Age group 8 to 16 years
Learn More about Rainforests
More information about rainforests is below. You can read through the whole page or use the links below to jump to a topic:
The impact of rainforest destruction
Geography
Rainforests cover just over 6% of the Earth's land surface. The major areas of rainforest are found in South America, Africa and South-eastern Asia.
The largest of them is called the Amazon and is in South America. It grows across 8 countries and covers four million square kilometres. It lies in three sections which you can see on the map below. The largest part lies in the Amazon and Orinoco basin, with the second lying across the Andes on the Pacific Coast of Ecuador and Colombia and extending up into Middle America. The third part lies on the Atlantic coast of Brazil in a strip about 50 km wide and lying on the mountains.
The second largest block of rainforest is in the Eastern Topics and it covers 2.5 million square kilometres. Most of this rainforest lies in Indonesia but it extends southwards into the pacific to form a trip of rainforest into north east Australia. It also extends north from Indonesia into south east Asia Burma, Thailand and Indo China.
The smallest block of rainforest lies in Africa and this covers an area of 1.8 million square kilometres. Lying mostly in the Congo Basin it reaches from high mountains in the east right across to the Atlantic Ocean. There are also tiny patches of rainforest on the east coast of Madagascar and Mascarenes.
So are all the rainforests the same?
No but they all need the same things in order to exist. They need high temperatures of an average 25°C all year. They get at least 2m of rain every year although some get up to 10m. In comparison the wettest parts of the UK get up to 50cm every year. The humidity (a measure of how much water is in the air) can be up to 100%. They lie very near the equator.
But the plants and animals that are found in the different areas of rainforest have some things in common but are different species.
The reason for this is that they all used to be linked together. 345-280 million years ago all of the land was joined together to form one big super continent called Pangea. But then 230- 195 million years ago this super continent started to break up. This is because the earth's surface is made up of plates known as tectonic plates and these started to move around or drift (known as continental drift) taking the land that was on top of them with them.
The super continent Pangea split into two smaller pieces of land. One was called Laurasia which was in the north and the other was called Gondwana and this was in the south. On Gondwana was what we call Antartica, South America, Africa, India, New Zealand, Madagascar and Australia. That is all the places that we now have rainforests. During this time lots of Plants had evolved and were all found across the whole of Gondwana.
However about 120 million years ago Gondwana itself started to break up, separating into lots of land masses. The plants and animals continued to evolve but without the opportunity to mix with the rest of the land masses they all evolved slightly differently. This makes the differences that we see in the species of plants and animals that we see in each of the different areas of the rainforest.
Ecology
There are 6 different categories of rainforest. These are distinguished when we look at the major differences in flora and fauna created by soil type, flooding and, perhaps most importantly of all, the types of nutrients carried in the floodwaters.
Vársea means flooded forest in Portuguese. The main feature of Varsea rainforest is that the floodwaters are very rich in nutrients which they deposit in the forest soil when the flow rate drops. The nutrient richness is explained by the water's origin - melt water from the Andes where relatively young rocks have yet to be leached of their salts and minerals. The floodwater in the Varsea is called whitewater rivers because these sediments keep it a dirty, yellowish colour. Varsea account for around a third of the world's rainforests although their rich soils mean they are obvious targets for soya and palm plantations.
Igapò forest is also regularly inundated with floodwater but unlike Varsea forest these floods don't bring much in the way of nutrients for the soil. Instead of the Andes, the water comes from lowland tropical Heath forests whose ancient soils provide no minerals. Instead the decaying leaves that the water flows through introduce dark coloured tannins that acidify the water and create blackwater rivers. The scarcity of nutrients and acidic conditions mean Igapò forest has a lower canopy and many of the trees, such as Cecropia, Ceiba, and Mauritia palms, have buttress roots to provide extra stability in the thin soils.
Heath forest exists on well drained sandy soils. This limits the height of the canopy level. The acidity also leads to less biodiversity although with more light reaching the forest floor, there is dense tree growth.
