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Rainforests - the Lungs of the Planet
Monkeys tend to occupy the canopy level of a rainforest where food is more abundant.

Rainforests - the Lungs of the Planet

In GCSE Geography students will look at different climates and environments. One environment they will study is that of the rainforests which act as the lungs of the planet, recycling carbon dioxide and providing us with oxygen.

The name rainforest comes from the high amount of rainfall that occurs in them each year. By definition no less than 168cm (some definitions refer to 250cm) of rain falls on a rainforest annually, although in rare cases it can exceed 1,000cm. Rainforests exist in temperate zones, but the tropical rainforests are much more extensive and incredibly important. The rainfall and the warm climate lead to hot humid conditions that the plants and animals living there have adapted to. Mean temperatures can exceed 18 degrees Celsius all months of the year and many of the creatures exist nowhere else on the planet. Many useful materials come from rainforests, including chemicals from plants and animals that provide the basis for modern medicines.

Rainforests act as the lungs of planet Earth. They are responsible for 28% of the world’s oxygen turnover. They convert carbon dioxide into oxygen and so help to slow global warming. Deforestation and the burning of the trees is both reducing the amount of oxygen turnover and increasing the amount of carbon in the atmosphere.

Why does rainforest land cleared for agriculture only remain fertile enough to grow crops for a year or two before it has to be abandoned?
Rainforest soils are thin and the nutrients are easily washed away
The high-intensity farming methods mean that the nutrients are removed
The deep soils mean that nutrients are locked deep underground
The soils become saturated with toxins from the farming methods in a single season
The thin soils are usually replenished with a deep leaf litter from the trees above. Without the trees the thin soils are eaily washed away and the nutrients lost
Huge trees need huge roots to support their weight. However, the nutrients in the rainforest soil are close to the surface meaning the roots need to be shallow. How have trees adapted to these conditions?
Wide roots that lead to only one tree in a large area
Buttress roots that stretch up to 2 m up the trunk to anchor the tree
The trees use vines and other trees to support their weight
All rainforest trees are softwoods so are very light weight
These huge buttress roots support the tree and provide unique places for specialised flora and fauna to live
Within a rainforest much of the water comes from convectional rainfall. What are the stages of this process?
Rivers and streams create small pockets of intense humidity. This humidity drips off the leaves and plants making rainfall
Rainfall is intercepted by the canopy which channels this to the floor. It then evaporates and is intercepted by the canopy again
The rainfall is intercepted by the canopy. As the rainforest heats up the water evaporates and forms clouds to make the following day's rain
The rainfall hits the ground and flows through the soil structure to reach the tree roots. These draw it up and the trees evaporate the water via their leaves
The process of convectional rainfall is the means by which most of the regular rainfall occurs in the afternoon of every day
What part of the rainforest ecosystem are the latsols?
Small rivers and streams
The soils
The shrubs
The highest trees
Latsols have a thick litter layer which is full of nutrients. However, rapid leaching means that once the vegetation is removed it becomes infertile rapidly
There are multiple layers in the rainforest. What is the top layer called?
Shrub layer
Climax layer
Canopy layer
Emergent layer
The emergent layer is occupied by birds and insects. This layer is where a few of the largest trees have managed to grow higher to get the light
Which of the following continents or islands does not contain rainforests?
South America
The British Isles
Not all rainforests are tropical. The UK has some small areas of temperate rainforest, for example the Celtic rainforest in parts of Wales and western Scotland
Where is most of the rainfall intercepted in a rain forest?
Emergent layer
Canopy layer
Under canopy layer
Shrub layer
The heavy leaf cover means that most of the rainfall is intercepted by the canopy layer. This reduces the amount that reaches the lower levels. Many of the plants that operate on the lower levels draw water from the humid air
Some trees use the trunks of others to climb up from the forest floor. What are these woody plants known as?
Strangler figs
Lianas climb up from the forest floor to the canopy where they spread from tree to tree
When a tree falls in the rainforest what happens to the small trees and other plants in the shrub layer?
The change in conditions kills them
The light coming through the gap allows them to grow fast to become part of the canopy
The lack of convectional rainfall dries the soil and destroys the under canopy
The tree decays within hours to form nutrients
The under canopy and the shrub level receive very little sunlight compared to the canopy and emergents. A missing tree provides a gap in the canopy to allow the sunlight to penetrate
Which layer is occupied by birds and monkeys?
Forest Floor
With little light reaching the forest floor and the presence of large predators on the lowest level, monkeys and birds tend to occupy the canopy level where food is more abundant
You can find more about this topic by visiting BBC Bitesize - Tropical rainforests

Author:  Ruth M

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