Dimensions of need - Forests of the world

More than half the earth's land area was once forest. Now, the figure is less than one-third - around 3 400 million hectares. Forests are cleared and degraded at a rate of 300 000 hectares per week.

The world's forests cover some 3 400 million hectares - an area the size of North and South America combined. They are sources of raw materials and food, and are essential for maintaining agricultural productivity and the environmental well-being of the planet as a whole.

Trees and forests anchor the soil and buffer the winds, thus protecting against erosion by wind and water. They produce oxygen and absorb carbon dioxide, the major agent in global warming. They intercept rainfall, releasing it slowly into soils, surface waters and underground aquifers. The water vapour released from their foliage in transpiration influences climate and is a vital part of the hydrological cycle.

Forests and woodlands vary from the dense rainforests of the tropics to East Africa's open woodland savannahs; from mangroves to the mixed temperate broadleaved and boreal forests. But unmanaged harvesting, ill-planned clearance for farming, or physiological pressures from pollution can pose a threat to any forest type.

During the 1980s more than 15 million hectares of tropical forests were lost each year: the overwhelming majority of the deforestation was intended to provide land for agriculture. The largest losses occurred in tropical moist deciduous forests, the areas best suited for settlement and farming. The extent of these forests declined by 61 million hectares - more than 10 percent of their area -while 46 million hectares, or 60 percent, of tropical rainforests were lost. Few of these areas have been replanted.

Tree cover is increasing in many temperate regions, mainly due to the establishment of forest plantations. Europe increased its forest and wooded land by 2 percent over the 1980s and there were small increases in New Zealand and Australia. In the same decade, however, a drop of some 3.5 million hectares occurred in the United States. The area of the former USSR reported an increase between 1978 and 1988. However, there is an urgent need to bring many of the Siberian forests under sustainable management to avoid their degradation. As well as managing some forests for production, diversity should be preserved in others by designating protected areas.

Many forests in industrialized countries have been damaged by airborne pollutants, including acid rain: the International Institute for Applied Systems Analysis (IIASA) has estimated that US$ 60 000 million would have to be spent annually for 25 years to protect Europe's forests from pollution.

Global distribution of forests

Natural forest, 1990
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