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Sustainable Agriculture and the Environment in the HUMID TROPICS 2 Sustainable Land Use Options In response to a combination of socioeconomic, agronomic, and environmental concerns, many scientists and policymakers are encouraging the implementation of sustainable agricultural systems (Altieri, 1987; Christanty et al., 1986; Consultative Group on International Agricultural Research, 1989; International Rice Research Institute, 1988; Ruttan, 1991; Vosti et al., 1991). Definitions of sustainable agriculture vary widely. For the purposes of this report, sustainable agriculture includes a broad spectrum of food and fiber production systems suited to the varied environmental conditions in the humid tropics. These systems attempt to keep the productive capacity of natural resources in step with population growth and economic demands while protecting and, where necessary, restoring environmental quality. This chapter provides a basis for identifying the technical and policy changes needed to make land use in the humid tropics more sustainable (see Chapter 3 and Chapter 4). It discusses a variety of land use options that can be used to formulate plans for restoring abandoned and degraded lands and for preserving natural resources, including the primary forest. These land use options are defined and presented here under 12 descriptive categories ranging from highly managed intensive cultivation to forest reserves. These categories represent sets of activities commonly practiced in the humid tropics, but not necessarily found or applicable in all regions or to both upland and lowland areas. Although these categories do not include all land use
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Sustainable Agriculture and the Environment in the HUMID TROPICS FIGURE 2-1 Examples of land transformation in the humid tropics. activities in the humid tropics, they represent land uses with great potential for stabilizing forest buffer zone areas, reclaiming cleared lands, restoring degraded and abandoned lands, improving the productivity of small farms, and providing rural employment. Examples of sustainable and nonsustainable uses are shown in Figure 2-1. Uses that reduce or eliminate forest cover have a broad range of requirements for capital and technical inputs, such as fertilizers and pesticides. Where social and economic conditions encourage resource depletion and short-term economic gain, however, land uses shift toward shorter and shorter production and harvest cycles, often leading to complete loss of economic production potential and abandonment. This pattern can be avoided if conditions encourage
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Sustainable Agriculture and the Environment in the HUMID TROPICS long-term maintenance of production potential—a goal that requires investments in long-term production systems and the implementation of soil-conserving production practices. Transformation processes vary widely within a region, or even within a country. In Mexico, for example, the conversion of forests to cattle pastures is the leading cause of deforestation. It often involves several intermediary steps: the opening of roads to facilitate timber extraction, colonization of cleared lands by landless peasants, eventual abandonment of these lands or removal of small communities of farmers by eviction, and the ultimate consolidation of these “clean” areas by cattle ranchers (Denevan, 1982; Gómez-Pompa et al., Part Two, this volume). In Peninsular Malaysia, deforestation has been primarily a consequence of conversion to tree crop plantations during the past 100 years (Vincent and Hadi, Part Two, this volume). In the neighboring Malaysian states of Sarawak and Sabah, however, the recent intensification of commercial logging has been the leading cause of deforestation, altering and even eliminating traditional patterns of resource extraction and shifting cultivation by indigenous peoples (Rush, 1991). Analysis of the processes of change is the first step in finding the pathways toward more sustainable land uses. For example, traditional low-intensity shifting cultivation systems remain a viable option where population pressures are low. Agroforestry, agropastoral and silvopastoral systems, and other labor-intensive mixed cropping systems are better suited to lands that are more fragile or under greater population pressure. More capital-intensive systems such as cattle ranching, perennial crop operations, forest plantations, and upland agricultural crop systems, while often environmentally destructive in the past, can present important opportunities for land restoration and improved land management. To be viable, they require secure land tenure, long-term investment, market access, and appropriate technologies. No one system will simultaneously meet all the requirements for sustainability, fit the diverse socioeconomic and ecological conditions within the humid tropics, and alleviate the pressures that have brought about rising deforestation rates. The biological, social, and economic attributes of the land uses described in this chapter are summarized in Chapter 3 and technical and research needs are discussed. The order in which these land uses are presented corresponds broadly to the degree to which they change the composition and structure of primary forests. Figure 2-2 is a generalized depiction of changes to primary forests as they relate to agricultural land uses.
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Sustainable Agriculture and the Environment in the HUMID TROPICS FIGURE 2-2 Pathways to sustainable agriculture and forestry land use. Management of land resources for sustainability depends on social and political forces as well as technological and economic development at local and national levels. National policy plays a significant role, particularly when maintaining various forest types (pathway A). Market forces determine the use of resource-rich areas following clearing (pathway B). The more critical pathways follow the clearing of resource-poor areas with less fertile soils. In some cases, with appropriate market incentives, sustainable use may evolve with modest public support (pathway C). Where the land resource has become severely degraded, more aggressive public sector involvement, such as incentives and subsidies, may be required (pathway D).
