Joseph A. Tosi Jr.
Robert F. Voertman
Joseph A. Tosi Jr. is Administrative Director and Land-Use Ecologist at the Tropical Science Center, San José, Costa Rica. Robert F. Voertman is Professor of Economics at Grinnel College, Iowa, United States. L.R. Holdridge, whose Diagram for classification of world life zones or plant formations is reproduced, is also with the Tropical Science Center. This article was developed for unasylva from one which the authors originally published in Economic Geography, No. 40(3), 1964.
It is a mistake, say the authors, to destroy the diversity of the tropics with temperate zone development techniques which are not suited to the tropics. Instead, full advantage should be taken of the biological diversity and high productivity which are intrinsic to tropical and subtropical lands. Potentially large-scale agricultural and industrial utilization of the tropics is seen to lie in forests in particular. The methods and technology for utilizing these forests are ready to be developed and in some cases are already present.
All of the major civilizations which emerged following the neolithic revolutions have been grain-and-beef civilizations. Grain-and-pasture systems, as a basis for sedentary agriculture, not only fitted temperate and cool temperate environments by virtue of their short, intensive growing seasons, but also provided a high-quality diet rich in protein. The historical tendency of the Europeans to avoid settlement in the low, humid tropics, and the parallel failure of the grain-and-pasture system to develop effectively there, are both related to basic environmental factors. Grains and high protein fodders of the temperate zones do not generally prosper in the tropical region, and indigenous tropical cultigens either did not fit the dietary demands of the Europeans or did not lend themselves to the energy-intensive exploitation patterns which have been associated with the technological revolution in western agriculture.
There is an informed judgement that the basic environmental traits which have historically restricted the productivity of tropical agriculture also seriously impair the prospects of its future development. ¹ But it is the opinion of the authors that this pessimism reflects a narrow conception of the high-productivity system as tied to the crops, techniques and organization of the grain-and-pasture systems. That is to say, the land-use systems, the raw-products processing systems, and indeed much else in the economic, social, and cultural life of the high-income economies that today claim the role of influencing and guiding low-income economies falling in the tropical category have been specialized by an environmental structure quite unlike that of the tropics.
¹ For example, see: Pierre Gourou, The tropical world: its social and economic conditions and its future status, tr. by E.D. Laborde, New York, Longmans, Green, 1952; see also Douglas H.K. Lee, Climate and economic development in the tropics New York, Harper, 1957; and John Phillips, The development of agriculture and forestry in the tropics, London, Longmans, 1961.
There are fundamental and well-known reasons for proposing that high-productivity land-use systems can be developed for the humid tropical regions and for urging that this be considered a high priority item in economic development research and planning. First of all, the tropics and adjacent subtropics contain over one third of the useful land area of the earth. This third of the earth is the heartland of underdevelopment despite the variety and productivity of natural life as organized in primary ecological systems. Furthermore, large areas of the potentially most productive environments, the low humid tropics in America and Africa, are relatively sparsely populated. Impeding great increases in human population in these regions dictate that there be an expansion of useful human habitat therein.
But the existence of this potential and need for high-productivity land-use systems in the tropical region must be combined with a mode of translating the potential into economic production. On the basis of ecological research already conducted, it is clear that the "tropics" are in reality composed of a very large and as yet indeterminate number of distinct natural environments, each with a significantly different complex of climatic, topographic and soils conditions as manifested in the primary vegetative growth. For example, the land area of Peru has some 70 distinct bioclimates or life zones, and each of these zones is further specialized into distinctive local associations related to soils and topographic variations of landscape.
A TROPICAL FOREST IN MALAYSIA an undetermined number of natural environments
The system of ecological analysis devised by Leslie R. Holdridge provides a uniform basis - on a global scale - for the comparative analysis of environments². It is our opinion that a research and development programme oriented to the Holdridge system could provide many criteria necessary for the "invention" of high-productivity land-use systems for the tropics.
² Leslie R. Holdridge, Life zone ecology, Rev. ed., San José, Costa Rica, Tropical Science Center, 1967.
