absorbed by vegetation through the soil.
• Rainforest soils form when dead organic matter mixes with weathered rock. However, these soils are usually thin and not very fertile.
• Heavy rainfall washes away nutrients in a process called leaching, which leaves the lower soil layers poor in minerals. Plants quickly absorb what nutrients are left in the top layer. Many rainforest soils appear red because they contain lots of iron.

The rainforest nutrient cycle is fragile. If something disrupts the flow of nutrients, the whole system is affected. For example, when forests are cut down, the litter layer stops receiving organic matter. The soil soon becomes infertile, and without vegetation cover, nutrients are rapidly washed away by heavy rainfall.

This rapid cycling of nutrients supports high biodiversity and complex food webs, as nutrients are constantly made available for plants, which in turn support a huge variety of herbivores, carnivores, and decomposers.

Vegetation Structure in the Rainforest

Tropical rainforests are stratified into layers:

• Emergent layer – the tallest trees (over 50m) grow above all others, with small leaves and flexible trunks.
• Canopy layer – a dense layer of trees whose interlocking leaves block out most sunlight, home to many animals such as monkeys and birds.
• Understorey layer – plants adapted to lower light, including smaller trees and shrubs.
• Shrub and ground layer – very dark and damp, with few plants other than those adapted to low light, such as ferns.

Layers in the tropical rainforest

Competition for sunlight is intense. When a large tree falls, a gap in the canopy allows light to reach the forest floor, encouraging the rapid growth of saplings.

Adaptations of Plants

Plants in the tropical rainforest have developed a range of adaptations to survive in the hot, wet climate and poor soils:

• Drip-tip leaves – to protect stems from heavy rainfall and discourage moss and algae from growing.
• Buttress roots – to support the height of trees and to extract nutrients from the shallow soil layer.
• Epiphytes – plants that grow on the surface of other plants, extracting moisture and nutrients from the air, rain, water, or debris around them.

Adaptations of Animals

With thousands of plants, the tropical rainforest is home to thousands of different species of mammal, amphibian, insect and bird. For example, in Madagascar, the rainforest has over 14,000 species of plants, providing a habitat and food source for more than 250,000 animal species. Other adaptations include:

• Monkeys have long prehensile tails and colour vision to help them travel through the canopy and find ripe fruit.
• Eagles have developed strong legs and sharp talons to catch prey, such as monkeys, from the canopy.
• Poison dart frogs secrete poison through their skin, with bright colours warning predators. Some non-poisonous frogs mimic this appearance as protection.