  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 died because of 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. First the leaves turn yellow and brown. Then the trees' needles or leaves fall. The roots and the trunk shrink. Finally the trees die. In the Black Forest in southern Germany 75% of the trees have died.
  But what is killing the trees? Nobody knows exactly, but it is probably air pollution or acid rain. Factories, power stations and cars give off tons of smoke with acid into the air. Sunlight turns these acids into poisonous substances which fall in rain or snow onto the trees.
  What can be done about acid rain? Why don't governments do anything to save the trees?
  Acid rain doesn't always fall on the countries that produce the pollution. The wind carries the poisonous substances from one country to another. The governments don't want to spend money on them, if the poisonous substances won't harm the trees in their own countries.
  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 cut down for firewood and building materials.
  Something must be done! If the trees die, we will, too.