It is axiomatic that all animal life, including mankind, is ultimately dependent upon solar radiation and the green plants for its existence. Green plants are the only organisms capable of directly utilizing solar radiation as energy to synthesize earth elements into the complex organic compounds essential to animal metabolism and growth. Solar energy, converted to heat-energy held usefully in the earth's atmosphere, is the elementary life source. In the terrestrial environments, carbon dioxide, nitrogen and water, the other main constituents of the photosynthesis process, are also supplied preponderantly by the earth's atmosphere. For these reasons, climate has long been viewed as a primary and essentially independent regulator of the earth's ecological system. That is, all other major components which interact in the coherently organized systems of living organisms and physical environment, termed "ecosystems" - the terrain phenomena, the soils complexes, and the communities of plants and animals - are basically subordinate to climate.
Holdridge's original working hypothesis was that such sessile organisms as the land plants should have evolved selectively to compete and survive only within very limited sectors of the broad climatic spectrum. He proposed that the growth habits, life forms, and physiognomy (structure) of individual species grouped into distinctive natural plant communities - provided that these were observed in an undisturbed, or primary (i.e., "virgin") state - should precisely reflect the climate prevailing in any given locality. The parameters and limits selected to diagram the theory, the physical and biological principles which are its premises, are all related to this basic proposition.
In essence, the Holdridge theory postulates a division of the earth's climate into ecologically equivalent units (approximately 120). Each unit, representing one sector of the climatic continuum, supports a distinctive set of possible plant communities, termed associations, and is designated a life zone. Any given life zone will include a variety of associations depending on soils, topographic features, drainage, winds, fog, and the like. The model which relates the critical climatic variables to the life zone is represented in the diagram. The climatic variables are: (a) mean annual biotemperature, (b) mean annual precipitation; and (c) the potential evapotranspiration ratio.
The three climatic variables are logarithmically scaled and the vegetational units thus inscribed are arithmetically scaled. The choice of scales and values for the model, suggested by preliminary field observations, has proved remarkably accurate as measured by field data subsequently gathered over a wide geographic area. Where adequate weather station data are available at high areal intensity, the approximate delineation of life zones can be accomplished by their application to diagrams and formulas already published.³ For most of the underdeveloped areas, however, the mapping of life zones must be accomplished largely through direct field interpretation of vegetation due to the scarcity of accurate, long-term weather records. However, 25 years of correlated field studies have enabled scientists working with the model to devise relatively precise and operationally efficient means of accurately identifying the vegetational parameters4 Today it is possible not only to identify most life zones and to distinguish the boundaries between them from observed or measured characteristics of plant life-form and physiognomy in undisturbed associations, but also to rely on secondary vegetation and some cultigens as life zone indicators in the more heavily populated rural areas.
³ Holdridge, op. cit.
4 Holdridge, L.R. et al., Forest environments in tropical life zones: a pilot study. Oxford, Pergamon Press, 1971.
The more specific interactions between soils, topographic and local atmospheric variables on the one hand, and plant associations on the other, also demonstrate pronounced regularities, and models have been constructed relating these patterns as well. The testing and development of the Holdridge hypotheses and field methodology are now sufficiently advanced to constitute a firm foundation for a system of multidisciplinary studies of comparative natural and cultural environments. An additional advantage is the ready availability of published maps and studies, founded in the life zone classification, lor large areas in the American tropics. Such maps and studies provide a firm basis for immediate further work in comparative analysis of environments on a geographic and interdisciplinary basis.
Classification of world life zones or plant formations
Patterns of settlement and land utilization in those parts of the American tropics which have been mapped under the Holdridge system reveal that the "settled" agriculturists, both the Indians and the Europeans, have been fairly good practical ecologists. Given their dietary preferences and their technologies, they have generally selected good, if not always optimal, sites for specific agricultural activities. Historical settlement patterns, which may be inferred from archaeological evidence as well as from the location of population concentrations and cities today, bear a strong relationship to the potential evapotranspiration ratio factor as revealed by their life zone locations.
As conceived by Holdridge, the potential evapotranspiration ratio, in practical agricultural terms, relates to the maintenance of fertility in the topsoil on the one hand and to moisture available for plant growth on the other. In a climatic situation where water (in the form of precipitation) is added to the soil at the same average rate at which it is evaporated and transpired (by plants) back into the atmosphere, water movement downward through the soil is offset by water movement upward through the soil. This means that soluble soil nutrients are not removed by leaching and yet a supply of water is present in the soil. The climatic situation is represented by the potential evapotranspiration ratio unity line (diagram) as an average and hypothetical position. This unity line (1.00) separates the dry, or humid, from the moist, or humid, life zones. Those life zones, then, which are adjacent to this unity line tend to combine adequate moisture with minimal leaching problems. The problem of maintaining fertility (under cultivation) is lessened as one moves into life zones to the left of the unity line but lack of moisture is an increasing limitation to agricultural production. To the right of the unity line, the fertility maintenance problem is rapidly intensified as humidity (rainfall) increases. The fact that concentrations of people, and agriculture, in the life zones immediately adjacent to the unity line are very high relative to life zones further to the right or left seems to be attributable in large part to this fertility-moisture relationship.
The fact that "history" has located the economic centres in the tropical highlands and drylands in the Latin American tropics, and has perpetuated there a quasi-temperate region land-use system with its associated dietary habits, raises several interesting problems related to our main thesis. How effective has the adaptation been to these environments? There are clear patterns of crop specialization which appear to reflect significant variations in climatic, soils and topographic conditions e within the densely settled areas, a but how efficient are these specializations? It is reasonably clear that while many of these environments are "temperate-like" they are certainly not midwestern United States maize land or European dairy land. How much, then, of the fruit of the temperate zone agricultural revolution can be brought to bear upon these areas?
It is quite likely that some extension of the high productivity of the temperate region system is possible in selected tropical and subtropical regions, especially in those which are relatively dry or relatively cool, or both dry and cool, given adequate research to develop suitable crop varieties and soil management techniques.5 But the experimental and developmental work needed to expand the productivity of the grain-and-pasture system in these regions can be greatly economized if the specific life zones and associations suited to the distinctive aspects of this system are carefully identified beforehand. Similarly, the distribution of the resulting improved agrarian technology will be greatly economized by correct identification and mapping of the life zones to which the plant varieties and techniques are applicable. Finally, to facilitate diffusion and acceptance of the new technology, environmentally related sociocultural and economic patterns need to be studied in their orientation to life zone characteristics and distributions.
5 The Rockefeller Foundation, with major projects of developmental research in the Mexican and Colombian highlands, has demonstrated the possibility of achieving increased yields in cereals, milk and meat in formations identified under the Holdridge classification as dry and moist forest in the tropical montane, lower montane, and pre-montane temperature belts. See: Rockefeller Foundation, Program in the agricultural sciences: annual report 1961-1962, New York, Rockefeller Foundation Office of Publications, especially p. 34-35 and 113.
There is a growing "conspiracy of urgency," of population pressure and of politics, to extend agriculture into the more humid tropical life zones. The historical reluctance to settle these zones is at an end. For better or worse, the very humid forest zones are the new frontiers of the tropics. But can they provide the expansion of useful habitat - the new natural resources supplies - which will permit the economies of the region to achieve high levels of per caput income on a sustainable, long-term basis? Given currently available land-use systems, these "pioneering" ventures into the tropical forests seem destined to produce at best an extension of rural poverty, and at worst, the destruction of valuable resources for the future.
Men have, up to this time, devised three primary modes of utilizing the humid tropical forest zones. The oldest, perhaps, and the most universal, is shifting, or "slash-and-burn" agriculture. This land-use system, in which a short period of open field cropping alternates with a long period of forest fallow, functions by using the natural regeneration of forest as a fertility-renewing and weed-control mechanism. It is a satisfactory subsistence system for a relatively sparse population in those life zones characterized by at least a one-month annual dry season.
ECUADORIAN FORESTER MAKING AN INVENTORY looking for natural regeneration
The wet-land or inundated rice cultivation system of southeast Asia permits much denser populations of farmers to subsist in the humid life zones. This system solves the fertility and weed-control problems by, respectively, impeding vertical soil water movement and by periodic flooding. But vast amounts of manual labour have traditionally been used in this form of agriculture and per caput incomes have not risen much above a simple subsistence level.
The third mode is the plantation system based upon the cultivation of perennial crops for the international market. The principal lowland tropical forest zone perennial crops are bananas, sugarcane, cocoa, oil palm, coconuts, and rubber. Other historical invasions of the humid forests - the selective cutting of high-value timbers, charcoal-burning, and the extraction of special trade products - are unstable invasions.
The essential difficulty with all these modes of exploitation is that the people remain poor. Such land-intensive and labour-intensive modes as are adapted to the ecology of these regions are essentially subsistence farming adaptations. The plantation system leaves the economy in the role of raw-product exporter, providing little basis for integrated economic and social development. Present attempts to extend the grain-and-pasture system into these areas are so contrary to the ecological structures of the several life zones involved that they are destined to create little more than an extension of rural poverty while destroying much of the real resource potential of original soils and biota.
The nineteenth century income revolution, concentrated in the temperate regions, was tailored to the resources of that environment. The argument presented here is that the tropics do not have a similar assortment of re sources and, although some extension of the high productivity of the temperate region system is possible in the cooler and drier tropical and subtropical highland areas, the "European" resources exploitation systems cannot be duplicated in the warmer and wetter tropical life zones. What we urge, then, is that the environmental structure of the tropics be related to the potential resources structure, a structure which is sufficiently distinctive to hold the key to the economic growth of the region. Moreover, we think that the socioeconomic forms required to develop these environments may not be simple replicas of the forms now common to the developed parts of the world but may indeed be quite distinctive in their own right.
Basic to our argument is recognition of the fact that the tropical forest ecosystems are vastly more complex and the tropical forest biotypes more specialized than their temperate region counterparts. When the natural communities of plants are compared, those of the humid and wetter tropics stand out as being much the richer in potential cultigens and, on an equal time-and-area basis, as the more productive of vegetable dry matter. For each specific tropical life zone and association there has evolved over the ages a unique complex of very specialized biological life-forms - plant and animal species - each distinctively adapted to grow and reproduce within a particular habitat-stratum or "niche" of the intricately organized and highly competitive community system. Although many individual species do occur in more than one community type, or in more than one successional stage of the natural regrowth following disturbance, their places are invariably limited and defined by the intense dynamics of competition and by their own specialized adaptations for survival. Generally speaking, there are a multitude of individual species, but locally, under natural and, especially, under "virgin" conditions, these species have comparatively few members.
The dominating members of the plant community - the larger trees, palms, ligneous vines, woody grasses, and indeed many of the herbaceous plants - are giants among their kind, not only in size but also in their capacity for synthesizing hydrocarbons in the growth process. All are perennials. Unimpeded by seasonal deficits of heat, sunlight or rainfall, their growth proceeds at a continuous high rate through the years. These same physical conditions, favourable to plant growth, are also conducive to rapid depletion of soils nutrients and to the reduction by oxidation of the organic debris. However, the hydrocarbon productivity of the full, natural biomass is so high that satisfactory levels of soil humus and fertility are maintained by continuous, heavy increments of such debris and the mineral-nutrient turnover cycle associated therewith. In the tropical as compared to the temperate regions, the forest community is probably an indispensable component of the natural productivity system. Experience has shown that its replacement, as in agriculture, by other, volumetrically inferior vegetational communities of less adapted plant species, results in disruption of the basic ecological equilibrium and, as a consequence, in sharply decreased soil fertility and plant productivity. It would be safe to assert that, until far more is learned about the humid tropical soils and their "artificial" management potential, high productivity can be achieved only by a calculated maintenance or a cultural imitation of the original community structure and by the use of naturally adapted animal and plant species.
The really critical problems to be overcome, then, if high productivity resources exploitation systems are to be developed for these life zones, would seem to be those of achieving an efficient economic utilization of the diversity of massive, fast-growing perennial plant species and vegetational types which these environments are themselves efficient at producing. Only a very small percentage of these plants are today in use as food or fibre domesticates, and those produced commercially number only a scant dozen. But among the wild species, from the herbaceous succulents to the tallest fruit - and nut-bearing palms and broadleaved tree species, there are possibly hundreds with an undeveloped potential for domestication. Up to the present time, however, there has been little or no official support or research interest in the search for such species, while plant improvement work has been limited to long-accepted export crops. Again, because efficient economic utilization involves consumer tastes and market acceptance of the product, potential new food and fibre cultigens will require nutritional analysis and food technology research directed toward means of preparation, processing, preservation and marketing. However, once the character and special context of these problems have been perceived, existing "temperate region" research and development techniques can be easily adapted to their solution.
In these same life zones, animal husbandry is in a primitive and chaotic state. Although climatically tolerant beef animals have been developed from Asian and African strains, the persistence of a temperate region "pasture" tradition among farmers and technicians alike has effectively inhibited the development of operationally efficient means of providing adequate high-protein forage foods for them. In these environments, of course, no artificially established low grass pasture can begin to compare with the natural secondary forest in hydrocarbon productivity, and field grazing has proved to be an extremely inefficient method of converting even the best tropical pasture grasses into meat, milk and leather. Under the constantly humid conditions, both planted and natural grasses become sparse or woody and unpalatable with overgrowth, trampling, declining soil fertility and compaction; pastures are costly to maintain free of weeds and invading bushes and trees, for seasonal burning is next to impossible in most years; commercial fertilizers, often prohibitively expensive, may be wasted by leaching and chemical recombination in the acid soils. For similar reasons, neither dairying nor small-scale animal meat production has achieved significant commercial success. The popular domesticated breeds of dairy cow, swine, sheep and fowl are specialized to temperate and temperate-like climates. When introduced into the warmer and wetter tropical areas they are plagued by unaccustomed parasites and diseases and appear unable to adjust to the kinds and qualities of native forage and fodder plants.
Clearly, then, an imaginative new approach to these problems is also called for if high productivity livestock enterprises are to be included in the development schemes for these life zones. Both new foods for livestock and new breeds and classes of animals could be sought and developed, using established techniques. What is first needed is only a change in outlook and an appreciation of the real potentials and limitations inherent in these environments. One might suggest, for instance, that alternatives to field grazing be evaluated as means of providing satisfactory nourishment for livestock, or that native leguminous trees and bushes be studied as possible sources of higher net-energy fodders, either for direct feeding or after conversion to simpler carbohydrates and proteins by chemical hydrolysis and biological fermentation.
Similarly, it is possible that the wild fauna of these life zones are a potential source of new and more adaptable domesticated animal species. Modern selection and breeding methods seem to be applicable to the rapid development from wild stocks of commercially valuable, disease-resistant breeds well adapted to available tropical plant foods. In this matter, at least, time is rather short, for the extensive modification of habitats, plus the uncontrolled slaughter of wild fauna now under way, is drastically reducing the quantity and variety of genetically desirable forms.
Perhaps the greatest possibilities for achieving a "revolutionary expansion of useful habitat" will be found in the enormous untapped potentials of the humid tropical forest itself. These forests are literally hydrocarbon "factories," and the innumerable streams and waterways which drain off the great rainfall surpluses from these life zones are among the greatest undeveloped sources of hydroelectric power known. Viewed integrally, the tropical forest environment offers at one and the same time raw materials for a diversity of industries, electric power, industrial water supplies, and even ready-made "highway" systems.
Only a decade or two ago, these forests were considered to be economically inaccessible except for immediate local usages, special trade products, and the production of a few extremely valuable cabinet woods so scarce in the stands that they could be extracted only by primitive hand methods, yielding little to local economies. Since that time, however, world consumption and demand for woody raw materials have increased markedly and promise to continue doing so, and the prospects for an integral and sustained industrial development of the heterogeneous forest growth have brightened remarkably. Newly devised extraction equipment and improved manufacturing processes now permit the economic exploitation of most tropical tree species heretofore considered worthless.
Indeed, the humid tropical forest environment is a hydrocarbon factory of enormous productivity, but unlike coal-beds or pools of petroleum it is not compacted, and is chemically and physically more heterogeneous. Its potentials are realizable only now that there is a body of science and technology capable of differentiating and utilizing its very complexity. Among its potentials are raw material inputs for the industrial production of lumber and agglomerated wood panels, paper and fibreboards, a wide variety of hydrocarbon compounds convertible to energy, and as chemical inputs for plastics, synthetic fibres and medicines, and a variety of protein foods as well. Undoubtedly, large-scale industrial development of these forests is a distinct possibility for the future, with industrial activity centred close to or within the forest areas themselves.
In forestry, then, rather than in agriculture, it would seem that something close to the full hydrocarbon productivity potential of these environments could be attained. Under undistrubed or virgin conditions, of course, the economic productivity of the forest is static, with natural death and decay balancing current growth increments at any time. These huge standing volumes, nevertheless, constitute an appreciable ready capital for the initiation of technically managed operations, and out of which the industrially most suitable tree species may be selected for managed regrowth. But recent studies indicate that given rational exploitation on a continuing basis, these forests will have volumetric growth rates several times higher than those of the temperate and cool temperate regions of the world, where the efficient modern forest industries are today concentrated. Especially high rates of growth have been recorded for the "secondary" forests which develop, spontaneously, upon lands abandoned from agriculture or after the logging of virgin stands. For many of the more valuable secondary forest species, average annual diameter increments of up to an inch, or more than one inch in "elite" genotypes, indicate that there would be an economical sawlog rotation of only 25 to 50 years with even simple management. Much shorter cropping cycles are in evidence for the bulkwood materials of smaller diameter required in the pulp and paper, chipboard and chemical wood industries. And this same research demonstrates that managed secondary forest growth, even under wet tropical conditions, is decidedly simpler in species composition than the virgin stands on the same sites.
Research in tropical silviculture has made noteworthy advances in recent years, and there is much in its findings to indicate a significant similarity between the technical aspects of forestry and agriculture. For instance, if regeneration and rapid sustained growth of tropical timber species are to be attained under management, it is believed essential that nature be followed closely in maintaining original forest soil structure and nutrient cycling. Refinement of the original primary vegetation body to favour simpler mixtures of the best indigenous species is preferred to the pure plantings of high-value cabinet woods on clear-felled areas. Again, because both agricultural crops and forest crops require the same soil conditions and the protection from vine and weed competition provided best by regulated tree shade, there is a definite possibility for the combination of these crops over the same terrain. Valuable timber crops or pulping woods can rejuvenate, by rotation cropping, soils rendered unproductive by short periods of open tillage; some tropical pasture grasses are known to thrive in symbiotic association with trees useful also for fruit or fodder production, and many of the best timber species can be utilized to provide cover for perennial crop species. Taken as a whole, evidence is beginning to accumulate suggesting that in the humid and wetter tropical life zones, agriculture and animal husbandry might be integrated with sustained forest production to mutual benefit.
IN A BANANA PLANTATION are monocultures good for people?
The ecological evidence points to a land-use system in which the structure of the natural vegetation is maintained or imitated on each site, with environmental gradients exerting a dominating influence over the areal patterns of land utilization. Maximum productivity might be achieved by associating a limited number of selected, well-adapted cultigens, fodder plants and timber trees, each with distinctive growth habits, microenvironmental needs and cropping cycles, on any given piece of ground or, alternatively, in segregated small plantings in ordered rotational systems. An efficient operational unit which included even a modest range of distinctive local site classes might include 10 or 20, or even more, species of plants, plus possible animal domesticates, with a dominant cover of forest timber trees providing protection for lesser food, fibre, fodder and special trade product species of trees, bushes, vines and herbaceous plants.
Clearly, the field care, and the handling and processing of the products in such a multiproduct land-use scheme, would call for the integrated development of a considerable variety of industrial processes. It would, in fact, involve the creation of a microcosm of an industrial complex specialized to the potential of the environment. None of the existing systems of exploiting the humid and wet tropical forest environments are, however, based on a conception of these environments as industrial regions, nor do they seem to contain the seeds of such a development. At first glance, the plantation system appears to offer possibilities. Plantations do cultivate plants indigenous to these life zones which generally are better suited to the environment than grains or pastures. Moreover, plantations are, in a sense, "factories" oriented to the production of "commodities." A plantation enterprise commonly supports a technical and managerial organization, and not infrequently a research and experimental programme as well, which tend to develop the productivity of the resources employed. However, as a model for a resource exploitation system geared to national social and economic expectations, the tropical plantation suffers major drawbacks.
In the first place, the orientation of the plantation is to raw commodity production for export to the high-income economies, it provides little or no basis for extension of the production chain in the tropical economy involving local processing of the product as an export commodity, or providing inputs for locally oriented industries. In the second, it characteristically practices monoculture, and commonly one or a few such cultures occupy very extensive areas. Moreover, monocultures are monotonous - socially, culturally and economically dull and stultifying, especially when the people are isolated in company towns. To live in a banana world, or a sugarcane world, is probably prejudicial to the development of the personality. It may be like existence in the textile town, or the coal town, but is usually even more isolated from the full diversity of human life. Lastly, because the tropical plantation system has generally been a monoculture oriented to foreign markets, it has been alien to the main stream of the socioeconomic life of the tropical countries themselves, neither contributing to it nor depending on it in major ways. And because it is alien it tends to be in conflict with the local society, and thus to view its own operations as risky, and to preserve its isolation.
But perhaps the most interesting aspect of the plantation system as it has evolved during the past century is that it has imitated the universal scheme of the modern, high-income economies. Following the precepts and examples of the industrial revolution, the plantation enterprise has not only practiced monoculture, but has conceived its survival and its future in terms of expanding its specialty.
Yet the very essence of the tropical environment is diversity, especially in the humid forest life zones. Thus, the precept of the plantation is in direct opposition to the tendencies of the humid tropical forest - simplification and monoculturalism opposed to incredible variety and complexity. The conception of the resources potential of these environments must, moreover, be primarily oriented to local (tropical) markets rather than to raw materials exports. And, at the present time, the domestic "capital and labour" of the tropical economies is neither acquainted with the processes nor is it capable of undertaking the sizable investments required to develop the potential experimentally. The conception of the opportunity is, in other words, blocked by an almost complete lack of knowledge and experience concerning these environments as potential industrial regions.
As a conjecture, and lacking the exploratory research suggested in our thesis it can only be a conjecture, it seems that these life zones might best be developed within the framework of autonomous regional "authorities" invested with the power to investigate, plan and administer their integral development on a long-term basis. Initially, it will be necessary to plan and construct such social overhead capital as electric power plants, communications networks and public services facilities, for these life zones are virtually empty of such capital at present. Again, the development of a high-productivity resources exploitation system will require both research and experiment in very novel directions if stable and enduring land-use practices, settlement and land utilization patterns and product-processing mechanisms are to be worked out effectively.
Within the structure of the regional development authority, of course, there would be wide latitude for more specific forms of both public and private enterprise, large and small, elaborated to encompass both cultivation and manufacturing operations. And once the scheme had been experimentally articulated, variations in pattern would probably emerge from imitation. While it is not inevitable that all such areas would have to be developed with public (international) capital, it seems likely that early models, at least, would have to be financed and, in part, staffed from international sources. However, the degree of interdependence of the parts of this process might prove to be more modest than they appear to us at this time.
The areas occupied by the humid and wetter tropical forest life zones are indeed large. In those countries already mapped under the Holdridge classification, they represent almost half of the total land area, and they constitute surely far greater areas in several of those which have not yet been mapped. It is likely that they represent a potential for development far greater than the areas of the countries which are at present occupied. If the heavy-rainfall upper slopes of the higher mountain ranges, where the hydroelectric power potential is greatest, are added to the total area, the resources are even greater. And as we have attempted to show, there is considerable urgency about investigation and decision with regard to all these areas because the combined effects of population pressure, short-term political expediency and related factors are rapidly creating attitudes and penetration patterns which will be hard to reverse. The men with the machetes are ahead of the road-builders trying, in the honest tradition of the pioneer, to carve a home out of the forest. We believe it all too likely that they are unwittingly destroying