Sir: Scientists have proved that the world was covered with trees a few centuries ago. With the increase in population, people started cutting trees and constructing buildings, homes and factories that brought a drastic change in the world climate. Due to the depletion of trees, fatal viruses and diseases have spread in different areas of the world. Trees are the best source of ensuring a balance in the environment. They provide us oxygen, absorb carbon dioxide and maintain the level of humidity in the air. They protect natural watersheds, which supply 75 percent of fresh water. The concerned authorities should take serious steps to protect forests and everybody should grow more and more trees in his surroundings. ZAHID HAIDER Turbat