Unit C4 - Forests and their Ecological Importance


Unit C4


Wherever there is land and enough water, seeds will be transported and plants and trees will start to grow. In time, if conditions are right, a forest will become established. Almost all land in the tropics was originally covered by forest, as was most land in the wetter parts of continents.

There are many different kinds of forest. The temperate and boreal forests of colder lands may be quite simple in structure with a few common trees. They have generally regenerated since the last ice ages. Warmer more tropical areas with enough rainfall usually have rain forest with many kinds of trees, some very tall and others shorter. Since these forests grow on the best and most accessible land, they are often cleared first for agriculture, villages or other uses. If there are mountains, different kinds of forest with shorter trees and more undergrowth may grow higher on the mountainside. Mountain tops and ridges that are kept wet by the clouds may have a cloud forest with many mosses and other plants growing in the trees. There can also be bamboo forest, swamp forests, and riverine forests along river banks that are frequently flooded. In areas where the rainfall is seasonal, there may be forests that lose their leaves in the dry season. A special kind of atoll/beach forest occurs on atolls and on the coral rock and sand behind beaches; it is made up largely of trees that have floating seeds or that are salt resistant. Mangrove forests that grow in sea water are discussed in a separate unit.

How the forest works

The forest is made up of trees, plants and animals that together make up a complicated and productive system. The plants and trees take water and minerals from the ground, carbon dioxide from the air, and energy from the sunlight in order to grow, producing more and more plant material (leaves, wood, roots) as they do so. Many animals and insects feed on the plants or on the dead materials they leave behind. Finally mould and microbes (bacteria) eat what is left and return the minerals to the soil. Thus all the life in the forest depends on the trees; if they are gone, much less food will be produced for everything else and the system will be less productive. The trees also shelter and protect the other life in the forest.

When a forest tree dies or falls over, its place is quickly taken by young trees or tree seeds waiting underneath. Some trees are better at growing quickly in open areas where there is sunlight, filling in any gaps in the forest. Others may grow more slowly, but they often grow taller and eventually dominate the other forest trees.

Many trees depend on birds and insects in the forest for their reproduction. Bees, moths or other insects go from tree to tree fertilizing the flowers. Birds, bats or other animals that feed on tree fruits may also carry the seeds away from the parent tree to places where the young trees will have a better chance to grow. If the insects are killed by pesticides, or the birds are all shot by hunters, some trees may gradually disappear from the forest because fewer young ones will grow up to replace the old ones.

This is why the forest is called an ecosystem, because each part helps the others and also depends on the others. If something hurts any part of the system, the other parts will also be affected.

Benefits of the forest

The forest brings many benefits to the land and its people. In many ways it is the forest that made the land into a place where people can live.

The forest changes lifeless rock into a living ecosystem. Over thousands of years the plants and animals of the forest establish themselves and build a living cover of green. The forest grew slowly. A newly exposed area of land will first be colonized by a few plants which were very strong and could live on bare rock. Slowly other plants and animals followed. The forest which covers the land today may be thousands of years old. You can cut down some trees and not hurt it at all. But if you cut down too many trees all at once, you can destroy it.

The forest makes the soil. The soil on the land is the old broken-down rock mixed with the dead plants of the forest and the many small animals and bacteria and plants which live in the soil. Forests made most of the soil on the planet. When garden soil becomes poor the forest grows over the old garden and makes the soil good again.

The forest protects the soil. It holds the soil with its roots. If the trees are cut down and no gardens are planted the soil gets hard and dry and no good for gardens. If heavy rains come and there are no trees, the soil gets muddy and washes away, polluting streams, rivers and the sea. Then the soil is gone and gardens will not grow on the hard rock.

The forest shelters the gardens. When strong winds and heavy rains come the trees protect the gardens. Strong winds can hurt crops and dry out the soil. Near the coast, salt spray can poison the soil or harm the crops without the shelter of trees. The forest can also protect homes and villages from strong winds.

The forest holds water. The trees and the soil they make are full of water and they store this water for times of no rain. The forest controls the flow of water over the land. When heavy rains come the trees help trap the water in the soil. They hold water in their branches, trunks, roots and leaves. When the land is dry the water from the forest keeps the land green. Without the trees of the forest the land can quickly become dry and the crops may die.