Peat forests are found when an area of forest does not drain. Dead vegetation and leaf litter can remain too damp to decompose and instead builds up into layer of peat. These are found in small parts of Africa, north-eastern South America, and large areas in Southeast Asia (especially Borneo and Sumatra). The layers of peat can be up to 20 metres deep and store lots of carbon stores. If they are drained for conversion to agricultural use, not only is the carbon held in the tree's biomass lost, but the peat can often ignite and burn for many months. Such forests are at considerable risk given the soil is well adapted for growing cash crops.
Terra Firme means "firm earth" and this type of forest is found on drier, well-drained land that has a more neutral pH and is never inundated with flood water. Since flood water can starve roots of oxygen and inhibit growth, the Terra Firme forest has taller trees and more biodiversity than Igapò forest. It is characterised by brazil nut trees and rubber trees which provide significant income for local communities. It also however is home to the highest quality tropical hardwoods which means it is susceptible to logging
The sixth category of forest is the Mangrove forest which is found along river deltas, estuaries, and coastal areas. It has less different types of trees with mangroves predominating. The proximity to water means Mangrove is relatively easy to gain access to if it is cleared. They are easily damaged by the wakes of boats and localised pollution.
Rainforests have different levels.
There are three main layers of trees which are usually described, but an additional layer to be discussed would be the forest floor itself. For now we will ignore the differences between the areas of Tropical Rainforests to just give a general idea of what may be found in these areas.
The forest floor
On the forest floor the air is still and dark. Only two percent of the light makes it through the canopy. This stops lots of plants that need light from growing and so the floor becomes covered with roots and fallen leaves twigs and branches. Only when a tree falls over does any light come through and when this happens, saplings and plants are able to grow. However you still find lots of animals on the forest floor. In particularly there are lots of insects and some of the bigger animals live here. For example in Africa you would find gorillas here.
The Understory
Under the leaves of the taller trees and above the ground is a cool dark area called the understorey. Being so dark makes it difficult for any plants to grow so most of what you find there is short, leafy and mostly non flowering. There are small trees, ferns, lianas (climbers or vines) and palms. Amongst these plants are animals including insects, arachnids, snakes, lizards and small mammals. Within the branches lurk some nesting birds and occasionally the odd jaguar.
An evergreen canopy in the middle
The canopy lies 25-45 m (80-150ft) above the ground. The tops of these trees form a layer 6-7m (20-23ft) thick and it acts as a roof, shielding the ground and absorbing the light. It also protects the ground from heavy rainfall and strong winds. This area is full of animals. There are birds including the scarlet macaw, insects, and mammals like the howler monkey, the orang-utan and reptiles.
Scattered tall trees which tower above the canopy, known as emergent.
Sometimes these trees reach heights of up to 60-70m (200-230ft). They have long straight trunks and the top is shaped like a cauliflower. Up at these heights it is much hotter and drier and there are greater changes in the temperature and humidity. This area is popular with birds.
The River Amazon
Winding their way through the rainforests are mazes of streams and other water features. One of the most well known is the Amazon River which is said to hold 2/3 of the worlds fresh water. The Amazon is the second longest river in the world, stretching for 3920 miles. It begins in the Andes, sourced from melting snow, and travels east across south America. It finally reaches the Atlantic Ocean at Belem in Brazil.
There was a time (15 million years ago that the Amazon flowed west into the Pacific ocean but the tectonic plate that carried South America moved into another plate to create the Andes Mountains. This blocked the river, casing the water to back up to create fresh water lakes. It took another 5 million years for the river to find its way eastward to flow into the Atlantic like it does today.
The drainage basin that fills the river covers 2,722,000 million square miles and about 1,100 tributaries feed into the Amazon. This all contributes to the 28 billion gallons of water that flow into the Atlantic every minute. At its mouth the river can be 200 to 300 miles across. Even up to 1000 miles inland the river can still be 7 miles wide and its is so deep that the big ocean liners can still travel up the river for about 2,300 miles.