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Sustainable Agriculture and the Environment in the HUMID TROPICS INTENSIVE CROPPING SYSTEMS Areas used for intensive (high-productivity) agriculture in the humid tropics generally are resource-rich lands that have adequate water supplies, naturally fertile soils, very low to modest slope, or other favorable environmental characteristics. These areas range from the flat lowland delta or river valley areas to gently rolling uplands, and include the broad continental, high rainfall plains of the Amazon and of Central Africa. They can support input-intensive management systems and yield multiple harvests of crops at high levels of productivity. Crops are usually planted in rapid sequence, using improved varieties. With adequate water and good growing conditions the crops are responsive to fertilizer inputs. However, crop yields are constrained during periods of high rainfall and by seasonal flooding in some river and delta areas. Pest management usually prevents economic loss but often entails heavy pesticide use that can have adverse environmental and health impacts. Intensive agriculture is agronomically feasible for most Oxisols and Ultisols of the humid tropics. This alternative may interest farmers near urban areas where favorable marketing infrastructure ensures that fertilizer-based continuous food crop production is viable. Large Amazonian cities import most of their food from other areas. Farmers would have a potential comparative advantage in growing food crops near these cities. In Peru and Brazil, respectively, sustained yields have been obtained with continuous cropping trials for 41 crops (17 years) in Yurimaguas Ultisols and 17 crops (8 years) in Manaus Oxisols (Alegre and Sanchez, 1991; Sanchez et al., 1983; Smyth and Cravo, 1991). The key to continuous production is effective crop rotations and the judicious application of lime and fertilizers. Intensive agricultural production in the humid tropics has historically concentrated on the highly fertile lowlands. These lowlands constitute only a small portion of land. For example, lowland areas comprise only 20 percent of the estimated 510 million ha of the Amazon located within the national territory of Brazil (Serrão and Homma, Part Two, this volume). They account for between 10 and 40 percent of the total land areas of Southeast Asian countries (Garrity, 1991). In some river bottom and delta areas, annual flooding and receding water cycles deposit enriching organic and inorganic sediments. However, these flooded areas represent an even smaller portion of the total land base. Soil characteristics coupled with water availability make these areas especially suitable for the intensive production of high-value food crops. Paddy rice production in Southeast Asia is one well-
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Sustainable Agriculture and the Environment in the HUMID TROPICS known example. Other intensive systems include terrace, mound, and drained-field systems of Africa, Asia, Central and South America, and the Pacific (Wilken, 1987a,b). These systems combine water control for drainage and irrigation through intricate systems of ditches, dikes, and shaping of the land. They provide harvests of high quality and quantity, and they are fairly predictable in their ability to provide consistent harvests from year to year. The Development of Intensive Agriculture Because of their high agricultural potential, resource-rich areas were the first to be developed, with early investment in roads, electricity, irrigation, and other infrastructural features. From the standpoint of national investment, these areas produced the greatest return per dollar. With few exceptions, most had been deforested and converted to high-productivity agriculture by the 1960s. Exceptions include malaria-infested portions of Nepal and Thailand, much of Mindanao in the Philippines, and large areas of inaccessible forestland in Brazil and Central Africa. These remaining areas may still be converted because of their value to agricultural production. Given social and economic pressures, the maintenance of forested areas can probably be justified only on the basis of preserving biodiversity. In most Asian countries, the few forested areas remaining on highly productive soils represent a small portion of total land area. Internationally supported research and development in the 1960s and 1970s focused on realizing the high-production potential of these resource-rich lands. International agencies perceived an increasingly critical need for food and recognized the potential for existing scientific understanding and research methods to contribute to meeting this need. The international agricultural research centers (IARCs), such as the International Rice Research Institute (IRRI) in the Philippines, Centro Internacional de Agricultura Tropical (CIAT, International Center for Tropical Agriculture) in Colombia, and the International Institute of Tropical Agriculture (IITA) in Nigeria, were purposely situated in high-productivity tropical environments. The crop varieties that were developed had the genetic potential to respond to physical and managerial inputs under favorable soil and water environments. The widespread application of these new agricultural technologies gave rise to the green revolution. The agencies' focus also influenced the selection of areas with high-development potential and the placement of research centers within them (Dahlberg, 1979). As a result of this concentrated investment in research and development, information and technology are readily available for high-
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Sustainable Agriculture and the Environment in the HUMID TROPICS productivity areas, both for individual crops and for high-intensity cropping systems (Chandler, 1979; DeDatta, 1981; International Irrigation Management Institute, 1987; Sanchez, 1976). Much of the information pertains to the major cereal, pulse, and other vegetable crops grown on a more intensive scale. By the mid-1970s, most of the available highly productive land in the humid tropics was devoted to cultivating input-responsive crop varieties, and increases in individual crop yields began to level out (especially for Asian rice production). Attention turned to increasing annual area yields through more effective farming systems. From this early work came a broad range of research literature on farming systems methodologies for intensive cropping systems (Bureau of Agricultural Research of the Philippines, 1990; Harwood, 1979; International Rice Research Institute, 1975; Sanchez et al., 1982; Sukmaana et al., 1989). In the 1980s several of these research efforts shifted to particular types of cropping systems, such as wheat and rice rotations in the northern portion of the humid tropic zone (Harrington, 1991). It has been only recently, as researchers turned their attention to the rolling uplands and steeply sloping areas in Asia and to the Intensification in Sustainable Agricultural Systems Intensification is essential to developing sustainable agricultural systems in the humid tropics and elsewhere, but it can have various meanings in different contexts. Intensification in sustainable agricultural systems generally refers to the fuller use of land, water, and biotic resources to enhance the agronomic performance of agroecosystems. While intensification may involve increased levels of capital, labor, and external inputs, the emphasis here is on the application of skills and knowledge in managing the biological cycles and interactions that determine crop productivity and other aspects of agroecosystem characteristics. This approach differs from that which has guided agricultural systems in the industrial countries in recent years. Over the past 5 decades, these systems have sought to maximize yields per hectare or per unit of labor through the development and dissemination of relatively few high-yielding crop varieties and through increased use of external inputs such as fuel, fertilizers, and pesticides. This model of agricultural development stresses intensification through progressively specialized operations and the substitution of capital and purchased inputs for labor. In general, it has entailed loss of diversity (in crop germplasm, cropping patterns, and agroecosystem biota) and high cash production costs.
