Theory:

A vast area of land that is covered with trees and other plants are called forests.
Various forests have different types of trees and plants due to the differences observed in their climatic condition and soil.
 
Common trees present in Indian forests are Neem, Sal, Sheesham, Semal, Amla, Bamboo, Teak, Eucalyptus, Peepal, etc. Some of the forest floor is covered with different varieties of creepers, climbers, herbs and shrubs. 

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How do tree grows in the forest?
  
Trees produce many seeds that fall on the forest floor. When there are favorable conditions like water, nutrients, and sunlight, the seeds germinate to saplings, and that grow into big trees. The herbs and shrubs also grow similarly in the forest.
  
Animals in the forest:
 
The forest contains insects, butterflies, honeybees and birds which helps in pollination of the flowering plants. Sometimes we see that a wide variety of animals present in one forest can vary from the other forests. Common animals present in the forest are monkeys, boars, elephants, porcupine, tigers, lion, snakes, ants, deer, and various other small animals.
 
Forests also contains decomposers or microorganisms like bacteria and fungi (mushrooms, puffballs, and toadstools).
  
Importance of the forest:
  
Forests also act as a purifier of air as the leaf of the plants and trees cleans up air (traps dust from the air), and also lets in oxygen through the process of photosynthesis.They also act as a purifier of water (as they suck in water with their roots) and also helps in the availability of pure water as rain (through the water cycle).
 
Important!
Forests are called green lungs of nature as they purify the air we breathe!
Reference:
https://upload.wikimedia.org/wikipedia/commons/4/4e/Sal_%28Shorea_robusta%29_forests_as_avenue.jpg
https://commons.wikimedia.org/wiki/File:Dalbergia_sissoo.jpg