Sustainable Agriculture and the Environment in the Humid Tropics (1993) / Chapter Skim
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2 Sustainable Land Use Options
2 Sustainable Land Use Options
Pages 66-137
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From page 66... ...
This chapter provides a basis for identifying the technical and policy changes needed to make land use in the humid tropics more sustainable (see Chapters 3 and 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.
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From page 67... ...
. I Low-lntensity | Forest Exaction —1 _ Commerclal Logging Cable Pastures Perennial Tree Crops l l Mix Or ~ C and systems I T - Neal IrW,s Intensive Cropping l Systems _ ~ 67 I Nonsustainable , Under Cun~nt ~ / Shifting Cultivation Abandoned Pastures and Grasslands r FIGURE 2-1 Examples of land transformation in the humid tropics.
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From page 68... ...
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.
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From page 69... ...
| Naturally Regenerating | Forests l , ~ ~ ~ L ABANDONED OR DEGRADED LAND | High-Resource | B 1 I Areas I Active Restoration and Reforestation with Higher Capital Investments _ | Forest | ~; Reserves | 1 LO | Secondary Forests Low-lntensity Shifting Cultivation _ Agrofor~y Systems Active Restoration and Reforestation _( Ag~s~ Syslems | with Lower Capital InveshT ents ~ Meted Tree Systems Perennial | · Tree Crop | Plantations | Plantation Forestry Intensive · Cropping Systems 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.
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From page 70... ...
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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From page 71... ...
The international agricultural research centers (IARCs) , such as the International Rice Research Institute (IRRI)
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From page 72... ...
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~.
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From page 73... ...
and belowground (for example, through the use of legumes and deeprooted tree crops)
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From page 74... ...
Population pressure on arable land is high in this area of Central lava. Credit: Food and Agriculture Organization of the United Nations.
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From page 75... ...
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.
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From page 76... ...
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 fertilityenhancing soil mulch.
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From page 77... ...
Conditions that limit crop yields, such as soil fertility losses, weeds, or pest outbreaks, are overcome during the fallow time, and after a certain number of years the area is ready to be cleared again for cropping (Sanchez, 1976~. While most shifting cultivation consists of various slash-and-burn methods, areas with high amounts of rainfall can use a slash-andmulch system, which has less adverse effects on the environment.
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From page 78... ...
protecting the soil surface and increasing the amount of organic matter in the soil (Thurston, 1991~. As long as the human population density is not too high and fallow periods are long enough to restore productivity, shifting cultivation can be ecologically sound and can efficiently respond to a variety of human needs (Christanty, 1986~.
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From page 79... ...
Stabilization Guidelines The length of the fallow period is the most critical factor for the long-term sustainability of shifting cultivation systems (Christanty, 1986~. Shifting cultivation becomes more intensified with the combined pressures of rapidly increasing human populations, demands for income above subsistence levels, and the growing demand for cash crops.
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From page 80... ...
Research institutions as well as policymakers should realize that stabilized shifting cultivation systems are most appropriate in more remote and economically limited areas. With proper incentives, and research to develop alternatives, stabilized and diverse shifting cultivation systems could become effective buffers against further encroachment into tropical forests (Sanchez et al., 1990~.
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From page 81... ...
These forest patches, along with other uncut areas where the mature vegetation is protected or where useful tree species have been encouraged or transplanted, are considered here to be forest gardens, managed forests, or modified forests. The conservation of a strip of forest along the trails and surrounding the milpas is also important.
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From page 82... ...
Feed is typically cut and carried from croplands. Livestock animals are also of some importance on tree crop farms where they either graze freely in pastures, are tethered to clean specific areas, or are fed with tree cuttings.
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From page 83... ...
The variety of agropastoral systems and the complexity of mixtures and interactions have discouraged systematic research and development. As farm diversification, soil and pasture management, and crop nutrient management become increasingly important to sustainable land use, these closely integrated systems should receive greater attention.
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From page 84... ...
. If the agropastoral farming systems employed by small-scale farmers are to be improved and promoted within the humid tropics, institutional and policy changes are required.
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From page 85... ...
