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Rainforests


What are ‘Rainforests’?

 

Rainforests are very dense (very thick), warm and wet forests. Rainforests are havens (a shelter serving as a place of safety or sanctuary) for millions of plants and animals.

 

Types of rainforests

 

Rainforests can be divided into two main groups.

 

types of rainforests tropical rainforests temperate rainforests

 

Temperate rainforests

 

Temperate rainforests are found where the weather is cool and mild, and very wet. There are wet and dry seasons in these forests. Just a few kinds of evergreen trees (trees that remain green throughout the year) grow there. Temperate rainforest are less abundant than tropical rainforests.

 

Places where temperate rainforests are located

 

  • Pacific coast of the USA and Canada (from northern California to Alaska)
  • New Zealand
  • Tasmania
  • Chile
  • Ireland
  • Scotland
  • Norway

 

Tropical rainforests

 

In this lesson we are going to learn only about the tropical rainforests.

 

What are ‘Tropical Rainforests’?

 

Some of the wettest places on Earth are tropical rainforests.

 

Where do tropical rainforests grow?

 

Tropical rainforests grow in hot or warm places near the equator. Biologists (scientists who studies living organisms) believe that more than half of the world’s plant and animal species live in tropical rainforests.

 

How much of the world’s land area is taken up by the tropical rainforests?

 

7 % of the world’s land area is taken up by the tropical rainforests.

 

What is the world’s largest tropical rainforest?

 

The Amazon rainforest in the Amazon River basin of South America is the world’s largest tropical rainforest. Over half of this forest lies in Brazil. The Amazon rainforest holds about one-third of the world’s remaining tropical rainforests.
 

 

Places where tropical rainforests are located;

 

  • South America
  • Central America
  • Africa (in the Congo basin)
  • Southeast Asia (in Indonesia, Sri Lanka etc.)
  • Australia and near by islands

 

Characteristics of a tropical rainforest

 

1. There is a very thick growth of plants.
2. There is a very large number of plant and animal species.
3. The plants are evergreen (with leaves throughout the year).
4. The emergent trees are very tall.
5. The stems or trunks of trees are erected (straight and vertical).
6. The bases of the trees are broad.
7. It is almost always raining all the year round.
8. The soil layer of a tropical rainforest is only about 3 – 4 inches thick and is poor in nutrients.
9. The leaves of trees are generally pointed for dripping water.
10. There is a plenty of climbers and epiphytes.
11. The forest is dark even during day time.
12. It is always hot and wet in the forest.
13. Generally the tops of the trees are spherical.

 

What is the average rainfall of a tropical rainforest?

 

The average rainfall of a tropical rainforest is 2500mm.

 

What is the range of temperature in a tropical rainforest?

 

Between 24ºC – 27º

 

Why is the soil in a tropical rainforest infertile?

 

The nutritious minerals have been washed out of the soil by heavy rainfall. Also, the giant plants absorb most of the nutrients left in the soil.

 

What are the useful plants grow in a tropical rainforest?

 

  • Rubber
  • Brazil Nuts
  • Kapok tree
  • Bananas
  • Nutmeg
  • Some medicinal plants
  • Teak (valuable hardwood)
  • Mahogany (valuable hardwood)
  • Rosewood (valuable hardwood)

 

Why are rainforests important?

 

1. Rainforests are homes to large numbers of plants and animals.

2. Rainforests recycles and cleans water.

3. Rainforests remove carbon dioxide from the atmosphere and store it in their roots, stems, leaves and branches.

4. Rainforests are good solutions for the green house effect (the process of trapping heat inside the Earth’s atmosphere)

5. Rainforests generate much of the Earth’s oxygen

6. Many of the rainforest plants are used in producing new drugs and medicine that fight disease and illness.

7. Destruction of the rainforests will badly affect the world’s climate.

 

Strata of a tropical rainforest (Layers of a tropical rainforest)

 

Strata mean ‘layers’ (Singular – stratum). Biologists have divided a tropical rainforest into different strata (or layers) for easy reference. These strata or layers in the same forest have differences in following areas.

 

a) The temperature of the strata

b) The wetness of the strata

c) The amount of sunlight that the strata receive

d) The amount and types of life forms living in the strata

 

In a tropical rainforest mainly five layers can be identified.

 

Tropical Rainforest Layers

 

What are the layers of a tropical rainforest?

