Tropical rainforests = hot and wet biomes renowned
for their biodiversity
○ Found in a broad belt across the Equatorial
region
○ Occupies only 7% of the world’s land
surface
○ Contains many useful resources
■ Mainly found in Brazil, Central
Africa, South East Asia
● 2 main characteristics that distinguish tropical
rainforests from other biomes
○ Climate
○ Vegetation
Climate:
● Occur close to equator → climate is warm and wet
○ Annual temperature = 26°C → temperature has little variation throughout year
○ Annual rainfall = exceeds 2500 mm
■ Abundant supply of water feeds rivers
● eg/ the Amazon River, Brazil
Vegetation:
● Renowned for rich vegetation cover
● Abundance of sunlight and rainfall allow huge amounts of plant growth via producers
● High competition between plants for light and space
● Rainforest is layered → plants take advantage of what space and light there is
○ Shrub layer = lowest layer of the rainforest
■ Plants have to cope with little sunlight
■ Ferns have large leaves to maximise energy taken from light
■ Animals eat seed and berries
■ Abundance of decomposers and insects
○ Under canopy = layer made of smaller trees waiting to grow up and occupy a place in the canopy
○ Canopy trees = tall trees where most animals are found in maximum light (30 – 40 m)
■ Grown tall to maximise sunlight for photosynthesis
■ Animals can access food (eg/ fruits, nuts) and be safe from predators on the forest floor
■ Many trees have leaves with flexible bases → turn to face the sun
■ Many trees have huge buttress roots
● Stabilise plant
● Increase SA for O 2 and CO 2 exchange
● Help transport water
■ Drip tip to stop water accumulating on the leaf
○ Emergents = the tallest layer of trees
■ Grown tall to maximise the amount of sunlight that they can receive
Soils:
● Soils are very deep → high rainfall weathers rock below
○ Masses of vegetation allow deep soils to grow
● Very nutrient poor → rainwater washes out/ leaches nutrients/minerals out of soil
○ Lower layers of soil lack nutrients needed by lush vegetation
○ Nutrient cycling allows vegetation to grow
■ Soil → developed by mixing of dead organic matter with weathered bedrock
● Plants take up nutrients which are dissolved in the soil
■ Biomass → all living things in ecosystem; plants and animals
● Plants and animals die , nutrients fall to the ground
■ Litter → dead organic material such as fallen leaves/tree trunks/dead animals
● Vegetation is quickly decomposed by insects, bacteria and fungi
○ Warm/humid conditions aid decomposition
● Releases nutrients back into surface of the soil which is taken up by plants
● Most of forests’ vital nutrients are in:
○ Biomass = living vegetation and animals
○ Litter = dead wood, leaves, animal remains
● Soils are often red in colour → rich in iron
● Nutrient cycle shows how tropical rainforest is interdependent
○ Changes in one part of the ecosystem could be very damaging
■ eg/ loss of tree cover would affect water and nutrient cycles and cause soil erosion
Biodiversity:
● Biodiversity in tropical rainforests are higher than any other biome
○ Over ⅔ of the world’s plant species are found in these forests
○ Forests contain around ½ world’s known animal species
● Human exploitation of rainforest resources is reducing biodiversity → decline in ecosystem productivity