CATTLE RANCHING The conversion of tropical rain forests to open pastureland for cattle ranching is governed by socioeconomic and political pressures existing in each country. This section discusses the potentials and limitations of pasture-based cattle raising, with emphasis on regions where cattle ranching has greater importance.
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From page 86... ...
In some countries vast expanses of originally forested land are increasingly being converted to low-forage-value Savannah grasslands of Imperata cylindrica due to intensive shifting agriculture on acid and infertile soils (Garrity et al., Part Two, this volume)
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From page 87... ...
Cattle Pastureland in Latin America The socioeconomic and ecological importance of cattle raising in Latin America is based on several factors, some of which are the following: · Biological and soil-related constraints on agriculture; · Low human population density; · Lack of infrastructure for transporting agricultural inputs and consumable products; · Tax incentives and lines of credit for cattle ranching in some countries; · Priority ranking and protection by Latin American governments; · Cultural traditions that give cattle ranchers respect and status regardless of production and profit; and · High levels of regional and international demands for meat. Another important factor is the ability of cattle to transport themselves to markets by walking long distances, regardless of road and
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From page 88... ...
In the Brazilian Amazon, Central America, and Mexico, cattle raising is a leading cause of forest conversion. In Central America, between 1950 and 1975, the pasture areas developed from deforested primary forest doubled; so did the cattle population.
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From page 89... ...
During the past 25 years, particularly in Latin America, commonly used grasses that demand more nutrients have been gradually replaced by less demanding species. For example, Brachiaria decumbens can grow satisfactorily despite low soil fertility and has been rapidly adopted.
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From page 90... ...
This situation is more typical of Latin America than elsewhere, especially in the Brazilian Amazon, where in the past two decades between 5 million and 10 million ha of pasturelands have reached advanced stages of degradation (Serrao and Homma, Part Two, this volume)
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From page 91... ...
The integration of annual crops with pastures that are established using residual crop fertilization can sometimes pay for upgrading the soil environment and further improve the soil's physical and chemical conditions through effective nitrogen fixation and nutrient recycling. Multipurpose trees can pump nutrients to the upper-soil layers, fix nitrogen, and provide supplemental animal feed, shade, and income.
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From page 92... ...
It encompasses a variety of land use practices and systems, some of which are presented individually in this chapter. This section presents a general overview of the principles of agroforestry and their implications for maintaining or developing sustainable agriculture and forestry practices.
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From page 93... ...
Based on their structure and function, agroforestry systems can be classified into the following three categories: · Agrisilviculture is the use of crops and trees, including shrubs or vines. It includes shifting cultivation, forest gardens, multipurpose trees and shrubs on farmland, alley cropping, and windbreaks as well as integrated multistory mixtures of plantation crops.
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From page 94... ...
In traditional shifting cultivation, trees and wood species are naturally regenerated over a period of 5 to 40 years and rotated with annual crops that are cultivated from 1 to 3 years. Improved tree species can be grown in place of native vegetation to achieve better soil conditions.
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From page 95... ...
The viability and sustainability of these systems can be attributed to some combination of the following factors: · A reduced fallow period and a greater ability to cultivate on a long-term basis, thereby eliminating the need to move to new land; · Reduced use of chemical fertilizers and other fossil-fuel-based inputs due to enhancement of soil organic matter and improvement in soil fertility; · improved soil structure and physical properties (for example, better sizes of pores and channels in the soil that allow better water penetration and drainage) ; · Decreased risks of soil degradation from accelerated erosion and other degenerative processes; · Increased production and a rise in economic status from subsistence to partially commercialized farm; and · Decreased need for clearing new land.
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From page 96... ...
Some improved species have several advantages in an agroforestry system, including their ability to fix nitrogen, grow fast, tolerate soil acidity, and withstand regular coppicing. Commonly recommended tree species are listed in Table 2-1.
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From page 97... ...
Alley cropping is a common example of a spatial arrangement. Food crops are grown in alleys formed by contour hedgerows of trees or shrubs (Kang et al., 1981~.
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From page 98... ...
However, the beneficial effects of these systems depend on many factors, such as the tree species, area of land allocated to trees, hedgerow management, crop management, soil type, and prevalent climate. In areas with nonacid soils, satisfactory yields of cereals can be attained with the added benefit of erosion control (Kang et al., 1984; Lal, 1989~.