 

  • Emergent layer
  • Canopy (Main canopy and Sub canopy (or Midstory))
  • Shrubs layer
  • Understory
  • Forest Floor

 
Emergent layer
 

This is the tallest layer of a tropical rainforest. The tops of the tallest trees form the emergent layer. This layer is much higher than the average canopy height. Trees are 40 – 60m tall (Very tall trees). Tops of the trees are spherical.

 
Canopy
 

The upper parts of the trees, with the average height form the canopy of a tropical rainforest. Trees are 20 – 40m tall. There are two divisions of the canopy.

 

a) Main canopy (Tall trees. They are 25 – 40m tall.)

b) Sub canopy or midstory (Medium-size trees. They are 20 – 25m tall)

 

This leafy environment is full of life.

 
Shrubs layer
 

This is the layer below the canopy. Trees are 5 – 15m tall.

 
Understory
 

This is the layer just above the forest floor. Understory is a dark, cool environment that is under the leaves but over the ground. Not much sunlight gets down to this layer. Plant growth is limited.

 
Forest Floor
 

The ground in a rainforest is called the forest floor. The soil on the forest floor is very thin and poor. Some plants living there get their food from dead plants. Other plants on the ground eat insects.

E.g. – The Pitcher Plant is an insect-eating plant that grows in tropical rainforests
 
 

Plants and animals in the different layers of a tropical rainforest

Layers or strata

Plants

Animals

Emergent layer

1. Brazil Nuts

2. Kapok tree

3. Orchids

1. Birds like sparrowhawk, toucan, parrots, eagle, bat etc.

2. Insects like butterflies and moths

3. Mammals like monkeys

4. Snakes and more

Canopy

1. Thick snake-like vines

2. *Epiphytes like mosses, lichens and orchids.

1. Insects

2. Arachnids

3. Many birds

4. Mammals like monkeys, slow moving sloths, jaguars, leopards

5. Reptiles like snakes, lizards etc.

6. Tree frogs

Shrubs Layer

1. Non-flowering shrubs

2. Small trees

3. Ferns

4. Palms (trees with unbranched trunk with large palmate leaves)

Animals in both shrubs layer and understory are;

1. Insects

2. Arachnids

3. Snakes

4. Lizards

5. Birds

6. Small mammals

7. Some larger animals like jaguars, spend a lot of time on branches in these layers surveying the area, looking for prey

Understory

Young trees and plants that like low levels of light grow in the shady understory.

Forest Floor

Insect-eating plants like the pitcher plant

1. Insects of every kind like ants, beetles, termites

2. Arachnids like tarantulas

3. Gorillas

4. Giant anteaters

5. Wild boars

6. Jaguars

7. Frogs

8. Lizards

9. Snakes like anacondas

10. People

 

What are *epiphytes?

 

Epiphytes are the plants without ground roots and usually grow on trees without harming the trees. They need moisture and nutrients from the air and rain. Epiphytes are also called ‘air plants’.

 

E.g. –  i) Mosses (very tiny leafy-stemmed flowerless plants)

            ii) Lichens (plants occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.)

        iii) Orchids
 

 

People living in tropical rainforests

 

There are many indigenous groups of people (native people) who have lived in the tropical rainforests for hundreds or thousands of years.

 

E.g. – Yanomami tribe of the Amazon Rainforests of Brazil and Southern Venezuela. 

 

These tribes get their food, clothing and housing mainly from the materials they obtain in the forest. Forest people are mostly hunter-gatherers. They get their food by hunting for meat and fishing for fish and gathering edible plants like starchy roots and fruits. Many also have small gardens in cleared areas of the forest. Since the soil in the rainforest is so poor, the garden areas must be moved after just a few years, and another part of the forest is cleared.
 

Why so few people live in the tropical rainforests?

 

Most indigenous populations are declining. There are many reasons for this.

 

  • Severe disease like smallpox, measles. These people don’t have proper medication and hospital facilities.
  • Governmental land attack.
  • Destruction of the rainforests.
  • Their young generation is moving to towns and cities to live a better life than in the forest.

 

What are the threats to tropical rainforests?

 

  • Loggers cut down hardwood trees for lumber.
  • Teak, mahogany and rosewood are used to make beautiful furniture.
  • Farmers clear the forest to grow crops.
  • When the poor rainforest soil soon washes away farmers will move on to another place from the old place.
  • Making ways through the forests for mines, factories, roads, large farms (ranches) and *plantations.

 

What is a *plantation?

 

An estate (a large area of land) where crops like tea, coffee, sugar cane, rubber or fruit trees are grown on a large scale for sale abroad.