Living in this vast water system are more than 2000 species of fish (that's more than those in the entire Atlantic Ocean). Also here are river otters, freshwater dolphins, turtles, manatees and caimans. See the section on animals to learn more about these.
Rainforests also have poor soils. They are naturally high in minerals such as aluminum and iron oxides which make them a red orangey colour. The only layer that is nutrient rich is the thin top layer where decaying leaves and other such matter leach nutrients. Figure 27 shows leaf cutter ants, one of the many organisms helping to turn dead plants into decaying organic matter. This is readily taken up by the vegetation to give the rich growth of plants that which it is so well known.
In order to deal with the poor soil the plants and trees have developed strategies that allow them to best utilise what is there. Most canopy trees are shallow rooted and lots have roots that grow out of the ground to make a mat on the forest floor which helps them take up more nutrients. However these shallow roots make the trees unstable. Some trees have roots systems that grow for many meters across the ground to provide stability. Some of the very tall emergent trees have a system of roots known as buttress roots. These roots start up 20 feet above the ground.
Not all of the rainforest soils are poor. The soils of the rainforests growing on the mountain sides (known as montane forest) are richer in nutrients. This is due to more recent volcanic activity where nutrients are brought up by the volcanoes and deposited on the ground and also these steep slopes have more erosion of the rocks that store the minerals that help make the soils rich. Areas of flooding or floodplains are also richer in nutrients as the floodwater also deposits nutrients on the ground.
Biodiversity
Surviving in the rainforest
With so much living in the rainforest it stands to reason that life here must be very competitive. Many of the species living here have evolved and or interact with each in order to make life a little easier or most likely safer for themselves.
Plants start with a struggle for light but even if they manage to reach that they still have to acquire nutrients and water for the process of photosynthesis. And if that isn't difficult enough then they have to try and hold onto those nutrients as others around them try to steal them. Within the armoury of the plants include the ability to produce chemicals. These chemicals can vary in their effect from making them taste disgusting, to being indigestible, to being poisonous.
Others work in partnerships trading a place to live in return for the organisms' aid in defence. Ants are particularly good at this job. Working together in this way is a process called Symbiosis- both working together for mutual benefit.
There are some plants that over the course of time have given up trying to make their food and have become carnivorous instead. Examples of this are the pitcher plants.
These pitcher plants have fluid filled jugs which they use to drown their prey. Once attracted to the plant by the sweet smell, they lose their footing and fall in. They are prevented form crawling back out by downward pointing hairs.
Animals are not able to make their own food as the plants do so they must go out and find it. For those that eat plants (herbivores) they must overcome the chemicals that plants produce. Some animals have become immune to the chemicals that particular plants produce and so only eat that particular plant. Others eat a wide range of plants but go for the young leaves, fruits or buds as these are usually poorly defended.
Those eating other animals (predators or carnivores) are adapted to chase, seek and fight with other animals. And whilst the predators become cleverer at seeking out their prey, their prey gets more clever at hiding and defending itself. Mechanisms used by prey and predators range from camouflage to elaborate colours that warn of their poisons. However the rainforests are full of animals (and plants) that are just ready to trick you into thinking that they are more dangerous than they seem or conversely are actually more dangerous than they are letting on. Some are even able to mimic other animals in order to get that bit closer.
What effect does this have?
The rainforests influence on our climate.
First we shall look at what the climate is like in the rainforest. The 'climate' describes the condition of the atmosphere over long periods of time. This takes into account the temperature and rainfall and how these change over the year.
In the tropical rainforests there are no seasons; therefore the weather remains the same all year round. The days will start off sunny, but by the afternoon most of water has evaporated back into the atmosphere to form huge rain clouds so the water falls back to the forests as rain. Temperatures vary little between the day and night (2-5 degrees) and there is a high humidity (a measure of how much water is in the air).