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Sustainable Agriculture and the Environment in the HUMID TROPICS reclamation of degraded pastures in Latin America, that on-farm, integrated animal systems have been studied (Amir and Knipscheer, 1987; Serrão and Toledo, 1990). As farming system research became an important aspect of agricultural intensification efforts, researchers introduced socioeconomic considerations more systematically into their studies (Bonifacio, 1988; Hansen, 1981; Lovelace et al., 1988). Intensive farming systems were then increasingly studied with respect to their use of geophysical resources within different social and economic environments. Methodologies were developed to address more complex systems and their interactions in fragile and resource-limited environments, where changing land use patterns often have major social implications. Intensive cropping systems face critical challenges. Questions are being raised about the ability of these systems to respond to the food needs of expanding populations. For several decades, lowland crop production has benefitted from the availability of improved varieties and hybrids, better agricultural chemicals, and mechanized farm equipment. For example, two to three crops of lowland rice with growing seasons of three to four months can now be produced In meeting the concurrent goals of increased productivity and reduced environmental risk, intensification can occur in both temporal and spatial dimensions. Farmers can intensify the use of the resources available to them at different times by using more diverse rotations and optimal harvesting schedules. They can intensify the use of resources spatially by adopting techniques and growing crops that take fuller advantage of available sunlight, moisture, nutrient reserves, and biotic interactions, both aboveground (for example, through mixed cropping) and belowground (for example, through the use of legumes and deep-rooted tree crops). Optimum resource use in hilly areas of heterogeneous slope, soil type, and water resources requires a diversity of systems and system components. In both the spatial and temporal dimensions, intensification through diversification involves the selection of crops, livestock, inputs, and management practices that foster positive ecological relationships and biological processes within the agroecosystem as a whole. These choices vary according to local environmental conditions and socioeconomic needs and opportunities. Improved agroecosystem performance is often sought through mixed cropping systems, while all internal resources (and necessary external inputs) are carefully managed to improve productive efficiency.
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Sustainable Agriculture and the Environment in the HUMID TROPICS Rice terraces in the upper watershed area of the Solo River, Indonesia, are carefully tended to cultivate every available portion of land through the use of many different agronomic land use types, which are shown here in a single landscape. Population pressure on arable land is high in this area of Central Java. Credit: Food and Agriculture Organization of the United Nations.
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Sustainable Agriculture and the Environment in the HUMID TROPICS each year. However, the growth in yield rates for cereal crops in Asia is increasing more slowly than demand (Harrington, 1991). Fallow periods that formerly allowed for the accumulation of nutrients and the suppression of pests have essentially been removed from the crop rotation sequence, their role being assumed by applications of purchased chemical inputs. Furthermore, pressures from pests and diseases are increasing as the area devoted to the cultivation of new varieties increases in size (Fearnside, 1987a). In many countries, lowland areas that are relied on for producing staple and cash crops are in danger of becoming unfit for crop production as a result of improper management. The inappropriate use of high-productivity technologies is being implicated in various forms of natural resource degradation, including nutrient loading from fertilizers, water contamination from insecticides and herbicides, and waterlogging and salinization of land (Harrington, 1991). Loss of lowland cropland could seriously impair the capacity of countries in the humid tropics to meet future food demands. The pressure to meet the subsistence needs of populations is causing governments to convert additional lowland as well as upland areas. In Indonesia for example, as transmigration programs continue, previously unmodified wetland ecosystems are being considered for cultivation of irrigated, monoculture rice or for mixtures of coconut plantations with secondary crops, which are grown to meet local needs rather than for cash or market (Kartasubrata, Part Two, this volume). In some areas, the high risk of malaria, schistosomiasis, and other diseases remains a significant barrier to the use of lowland areas. At present, these health concerns are greatest in the humid tropics of Africa and Asia. Programs and Research Activities To the extent that productivity in lowland areas declines and forested upland areas are environmentally degraded for future food production, sustainability in the humid tropics is placed at risk. These concerns are becoming the focal points of the preservation programs and research efforts of regional and international agricultural research centers. Efforts are being made to preserve lowland areas that have unique qualities. The Chitwan National Forest in Nepal is one of the few lowland rain forests successfully protected from development pressure. It constitutes a rich source of biological diversity in undisturbed Asian lowland, high-productivity ecozones. Further development of the Chitwan area for agriculture has so far been rejected. Throughout the humid tropics, efforts are also being made to