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From page 99... ...
Zeucocephala hedgerows must also be considered in evaluating the economic impact of an alley cropping system. Data on soil properties indicate that intensive cultivation resulted in decreases in soil organic matter content, total nitrogen, pH, and exchangeable calcium, magnesium, and potassium in all systems including alley cropping and control (Lal, 1989~.
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From page 100... ...
~ ~ . VJ MIXED TREE SYSTEMS Mixed tree systems, also known as forest or home gardens and mixed tree orchards, constitute a common but understudied form of agriculture.
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From page 101... ...
for livestock production combined with annual and perennial crops (Altieri and Merrick, 1987; Fernandes et al., 1983; Russell, 1968~. Mixed tree systems can also be found in the fallow fields of shifting cultivators, where useful tree species are spared or planted in the cleared agricultural plot and the subsequent forest regeneration is managed to encourage forest patches that provide desired products (Caballero, 1988; Soemarwoto and Soemarwoto, 1984~.
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From page 102... ...
Past and Present Forest Management Limited studies have begun to reveal the complexity of crop and tree interactions. For the most part, these studies involve time-tested selections and local experimentation with tree species.
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From page 103... ...
(G6mezPompa, 1987a,b; Harlan, 1975; Hynes and Chase, 1982; Kunstadter, 1978; Posey, 1990; Roosevelt, 1990; Turner and Miksicek, 1984~. Various types of mixed tree gardens coupled with other agricultural systems, such as shifting cultivation, were able to maintain high-density populations (Lentz, 1991~.
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From page 104... ...
More than 200 fruit tree species are found in the humid tropics today. Many of the tree fruits of Southeast Asia evolved from wiled rain forest species and were gathered for thousands of years prior to the advent of agriculture (Franker and Soule, 1981~.
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From page 105... ...
By spreading out cultural and management requirements over the year, these systems can also reduce peak workloads and ensure a more stable subsistence and cash economy. The ecological advantages of mixed tree systems have-allowed their regeneration over centuries of use, and are thereby instrumental in the design of sustainable agriculture systems and biodiversity conservation in the humid tropics.
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From page 106... ...
Mixed Tree Systems Throughout the World Agroforestry systems using mixed trees are common forms of small-scale production for farmers throughout the world (see Alcorn [1990] and Brownrigg [1985]
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From page 107... ...
Other important agroforestry systems within Indonesia are similar to the pekarangan. Mixed tree plantations occur on uninhabited private lands, usually associated with shifting cultivation.
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From page 108... ...
The Role of Mixed Tree Systems in Tropical Forest Conservation Mixed tree systems represent one of the most promising land use options available for integrating tropical forest conservation with production. The cultivation techniques already exist, local residents are already knowledgeable in cultivation practices, and the local to inter
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From page 109... ...
Unfortunately, international promotion of various local tree-based systems, from home gardens to managed forests, has not been accompanied by strong, interdisciplinary research programs to guide and assess their efficacy. This also holds for mixed tree systems.
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From page 110... ...
PERENNIAL TREE CROP PLANTATIONS Perennial tree crop plantations can be a useful means of converting deforested or degraded land into a system that is both ecologically and economically sustainable. They are part of a broader category of plantation agriculture that includes short rotation crops, such as pineapple and sugarcane, as well as tree crops, such as bananas A cacao plantation was carved out of the tropical rain forest in Malaysia.
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From page 111... ...
Plantation forestry, which involves lumber, pulpwood, and fuelwood production or environmental protection, is discussed later. Plantation Crops and Economic Development The role of plantations in the agricultural and economic development of countries in the humid tropics has been controversial (Tiffen and Mortimore, 1990~.
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From page 112... ...
Plantation crops are sometimes equated with tropical export crops such as rubber or palm oil, or even with cash crops, as distinguished from subsistence or food crops, such as rice, maize, and cassava. In practice, however, a crop such as coffee or sugarcane may be grown for local consumption as well as for the export market.
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From page 113... ...