The forest makes clouds and rain. When the wind blows over the land it moves through the trees and the trees put water into the wind. When the wind goes through the trees, the trees also put excess heat from the sun into the wind. The heated, wet air then lifts up because hot air rises. When the hot, wet air hits the cooler wind above the land, it becomes clouds. If you cut down the trees there may be less rain and the land may dry up; people will then not have enough water to drink or wash in and the crops will die.

The forest controls garden pests. Inside the forest many insects and birds and animals live in a balanced system. When the balance is good, the life systems work together and there are not too many of any kind of plant or animal or insect. Many of these animals and insects eat garden pests and mosquitos. When the forest dies the natural balance is lost and many of the good animals and insects disappear. In this way mosquitos and diseases can increase and gardens can be attacked by pests if the forest is cut.

The forest prevents fires. When the forest is dead the land becomes dry and can quickly catch on fire and burn away all the life.

The forest provides wood for people to use in making homes, tools, boats, carvings and fuel for cooking. If the forests are cut the people will have to import wood for these needs at a cost many times the money they may now be paid for the same wood.

The forest has many plants which may be of great economic value. Not just trees, but foods, spices and medicines grow in the forest. Maybe some of the plants killed during forest cutting are worth more than the trees. When they are killed and thrown away or burned, the land may be losing plants with food or medicinal value which can never be replaced. The medicinal plants and the plants used for many generations by the local people for special purposes need the forest to survive.

The forest has some special trees of very great value, like ebony (black wood) and sandal wood, nut trees and trees which are just right for making canoes or foundations for houses or tools. While these trees are replaced naturally in the forest, they are not replanted when the forest is cut because they grow too slowly. Many trees and bushes valuable to the local people are considered rubbish by commercial loggers and these are often killed when other trees are cut.

The forest is the heritage of the local people. Treated with love and respect it will last forever and supply the people's needs. Many people have sacred ties to the trees and the forest that are part of their traditional cultures, and are still important to them today.

The problem of non-sustainable use

Since a healthy forest is able to renew itself, it should be possible to harvest from a forest indefinitely, in a way that can be sustained. Unfortunately today this is rarely done. The forest is mined rather than harvested. People are cutting down the forest so quickly that in a short time it will be gone from many areas. They cut down the trees for many reasons. In the past, the trees were cut down to clear the land for gardens. With modern large-scale agriculture, the forests are being cleared faster than ever. Trees are also cut down to provide fire wood for village people. As the number of people increases, the forests vanish faster and faster.

But perhaps the worst problem for many forests is the timber industry. Trees can easily be sold for money to be exported to other countries. As long as the trees were just being cut for local use, the demand for wood was limited to what the local people needed and could use. Most forests grew fast enough to supply these local needs, but the export market can never be satisfied. Timber companies can easily and quickly strip the land of its forests and still supply only a small fraction of the world's desire for wood.

Thus a forest resource which should be able to supply local people's needs forever if carefully managed is rapidly being destroyed. The most immediate and dangerous threat to forests is the open and limitless desire of the export market which can never be filled. Modern forestry equipment is very rapid and efficient, and many countries have already sold most of their forests to timber companies for the export market. Clearing the forest for large scale agriculture or to make pasture for livestock is the second most dangerous threat. Clearing the forest for gardens and firewood is also a major danger where the local population is growing quickly. The threats to the forest from agriculture and the growing numbers of people require careful land management programmes, and this need is already recognized by most governments.

Consequences of forest loss

It should be clear from the many benefits of the forest that its destruction can have a serious effect on local resources. The quality of the soil, one of the most basic resources, will tend to decline, and this loss of soil structure and plant foods will mean that agriculture will produce less. There will tend to be floods after heavy rains as the water runs of the land faster, and droughts will be more frequent as rivers dry up and the water table drops during dry periods. Storm damage by wind and waves will also increase. There are also the genetic resources of the unique kinds and varieties of plants and animals which depend on the forest for their survival. The loss of the forest means the loss of these resources which can never be replaced.

The development of forest land often brings progress in the short term. It is only after several years that the bad effects may become apparent. In areas where there is a lot of forest, obviously some can be developed wisely without creating major problems. As an increasing proportion of the forest is lost, the effects will become more severe. Since the most vulnerable areas are often developed last, it is the loss of these last forest remnants that may be the most catastrophic for a country.

Sustainable use of forests

In countries where all natural resources are limited, it is important to make full use of those resources that are present, but in ways that do not damage their ability to keep producing on into the future. Since forests are important in many different ways, they can only be managed wisely if all the different factors are considered together. In many places a forest is seen only as a source of wood; however its role in soil protection and water supply regulation may be just as important. If several basic principles are followed, it is usually possible to draw many kinds of benefits from forest areas, but this requires a good knowledge of the forest and its limits, and careful observation of the effects of any use or change on the way the forest works. Since forest trees may live to be hundreds of years old, some effects, such as on the kinds of trees that make up the forest, may only appear very slowly. It is always wise to leave some areas undisturbed as a protection against the total loss of some valuable forest resource.

The first principle for sustainable use is that any harvesting of forest resources must remain within the limits of what the forest can replace. Some trees can be cut, but enough should be left behind to re-establish the same species. If only one kind of tree is being taken, it may be replaced in the forest by other less desirable species unless special efforts are made to ensure that young trees of the same species can grow back again. The same principle of moderation applies to the percentage of forest area disturbed at any one time. Enough undisturbed forest should always remain to shelter wildlife and wild plant species and to allow them to repopulate forest that is growing back after being disturbed. Too often the economic pressures for rapid development go against respect of this principle, and the forest is destroyed or degraded.

The forest should always be left intact in vulnerable places such as on steep slopes, along stream banks and on shorelines where its importance in protecting against erosion outweighs any other value. Examples all through the world show that the cost of repairing the damage done far outweighs any benefit from developing these forest areas.

Most forest areas can be developed for or serve several different uses at the same time. A watershed essential for a village water supply can also protect wildlife and be a place to collect fruits and medicinal plants. A forest that is carefully and selectively logged while preserving the cover of trees may continue to build and protect the soil. Sites for tourism or recreation can be developed in a coastal forest while protecting its importance in sheltering the interior from storms. What is important is to know the different values of the forest and to be certain that the uses chosen are compatible and that no essential function in threatened.

Where uses are not compatible, they can be planned for in different parts of the forest. A village may decide to leave a block of forest close to the village to supply firewood and wood for construction. Another part of the forest might be set aside for hunting, while still another might be protected from hunting to allow the birds or animals a place to reproduce.

A forest can also be used for agriculture as shown by recent approaches to agroforestry. Many crops can be grown among or between trees, so the same area of land can produce both foods and tree products. This can be especially good on sloping land where fields cleared for agriculture would be subject to erosion.

It is also possible to plant a forest specifically to produce wood or other products. Many countries have tree planting or reforestation programmes. Sometimes an area is replanted with trees after logging. Land may also be planted to create a forest again where it was destroyed long before. The trees that are planted may be fast-growing imported species like eucalyptus or Caribbean pine, or other important timber species. Usually only one kind of tree will be planted in an area. They are almost always planted with the idea that they will be cut as a tree crop to pay for the investment in planting them. The native trees that originally grew in the forest are seldom replanted because they grow too slowly to give an economic return. Such forest plantations may be an appropriate use for some lands, and they may help to protect the soil and hold water, but they rarely work as well as the original forest did, and some damage is always done when the trees are cut. They also do not shelter as much wildlife or medicinal plants, nor are they as valuable for tourism, recreation or protection from storms. Where such plantations are used to restore land that has been damaged or degraded, they can make a valuable contribution to local resources.

Forests must have an important place in the balanced development of any country for the many reasons given in this unit. Even at the local level, land owners would be wise to maintain the forest on appropriate parts of their land, or even to replant forest trees where they have all been destroyed. Making or protecting a forest is not necessarily something that will give a quick return, but it may well ensure a better future for your children and their children.


How did the forest come to grow on your land?

How many kinds of forest can you think of in your area?

What local animals, birds and insects are important in helping trees to reproduce and in spreading their seeds?

How does the forest bring water to the land?

What does the forest do to the soil, and how does it do it?

List as many benefits from the forest as you can. Can you think of some that are not mentioned in the unit?

How much of your country used to be covered by forest long ago?

How much forest is left today?

Will there be much forest left in 20 or 50 years from now?

What would your land be like with no forest left?

What are the things that are destroying the forest? Give local examples.

Can you give some examples of good sustainable uses of the forest?

How would you solve the problems faced by forests in your country?

Instructions for trainers in the use of this unit

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Last updated 15 November 2006