Tropical deforestation has been measured statistically: 0.64% per annum in tropical America, 0.61% in tropical Africa, 0.60% in tropical Asia, according to the most authoritative figures currently available. This statistical uniformity belies the variety of conditions in which deforestation occurs, and threatens to dull our sense of the impact it can have on individual people’s lives.
In this chapter we look at different reasons why people want to save forests, and the different types of forest they want to protect.
Types of Forest
29 million km2 of the land surface of the tropics may be classed as forest land: about two-thirds of the total land surface of the countries concerned (FAO 1982). Of these 29 million km2, about 11 million are still covered in closed forest, much of which benefits from a tropical moist climate. This is the tropical moist forest to which we return later in this chapter. Few people live under the closed forest , but many parts of it have been cleared and sett led, and much of what remains has been more or less severely disrupted by human activities such as timber extraction.
Of the remaining 18 million km 2, 14 million are open forest and shrubland, including types of savanna, pasture and grassland which are partly wooded. The remaining 4 million km2 are forest fallow, areas recently farmed which have been abandoned or left to regenerate naturally. In and around all these areas are the farms of today, some of them permanent farms on fertile soils, others destined to be abandoned in their turn as their occupants move on in search of better land.
Climate patterns may themselves be influenced by deforestation, as we discuss later. It is customary to class as tropical forest some areas outside the Tropics of Cancer and Capricorn, such as forested areas of Northern India and Nepal, which share some of the ecological and development problems characteristic of the tropical zone: we follow that convention in this report.
It is estimated that 0.6% of both closed and open forest are being deforested ever y year. Although this figure may seem low, it implies that a further 10% of the tropical forest will be deforested by the year 2000. But this outright deforestation is merely one aspect of a far greater problem, the degradation of tropical forest and tropical forest lands. As forest areas are logged, burnt, grazed, farmed and fallowed, their resilience is steadily being decreased, their soils eroded and impoverished, and the diversity of their natural life curtailed.
The humanitarian problems discussed in Chapter 1 affect different areas in very different ways. The forest’s economic value as a timber reserve and as an ecological resource can be quite distinct from its real value to people and society as a whole. Perhaps 140 million people now live in and around the closed forest. Many more are affected by the way the forest is being converted; many live on lands which were once forested, and are no longer.
Tropical Deforestation: Reasons for Concern
Tropical forests are disappearing. Somewhere along the road to complete deforestation, people begin to place a high value on the remaining forest.
In most temperate countries, the area of forest cover has already declined to a point at which populations see clearly the value of the remaining forest, and are prepared to protect it. This time will come in the trop ics, but if present trends are not reversed, it will inevitably come too late in many cases. Such is the vulnerability of tropical soils to leaching, compaction and erosion under the play of tropical heat and rainfall, and such is the cumulative effect of population growth and economic change, that the forest destruction will be ecologically irreversible and, in many cases, complete.
Many people involved in different aspects of tropical conversion are now acutely worried about the consequences of deforestation.
Others see forests as a more or less inexhaustible source of raw materials, yet their importance goes far beyond the mere appropriation and use of timber, fruits, chemicals or animals.
The forest system fulfils extremely important protective, regulatory and productive functions both for the natural environment and for the well-being and development of society. These functions are summarized in the Table that follows.
Tropical Moist Forests as a Genetic Reservoir
Tropical moist forests are of great ecological value. The ecology of tropical moist forests is distinguished by two characteristics: an exceptionally high rate of vegetation growth and an exceptional biological diversity (Jordan 1982). The richness of these forests in terms of the number of species they contain is one of the main reasons why they have attracted particular attention, and why many people feel that their protection is of paramount importance. Scientific research has shown that the study of a single hectare of moist forest reveals the existence of many species hitherto unknown to modern science. We know of some cases where forest species – particularly mammals and birds – have become entirely extinct because of disruption of their habitat. But we can also be quite sure that many species as yet unknown are also becoming extinct as the area of forest declines. Indirectly, this is a matter of considerable humanitarian concern.
In the past, species discovered in the forest have provided the source of many medicines and crops of great value to the human race. Destruction of these forests is undoubtedly against the interests of future generations. To quantify this: it has been estimated that tropical forests contain 50% of all world species. Amazonia alone has one million animal and plant species, 1,800 bird species, 2,000 fish species (four times more than the Zaire basin, eight times more than the Mississippi basin and 10 times more than the whole of Europe). Only 1% have been studied from the point of view of their economic use. The area is indeed the world’s largest genetic reservoir.
If a small area inside the forest is cleared and allowed to regenerate naturally, the species composition of the secondary forest should eventually return to normal, as different species invade in turn from the surrounding forest. But when very large areas are cleared or damaged, or when deforestation takes place at the edge of the forest, propagation becomes more difficult for the forest species and the area will tend to have a permanently weakened species structure even if left to regenerate naturally.
