Depletion of tropical moist forests : A comparative review of rates and causes in the three main regions

Information on depletion of tropical moist forests throughout the world is reviewed, including its causes, course and consequences in Latin America, Africa and Southeast Asia. Primary, or undisturbed, forest under goes varying degrees of perturbation depending on ex­ ploitation practices. Timber exploitation has been par­ ticularly important in Southeast Asia. Slash-and-burn agriculture often follows due to improved access. Shifting cultivation is especially important in Africa, where high population pressure makes the access roads opened for logging an even stronger catalyst to entran­ ce of slash-and-burn farmers. Cattle raising is a major cause in Latin America, often influenced by foreign market pressures and government policies.


INTRODUCTION
Tropical moist forests (TMFs) are under going progressive depletion, it present rates of exploitation persist -and they are likely to accelerate -the end of xhe century may find that extensive sectors of the forests have been grossly disrupted if not destroyed out right.The remaining segments may not sur vive, except in severely degraded state, beyond another two or three decades.This means that the biome with the richest biotic en dowment on earth is being impoverished faster than any other biome ( Mye>-s, 1979a andb, and1980a andb;Persson, 1974Persson, , 1975Persson, and 1977;;Sommer, 1976;Synnott, 1977;Unesco, 1978;Whitmore, 1975).This is not to say, however, that "depletion", "disruption", "degradation" and "impover ishment" are necessarily the same as "final elimination".In another 50 years' time, many of the areas that are presently under primary forest will still feature forest of some kindoften secondary forest of various stages of sera! succession, sometimes brush and scrub growth occasionally even a new form of stable climax forest (such as bamboo forest) in those areas where edaphic and climatic factors have been sufficiently altered to foster a different kind of forest.Thus it can be valid to assert, as dc certain observers (e.g.Lanly & Clement, 1979), that the total amount of TMFs of all sorts may not decline nearly os fast as has been proposed for primaiy forests.For purposes of this paper, however, the author focuses on those forest formations that are often considered of most interest to the scientist by virtue of their intrinsic biological value, viz.primary forests.These are the forests that have remained more or less undis turbed for appreciable periods -at least, "undisturbed" as compared with the disrupted state imposed by modern man in the recent past.
It is in these primary forests that are to be found the complex ecosystems and di versified relationships of unsurpassed interest.
For purposes of basic research, these primary forests appear to be more rewarding than an/ other forests.Even marginal modification, such as results from light logging, reduces their value as "living laboratories".So this paper considers that any forest tract that has been disturbed by modern man can no longer be regarded as primary forest; and it is within these terms of reference that the paper as sesses the extent of forest depletion in each of the three main regions of the TMF biome.This is not to say -and the point is stressed -that depletion of TMFs in the sense adopted here is in any way to be deprecated in principle.In certain instances, forests are now exploited in rational sustainable manner, with explicit recognition of consequences en tailed.When forests are caused to produce goods and services that contribute to the welfare of all human communities concerned ( 1 ) -Consultant in Conservation and Development, Nairobi, Kenya.
both now and in the future, this constitutes a "wise use" for the forests in question.To be sure, there are occasions when wise use can lie in preservation of forest tracts for scientific research.But in the main, legitimate exploi tation entails some degree cf disruption for the primary forest -and to the extent that this promotes the general well-being of society now and forever, this action is to be welcomed,   (*") -North America's hardwood forests account for just over one-tenth of this total.

NOTE:
As trop'cal developing countries themselves start to consume more of their hjrdwcod output, there will be (except in the eventual case of Latin America) a smaller short available for export to developed countries.At the same time, developed countries demand will steadily expand.So there will be compounded pressure to exploit trcpicol hardwood forests.

