Millions of years before animals lived on land, there were trees on the Earth. But today trees are in serious danger.
In the 1970s, many of the elm trees in Europe were killed by Dutch elm disease. Now an even greater danger is threatening the forests and woods of Europe from northern Sweden to southern Italy. This new danger attacks all trees – deciduous trees like oak, beech and birch as well as coniferous trees like fir and pine. First the branches turn yellow and brown. Then the trees' needles of leaves fall. The roots and the trunk shrink. Finally the trees die. In the Black Forest in southern Germany 75% of the trees have been damaged or killed.
But what is killing the trees? Nobody knows exactly, but it is probably air pollution or acid rain. Factories, power stations and cars emit tons of smoke into the air. This smoke contains 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.
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 forest 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.