Chapter 12 — Forests: Our Lifeline

The canopy is the roof-like layer formed by the overlapping branches and leaves of tall trees over the other plants in the forest.

Understoreys are the different horizontal layers formed by trees with crowns of varying types and sizes. Giant trees form the top layer (canopy), followed by shrubs and tall grasses, while herbs form the lowest layer.

Decomposers are micro-organisms that feed on dead plant and animal tissues and convert them into a dark substance called humus. Examples include mushrooms and beetles. They recycle nutrients back into the soil so that living plants can absorb them again.

Forests are called green lungs because plants release oxygen through photosynthesis and absorb carbon dioxide, helping to maintain the balance of these gases in the atmosphere — much like lungs supply oxygen to the body.

Humus is a dark-coloured substance formed when decomposers break down dead plants and animal tissues. It enriches the soil with nutrients and ensures these nutrients are available for the roots of living plants to absorb.

The forest canopy intercepts falling raindrops and slows their flow. The layer of dead leaves on the forest floor acts like a sponge, and the root systems of trees help water seep into the ground. This prevents water from stagnating, maintains the water table, and controls flooding. Without trees, rain hits the ground directly and may flood surrounding areas.

A food chain shows how energy passes from one organism to another. An example from the forest text is: Grass → insects → frog → snake → eagle. All food chains in a forest are interlinked; if one is disturbed, it affects all the others.

Animals disperse seeds of plants through their droppings, helping new plants to grow. Decaying animal dung provides nutrients to seedlings. The variety of animals also supports food chains that keep the forest ecosystem balanced.

Forests provide timber (such as plywood and furniture), gum, medicinal plants, honey, and sealing wax. Other products include fuel wood, paper, matchsticks, oils, spices, and fodder for animals.

The branchy part of a tree above the stem is called the crown. Trees have crowns of different types and sizes, which create the different horizontal layers (understoreys) seen in a forest.

Trees take in water through their roots and release water vapour into the air through evaporation. This moisture contributes to cloud formation and rainfall. If trees are cut down, less water vapour enters the atmosphere, which can reduce rainfall in surrounding areas and lower the water table.

Dead plants are broken down by decomposers into humus, returning nutrients to the soil. Dead animals are consumed by vultures, crows, jackals, and insects. Nutrients are continuously cycled so that nothing is wasted in a forest.

If forests disappear: the amount of carbon dioxide in the air increases, raising Earth's temperature; animals lose food and shelter; soil is not held by roots, causing floods; and deforestation endangers all life and the environment.

Different climatic conditions in different regions lead to variations in the types of trees, other plants, and animals found in each forest.

Yes — you can download the Class 7 Science Chapter 12 'Forests: Our Lifeline' PDF for free on cbseprepmaster.com with no sign-up required.