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Sustainable Agriculture and the Environment in the HUMID TROPICS curtail soil erosion on intensively cultivated sloping lands. In the 1980s the Philippine Department of Agriculture initiated the Sloping Agricultural Land Technology Program, which proposed an intercropping system to produce permanent cereal crops with minimal or no fertilizer use. Between hedgerows of Leucaena leucocephala, a commonly grown fodder source for cattle, rows of woody perennial crops, such as coffee, were planted in contour strips alternating with several rows of food crops. Versions of this cropping system, using various plant species, provide farmers with a diverse income source and fertility-enhancing soil mulch. They can also reduce by as much as 90 percent the amount of soil lost under conventional cropping practices on open fields (Garrity, 1991). More generally, agriculture production programs and research agencies that have traditionally focused on intensive cropping systems are reevaluating and redirecting their efforts. The IARCs of the Consultative Group on International Agricultural Research (CGIAR) now focus not only on increasing yields of intensive agriculture in favorable environments, such as irrigated lowlands, but also on developing programs to increase productivity and sustainability of cropping and livestock systems in less fertile, marginal environments, like sloping and hilly uplands (Consultative Group on International Agricultural Research, 1990). The CGIAR has not defined the limits of the IARCs' research activities on issues of sustainability. Rather, those decisions are made by each center. For example, the CGIAR has not advocated the rehabilitation of degraded lands as a central priority of its system. However, most centers acknowledge that an increased percentage of arable land in their mandate areas has been degraded or removed from production and some have begun initiatives to address this issue (Consultative Group on International Agricultural Research, 1990). Some centers, such as the IRRI and Centro Internacional de Mejoramiento de Maíz y Trigo (International Maize and Wheat Improvement Center), have emphasized sustainable agriculture through reallocation of internal resources, while others, such as the CIAT, IITA, and International Livestock Center for Africa, have developed explicit goal and mission statements. The International Center for Research in Agroforestry focuses its resource management agenda on mitigating tropical deforestation, land depletion, and rural poverty through improved agroforestry systems. In addition, several centers have increased the role of social science research to address the human and socioeconomic constraints on improved natural resource management practices (Consultative Group on International Agricultural Research, 1990). Perhaps the most important aspect of this in-
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Sustainable Agriculture and the Environment in the HUMID TROPICS can remain sequestered. Long-term nutrient loss through removal of biomass may serve as the ultimate limitation on the sustainability of managed forests, but these losses can be minimized through careful logging operations. A degree of risk is inevitably incurred in the opening of access roads. Even where selective timber harvesting is feasible and well regulated, postharvest management may not be, which sets the stage for more intense forms of forest conversion. The socioeconomic attributes of natural forest management are also variable. Compared with plantation and agroforestry systems, natural forest management systems are less labor intensive, require fewer capital inputs, and yield forest products at relatively low levels. At the same time, they create more employment opportunities per investment unit than do cattle ranches (Goodland et al., 1990). If planned and undertaken with care, they can provide employment and income for forest dwellers and protect cultural integrity. For this reason, local participation is especially critical. Several reviews of sustainable forestry methods and natural forest management systems have been published in recent years (Moad, 1989; Office of Technology Assessment, 1984; Schmidt, 1987; Wadsworth, 1987a,b; Wyatt-Smith, 1987). Natural forest management systems are usually grouped into three broad categories: uniform shelterwood systems, strip shelterwood systems, and selection systems. UNIFORM SHELTERWOOD SYSTEMS Uniform shelterwood systems are designed to produce even-aged stands rich in timber species (Office of Technology Assessment, 1984). Under these systems, all marketable trees within a given area are harvested during the initial phase of management. Subsequent silvicultural operations further open the forest canopy, allowing seedlings and saplings of commercially valuable species to thrive. Logging is monocyclic, taking place once at the end of each rotation. The foremost example of uniform shelterwood systems is the Malayan Uniform System (MUS), first developed in the lowland dipterocarp forests of the Malay Peninsula after World War II (Buschbacher, 1990) and commonly practiced from the early 1950s to the 1970s. After the initial harvest, forests were managed according to a 60-year rotation cycle of regeneration, periodic low-intensity silvicultural interventions (for example, removal of vines and elimination of noncommercial species, defective stems, and competing stems), and reharvesting. The aim of this system was to produce a relatively uniform growth of young Shorea spp. It offered acceptable rates of regeneration and appeared to be biologically sustainable. However,
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Sustainable Agriculture and the Environment in the HUMID TROPICS the widespread conversion of the lowland forests to oil palm and rubber plantations and other more intensive agricultural systems almost completely removed these forests, obviating the need to manage them. Hence, the MUS was not in practice long enough for second rotation cuts to be made. Today the MUS is practiced in a modified form, with an emphasis on selective management systems. The Malaysian experience illustrates difficulties in the transferability of the MUS to other regions. The uniform system, as developed in Malaysia, was most applicable in fertile, lowland forests with high seedling densities. Attempts to transfer the MUS to nearby hill forests were generally unsuccessful due to less predictable seedling production, greater topographic effects on tree species composition and abundance, and greater damage to regenerating seedlings during logging operations (Gradwohl and Greenberg, 1988; Lee, 1982). As a result, uniform systems appear silviculturally appropriate only when an adequate stock of seedlings of desirable species exists prior to harvesting and a large