Where's the beef?: Incorporating cattle into sustainable agroforestry systems in the Amazon Basin. W. M. LOKER. Department of Sociology, Anthropology ...
Agroforestry Systems 25: 227-241, 1994. 9 1994 Kluwer Academic Publishers, Printed in the Netherlands,
Where's the beef?: Incorporating cattle into sustainable agroforestry systems in the Amazon Basin W. M. LOKER Department of Sociology, Anthropology & Social Work, Mississippi State University, Mississippi State, MS 39762, USA Key words: Amazonia, agro-silvo-pastoral systems, sustainability, cattle
Abstract, Low external input agroforestry systems hold great promise as alternative, sustainable production systems for small-to-medium farmers in the Amazon Basin. The design of such systems is considered essential to stabilize agricultural production and avoid the cycle of continuing destruction of primary forest [Anderson A (1990) In: Anderson A (ed) Alternatives to Deforestation: Steps toward Sustainable Use of the Amazon Rain Forest pp 3-23. Columbia University Press, New York]. In order to be successful, these systems must be compatible with local ecological conditions and adoptable by farmers. Currently, many small-to-medium producers in the Amazon Basin use a slash and burn agricultural strategy that combines annual cropping with cattle grazing in mixed farming systems. While cattle play an important role in household economic survival, grazing-inducedland degradation threatens the long-term viability of these farms [LokerW (1993) Human Organization 52(1): 14-24]. This paper presents a model of a low external input agroforestry system that incorporates farmer preferences and practices but uses well-adapted grass-legume pastures, rotational grazing and the management of natural forest regeneration to enhance productivity in an ecologically sound manner. This system provides farmers with the benefits of both annual crops and cattle raising, avoids the land degradation that characterizes current practices and effectively incorporates trees into the production system.
1. I n t r o d u c t i o n Tropical forest destruction at the hands of agricultural colonists is a human and ecological problem of growing importance. The deforestation problem is particularly acute in the Amazon Basin where thousands of families have been encouraged to migrate by government subsidies, cheap or free land, new penetration roads and poverty and unemployment in their locations of origin. Many of these recent arrivals end up with small-to-medium holdings (20-500 ha) which they farm using some form of slash and burn cultivation, often combined with cattle raising. Deforestation is caused, in part, by the continued expansion of cultivated area, driven by economic necessity and the lack of readily adoptable ecologically conservative production practices. There is an urgent need to design low-input, sustainable agricultural systems (LISAS) for these farmers that can slow the cycle of forest destruction and provide adequate incomes for these households. Cattle are a particularly controversial component of agricultural production systems in the Amazon Basin. Raising cattle is currently a widespread
228 activity among small-to-medium producers in the Amazon Basin. [See AcostaMufioz, 1989; Estrada et al., 1988; Hecht, 1989; Loker, 1993; Ramfrez et al., 1990; Stearman, 1983 for descriptions of cattle raising in various Amazonian settings.] The most widespread system involves the use of slash and burn techniques to grow annual food crops (for home consumption and/or sale) followed by planting of pastures and grazing. These activities may be combined with perennial cash crops (e.g. coffee in Ecuador). In general, farmers are interested in cattle for the multiple economic benefits this activity provides including: (1) Planting pastures extends the useful life of a cleared area; the land is already cleared for food crops and the pasture essentially represents a substitution of planted grass for the native vegetation that would recolonize the plot in the usual slash and burn cycle; (2) Planting pasture demonstrates effective occupancy and 'improvement' of the land, which discourages encroachment by squatters and aids in claiming definitive title; (3) Cattle represent a capital good that retains its value even in the highly inflationary economies typical of many developing countries; (4) Cattle represent a readily marketed, high-value, low labor input commodity for colonists who may need to obtain cash for family needs requiring substantial monetary outlays; (5) Cattle are 'dual purpose' animals; in addition to supplying beef for sale, cattle may supply diary products for sale (providing much-appreciated cash-flow) or home consumption where it can make an important contribution to child nutrition. Therefore, while standard economic analyses may indicate that cattle raising in not a profitable economic activity in the humid tropics (due to low rates of weight gain and low daily milk productionl), for the Amazonian colonist, cattle fulfill multiple objectives within the farmer's adaptive strategy of diversified food production and income generation. Unfortunately, cattle raising as currently practiced does not appear to be a sustainable land use in this region for two related reasons. First, there