Supporting this wealth of plants and animals is only part of the benefit that rainforests have. The rainforest is often called the 'lungs of the earth'. Forests soak up carbon dioxide and give out oxygen.
On top of this they also help to maintain the weather across the rest of the world. The water that evaporates from the rainforests falls as rain in other parts of the world.
The impacts of destruction
By now you will have seen how important the rainforests are. Unfortunately it is estimated that, every year, 150,000 square kilometres of tropical rainforest is destroyed. That is the size of England and Wales. On top of this the same amount of area is being damaged. In 1950 rainforests covered about 30% of the earths land surface, this is now reduced to 6% and it is still being destroyed.
It would be nice to have pictures here that show the size of England and Wales compared to the rainforest
Why is the rainforest being destroyed?
Unfortunately the wealth of plants and animals has attracted people to the rainforest for the purpose of removing them. One of the greatest examples is wood.
We have already seen the many ways which wood has been used. However it is not always taken from the rainforests in a way that makes it easy for it to be replaced. This work badly damages the forest making it impossible for the plants and animals to return at all. Some species of tree are now facing extinction.
As well as damaging the trees and other plants the people taking the trees often damage the areas where indigenous people live. The logging companies move further and further into the rainforest and are often permitted to move into areas where the indigenous people live. This means that they have to move from their homes to find somewhere else to live.
It is often the case that the trees are cut down without permission. They may be cutting down more than allowed or cutting down areas that are protected. 60% of the tropical timber entering the UK is cut down illegally. Across the tropical rainforests only one tree is replanted for every ten cut and it can take up to 60 years for it to grow big enough to be used for timber.
Leaving the forests damaged has increased their vulnerability. Areas that have been logged in the past are now vulnerable to fire which caused lots of damage in Indonesia during the 1990s. In 1987 a satellite picture of the Amazon River Basin showed a total of 7,603 fires burning in the rainforest.
Some trees are selected specifically because they are worth more money, but this usually means that the rest of the trees are destroyed in order to make the desired tree accessible. These roads make it easier for other people to come in and clear the land for farms.
There are also areas of the rainforest that have lots of valuable minerals such as oil, gold, aluminium and iron. Testing for some of these disturbs the wildlife and creates even more roads that open up the way for others.
Clearing land for farming is a major cause of forest loss. Farmers from other areas often come in and do not understand the environment that they are working in. They use up the thin layer of nutrient rich soils very quickly and are left with the poor soil. From here they must move on, causing more destruction.
Cutting down the trees causes big problems.
The indigenous people lose their homes.
The rainforests are home to an estimated 50 million indigenous people. Cutting down the rainforests removes them from their homes and destroys their societies. During the 20th century in Brazil alone 90 native tribes were wiped out. We still have much to learn from the indigenous people and by displacing them we are perhaps losing all of that knowledge. This includes potential medicinal uses of plants and how to manage, use and repair the rainforest for the long term (sustainable). The decline of indigenous people has been massive. It is said that in 1942 when Christopher Columbus first got to the Americas there was 1.5-2 million indigenous people, now there are just 940,000.
It threatens plants and animals
It is estimated that up to 50,000 species a year may be coming extinct through the destruction of the rainforest. Another way to express this is that we are losing 50 species every day (that's 2 species every hour). Some species facing extinction include chimpanzees, giant ant eaters, giant otters and mountain gorillas. We are losing species before we have had a chance to discover them. The rainforest in Madagascar has 10,000 species of plants and of these 80% are found no where else in the world. It is also home to all the worlds' lemurs. Unfortunately 90% of Madagascar's rainforest has already been destroyed.
On top of this there are still hundreds of species that we still haven't discovered. As well as meaning that we have lost these animals forever it also removes the potential for new medical discoveries. There are thousands of species of plants that have reported medical uses in the native communities of the rainforest that have not yet been tested for use in the rest of the world. So far over 2000 tropical forest plants with anti-cancer properties have been found. But only 1 in 10 of tropical forest plants has been tested for these anti- cancer properties.