enough proportion of commercially valuable species exists in the original forest canopy to justify complete canopy removal (Buschbacher, 1990). The Tropical Shelterwood System (TSS), analogous to the Malayan system, was tested and introduced in several African countries in the 1940s, but results were less promising. Seedlings in the African forests were less abundant and distributed less uniformly, requiring more extensive and more frequent interventions to open the forest canopy. This led to greater infestation by weed trees and vines, higher labor costs, and ultimately poor regeneration of the desired species (Asabere, 1987). Plantation and other more intensive land uses, as well as intensified logging, precluded further systematic development of uniform shelterwood systems suitable to Africa. STRIP SHELTERWOOD SYSTEMS Strip shelterwood (or strip clearcut) systems are still largely in the experimental phase, but they show high potential for small-scale, sustainable management of tropical forests. In these systems, narrow strips of forest are cleared on a rotating basis, and regeneration occurs by seed dispersal from adjacent undisturbed forest and by stump sprouting. Careful harvesting plans and operations are designed to simulate the natural processes of tropical forest gap formation and regeneration (Hartshorn, 1989). The rotation schedule allows equal areas of forest to be harvested annually, the size of the cuts determined by the total area of managed forest and the period required for regeneration (Moad, 1989).
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Sustainable Agriculture and the Environment in the HUMID TROPICS Extraction operations are carefully planned to minimize environmental damage. Local topographic and ecological conditions determine the size, location, and orientation of strips. Access roads are designed to minimize erosion and compaction and to protect areas of adjacent undisturbed forest, which is critical for regeneration. The use of heavy machinery is minimized and draft animals are often used to remove sawn logs. Logs are cleaned on site, and the slash (the bark, leaves, and branches of the harvested trees) is left to decompose rather than be burned or removed, allowing more retention of nutrients. The most extensive test of a strip shelterwood system has taken place in the Palcazú valley of eastern Peru. Demonstration strips were first harvested in 1985. Initial postharvest inventories indicate abundant regeneration, with twice the tree species diversity of the preharvest strip (Hartshorn, 1990). This project has also placed high priority on social and economic considerations in its design. Project planners and indigenous communities work closely to coordinate harvesting, processing, and marketing operations; to distribute project benefits; and to ensure sustainable management of the communal forestlands (Buschbacher, 1990; Hartshorn, 1990). The success of strip shelterwood systems depends on the ability of early successional stage trees to establish themselves rapidly in forest gaps, grow quickly, and produce marketable wood (Moad, 1989). Consequently, strip systems may be less applicable in Asian forests, where most timber trees, including the dipterocarps, are unlikely to regenerate rapidly on cleared sites. The potential for use is higher in the humid tropics of West Africa and Latin America, where suitable tree species and genera are more abundant. Further research may establish how variables, including the regenerative biology of tree species, postharvest silvicultural treatments, and the size, location, and frequency of cuts, can be altered to suit local conditions. For example, studies conducted at the Bajo Calima Concession in Colombia suggest the need to adjust the size and rotation schedule of cuts as well as the extent and placement of forest reserves to allow nonpioneer tree species, many of which have large seeds and depend on dispersal by birds and mammals, to regenerate (Faber-Langendoen, 1990). SELECTION SYSTEMS Most forests managed for timber in the humid tropics employ selection (or polycyclic felling) systems. In selection systems, trees are removed on a limited basis from mixed-age forests in a series of fellings, rather than in one large harvest (Wyatt-Smith, 1987). Less
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Sustainable Agriculture and the Environment in the HUMID TROPICS timber is extracted from the forest during each harvest, but harvesting occurs more frequently than in monocyclic systems. Two or more cuts, generally on a cycle of 25 to 35 years, take place in the course of a single rotation. Selection systems were developed in response to site limitations, low regeneration rates, high labor costs, and other difficulties associated with even-aged forest management (Buschbacher, 1990). Variations include the Modified Selection System, employed in Ghana in the 1950s; Malaysia's Selective Management System (which began to replace the MUS in the early 1970s); and the Selective Logging System in Indonesia and the Philippines. Other polycyclic systems have been implemented or tested in Australia, Cameroon, India, Mexico, Myanmar, Nigeria, the Philippines, Trinidad, Uganda, and other humid and subhumid tropical countries (World Bank, 1991). Relatively little attention has been given to research and development of polycyclic systems appropriate for the Amazon Basin (Boxman et al., 1985; Rankin, 1985). The Celos Management System, recently developed on an experimental basis in Suriname, has yielded favorable early results in terms of minimizing ecological impacts and providing relatively high economic returns (Anderson, 1990; de Graaf and Poels, 1990). Selection systems rely on the advanced regeneration of young, pole-sized trees to produce the subsequent timber crop (in contrast to shelterwood systems, which rely on seedling establishment). In some selection systems, advanced regeneration is promoted through improvement (or liberation) thinning (Moad, 1989). Improvement thinning usually involves the poisoning or girdling of less economically valuable trees and vines that compete with the most promising understory trees. Thinning removes 15 to 30 percent of the total number of stems and can reduce the time required to second harvest from 45 to 30 years, or as much as 33 percent (Buschbacher, 1990; Moad, 1989). Thinning has been employed most extensively in Southeast Asian forests, but it has also been tried in Côte d'Ivoire, Gabon, Ghana, Nigeria, Suriname, and Zaire. In most of these cases, however, the practice has been curtailed due to inadequate funding and a shortage of trained personnel (Moad, 1989). In practice, successful selection systems still face significant obstacles. Tree regeneration and growth rates are often inadequate to meet projected rotation goals, and economic pressures force forest managers to shorten cutting cycles. High-grading (the unregulated extraction of only the most valuable trees) is prevalent throughout the tropics, but less so in the Southeast Asian dipterocarp forests. Poor planning of felling and transport operations results in excessive
