Saturday, 6 October 2007

Introduction to the Tropical Rainforest

The lesson objectives were:
  • To know where the tropical rainforest biome is found.
  • To practice describing the distribution of the tropical rainforest.
  • To know that the tropical rainforests can be divided into four distinct vertical layers and to be able to name the layers.
  • To understand that the climate affects the nutrient cycle of the forest.
Tropical rainforests are found in equatorial areas, between the tropics (concentrated between 10 degres north and south of the equator). They cover about 6% of the earth's surface. The main areas covered by rainforests are: Central America; the Amazon Basin (in South America); Central Africa; Madagascar (much of this has now gone); Southern Asia; Australasia. This is shown on the map below.

You may well get a question along the lines of 'Describe the location of the tropical rainforests' in your final exam. This type of question is usually worth 2 marks. Make sure you mention the general pattern (equator/tropics) and specific rainforests in your answer.

We watched a video about the structure of the rainforest and the way in which nutrient cycles work. Unfortunately, the video is not available online... here's an alternative for you...

The key things to remember are:

  • In general, the rainforest is a hot and humid environment. There is relatively little variation in temperature throughout the year (approx. 2 degrees). There is a wet season and a dry season. The growing season is very long.
  • The rainforest has four main layers: shrub layer, under-canopy, canopy and emergents.
  • The shrub layer (ground level) is dark and gloomy because the trees of the canopy block out 95% of the sunlight. There's not much growth here.
  • The under-canopy has limited sunlight. Saplings wait here for a spot in the canopy to become available for them!
  • The canopy is like a vast green ocean when viewed from above! Its full of life.
  • The emergent trees can be up to 50 metres high.
  • The nutrient cycle operates very quickly due to hot, humid conditions in which dead plant matter decays very quickly. There are very few nutrients stored in the soil because they are quickly absorbed by plant roots.
The diagram below shows the structure of the rainforest. The examiners often ask you to describe the structure of an ecosystem, so make sure that you are able to draw a fully labelled diagram to show the layers of the forest.

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