Soil deterioration is a second factor which will often prevent regeneration of tropical moist forest. Most soils under tropical moist forest are shallow, and their nutrient availability is low. When forest is cleared, exposure to sunlight, wind, water and other factors such as the impact of the wheels of logging machines destroy soil structure, leading to erosion. Soil deterioration and the difficulties of regeneration of key plant species together mean that the destruction of tropical moist forest is in many cases virtually irreversible, hence the considerable loss of genetic varieties.
Tropical Forests and World Climatic Regulation
Tropical moist forests are of great significance for global, regional and local climate regulation. The contribution of deforestation to the ‘greenhouse effect’ is probably modest in the short run although this is a controversial issue. But deforestation in moist areas may well be reducing or disturbing rainfall, preventing forest regeneration and having an impact on local and more distant climatic variations which is difficult to assess.
The forest constantly returns water vapour to the air and by shading the soil helps it retain its moisture. In tropical areas, radiation at the earth surface is very high.
This is due to low reflectivity (5-10% below other areas), the fact that the sun is closer to the zenith, and the low temperature of the canopy. Tropical moist forests are therefore efficient absorbers of solar energy which is used in water conversion.
In general, forests return rainfall to the atmosphere in greater proportion than any other vegetative cover. Forests evaporate 50–90% of received rain, whereas grassland returns 40% and bare soil only 30% (Reifsnyder, 1982) . Precipitations in the tropical belt are more than three times the world average of 746 mm.
The average surface run-off in tropical areas in 879 mm compared to the world average of 266 mm. Three tropical rivers alone – the Amazon, the Orinoco and the Congo – carry 23% of all surface–water run-off. The Amazon and its tributaries contain two-thirds of all the river waters of the world and 20% of the world fresh water area. But this represents less than 50% of the precipitation in the area: in other words, the evaporation in tropical areas is so high that tropical land surface contributes 62% of the world water vapour. The tropical regions (land surface plus sea surface) which represent 40% of total earth surface contribute 58% of the total volume of vapour. This vapour is transported to the atmosphere outside the tropics as latent heat and plays an important role in the world thermodynamic system.
The ‘roughness’ of the forest surface, caused by irregularities in the forest canopy and by emergent high trees, slows down the movement of air masses and causes turbulence. This leads to ascending air fluxes, air cooling, cloud formation and, consequently, greater precipitation. It is possible that 20% more rainfalls on forests than on any other vegetation (Shiklomanov and Krestovsky, 1984). In Amazonia it is common to see great pillars of cumulus clouds appearing to rise from the top of the forest, and less cloud where the trees thin out.
This influence of tropical forests on climate is generally agreed, but many contradictions and gaps in knowledge remain as regards the relationship between the clearance of tropical forest lands and local climate. If deforestation leads to a reduction in water returned to the atmosphere, it is likely that the effects vary according to the size of the area cleared. There will be little measurable effect within one small area, such as that cleared by a slash-and-burn agriculturalist. The decrease in moisture return may not result in detectably drier atmosphere because of swamping by moist air from surrounding forest. But the effect of many small clearings could be cumulatively very large (Salati et al, 1983).
A possible effect of the clearing of large areas of forest (greater than 100 km2 would be the increase of the albedo and consequently a reduction in rain fall. A 0.1% increase in albedo can cause a 23% decrease in precipitation. The reduction in rainfall immediately downwind, if focused, could result in a complete change in the structure of the adjacent forest. Essentially such deforestation would trigger a process that would slowly but continuously eat away at forest downwind. Regrowth of vegetation on a small area of clearance can restore the climatological balance within 10-20 years. But again, as with biological diversity, it is unlikely that forest regrowth after large-scale deforestation would achieve this effect.
Types of Forest Conversion
Forest conversion has been a normal feature of development which will not be avoided in tropical areas. But it is important that such a transformation should not disrupt the role that each specific ecosystem plays in the normal functioning of the natural environment. Moreover people living in those areas should remain able to satisfy their needs and the complete process of development should not be jeopardized. The transition should follow certain principles and specific limits. The conversion of tropical forests, in particular, brings about changes in the natural environment which can be beneficial, yet too frequently damage human interests.
Recent concern is focused on over-exploitation of the natural resources, biological productivity and the destruction of the natural environment. The natural ecosystem is disrupted. FAO reports use the term deforestation in the strict sense of complete clearance of tree formations and the conversion of tropical land to other uses. Man-made disturbance ranges from minor quantitative changes to fundamental qualitative and quantitative transformation.
In theory, forests can regenerate within a reasonable period provided there is no permanent loss of biological potential. But rapid destruction of the forest affects its biological potential as well as its protective and regulative capacity and its role as a source of raw materials and other products.
Whether conversion can be achieved without disruption and depletion will depend on forest land-use patterns and on the scale of the process. One of the most ancient agricultural uses of forest land is shifting cultivation or swidden agriculture. Essentially this starts with the rather incomplete clearance of a small area, the burning of the debris and the cultivation of the land for a few years (normally five). Then the land is left and reverts to the state of a secondary forest before it is cleared again. The impact of shifting cultivation varies considerably depending on the type of forest cleared, the fallow period, and population pressure. If the period of cultivation is short and the fallow period rather long, the practice can be regarded as ecologically sound. Soil fertility is renewed and the forest recovers. If not, the original forest will recover only partially or not at all. Where the full recovery of fertility and vegetation is not possible, the land is covered by grass and shrubs. Deterioration becomes permanent. The tropical forest turns into grassland or savanna, and gradually cattle grazing replaces shifting cultivation as a form of land use.