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Sustainable Agriculture and the Environment in the HUMID TROPICS reduction in forest cover and damage to soil and water resources. Especially critical is damage to seedlings and pole-sized trees, on which successful forest regeneration depends. Improvement thinning and other silvicultural treatments are hindered by a lack of economic incentives and trained personnel and by ineffective government control and enforcement of forestry operations (Wyatt-Smith, 1987). Constraints on Sustainable Forestry It is not yet possible to find a natural tropical forest that has been successfully managed for the sustainable production of timber, because no management system has yet been maintained through multiple rotations (Poore et al., 1990). Some critics dismiss sustainable forestry in the humid tropics as a “myth” on the grounds that it remains unproved, provides low yields and slow economic returns, and is liable to be superseded by more disruptive or lucrative land use practices (see Spears ). Others respond that natural forest management has been proved to be feasible on technical grounds, but it has generally failed for social and economic reasons (Anderson, 1990; Buschbacher, 1990). Forestry in the humid tropics may be sustainable, but it will require changes in logging practices, in the economics of the forestry sector, and in the land use policy environment (Goodland et al., 1990; Poore et al., 1990). Past experience suggests a combination of silvicultural and socioeconomic factors behind the lack of successful implementation. On most sites, the key silvicultural constraint on sustained timber production is inadequate regeneration of seedlings, saplings, and polesized trees (Wyatt-Smith, 1987), usually resulting from excessive damage during logging operations. In other cases, biological constraints, such as weed and vine infestation, lack of seed dispersers, and lack of trees with appropriate regeneration capabilities, are more important. Socioeconomic factors include insufficient tenure provisions; lack of local involvement in management decisions and project benefits; ineffective regulation, supervision, and monitoring of forestry activities and methods; and the inability of forest managers to control land use over the long term (Buschbacher, 1990; Moad, 1989). The economic viability of sustainable forestry systems is hindered by a lack of adequate information on the resource base and potential markets, by international market forces that focus on a few tree species that are difficult or expensive to regenerate, by incentive policies that favor short-term timber exploitation, and by the undervaluation of timber products, nontimber products, and other forest services (World
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Sustainable Agriculture and the Environment in the HUMID TROPICS Bank, 1991). In many cases, these are the same forces that hinder implementation of other sustainable land use systems described in this chapter. MODIFIED FORESTS As a land use option, modified forests can only be considered viable where the human population remains low and the extractive activities of forest dwellers is limited. By studying these ecosystems and societies, researchers gain insights into the processes of landscape change in the humid tropics and human influences on those processes. Indigenous people often modify the structure and composition of primary forests. Technically, a primary forest is one without human influence (Ford-Robertson, 1971). Even in the least disturbed forests, however, human influence is evidenced by the presence of stumps, charcoal in the soil profile, artifacts, or exotic species. Indigenous people also modify forests by altering the frequency of native species or the size of wildlife populations in ways that are difficult to detect. Only through detailed study and long-term analysis can the effects of people be detected. For example, Maya cultures apparently managed forests for food, fiber, medicines, wood, resins, and fuel, thereby modifying the species composition of large areas of Central American landscapes long believed to be primary forest (Barrera et al., 1977; Gómez-Pompa et al., 1987; Rico-Gray et al., 1985). The human-modified forest is almost impossible to segregate from pristine primary forest. It is clear that even limited human presence can change the structure of forest ecosystems. It is doubtful, however, that forest processes, such as rates of primary productivity or the velocity and efficiency of nutrient cycles, are significantly altered. The key point is that wherever humans interact with natural forest ecosystems, forest modification is unavoidable. It is equally clear that there are thresholds beyond which modification is incompatible with the conservation of forest resources. In practice modified forests are likely to be most appropriate where indigenous peoples and local communities retain secure tenure over large areas of forestland and where strong national policies support and protect these cultural groups and their ways of life. In recognizing modified forests for what they are—ecosystems that have been managed in subtle but sophisticated ways to provide their human inhabitants with sustainable livelihoods—their value as primary forests is not diminished. Rather, they acquire even greater sociocul-
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Sustainable Agriculture and the Environment in the HUMID TROPICS tural value as models and examples of successful human interaction with tropical moist forests. FOREST RESERVES Although a complete examination of the role and value of forest reserves is beyond the scope of this report, they need to be considered in devising comprehensive land use strategies in the humid tropics. The lack of secure protection for primary forests and wildlands diminishes the potential for sustainable agriculture, land use, and development throughout the tropics. These lands provide the biotic foundation on which human activity can be sustained and enhanced, and they protect the biological legacy of the humid tropics along with its many values. Protected forests now constitute a small fraction of the tropical landscape—about 3 percent in Africa, 2 percent in Asia, and 1 percent in South and Central America (Nations, 1990). The protection mechanisms are as diverse as the number of countries and organizations that strive to protect forest ecosystems. They include biosphere reserves, wildlife preserves, national parks, national forests, refuges, sanctuaries, extractive reserves, privately owned lands, and land trusts. These efforts, however, require stronger political and financial support, especially for law enforcement, local community involvement, land acquisition, and effective reserve management. Without this support, the contribution these lands can make toward sustainable land use more generally is undermined (MacKinnon et al., 1986). At this point, biologists cannot accurately determine the amount of land to preserve for optimal protection of biological diversity. No single standard exists for determining the amount or location of lands that should be set aside. However, long-term ecological studies are under way to understand the dynamics of species loss in tropical forests so that reserves of adequate size and configuration may be established (McNeely et al., 1990; Myers, 1988; Reid and Miller, 1989). Many social and ecological factors endanger forest reserves. Conservation biologists are concerned with the sizes and shapes of reserves, global climate change, and the fragmentation of forest habitats by roads and other developments as some of the most urgent ecological factors that determine the integrity of reserves (Diamond, 1975; Harris, 1984; Peters and Lovejoy, 1992). Research on the effects of these and other factors on reserve function and effectiveness is a high priority (Ecological Society of America, 1991; Soulé and Kohm, 1989). Social forces that affect forest reserves revolve around the growing human pressures on reserve boundaries and resources, and
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Sustainable Agriculture and the Environment in the HUMID TROPICS This border of a 10-ha (25-acre) reserve near Manaus, Brazil, illustrates the edge effect. Trees and other vegetation that form a barrier between natural and disturbed vegetation often experience a reduced vigor and are challenged or replaced by species that are well adapted to colonizing newly disturbed or cleared areas. In this case, the reserve is separated by only a few meters from agricultural fields of cassava (Manihot esculenta). The reserve is part of a project to determine the minimum critical size of ecosystems. Credit: Douglas Daly. the difficulties associated with granting protection status without providing proper institutional, educational, and on-site support. Much interest has focused on extractive reserves as a solution to deforestation in tropical areas. A discussion of its potential as well as environmental, social, economic, and research issues follows. Defining a Role for Extractive Reserves Extractive reserves can be among sustainable land uses in the humid tropics. They are forest areas where use rights are granted by governments to residents whose livelihoods customarily depend on extracting rubber latex, nuts, fruits, medicinal plants, oil seeds, and other forest products (Browder, 1990). These rights enable people to use and profit from land resources not legally belonging to them. Extractive reserves protect traditional agricultural practices and the forestlands on which they depend.
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Sustainable Agriculture and the Environment in the HUMID TROPICS The development and long-term viability of extractive reserves face significant social, economic, and ecological obstacles. Under some circumstances, extractive reserves can contribute to sustainability in the humid tropics as components within more comprehensive land use strategies. Expectations, however, need to be tempered by a better understanding of their real potential and inherent limits. The concept of extractive reserves originated in the mid-1980s as rubber tappers gained support in the state of Acre in western Brazil (Allegretti, 1990). Since then, the national government has designated 14 reserves, covering 3 million ha, within the Brazilian Amazon. The National Council of Rubber Tappers is trying to obtain reserve status for 100 million ha, or about one-fourth, of the Brazilian Amazon (Ryan, 1992). Other efforts to establish extractive reserves are occurring both within and beyond the Amazon Basin. In Guatemala, for example, half of the 1.5 million ha in the Maya Biosphere Reserve has been allocated for traditional extraction of chicle, a gum derived from the sapodilla tree (Achras zapota), and the leaves of the xate (Chamaedorea spp.), which are used as ornamentals (Ryan, 1992). Interest has been further stimulated by studies indicating the economic value and potential of nontimber forest products (Balick and Mendelsohn, 1992; Peters et al., 1989a,b). In weighing extractive reserves as a land use option, it is important to recognize that the primary goal in establishing reserves in the Brazilian Amazon has not been to protect biological diversity or tropical forests, but to secure reforms in land tenure and land use (Browder, 1990; Sieberling, 1991). Because opportunities for extraction are most advantageous where marketable species—especially tree species —are found in relatively high concentrations, extractive reserves are less likely to be located in the most species rich areas of the humid tropics (Browder, 1992; Peters et al., 1989a). In effect, reserves often will serve to maintain and protect biological diversity, forest cover, and the environmental services that intact tropical moist forests provide, but these functions are incidental to their social and economic benefits, and thus subject to changing socioeconomic conditions. Commercial extraction is less intrusive than other forms of forest conversion, but it does alter forest ecosystems. In general, little research has focused on the long-term impacts of commercial extraction on the function and composition of tropical moist forests or on the ability of forests to sustain harvests of fruits, nuts, or other products (Ehrenfeld, 1992). Impacts can vary depending on the type of product extracted, the scale and methods of extraction, and the nature of the forest in which extraction occurs. Commercial extraction
