Study figure 2.4 and tell about Bark beetle life cycle

Acid rain is not new. We started producing acid rain when we started building a lot of factories and power stations which burned coal or oil. When you burn these fuels, you produce the gases SO₂, and NO_x (sulphur dioxide and nitrogen oxide). These substances mix with water vapour in the atmosphere and form sulphuric acid and nitric acid. Sunlight turns these acids into poisonous oxidants which fall in rain or snow onto the trees.

Britain produces about five million tonnes of these gases every year. China produces eighteen million tonnes. The USA produces more than twenty million tonnes. The wind carries the gases high into the sky. There they come together with water in the air and make acid rain, acid fog and acid snow. In Canada and northern Europe many millions of trees have died because of acid rain from power stations and factories thousands of kilometres away.

What can be done about acid rain? Why don’t governments do something to save the trees? Unfortunately, acid rain doesn’t always fall on the countries which produce the pollution. The wind carries the poisonous substances from one country to another. Why should the people of one country pay to save another country’s trees?

In other parts of the world trees are threatened by people, not by pollution. The great rain forests of Asia and South America are being destroyed for firewood and building material. Something must be done. Trees are important because they provide a home for many other plants, and animals too. They protect the flowers which grow on the forest floor. They provide food for insects, reptiles, birds and mammals. They protect the soil from the wind and the rain. Most important of all, the forests are the lungs of the planet. Trees produce the oxygen which we breathe. If the trees die, we will, too.