Recently the agricultural use of tropical forest has been accelerated by the influx of peasants following the opening up of forests by logging contractors and highway construction. These migrants know little about tropical forestland. They establish subsistence farming which has little to do with shifting agriculture; they deplete the soil and tend to abandon the area when productivity has fallen.
The felling of trees has been encouraged by the increasing international demand for tropical hardwood. Demand in industrial countries today is 14 to 16 times greater than in 1950, yet the tropical moist forests contribute little more than one-tenth of the current world consumption of wood for construction, pulp and paper and industrial uses.
According to FAO, between 1958 and 1978 about one million square kilometres of forests (385,000 square miles) were leased for tropical timber extraction mainly in South East Asia and West Africa. The great potential of tropical forests is ignored and irreversible damage is often caused to the remaining species in the forest. There are about 2,500 tree species in Amazonia of which only 400 have been assessed for economic purposes. Not more than 50 are exploited. Out of 150 trees per acre, only 6 or 8 are used, but because of inadequate or even predatory logging techniques, the remaining trees and the soil are sever ely damaged. Selective logging in South East Asia reportedly damages between one-and two-thirds of unused species. One-third of the logged forest soil is left bare and the heavy logging equipment causes severe soil compact ion. Some 11,000 square miles of tropical forests are converted every year for commercial timber.
In addition, it has been argued that today the greatest threat to tropical forests is the increasing area devoted to cattle ranching and savanna–type vegetation which preclude forest regeneration. Intensive grazing rapidly weakens a soil ill-suited to this type of use. This kind of conversion is particularly important in Central America and Amazonia in order to supply lower grade meat to the very large North American market (mainly for fast food and pet food). It is reported that since 1950 the pasture area in Central America has doubled at the expense of tropical forests. 38% of deforestation in Brazil between 1966 and 1975 is said to have been caused by ranching.
Road and highway construction is one of the irreversible types of forest conversion which has the additional effect of opening the forest to new uses and facilitating contacts with previously isolated forest dwellers. This kind of deforestation is particularly important in Brazil whose ambitious highway programme between 1966 and 1977 accounted for 25% of Amazonian deforestation.
Industrial agriculture is another type of conversion too frequently ignored. Oil palm and rubber are among the main commodities produced for the international markets.
Finally, minor types of conversion are associated with forest clearing due to mining and hydro-electric schemes.
Six Humanitarian Situations
Six situations require close scrutiny from the humanitarian point of view both because of short-term and long–term effects of forest clearing:
- Situations where an extraordinary and untapped biological wealth with enormous potential for social development is seriously threatened;
- Situations where extensive forms of agricultural or pastoral land–use threaten to diminish the long–term suitability of the land for cultivation or forestry;
- Situations where forest loss may jeopardize climatic balance at local, regional and global levels and trigger a cumulative deterioration in ecological potential;
- Situations where forest clearing activities and/or an influx of population involve a sudden transformation of land-use;
- Situations where the survival of indigenous dwellers is threatened by deforestation;
- Situations of increasing malnutrition and ill-health.
Notes
- These are the regional estimates presented by Lanly in FAO (1982). They are figures for deforestation of closed forest areas; percentages for deforestation of all forest (closed and open) are slightly lower. These estimates correspond to a fairly narrow definition of deforestation, and do not include many more or less severe kinds of forest degradation. As a general rule , positive transformation to completely different, and valuable, forms of land-use is classed as de forestation; much of the real problem thus lies in degradation rather than outright deforestation.
- A good example is the case of Sierra Leone, one of the few African countries where forest cover is no longer declining, but only because hardly any forest remains! Two hundred years ago the country had a high forest cover of 75 %. Ruthless exploitation, mainly for the British market, helped to reduce this area to a mere 3% , spread over the country in remnants of negligible size. The only remaining forest which still merits the name is the Gola Forest, on the Liberian border. Now, with German development aid financing a saw-mill, this last pocket will disappear within the coming years.
- Loss of species has been discussed by Myers (1980), R. and C. Prescott –Allen (1983), the U.S . Department of State (1982) and others. There is also a substantial economic literature discussing the inter-generational equity problem presented by species loss. The welfare of future generations is an important humanitarian issue which this paper has not sought to address in detail.
- NAS (1983) illustrates a growing consensus that , although deforestation (and more generally use of fire in forest areas) has contributed to a CO2 build-up, this contribution is less critical than fossil fuel combustion. For a somewhat different view, cf. Myers (1982).
- Albedo: the ratio of solar radiation which is returned to the atmosphere. The albedo of a well-developed forest is 0.1, that of a desert 0.4.