is a well-known tendency for planted pastures to undergo a process of degradation after variable periods of use. This process had been described and modelled by Toledo and Serr5o [1982] and is illustrated in Fig. 1, which depicts the evolution of soil nutrients before, during and after pasture establishment and grazing. Starting in Year 0, under mature forest, soils are depicted as having low natural fertility. After cutting and burning the vegetation, soil nutrient content is increased via the ash of the burned vegetation, effectively transferring nutrients from the biomass to the soil where it is made available for crops and the newly established pasture. Soil nutrients peak after burning, followed by a protracted decline in soil fertility. The ultimate level of soil fertility depends on a number of factors including endogenous soil and climatic conditions and, most importantly, on the management given to the pasture. Two trajectories of nutrient decline are illustrated in Fig. 1, one labelled 'rational management' and a steeper decline, leading to degradation (levels below that of mature forest) under 'traditional management'. While it is impossible to define 'rational' versus 'traditional' management as used in this model,
229 /-
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it is fair to say that virtually all pastures in the Amazon (outside of agricultural experiment stations) are subject to traditional management. Second, grazing appears to retard the process of secondary succession, impeding the colonization of old pastures by woody vegetation and slowing the accumulation of biomass. Biomass accumulation is essential to restore the productivity of agricultural plots and enable their recultivation after an extended fallow period. Data collected at widely separate sites in Amazonia indicate that grazing as currently practiced slows accumulation of biomass by about h a l f - that is a grazed plot requires twice as long to accumulate an equivalent amount of biomass compared to a plot used for annual crops (See Uhl et al. [1988] for the Brazilian Amazon, Loker [1993] for the Peruvian Amazon.) The impact of this process on the sustainability of these farming systems should not be underestimated. These farmers, like other slash and burn cultivators, rely on the natural regenerative forces of the fallow process to restore
230 the productivity of their land. Given the importance of annual crops to household survival, and the fact that farm sizes are limited, retarding the rate of biomass accumulation either (1) creates a situation in which no land is available for annual crop production, or (2) forces farmers to bring land back into annual crop production before sites have fully recovered leading to the wellknown downward spiral of land degradation and declining yields. Therefore farmers are presented with a situation in which the economic viability of farms - based on annual cropping and cattle - is in conflict with the long-term sustainability of the farming enterprise which is imperiled by grazing-induced land degradation. Can agroforestry-based LISAS be designed that accommodate cattle, yet avoid land degradation?
2. Design features of LISAS for the humid tropics In order for low-input, sustainable agriculture systems (LISAS) to be ecologically sound and economically viable they must: make optimum use of resources available at the farm level, have a low rate of consumption of nonrenewable energy sources and raw materials and produce food above the subsistence level [Prinz, 1986]. Ewel [1986] has outlined several salient characteristics of the humid tropics that influence the design of LISAS. These include: (1) high rates of chemical weathering that lead to the formation of deeply weathered soils with little opportunity for fresh inputs of minerals from bedrock; (2) levels of rainfall that exceed the rate of potential evapotranspiration in most months leading to excess rainfall that runs-off or infiltrates the soil profile removing soil nutrients and cations, and (3) warm, moist climatic conditions that lead to thriving populations of pests and diseases whose growth cycle is unbroken by periodic fluctuations in temperature or moisture. These constraints may possibly by overcome by high applications of chemical inputs but these are scarce and/or expensive in most areas of the humid tropics and may have negative long-term consequences for the ecosystem. If high external inputs are to be avoided, LISAS must be developed that work with the biogeochemical cycles that characterize the humid tropic ecosystem. LISAS for the humid tropics will probably incorporate the following features, which are all elements of the model proposed in this paper: (1) a variety of mechanisms to supply, retain and recycle plant nutrients; (2) high species diversity; (3) inclusion of a woody, perennial component; (4) utilization of well-adapted germplasm; (5) periodic biomass burning, and (6) adoptability. Plant nutrition: Sustainable, productive agricultural systems must solve the critical problem of providing and maintaining adequate nutrient supplies to plants. This is particularly challenging in the humid tropics given the rapid turnover and potential for loss of nutrients in this ecosystem [Prinz, 1986].