Furthermore underneath the thin layer of decomposing organic matter the soils of the rainforests are very poor. Without the trees and plants to add to the layer and also provide structure to it, the organic nutrient rich matter will just blow or get washed away, leaving the poor soil on which nothing can grow.
Climate change
The rainforests play a great part in regulating the climate. Not only do they provide rain but they also soak up carbon dioxide. Destroying the trees has a major impacts related to these things.
Let's start with the bigger picture. The difference between climate and weather is time. Weather is what it is doing today and tomorrow, climate is what we expect it to do over the year. We expect it to be warm in the summer and cold in the winter. Both the weather and the climate can change.
What our weather is like depends on lots of things from all over the world. Heat and rain are the more important factors.
Our heat comes from the sun. It sends it down in rays and the areas that get most of the heat are around the equator as these are the parts that are closest to the sun. When the rays hit the earth some are absorbed and some will bounce back. However there are gases in our atmosphere that trap the rays in, therefore keeping the heat in. These gases are called greenhouse gases. Some examples are Carbon dioxide and methane. Carbon dioxide is one of the most important of the greenhouse as it is believed to be responsible for approximately half of global warming.
So the heat that is trapped in gets moved around the earth in currents creating the warm (or cold) weather.
Coupled with this is water. Water moves around the world in a great big cycle. There is an infinite amount of water in the world so we can't get more if we run out. So how does this cycle work?
Starting in the ground is water table, this is where all the water collects when its hits and sinks into the ground. From here it feeds into the streams and rivers, into ponds and also gets sucked up by trees and plants. The water that flows in the streams and rivers eventually gets into the sea. During its time in the streams and rivers some of it will get taken away to be used by us in our homes or for drinking. Once in the sea, large amounts of it gets evaporated by the sun and when there is enough of it in the atmosphere it forms clouds that get moved around in the air currents. From here the cycle starts again as these clouds will rain and the water will fall back to earth.
How this is affected by the rainforests.
We must remember that the rainforests lie very close to the equator where it is hottest. The trees in the rainforest play a very important part in the water cycle as they are able to remove water from the water table to use during photosynthesis. However with all the heat from the sun a lot of this water gets evaporated into the atmosphere where it forms clouds and rains. Without the trees the water in the water table stays locked in the ground and there is less rain. This makes the rainforests a lot drier and also means that less water gets moved around the world.
When it does rain the dry soil gets washed away easily. This clogs up the streams and rivers making it difficult for plants and animals in the water to live. Without any forest to soak up the rain there is more chance of floods.
So by cutting down the trees there is less soil and less rain. This makes is very difficult for any thing to grow back. The remaining forest becomes hotter and drier and at more risk of fire. Natural parts of the rainforest very rarely catch fire.
Rainforests also play a very important role in climate change. Trees act as a carbon store or sink.
Global warming is being caused as too many greenhouse gases are getting released into the atmosphere. One of the major things that release greenhouse gases are burning fossil fuels, this could be by factories and industries, for the energy used to power your home and the fuel used in your car. The result of this is that more heat is being trapped and so the temperatures are increasing.
However all plants use Carbon dioxide as part of the photosynthesis process. The carbon gets stored inside the trees and as a by product they release pure oxygen back into the atmosphere.
But, the rainforests are being destroyed. A lot of the time the trees are burnt in order to clear large parts of the forest for farms. Doing this contributes greatly to global climate change. Burning the rainforests releases all of the carbon back into the atmosphere as carbon dioxide. Therefore contributing to the increasing temperatures. The more that is cut down the more that is released. Furthermore the more that is cut down the less that can be soaked up again. It is estimated that up to one third of the carbon dioxide being released is from rainforest fires, the rest is released from burning fossil fuels (coal, oil and gas).
Increasing the temperature of the world can lead to changes in our weather, melting of the icecaps and causing the sea levels to rise.