· The conversion of natural forest into plantations may be accompanied by substantial soil erosion. The extent of erosion will differ according to the method used for land clearing and the production systems used for each plantation crop.
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From page 114... ...
In contrast, the regional research system for tropical tree crops in the former British colonies in West Africa fell into disrepair in the 1960s and 1970s. In the former French colonies of West Africa, the regional research institutions remained viable, with substantial support from France into the early 1980s.
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From page 115... ...
. PLANTATION FORESTRY Tropical tree plantations cover about 11 million ha of land and are composed of many tree species (Brown et al., 1986~.
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From page 116... ...
Failures can result from insect or disease outbreaks, poor species response to local conditions, or catastrophic events, for example. Most tropical countries have identified tree species that grow well in sites available for tree plantation establishment, and adaptability
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From page 117... ...
i .:: .:: :: ? :: f ; trials are advanced in those countries with established forest management agencies.
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From page 118... ...
REGENERATING AND SECONDARY FORESTS The development of sustainable agriculture and land use systems in the humid tropics requires an understanding of the forest regeneration process and the factors that influence it. Regenerating forests can be viewed as a transitional land use option, preparing tracts of deforested land for more intensive management, or as a permanent land use itself, maintaining forest cover and maturing into secondary (and eventually primary)
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From page 119... ...
Uniform raw materials with respect to wood density and species richness Woods low In resins and waxes, which facilitates their use Biomass production at a fast rate Ease of natural regeneration Ability to support higher animal production and serve as productive hunting grounds Habitat for greater numbers of vertebrates, which may enhance tourism Tree species with properties often sought by foresters for establishing plantations Generally more accessible to markets man remaining primary forests Availability as foster ecosystems for valuable late secondary species A useful template for designing agroecosystems Restoration of site productivity and reduction of pest populations Sabhasri (1978) Richards (1955)
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From page 120... ...
Young tree seedlings in abandoned fields are also subject to higher temperatures, higher vapor pressure deficits, and lower soil moisture availability than seedlings established in natural treefall gaps, where many forest tree species regenerate (Nepstad et al., 1991~. Little is known about the ability of forest tree seedlings to tolerate these extreme physical conditions.
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From page 121... ...
Young forests that lie along roads or are adjacent to agricultural lands are at much higher risk than those surrounded by a matrix of primary or late-secondary forests. Acceleration of Forest Regeneration The best techniques for accelerating forest regeneration are based on knowledge of the specific barriers to tree establishment and tree growth.
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From page 122... ...
122 ~~ ~~ .,~..~.~.~-~.~-~..~.~ ~~ ~~ ~~ ~~ ~~ SUSTAINABLE AGRICULTURE IN THE HUMID TROPICS A view of secondary forest in the foreground with primary forest in the background. Secondary forest is the regrowth after major disturbance, such as logging or fire.
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From page 123... ...
Indigenous people learned to use the characteristics of secondary forests to their advantage (Clay, 1988; Rico-Gray et al., 1991~. Rather than just occupying space and repairing soil fertility, forest fallows in shifting cultivation cycles became elements of complex land use patterns.
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From page 124... ...
Secondary forests, because of their diverse ecological and social attributes, offer many opportunities for improving production. However, to take advantage of these opportunities, policymakers, conservationists, agriculturalists, and development officials must focus on their potential, and not just on what has been lost with the primary forests.
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From page 125... ...
Silvicultural practices in the humid tropics must consider the high degree of tree species diversity, the vulnerability of tropical forest soils, and the regeneration biology of leading commercial tree species. The high degree of diversity in tropical moist forests complicates the harvesting, extraction, marketing, and regeneration of forest trees.
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From page 126... ...
The capacity to manage tropical forests effectively is limited by a lack of understanding of forest regeneration processes (Lugo, 1987~. The reproductive requirements of many leading commercial tree species are neglected under current management systems.
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From page 127... ...
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~.
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From page 128... ...
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~.
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From page 129... ...
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.
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From page 130... ...
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)
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From page 131... ...
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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From page 132... ...
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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From page 133... ...
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.
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From page 134... ...
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~.
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From page 135... ...
. 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~.
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From page 136... ...
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~.
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From page 137... ...
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.
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