231 The most widely successful form of low-input cropping in the humid tropics, the various forms of slash and burn agriculture, solve this problem by using the natural successional process to restore site productivity during an extended fallow cycle after relatively brief cropping periods. Unfortunately successful slash and burn systems are under pressure in many parts of the world due to increasing population and the need felt by many farmers to increase surplus production to raise cash incomes. As the sustainability of these systems is undermined, the urgency of finding low input replacements or modifications increases. According to Lal: If the forest fallow system is to be replaced by continuous farming, the nutrient capital will have to be replenished for each cropping cycle and systems developed for restoring soil structure and soil water relationships. Similar to the addition of organic matter through litterfall, a system of continuous supply of organic matter to the soil surface will be mandatory. [Lal, 19861. Maintaining adequate levels of soil organic matter is thought by many to be critical to the success of humid tropic agroecosystems because it is: (1) the main substrate for cation exchange; (2) the principal storage medium for much for the nitrogen, phosphorous and sulfur found in tropical soils; (3) the main energy source for soil micro-organisms, and (4) the key determinant of soil structure [Ewel, 1986; Sanchez, 1979]. Soil organic matter in successful slash and burn systems is provided by plant litter and detritus contributed by successional vegetation. The recolonization of previously cultivated sites by pioneer species also creates environmental conditions that favor soil organic matter retention. Successful LISAS should build on the high rates of net primary productivity of the humid tropic ecosystem and use its regenerative capacity to supply plant nutrients. Intensification of slash and burn systems will require improvement of the fallow cycle (see [Prinz, 1986] for a review of improved fallow techniques). Considerable agronomic research has been expended in attempting to improve on Nature's regenerative abilities in the humid tropics - with mixed results. For example, the inclusion of nitrogen-fixing trees as substitutes for or in association with natural vegetation has been an active areas of research. There are two main difficulties that have been encountered with improved fallows. Few species have been encountered that significantly outperform Nature, especially on low base saturation soils. Or systems that have been proposed have required high levels of inputs - either in human labor or chemical inputs and are therefore unattractive to many farmers. An example of the former is found in the research of Szott and collaborators in Yurimaguas [Szott et al., 1987a]. An example of the latter is the limited adoption of alley cropping. Species diversity: The humid tropics are characterized by the richest species diversity of any terrestrial ecosystem. Human efforts to replace that diversity with monocultures entail high energetic and ecosystemic costs [Giampietro
232 et al., 1992]. Therefore successful LISAS in the humid tropics (like successful slash and burn systems) will include a variety of species. According to Ewel [1986] there are several functions of species diversity: (1) more complete use of resources - use of complementary species with varying metabolic pathways (C3 and C4 plants), stature, phenology, rooting habits, shade tolerance, and nutrient requirements (N-fixers with non-Nfixers); (2) pest protection - through reduced apparency of the pest target, diluting host species, physically interfering with pest movement, creating an environment inhospitable to pests and/or favorable to pest predators, and; (3) compensatory growth; builds in redundancy into the agroecosystem, reducing risk (if one species fails, others replace it), sustained vegetation cover, enhanced nutrient cycling, and to maintain productivity, even as species mix changes over time. The model presented here incorporates a variety of plants (annual crops, tropical grasses, forage legumes, native tree species) in order to capture some of the benefits outlined above. The difficulty lies in associating species that are mutually compatible to minimize competition and maintain productivity. Multiple species also require increased management skills on the part of cultivators; a balance must be struck between the benefits of multiple species and the need to 'keep things simple' for ease of management [Ewel, 1986]. Inclusion of woody perennials: Humid tropical ecosystems are largely forested ecosystems. Excluding trees entails a tremendous exertion of energy, extreme degradation of the ecosystem, or both [Giampietro et al., 1992]. Agroforestry, the deliberate retention, introduction or mixture of trees or other woody perennials in crop/animal production fields to benefit from the resultant ecological and economic interactions [MacDicken and Vergara, 1990] has long been seen as a potential strategy for the intensification of slash and burn systems [Raintree, 1990], and indeed, a component of successful forest fallow systems of indigenous cultivators [Alcorn, 1990]. The attractiveness of agroforestry systems lies in the incorporation of multi-purpose trees to achieve many of the functions of forest fallow - especially regarding improvement of the soil - either more quickly and efficiently or while providing direct economic benefits to the farmer. Nair [1984, 1987, 1990] has provided a series of reviews of the role of agroforestry in improving soil quality. Nair [1987] lists 8 hypotheses regarding the positive effect of desirable woody perennials on soils including: (1) an increase in organic matter through leaf litter and other plant parts; (2) more efficient nutrient cycling; (3) nitrogen fixation and access to P through micorrhizae; (4) reduction of loss of nutrients to subsoil via leaching; (5) complementarity of resource use by diverse species, increasing efficiency of nutrient use; (6) enhancing the presence, activity of soil microorganisms; (7)
233 improve soil physical properties (permeability, moisture holding ability, aggregate stability, temperature); (8) reduced soil erosion. Problems of including trees include: (1) fast-growing trees place heavy demand on soil moisture leading to competition with other crops; (2) nutrient depletion may cause temporary deprivation of nutrients to adjacent, lesscompetitive species; (3) allelopathy; (4) competition for light [Nair, 1987]. (Many of these problems apply to the inclusion of non-tree species as well.) One of the principal agronomic challenges in incorporating woody perennials into cropping systems is choice of species and their temporal and spatial placement to minimize competitive relationships (that may depress crop yields and farmer incomes) and maximize beneficial interactions. The social and economic challenge is to ensure that trees provide direct benefits to farmers proportional to the effort expended in including them in the production system. In the words of Raintree [1990] we must ' p i g g y b a c k . . . long-term sustainability benefits with short- and medium-term productivity gains in cleverly designed systems'. Still, according to Nair, 'there is now more than enough evidence to indicate that trees and shrubs, if managed properly, can make a significant contribution to maintaining and improving the fertility and overall productivity of the soil beneath them' [Nair, 1990, p. 10]. Other investigators take a more sanguine view of the potential benefits of agroforestry (e.g. [Lal, 1989; Sanchez, 1987] drawing attention to the need to investigate the site specificity of soil-plant interactions. In an example that is highly relevant to the present case, Sanchez points out that the putative benefits of trees as 'nutrient pumps' extracting and making available nutrients from the subsoil is not confirmed for the low base saturation soils of Yurimaguas. Data from Yurimaguas 'cast considerable doubt on the relevance of the 'recycling' hypothesis where subsoil is extremely low in nutrients and cations. There must be something to recycle if recycling is going to be an advantage of the alley cropping system' [Lal, 1989]. The failure of Leucaena leucocephala in the Yurimaguas trials due to lack of tolerance to aluminum toxicity and low nutrient base status of these soils also influenced experimental results. This characteristic of Leucaena leucocephala is shared by other widely-touted nitrogen fixing trees (e.g. Calliandra calothyrus, Glyricidia sepium) while some native leguminous trees (e.g. Inga edulis) are more promising in this regard. This highlights the importance of using germplasm well-adapted to local agroecological conditions [Sanchez, 1987]. Well-adapted germplasm: The use of germplasm well-adapted to local biotic and abiotic conditions is critical to the design of LISAS in any ecological context, including the humid tropics [NRC, 1989]. The goal is to use species and varieties that fit local conditions instead of expending prodigious quantities of energy modifying the existing ecosystem. Various strategies exist for reaching this goal, of which the following are emphasized in the model proposed here: (1) plant breeding efforts designed to develop varieties of con-
234 ventional food crops adapted to the humid tropics (acid-tolerant varieties of maize and rice for example); (2) exploring reservoirs of natural genetic diversity for tolerance to local ecological conditions (screening of native and exotic grass and legume species for use as forages, for example), and; (3) management of native secondary forest species whose ubiquity demonstrate their adaptability to ecological conditions to enhance the fallow process. Efforts at developing well-adapted varieties are occurring at many levels from that of the International Agricultural Research Centers (CIAT's efforts with rice and forages, detailed in [CIAT, 1991]) to the informal experimentation with a rich variety of plants among peasant and indigenous households. Research on LISAS for the humid tropics should take advantage of these varying sources of germplasm. Biomass burning: This is one of the more controversial elements of the model proposed in this paper. Biomass burning clearly has negative ecological consequences (generation of greenhouse gases, loss of some nutrients), yet strong arguments can be made for including this as part of LISAS for the humid tropics. Biomass burning generates multiple benefits for farmers (nutrient release, depression of pest populations, land clearing) making it most difficult to eliminate. Successful LISAS should build on existing farmer practices where possible; burning is ubiquitous and considered essential by most small-to-medium farmers in the humid tropics. One of the goals of the model presented here is to decrease the frequency of burning but use it strategically to reap its many valuable benefits for farmers. The model presented below conforms to the ideotype of LISAS for the humid tropics outlined by Ewel: One land use scenario for the humid tropical lowlands consists of a mosaic of agroecosystems. High yields would come from annual crops . . . . Fields would change in composition, however, and eventually become dominated by long-lived plants. At the end of the rotation, the forest-like ecosystem would be harvested for wood or destroyed, and the site would again revert to a cropping system dominated by annuals (emphasis added JEwel, 1986]).