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Sustainable Agriculture and the Environment in the HUMID TROPICS can result in degradation if large quantities of biomass (or small quantities of key ecosystem components) are removed, or if harvesting techniques cause excessive damage. In addition, researchers have noted the tendency to exploit extracted forest products to the point of depletion, for example, in the case of wild fruits and palm hearts in Peru and rattan in parts of Southeast Asia (Bodmer at el., 1990; DeBeer and McDermott, 1989; Vasquez and Gentry, 1989). At the species level, changes in population levels may affect the reproductive biology of extracted species and the status of associated plant and animal populations. Enrichment planting—the enhancement of populations of economically advantageous species by artificial means—may reduce species diversity within the forest as a whole. At the genetic level, market forces may result in the selection of specific individuals or traits, altering genetic variability within the species. Extractive reserves, depending on the scope and effectiveness of their management strategies, may amplify or minimize all of these effects. The economic viability of extractive reserves is compromised, in both the long and short term, by a variety of factors. The economic base of most extractive reserves will be narrow. Existing reserves in the Brazilian Amazon depend primarily on production of rubber and Brazil nuts, and thus depend on volatile market conditions and subsidy policies (Browder, 1990; Ryan, 1991). Other factors complicate the sustainability of trade in extracted products. In most cases, viable commercial markets must be developed. The perishability of many tropical products may limit the ability to create or supply distant markets. Many products will not be conducive to standardized production because of highly varied harvest, transport, packaging, and storage needs. Where markets for products do exist, extraction is vulnerable to increased competition from domesticated and synthetic sources. Extraction from wild sources is labor intensive, thus inviting artificial cropping and plantation systems (Browder, 1990). For example, Brazil nuts are being produced on plantations in Brazil. Finally, the capacity of extractive activities to improve standards of living may be limited as profits are absorbed by intermediaries before they reach harvesters (Browder, 1992; Ryan, 1992). These biological and economic constraints should not obscure the social benefits that extractive reserves can provide (Sieberling, 1991). Most extractors in the humid tropics are poor and must contend with limited economic opportunities, threatened or inequitable land and resource rights, and unresponsive political structures. Most of them also engage in subsistence agriculture and depend on extractive activities for primary or supplementary income as well as food, fiber,
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Sustainable Agriculture and the Environment in the HUMID TROPICS and medicines. As the Brazilian experience has shown, the process of organizing, advocating, and managing extractive reserves can stimulate local participation and affect other areas of need, including health and extension services, housing, education, tenure reform, and marketing and infrastructure development. As the extractive reserve concept develops, it will provide valuable lessons for rural development efforts. Extractive reserves should not be viewed as the solution to either deforestation or sustainable development in the humid tropics. They can, in the immediate future, stimulate needed land reforms, supply income and employment for limited local populations, protect some forestlands from more intensive forms of conversion, and provide important models of sustainable forest use. They cannot, however, meet the long-term needs of the growing numbers of shifting cultivators arriving at the forest frontier, provide full income or economic independence for the rural poor, preserve areas of the humid tropics that are especially diverse, or restore lands that are already in advanced stages of degradation. They may provide an important complement to other land uses, but they are not a substitute for forest reserves or for better managed agroecosystems, restoration areas, or more comprehensive and equitable land use strategies. The record in creating and managing extractive reserves suggests several key guidelines for their further development. First, the limits and opportunities of extractive reserves should be clearly recognized. Designation should be initiated and supported by local people and communities, and the intended beneficiaries should be involved at all development stages. Government commitment—financial, political, and technical—is needed during the initial stages of reserve establishment and over time. As demographic, economic, and ecological conditions change, reserve management goals and methods need to remain flexible. Economic strategies should initially stress opportunities to develop known products, but they should also emphasize the need to diversify with time, to secure local benefits through value-adding processes, to work with all local resource users, and to reinvest in reserve operations (Clay, 1992). Local forest management skills need to be strengthened, with particular emphasis on improved extension services and increased interaction between biologists and extractors. Research should seek to clarify the social, economic, and ecological factors that influence the long-term viability of extractive reserves and activities. Specific biological research is needed on commercially important species, their reproductive biology and ecological functions, and the impacts of extraction on forest composition, structure, and function (Ehrenfeld, 1992).
Representative terms from entire chapter: