Chapter 2 The world's forests

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Temperate and boreal forests
Tropical forests
Deforestation and its impacts

The world's forest resources are still substantial. In 1980, their total area was about 3 600 million hectares. In addition, there were 1 700 million hectares of wooded lands not classified as forests. In all, about 40 percent of the world's land surface is still under some type of tree cover.

But despite the immense size of this resource, there is ample reason for concern. The estimated rate of forest depletion in the tropical zone in the decade 1981 to 1990 was 15.4 million hectares per year, significantly greater than the annual depletion of 11.4 million hectares assessed in the decade 1971 to 1980. In addition, there has been severe forest degradation over a very large area, perhaps even larger than the area of forest depletion.

There are, however, major differences in the rates of forest depletion in different parts of the world. The area of the temperate and boreal forests has now broadly stabilized. It is the tropical forests that are being so rapidly destroyed.

Temperate and boreal forests

The temperate and boreal forests together make up almost half the total area of forest in the world. Virtually all the wood harvested from these forests is used for industrial purposes, with only a small proportion used for fuel. In all, the temperate and boreal forests provide over 80 percent of the world's industrial wood supplies.

The total area of temperate and subtemperate forest, including plantations, is about 760 million hectares (Lanly and Allan, 1991). The proportion of the land area occupied by forests (mainly temperate forest types) in the industrialized countries of the Northern Hemisphere is surprisingly high. In the former USSR, it is over 40 percent; in France, Germany, Italy and Poland it is 25 to 30 percent each; and in Greece and Austria it is about 45 percent. The United States has about 300 million hectares of forest, covering about one-third of its land area; the area of forest, in fact, is 50 percent greater than that of cropland.

The total area of temperate forest is now broadly stable. In the United States, for example, the decline in the total forest area between 1952 and 1987 was about 5 percent, mostly as a result of conversion of forest land for residential building, but during the same period the total standing volume of wood increased by about 25 percent. In Europe there has been a slight increase in forest area, while the total standing volume has significantly increased.

It is estimated that most of the temperate forests are under some form of management, although there is no reliable figure for the actual area. Usually the main emphasis is on producing a sustained timber yield, and foresters have a large body of research findings and practical experience dating back over 100 years on which to draw. Multipurpose management also has a long history in some of the state and communal forests in mountainous areas of western and central Europe, where it was introduced a century ago with the triple objectives of sustained timber production, soil and water conservation and the collection of fuelwood and non-wood forest products. In recent years, the conservation of ecological diversity and provision for recreational uses have become increasingly important objects of management in the temperate forests.

The Mediterranean forests form a special case within the temperate zone. They comprise, rather than a single forest type, a series of ecosystems ranging from high closed coniferous forests through all the intermediate stages to sparse and-area scrub. Although they have been greatly reduced in area and in many areas are heavily degraded, they are generally much more complex and rich in species than the other temperate forests.

The Mediterranean region, with a population of around 1000 million, was once heavily forested but now the forest cover is less than 5 percent of the area, concentrated mainly in the northern countries of the region. Even the 5 percent overstates the area under forest; in Morocco, for example, more than half of the 8 million hectares classified as forest are, in fact, grasslands. Clearing for agriculture and overgrazing are the main destructive agents; frequent forest fires and the harsh climate with its periodic droughts are additional pressures on the forest resources of this region.

While the area of the temperate forest types may be stable or even increasing, there is a loss of quality in some places. "(Quality" refers to such attributes as health, environmental and social benefits and comparability of substitutes such as plantations with natural associations (see e.g. Dudley, 1992). Dieback and decline over large areas of temperate forests have been seen as symptoms of poor health, caused by a wide variety of factors including climatic stress and air pollution. Dieback and decline can also occur in tropical and subtropical forests.

The boreal forests encircle the northern part of the globe, extending through Alaska (USA) and the northern regions of Canada, Finland, Norway, Sweden and the former USSR. Their area is vast, a total of about 920 million hectares of closed forest with a further 300 million hectares of open woodland. Almost three-quarters of the total is in the former USSR. A further 20 percent is in Canada and Alaska and about 5 percent in the Nordic countries.

Production from the boreal forests accounts for about 50 percent of the world's newsprint, nearly 40 percent of the sawnwood and 20 percent of the paper pulp. Although large areas of forest are harvested every year, the quantities of wood removed are substantially less than the overall annual growth of the boreal forests. Because of the harsh climate, difficult and often dangerous terrain and long distances, a large proportion of these forests is likely to remain outside the scope of commercial logging for the indefinite future.

Since the early part of the present century, the boreal forests have been actively managed for sustained yield in the Nordic countries. In Canada and the former USSR, in contrast, control over logging has generally been weak, although significant efforts to improve the position have been made in recent years. The political and economic uncertainties in the former USSR, and the manner in which these are likely to be reflected in the management of the region's huge areas of boreal forest, are at present a major cause of concern.

Tropical forests

Tropical rain forests
Moist deciduous forests
Forests of the dry ant very dry zones
Tropical upland formations

The tropics are, geographically speaking, the area between the Tropic of Cancer and the Tropic of Capricorn, 23 30' south and north of the equator, respectively. The area includes most of Africa; Mexico, Central America and South America to about the latitude of Rio de Janeiro (Brazil); most of the Indian subcontinent, southern China, Southeast Asia and the northern half of Australia. Within this vast area there is a wide range of forests, but they can be broadly divided into four main types: the lowland formations, comprising the tropical rain forests; the moist deciduous forests; the dry and very dry forest zones; and the upland formations. In total, the tropical forests cover about 1 700 million hectares, an area roughly that of South America.

Only a small proportion of the world's tropical forests are under management in any meaningful sense. Even where there is management, it is often confined to the collection of revenue from logging operations or the protection of national parks by government forest services. Where these forest services are weak and ill-equipped and the staff is poorly paid the beneficial impact of such "management" is likely to be small.

As public awareness of tropical deforestation has grown, the main public focus has, misleadingly, been on forest loss caused by logging. In fact, the main reason for tropical deforestation is agricultural expansion, which in all its forms, from shifting cultivation to cattle ranching, accounts for about 90 percent of the total forest loss presently taking place. Furthermore, and contrary to popular perception, the largest losses of forest area are not occurring in the tropical moist forests but in the tropical moist deciduous forests, while the most rapid rates of deforestation are occurring in the moist deciduous forests, the dry zone and the upland forests, as the following sections will show.

In the decade between 1981 and 1990 there was an average annual loss of forest in the tropical zone of 15.4 million hectares yearly, or an annual rate of loss of 0.8 percent. The situation is summarized in Table 1.

Tropical rain forests

The tropical rain forests are so called because they occur in areas with annual rainfall of more than about 2 500 mm. They are evergreen, luxuriant and rich in tree species as well as in other plant and animal life. They are a major source of the world's hardwoods; mahogany, rosewood, ebony and sapele are the most popularly known but there are dozens of other species which are used in fine furniture, veneers and other high-grade uses. There are also many other species of lesser commercial value which are used for construction, plywood and other purposes.

The soils on which the rain forests grow tend to be shallow and poor in nutrients. The high growth rates and intense biological activity of the forest is based upon a quick recycling of organic waste material back into the growing plants. In many areas, if the trees are removed and the land is used for agriculture, the nutrient cycle is broken and the inherent lack of fertility of the soil is quickly revealed. Crop yields fall after a few years and the land may become susceptible to erosion or laterization - the formation of a hard infertile crust

Table 2 shows that the total land area of the rain forest zone is 947 million hectares, of which 718 million are covered by forest. The moist forests of Africa remain largely intact; they still occupy 73 percent of the zone. Contrary to what is widely believed, the same is broadly true in Latin America, where 87 percent of the zone is forested. In Asia, however, tropical moist forest depletion has proceeded further, and just over half of the land area of the zone is forested.

By far the greatest concentration of the tropical rain forest is in the Amazon Basin. This huge area of forest, which covers northwestern Brazil and stretches into the neighbouring countries of Colombia, Ecuador, Peru and Venezuela, accounts for two-thirds of the world's tropical moist forest. Asia has the next largest area, mostly in Indonesia, Malaysia and Papua New Guinea. Africa has about IS percent of the total, almost entirely in the Congo and Zaire.

The total area of rain forest cut from 1981 to 1990 was 4.6 million hectares per year or, more graphically, nearly 9 ha per minute. This gives an overall rate of deforestation of 0.6 percent per year, but the rate was almost twice this in Asia.

Mangrove forests are included in the area of tropical rain forest; it is estimated that there are about 24 million hectares of coastal mangrove forests in the subtropical and tropical countries (FAO, 1988a). Human pressure to overcut mangrove forests for the provision of wood products or to clear them for salt pans and for infrastructure development is heavy, particularly near urban areas, despite the many products and important protective functions that they provide.

Moist deciduous forests

The moist deciduous forests occur in areas with annual rainfall of 1000 to 2000 mm. These forests vary greatly depending on factors such as the amount of rain and its distribution throughout the year, the temperature and the type of soil. They are generally much less rich in tree species and less biologically diverse than the tropical moist forests.

The total area of the zone is nearly 1300 million hectares. Because the zone is well suited for human settlement deforestation has proceeded much further shall in the rain forest zone. The proportion of the area still forested is 46 percent, although it is only 29 percent in Asia (see Table 3). The actual forest area is less than that of the rain forests, with most of it shared between Africa and Latin America.

The rate of loss of these forests in the decade 1981 to 1990 has been enormous, at about 6.1 million hectares per year.

Forests of the dry ant very dry zones

The tropical dry forests occur in areas with rainfall of 500 to 1000 mm per year. They are relatively open and, especially in Africa, are rich in wildlife. The people living in and around these forests tend to rely heavily on them for livestock grazing as well as for fuelwood, building poles and other products. Many of these forests are fragile, and improper exploitation, even if light, can lead to severe degradation, weed infestation and increased susceptibility to fire and insect damage. Large areas have degenerated into grass and scrubland.

More than half the world's dry tropical forests and savannah woodlands are in Africa (see Table 4). Its distinctive savannah landscape stretches all across the continent to the south of the Sahel and covers much of eastern and southern central Africa. Dry forest zones are found also in northeastern Brazil and much of India. In many areas, these forests merge into arid or even desert margin zones where the natural tree cover becomes increasingly sparse.

The total area occupied by the dry forest zone is roughly one-third that of the rain forest zone but depletion has reached an advanced stage, especially in Asia where only 15 percent of the zone is now forested.

Tropical upland formations

Forests occurring at an altitude of 800 m or above are referred to as upland or sometimes hill and montane forests. Their characteristics can vary greatly depending on their altitude, rainfall, temperature and other factors.

The upland forest zone is surprisingly extensive (see Table 5). Its area is almost as great as that of the forests of the dry and very dry zones. In Asia the forests of the zone cover the Himalayas and stretch south into Myanmar and the mountains of Thailand and Vietnam. In Latin America, the zone includes the Andes and the highlands of Mexico, and in Africa it covers the highlands of Ethiopia and the mountainous areas around Lake Victoria.

Depletion of these forests has reached an advanced stage, especially in Asia and Africa, and is continuing at a rapid rate.

Deforestation and its impacts

The term deforestation summons images of devastated landscapes, eroded soils, desertification and human misery. Yet visitors to highly deforested areas, for example in parts of the Sahel, are surprised to see landscapes in which many trees still remain. Such confusion arises from the way in which the term deforestation is used.

A forest in the tropics, according to the FAO definition, is an area of land of which at least 10 percent is covered by the crowns of the trees or bamboos growing upon it and which is not subject to agricultural practice. Deforestation implies a reduction in the crown cover to less than 10 percent or a change in land use. Thus an area of well-wooded productive agricultural land will be officially classified as deforested.

An area of forest that has been badly damaged by, for example, careless logging but that has not been converted to another use and still retains at least 10 percent crown cover, is designated as degraded. It is only if it is taken over for agriculture or other uses or if the crown cover falls below 10 percent that it is described as deforested. Outside these FAO definitions, the terms deforestation and forest degradation are used much more loosely and often interchangeably.

All interference with a natural forest alters its ecology to some extent, and many of the world's forests have been subject to a considerable amount of human interference. In Europe, for example, virtually none of the original forest survives. Traditional forest-dwelling peoples, though they may leave much of the structure of the forest intact, can also bring major changes in the species composition as well as the wildlife through selective utilization. The bulk of the world's remaining untouched forests are in the far north of Canada and the former USSR, areas too remote and inhospitable for human habitation, or in the dense moist forests of the tropics as in the Amazon and Zaire river basins.

Deforestation and its impacts

Logging, which is often popularly equated with deforestation, does not normally bring about the disappearance of forests. Logging in the tropics is selective, removing relatively few stems per hectare, in contrast to logging of natural forest in, for example, the United States or Canada, where it is closer to clear felling. But removal of even some of the trees, no matter how carefully done, obviously alters the spatial and size class distribution of tree species in a forest, although this is a long way from eliminating the forest completely. Provided the area is not converted to other uses and the soil cover remains intact, new trees replace those that have been felled and in a few decades the difference is only discernible to the expert eye or revealed by forest inventory data.

Improper logging can, however, seriously degrade a forest. This is particularly true if the logging is carelessly carried out on steeply sloping ground or if the access roads have been poorly built or positioned so that heavy erosion occurs. But trees can usually manage to establish themselves again, even in badly eroded areas within the forest, provided they are protected; this leads eventually to the restoration of forest cover.

A decade ago, cutting for fuelwood was widely believed to be one of the major causes of deforestation. This is not generally the case, although it is true that heavy cutting for charcoal making or urban fuelwood supplies can result in forest clearance, especially in savannah woodland. In the rural areas, rather than felling trees for fuelwood, most families tend to harvest branches of trees or shrubs on a sustainable basis. In comparison with clearing for agriculture, the impact of rural fuelwood collection is usually small.

But even clearing for agriculture does not necessarily lead to the complete disappearance of forests. Many traditional farming systems incorporate a fallow system. An area of forest is cut and burned, usually leaving some trees still standing. It is farmed for a few years and then left fallow while the family moves on to another location. Eventually, the tree cover regrows on the previously farmed area. Shifting cultivation can be a stable and effective land-management system which preserves much of the tree cover as well as the fertility of the land, provided the fallow period is long enough.

It is when population density begins to increase that problems arise with fallow systems. Because there is no longer enough land for everyone, farmers find they are unable to allow fallow areas sufficient time to restore the fertility of the land fully. The soils are progressively degraded and in some cases are colonized by weeds. This has happened, for example, in Asia, where tens of millions of hectares have been lost to cogon grass (Imperata cylindrica).

Similar problems occur when forest land that is not suitable for agriculture is cleared. If the cleared land is used for subsistence farming, in which there are no fertilizer inputs, then the fertility of the soil is quickly exhausted and its structure is destroyed. The end result is an area of degraded land capable only of supporting a sparse growth of scrub or weeds or, where this is lacking, often subject to heavy wind or water erosion.

On the other hand, much of the forest clearing carried out in the past has led to the creation of fertile and sustainable areas of agricultural and grazing land, as has been shown in virtually every country in the world. The human race depends for the bulk of its food supplies on such areas. When, therefore, the conversion of forest areas that have the potential to support permanent agriculture is properly planned and the subsequent cultivation methods are appropriate, the transition can be both successful and highly beneficial.

Table 1 Forest cover and deforestation in the tropical zone

Note Table 1 gives figures on forest cover in the tropical zone as a whole including forests growing in zones not regarded as zones of natural forest growth such as deserts or alpine areas The data for Tables 2 to 5 are restricted to the zones of natural forest growth The sums of the figures in these tables do not necessarily agree with Table 1

Table 2 Deforestation in the tropical rain forest zone

Table 3 Deforestation in the moist deciduous forest zone

Table 4 Deforestation in the dry and very dry zones

Table 5 Deforestation in the tropical upland formations

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