Class 7 Science Forests Our Lifeline Chapter Notes

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Forests: Our Lifeline

INTRODUCTION
About one-third of the world’s land surface is covered by forests. It is an eco-system (plants and animals) which is dominated by trees. Forest provide the most useful renewable resources. They prevent soil erosion, replenish oxygen in the air and maintain the fertility of the soil. A forest is a biotic community spread over a large tract of uncultivated land and is predominantly composed of trees, shrubs, herbs and climbers. Forests occupy a special place in the life of people. They are invaluable wealth of a nation and a renewable natural resource. In the last hundred years, utilization of forest products has gone up mainfold to meet the growing demands for wood and timber. Excessive felling of forest trees because of setting up industries, building of roads cities and
for cultivation is very common. Deforestation poses serious threat to our economy, quality of life and environment. However, the State of Forest Report (SFR-2009) gives an encouraging picture. Our forest and tree cover stands at 23.84% which is an increase of 4.75% over ten years. Forests provides home for different animals, birds, reptiles, insects, worms and microbes., Some live on the floor, others on tree twigs. Some walk on the ground, some burrow and others fly.

FOREST TYPES IN INDIA

The distribution of natural forests in India is governed principally by rainfall. Rainfall varies from 12 cm to 125 cm annually in different parts of the country resulting in a wide variety of vegetation - from xerophytic scrub forest in the arid zones of Rajasthan to evergreen rainforests in the tropics as in the Western Ghats, Assam, North Bengal, Andamans and Conifers in the temperate regions. In between the extremes, there are many intermediate types of forests.

Due to different climatic conditions different forests show variation in the type of trees and animals inhabiting the forests.
In North-East India, Sal is most common tree, while in South West the common tree is Teak. In the arid zone, species such as Cacti and Acacias are dominant. The Himalayan mountains have Coniferous as well as trees with broad leaves. Between the foothills of the Himalayas and the plains of river Ganga lie the great terai forest in which Sal is a common species. The dense forest consists of distinct horizontal layers. These are:

Canopy

The canopy is the uppermost levels of a forest formed by the crowns of trees and shrubs. The crown of a tree is the branched part of the stem and leaves above the main trunk. Tree crowns are of different shapes and sizes. The canopy layer is formed by the largest trees. This layer is very crowded and blocks out most of the sunlight. It also acts as wind breaker. The canopy is the densest layer and home to unique flora and fauna.

Understorey

The understorey layer lies between the canopy and the forest floor. This layer is home to a number of birds, snakes and lizards, as well as predators such as jaguars and leopards.

The leaves are much larger at this level. A wide range of insects are also found. Only about 5% of the sunlight shining on the forest reaches the understorey. Forest understorey also have higher humidity than the exposed areas.

Forest Floor
The forest floor layer receives only 2 per cent of sunlight. The forest floor has almost no vegetation because of the low sunlight penetration. Only plants adapted to low light can grow in this region. Many forms of fungi grow here which help in decaying of dead animals and plants thus converting them into dark coloured organic matter. This forms the humus. 

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