SOURCES:
Food and Agriculiure Organization, 1978 and 1979a and b.
Due to the diversity of tree species in tropical forests, coupled with the reluctance of international timber markets to take more than a small proportion of wood types available, the commercial logger is inclined to aim for a highly selective harvest, taking a few choice specimens with disregard for the rest.In short, a "creaming" operation.Of Amazonia's thousands of tree species, only about 50 are widoly exploited, even though as many as 400 have some commercial value (Amaya, 1977).
Africa exports only 35 principal species (albeit twice as many as in 1950), with 10 accounting for 70 percent of the total (Erfurth, 1976) .In Soutneast Asia, loggers focus on less than 100 tree species, with exports consisting mainly of only one dozen or so (Sumitro, 1976: Whitmore, 1975 (Burgess, 1973;Hadi & Suparto, 1977;Kartawinata, 1975;Nicholson, 1979;Suparto, 1978;Tinal and Balenewen, 1974).On top of this, almost one third of the ground may be left bare, in many instances with the soil impacted through heavy ma chinery.With greater care the damage could be reduced by half.But less disruptive exploi tation would raise timber prices for the endproduct consumer -something that the main markets, viz.developed nations, are ostensibly unprepared to accept on the grounds that it would be unduly inflationary.
Clearly, logging impact varies from area to area.In some places, e.g.(Myers, 1979a and b;Sommer, 1976).The area of forest in Southeast Asia that was being newly affected each year in the mid-1970s amounted to 10,000-27,000 km 2 ; in Latin America, 8,000-25,000 km 2 ; and in Africa (mostly West Africa), 32,000 km 2 .
This made a total for the tropics of 53,000--87,000 km 2 .Moreover, these figures refer only to legal fellings of industrial timber; illegal fellings could swell the totals a good deal iflore (as in Thailand and Indonesia where "timber poaching" is a great and growing porblem), sometimes by twice as much.

SLASH-AND BURN CULTIVATION
The logging impact can be grossly aggra vated by what happens after the commercial exploiter leaves his patch of iorest.Along the timber tracks come subsistence peasants, able to penetrate deep into forest areas that have hitherto been closed to them.Clearing away more trees in order to plant their crops, they may soon cause far more damage and de struction that the lumber man did.Not only do they arrive in iarge numbers, mut they stay in the locality permanently.
Not that the slash-and-burn cultivator has always been destructive.Before he became so numerous, he could operate as a shifting cultivator.He would fell and burn a patch of forest, raise crops for two or three years until the soil lost its fertility, or until weeds moved in, then he would move on and repeat the process in another part of the forest.This was a style of agriculture that allowed the culti vator to make sustainable use of the forest environment.As long as there were not more than four or five persons per square kilo meter, and a patch of farmed forestland could be left fallow for at least ten years in order to renew itself, the system worked (Clarke, 1976;Denevan, 1977 and1978;Food ana Agriculture Organization, 1974;Greenland & Herrera, 1977;Hauck, 1974;Kundstadter et al.. 1978;Sanchez, 1976;Watters, 1971).Now, however, the situation has changed.
Cultivators have increased in numbers to a point where there are often three times as All in all, these forest farmers have been estimated in the mid-1970s to total at least 140 miliion persons, occupying some 2 million sq.kms.(or over one-fifth) of the TMF biome (King & Chandler, 1978;Myers, 1979a and b;Persoon, 1975 and1977;Sommer, 1976).Some 50 miliion are considered to be occupying at least 640,000 sq.kms.(a Texas-sized area) of primary forest, while another 90 million exploit twice as much land in secondary forests.According to preliminary reckonings, these cultivators are believed to eliminate at least 100,000 sq.kms. of forest each year.
The greatest loss occurs in Southeast Asia, where farmers clear a minimum of 85,000 sq.
kms. each year (some of which are allowec to regenerate), adding to 1.2 million sq.kms.
How much reliability can be placed on these statistical estimates?A question diffi cult to evaluate.We can, however, make a comparative assessment by coming at the problem from a different direction.
Brazil tried to expand its beef production ra pidly, with the eventual aim of becoming one of the world's leading beef exporters by the early 1980s.This latter goal has now been shelved to a later date, but Brazil still seems for Volkswagen with S35 million, (Davis, 1977;Irwin, 1977).Volkswagen believes that although people may come to purchase fewer cars in the wake of the oil price hike, they will hardly be inclined to eat less beef.Volkswagen holds a concession of 1400 km 2 in the eastern Amazon, of which half is to be converted into pastureiand.To date the Company has burned over 100 km 2 of forest, enough for a herd of 10.000 cattle.The eventual aim is to increase the grasslands to 700 km 2 , to support 120,000 cattle.
In both Brazil and Central America, how ever, raising beef in tropical forestlands is not so straightforward as it might seem Kirby, 1976;Osbourn, 1975;Smith, 1976 and1978) Stocking rates are low, a mere one animal pe' hectare.Steers take 4 years before they are ready for slaughter, at a weight of 450 kg.What, then, is the overall impact of cattle raising on TMFs? Between 1962 and1985, it is expected that at least 325,000 km 2 of Latin America's tropical forests, or an area the size of Norway or New Mexico, will have been cleared for pasturelands (Brazil,125,000,and Colombia,66,000) .This works out at an average of just under 13,500 km 2 per year.
Since the rate iis likely to be greater at the   (Myers, 1978(Myers, , 1979a))).

Depiction
Indeed, it would be a welcome prospect if TMFs were to be exploited for the high Whatever lies ahead, it would be a rash conjecture to suppose that the future for TMFs will amount to a simple extrapolation of the present.

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committed to boosting cattle ranching as a mode to exploit, or at least to settle, extensive sectors of Amazonia.Between 1966 and 1979, more than 300 ranches have been established, under the auspices of the Superintendency for Development of Amazonia (SUDAM); these ranches have caused the conversion of at least 80,000 sq.kms. of forest into pasturelands, supporting some 6 million head of cattle (an average of one animal to 1.3 hectares).In addition, another 20,000 ranches of smaller scale have been established.Interesting enough, a number of the largest ranches in Brazilian Amazonia are set up through foreign capital.A U.Grubo Bradesco from Japan, Liquigas from Italy, and George Markhof from Austria, among many more from industrialized nations.Investment on the part of the twelve largest enterprises totals S21 million, except We could even find that TMFs are subjected to forms of utilization that cio not yet rank among major types of land use.In the wake of deforestation-caused debacles in all parts of the biome, forests may come to be as timber.In the wake of OPEC price rises, forests may come to be exploited as sources of bio-energy -after all.TMFs are unmatched as natural generators of plant biomass for pyrolisation into alcohol fuelr.Also as a consequence of OPEC's price hikes, which are placing petroleum beyond the reach of petro-chemical industries, TMFs may start to supply feedstocks of phyto-chemicals: with almost half of earth's 5-10 million species ; a host of other important items in the pharmaceutical trade -a commerce that is now worth, in terms of sales to end-product consumers world-wide, several billion dollars per year , for instance, could prove an exceptionally selective mode of exploitation, leaving the forest virtually undisturbed.It is by virtue of their vast stocks of unique raw materials that TMFs represent some of the most valuable natural resources with which society can confront the unknown challenges of the future.What a change in exploitation patterns it woult represent, were TMFs to be utilized in ways that produce most benefits for most people, now and forever.It could amount to the most rational, and the least disruptive, form of exploitation in view.

TABLE 1 -Hardwood and Softwood Forests of The World
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spreading crowns, as much as 15 ms.across When one of these giants is felled, it is likely to cause several others to be broken or pulled down with it.Furthermore, tropical trees are highly susceptible to attack by pathogens; as a result, a minor-seeming injury, such as a patch of bark torn off, can leave a tree vulner able to irreparable damage.Logging roads and haulage tracks, sometimes averaging as much as 10 kms.for each one sq.km. of forest .exploited,can, together with dumping zones and iandings for logs, account for 10-30 percent of the forest area.

Exports are almost entirely made up of better-quality parts of cattle. Local consumption is mainly confined to v'scera and other less desirable parts. FAO projections for Central American consumption of tbeef indicate that it will increase from 8.2 kg per head in 1970 to 10 kg in 1980 -as compared with similar figures for the main foreign-market country, the United States, of 53 kg and 61 kg. (**) -Figures for El Salvador, Panama and Belize are too small to be detailed separately, SOURCE': Information supplied by Dairy; Livestock and Poultry Div., Foreign Agric. Service; U.S. Dept. of Agriculture, Washing ton D.C.
that, in the areas in question, 62,400, 162,000.51,000 and 298,000 km' of forest were eliminated by slash-and-burn cultivators.The last figure, almost 300,000 km 2 for the tropics, of 149 million.Using the very rough rule of thumb developed in Ivory Coast, this could mean (*) -NOTE: