GCSE Revision - Ecosystems - Tropical Rain Forests

The dark green areas are where the Rainforests are located
 

Tropical Rainforest Facts

  • Tropical Rainforests are found in a narrow belt either side of the equator

  • There are more plant and animal species in the rainforest than anywhere else on earth - in fact 90% of it is found here

  • Temperatures are hot throughout the year - mainly between 26 & 27 degrees C

  • Rainfall is heavy and mainly convectional - up to 1800 mm a year

  • It rains everyday in the afternoon and in every month of the year

  • Its growing season is 365 days a year - in other words no seasons!
rainforest structure

Rainforest Structure

Emergents - or forest giants, 50 metres or taller. These trees are ususlly supported by buttress roots.

Canopy - This is adense layer forming almost complete cover. Trees 20 - 30 metres tall include many hardwoods such as mahogony.

Under Canopy - This dark and humid area contains saplings between the trunks of larger trees.

Shrub Layer - This contains small trees and shrubs especially near rivers.

Forest Floor - This is covered with ferns and a deep litter of fallen leaves & branches.

 

How has the Rainforest adapted to the climate?

  • Trees are evergreen - plants grow all the year round and come into bud and shed their leaves at any time

  • Thick leathery & shiny leaves protect the trees against sunlight and rainfall

  • Leaves have drip tips that shed moisture quickly after heavy downpours

  • Trees are tall with few branches as they strive to get to the light and photosynthesise

  • Shallow butress roots help to give support in the thin infertile soils

  • Llianas climb up the tall trees and act like vines

Tropical Rainforest Soils - Latosols

  • Tropical rainforest soils are shallow and acidic - iron oxides stain the top layers red.

  • The soil is infertile and one of the poorest in the world

  • Heavy rainfall quickley washes away any nutrients that are not taken up by the trees

Despite the infertile soil the rainforest survives because

  • Plant and animal remains soon decay in the warm, humid climate

  • Shallow rooted trees quickly absorb the nutrients released by decomposition

  • Few nutrients are lost from the nutrient cycle as the forest literally feeds on itself

  • Most nutrients are stored in vegetation, when they die they decay and are then absorbed by the trees. (click on diagram for animation)

Logging

The timber industry is responsible for about 40% of forest destruction. Commercial logging provides important income for many LEDC's. Also large scale damage is done to the forest as the sought after trees are removed.

Cattle Ranching

This destroys large parts of the rainforest to make way for grazing land. The land only lasts a few years as the heavy rain turns the soil infertile and acidic, so ranchers clear even more forest for more grazing land - usually illegally.
 

Why is the forest being destroyed?
 40 Hectares are lost every minute
5 times the size of Switzerland every year

  

Mining

In the Amazon there are huge reserves of minerals such as gold, iron Ore and copper. These are used throughout the world and Brazil can earn a great deal of money from them. Unfortunately large areas of forest have to be destroyed to excavate the minerals such as the Carajas project

Other Reasons

  • Large scale projects such as Hydro Electric Dams - Tucuri

  • Subsistence Farming

  • Cities such as Manaus

  • Roads such as the Trans-Amazonian Highway
 

What are the effects of Rainforest Deforestation

  • Changes in Biodiversity - Removal of the forest causes the loss of plant species. Animals are forced out as their food supply and habitat are destroyed. Many rainforest species have become extinct and others threatened.

  • Changes in Hydrology - Without the trees the water cycle is disrupted. Interception and transpiration are both reduced and surface runoff increases. Water and silt pour into the rivers, making them flood.

  • Changes in Soils - Without trees to protect it, the soil is easily eroded. Torrential rain removes nutrients via surface runoff and leaching with the soil becoming infertile. Surface runoff on steep slopes can cause gulleying and mudslides.

  • Changes in Climate - Transpiration is reduced and evaporation increases. This leads to a drier climate. Deforestation contributes to global warming because trees use up carbon dioxide during photosynthesis. As a result sea levels will rise and the world's climates could be affected.

  • Indigenous Indians - These have great knowledge of the uses of plants and animals in the forest and many could be used in medicine with new drugs etc.

How can the rainforest be managed for sustainable development?
(Sustainable Development - means using the resources in such a way to be able to preserve them for future use)

  • Harvesting the forest - Rubber Tapping - This collects latex from trees and causes no lasting damage to trees. Likewise collecting fruits such as Brazil Nuts does not harm the forest and can bring in more income than cattle ranching.

  • National Parks & Reserves - Some countries have set up parks to protect their rainforest as in the Korup National Park in Cameroon. The aim is to preserve their unique flora and fauna and try to develop ecotourism.

  • Sustainable Logging - The aim is to produce timber in such a way that the forest is not permanently damaged and recovers quickly. Trees are replanted and there needs to be a strict quota on how much timber is allowed to be cut down. This takes place in Peru.

  • Agroforstry - This is where a variety of plants are grown to produce crops, fruit and larger trees. The idea being to use some large trees to protect the soils and smaller plants but allowing more light in to enable more produce in the form of palm trees, oil palms, coconuts, pineapple and bananas as well as crops on the forest floor.