Forests: Our Lifeline Class 7 Notes Science KEYWORDS and SUMMARY II Class 7 notes II NCERT based II

Ch:12 Forests: Our Lifeline

 A forest is a large area covered with trees, shrubs, herbs, grasses, and animals.

It forms a complex ecosystem where plants, animals, and microorganisms interact with each other and with their physical environment.

Components of the Forest

(a) Biotic (Living):

• Plants: trees, shrubs, herbs, climbers, grasses.
• Animals: herbivores, carnivores, omnivores, decomposers.
• Microorganisms: fungi, bacteria.

(b) Abiotic (Non-living):

• Sunlight, air, water, soil, and minerals.

Layers in a forest

In a forest, trees form the uppermost layer, followed by shrubs. The herbs form the lowest layer of vegetation.

The branchy part of a tree above the stem is known as the crown of the tree.

The canopy of a forest is the uppermost layer formed by the tops of trees.

Under storeys in a forest refer to the layer of vegetation that grows beneath the taller trees of the forest canopy.

The forest floor is the bottom layer of a forest, located beneath the understorey. It is covered with soil, fallen leaves, branches, and decaying plant material.

Food Chain

A food chain is a series of organisms each dependent on the next as a source of food. It shows flow of energy and nutrients.

Food web consists of several inter-connected food chains.

Interrelationship in the Forest

• Plants make food (producers)
• Herbivores eat plants
• Carnivores eat herbivores
• Decomposers break down dead remains and return nutrients to soil
• This forms a food chain.

Importance of Forests

• Provide oxygen and absorb carbon dioxide.
• Maintain water cycle through transpiration.
• Prevent soil erosion by holding soil with roots.
• Provide habitat to a variety of organisms.
• Provide useful products: wood, fruits, gum, resins, medicines, and fodder.
• Maintain balance in nature (oxygen–carbon dioxide balance).

Role of Forest in Water Cycle

• Trees release water vapour by transpiration → forms clouds → causes rain → maintains water level in the ground.

Forest and Soil

• Roots bind the soil thus prevent soil erosion.
• Decomposed leaves make soil rich in humus and fertile.

Deforestation

Cutting down of trees on a large scale is called deforestation. It causes are:

• Loss of habitat for animals
• Increase in CO₂ leads to global warming
• Soil erosion and floods
• Disturbance in rainfall pattern

KEYWORDS

1. Canopy:

The uppermost layer of branches and leaves formed by the crowns of tall trees is called the canopy.

2. Crown:
The branchy part of a tree above the stem is known as the crown.

3. Decomposers:
The microorganisms which decompose the dead remains of plants and animals are called decomposers.

4. Deforestation:
The cutting down of trees and clearing of forests for various human activities is called deforestation.

5. Humus:
The dark-coloured substance formed by the decomposition of dead leaves and plants is called humus.

6. Regeneration:
The process by which forests grow again naturally after being destroyed is called regeneration.

7. Seed dispersal:
The scattering of seeds by wind, water or animals away from the parent plant is called seed dispersal.

8. Soil erosion:
The removal of the top layer of soil by wind or water is called soil erosion.

9. Understorey:
The layer of smaller trees, shrubs and young plants that grow below the canopy is called the understorey.