Download Tropical rainforest Key words: equatorial climate, rich ecosystem

Tropical rainforest
Key words: equatorial climate, rich ecosystem, continuous growing season, temperature, rainfall, humidity, water
cycle, dense vegetation, four layers, expansion, shrub, under canopy , canopy , emergents , leaves, height, lianas,
light, flood, undergrowth, fragile, nutrients cycle, re-establish, adapting, intervention,
The tropical rainforest is a unique biome with a constant temperature and a high rainfall. The level of humidity
and denseness of the vegetation give the ecosystem a unique water and nutrient cycle. Rainforests around the
world are threatened by the expansion of man. They contain the most diverse range and highest volume of plant
and animal life found anywhere on earth.
Rainforest vegetation levels
Tropical rainforests have dense vegetation, which typically occurs in four levels. From ground level up these levels
of vegetation are:
 The shrub layer is at ground level in a tropical forest. It is dark and gloomy with very little vegetation
between the trees. During heavier rainfalls this area can get flooded.
 Under canopy is the second level up. There is limited sunlight. Saplings wait here for larger plants and
trees to die, leaving a gap in the canopy into which they can grow. Woody climbers called lianas avoid
having to wait for gaps by rooting in the ground and climbing up trees to get to the sunlight.
 Canopy is where the upper parts of most of the trees are found. The canopy is typically about 65 to 130 feet
(20 to 40 metres) tall. This leafy environment is full of life such as insects, arachnids, birds and some
mammals.
 Emergents are the tops of the tallest trees in the rainforest. These are much higher, and give the trees an
advantage (in terms of light) than the average trees that populate the forest canopy.
Adapting to rainforest life
Vegetation in the rainforest has evolved characteristics which help it survive in this unique environment. Each of
these plants is adapted to rainforest conditions in a different way.
 Fan palms have large, fan-shaped leaves that are good for catching sunshine and water. The leaves are
segmented, which allows excess water to drain away.
 Rainforests have a shallow layer of fertile soil, so trees only need shallow roots to reach the nutrients.
However shallow roots aren't great for supporting huge rainforest trees, so many tropical trees have
developed huge buttress roots. These stretch from the ground to two meters or more up the trunk, which
help anchor the tree to the ground.
 Lianas are woody vines that start at ground level, and use trees to climb up the canopy where they will
spread from tree to tree to get as much light as possible.
Rainforest water and nutrient cycles
Rainforest ecosystems are characterised by heavy convectional rainfall, high humidity and lushness of vegetation,
and nutrient-rich but shallow soil. These factors give rise to a unique water cycle and nutrient cycle.
Rainforest water cycle
The rainforest climate is very humid. The vegetation is very lush as water is taken up by the roots and rain is
intercepted as it falls - much of it at the canopy level. The next day, as the rainforest heats up, the water given off
by the plants and trees evaporates into the atmosphere - where it forms into clouds to make the next day's rain.
This is called convectional rainfall.
Rainforest nutrient cycle
Plenty of dead plant material and the hot, damp conditions on the forest floor allow rapid decomposition. This
provides plentiful nutrients that are easily absorbed by plant roots. But because these nutrients are in very high
demand from the rainforest's many fast-growing plants, they do not remain in the soil long, and remain close to the
surface of the soil.
This means that if the rainforest is cleared for agriculture it will not make very good farm land as the soil is not rich
in nutrients. Also once the trees (with their roots) are removed the soil can be easily washed away.
human intervention in the Amazon
Humans intervene in tropical rainforests in order to bring real or imagined benefits to themselves or the local
population. The short-term benefits of clearing rainforest areas usually include:
 land for agriculture, houses and roads
 jobs for local workers in road building, logging agriculture, extractive mining, building etc
 The generation of income (often in valuable foreign currency) for the LEDC where the rainforest is located,
when wood, minerals, and other resources are sold.
 Scientific investigation into the rainforest plants may provide new food sources and medicines.
These benefits, however, come at a heavy cost. Clearing rainforest threatens the survival of many plant and animal
species and can lead to serious environmental degradation. Widespread deforestation damages the whole biosphere
- the balance of living and non-living things on planet Earth - with serious long-term consequences for humans.
Positive impacts of human intervention
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Improving transportation by building roads and airports provides jobs and benefits local people who use
the roads.
Transportation improves access to raw materials like minerals and timber. Rainforest resources can be
transported away and sold.
Profits from selling resources can be used to bring more development to a relatively poor country. For
example, the tax a country raises from the sale of rainforest resources can be used to build schools and
hospitals.
Selling raw materials, for example tropical hardwoods such as ebony and mahogany, are valuable
resources that can be sold for a good price abroad, bringing in foreign currency. People in MEDCs such as
those in Europe and North America use hardwoods for garden furniture and hardwood flooring, for
example.
Mineral deposits in the Amazon include bauxite (the main constituent of aluminium), iron ore, manganese,
gold, silver and diamonds. Minerals can be sold with profits benefiting the LEDCs.
Infrastructure, hospitals and education can be improved from the money gained from selling natural
resources.
Large-scale farming is another important way to bring money into a poor country, and to provide food for
the country's growing population. Large-scale farming also employs local workers.
Small-scale farming is important for providing food for rainforest communities and landless poor of
Brazil. Often these people have been displace from land in other parts of the country and have no other land
to live on to produce the food they need to survive.
Problems of human intervention
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Roads divide up parts of the rainforest and can cut off connections between different biotic and abiotic
systems. For example, a road can stop monkeys such as the Golden Lion Tamarin from travelling to gather
food and, in turn, distribute seeds to re-sow plants in the forest.
Land clearance for farming, transportation and mining can lead to deforestation. Hardwood trees take
many years to grow, so can be difficult to replace.
Farming is estimated to be responsible for 25 percent of the Amazon forest being cleared.
Fertile soils that make farming possible are quickly washed away when the forest is cleared for farming,
mining or transportation.
Loss of animal habitat occurs when trees are cut down and animals that live in them have to find
somewhere else to live. Hence, deforestation can result in endangering animals and plant life, or even
causing them to become extinct.
Profits from large-scale farming and selling resources often go back to MEDCs or large companies and
don't benefit rainforest communities.