Adoptability: 'Adoptability' is a simple term for the complex set of relationships that governs the choices made by farm households regarding available agricultural technologies. A voluminous literature has emerged regarding the adoption and diffusion of agricultural technologies (the review of which is beyond the scope of this paper). This literature reflects in part, the frustration felt by agricultural scientists that perfectly good technologies are rejected by farmers in the developing world. Explaining this behavior has become a major social science industry. Various schools of thought and methodologies have been generated to study farmer behavior such as Farming Systems Research [Gilbert et al., 1980; Baker and Norman, 1989], On-farm Research [Ashby, 1987], the Farmer-Back-to-Farmer model [Rhoades, 1986] and the Diagnosis and Design methodology of Raintree and collaborators aimed specifically at agroforestry interventions [Raintree, 1990].
235 From this literature a few areas of consensus have emerged regarding the decision-making of smallholders in the tropics: (1) resource-poor farmers do make rational assessments of alternative technologies and behaviors (technology rejection is usually n o t due to ignorance or irrational clinging to traditions); (2) many of the technologies offered to these farmers do not perform as expected under on-farm conditions so their rejection by farmers is entirely rational; extensive on-farm testing of new technologies is required; (3) formidable economic and institutional barriers hamper the adoption of radically different agricultural practices, therefore most new technologies should build on existing farmer practices rather than seeking to radically transform them, and (4) farmers often have extensive knowledge and understanding of the local environment and have developed rational adaptive strategies to cope with this environment; researchers should learn from and incorporate 'indigenous technical knowledge' into the design of improved technologies. Many of these conclusions - and others regarding the intensification of slash and burn systems and the design of agroforestry systems - are eloquently expressed by Raintree: (C)onfronted with a choice of land-use options of differing labor intensity, subsistence-oriented farmers will choose the least labor-intensive methods of meeting their production needs and will be reluctant to adopt more labor intensive practices until population pressure compels them to do so . . . . Trying to introduce a technically elegant and environmentally sustainable but highly labor intensive technology to farmers accustomed to much less intensive farming methods is like trying to fit the proverbial square peg into a round hole. [Raintree, 1990] The model described here takes particular recognition of this general principle. Most small-to-medium farmers in the Amazon face serious constraints regarding the availability of labor. In order for LISAS to be adoptable, they must not be overly labor intensive. The model presented for these systems therefore builds on current practices and places minimal demands on scarce household labor by taking maximum advantage of the regenerative capacity of the humid tropic ecosystem and the accumulation of biomass through processes of secondary succession.
3. Description of a LISA agroforestry model with cattle
Figure 2 presents a model of an agro-silvo-pastoral system that fits the design criteria for LISAS in the humid tropics outlined above and includes cattle as an important component. The model begins (T-0 in Fig. 2) with the cutting and burning of an advanced secondary growth forest (or virgin forest, though this is not necessary), following traditional practices. Time-1 represents the sowing of an annual crop (such as rice or maize, preferably an acid-soil
236
Trees
Maize
T-3 Grass
Forage Legumes
Kudzu
Fig. 2. Model of a low-input, sustainable agroforestry system incorporating cattle appropriate for many areas of the Amazon Basin. T-O represents an advanced secondary or virgin forest. T-1 (Year 1) represents the use of the plot for annual crops such as rice or maize along with improved grass-legume pastures which are sown along with the annual crops. T-2 (Years 2-5) illustrates the grazing of the grass-legume pasture for four years at about 2 animal units per hectare together with the selective regeneration of naturally occurring trees. T-3 (Years 6-7) represents a reduction of stocking rate to 1 animal unit per hectare as trees grow and begin to shade out pastures. T-4 (Years 7-9) represents a fallow period in which trees and other naturally occurring vegetation colonize the plot without grazing, perhaps accompanied by the sowing of kudzu (Pueraria phaseoloides) or other rapidly growing, high N-fixing legume. At the end of T-4 (Year 10) any economically useful trees are harvested and the plot is then cleared and burned in preparation for recultivation.
237 tolerant variety) followed by pastures. In contrast with the traditional system, the pasture sown is a grass-legume association, with legumes included to fix nitrogen, help maintain soil fertility and raise animal production. Typical combinations of grasses and legumes would be the use of various Brachiarias (B. decumbens, B. humidicola, B. dictyoneura, B. brizantha)) for the grass (depending on soil and biotic pressures) together with legumes such as Stylosanthes guianensis cv. Pucallpa, Desmodium ovalifolium (CIAT 350), Arachis pintoi and Centrosema spp. (again the choice depending on local conditions). It is important that a mix of legumes be used to enhance species diversity, with the attendant benefits such as compensatory growth and pest resistance. All of these species are in some stage of agronomic trial for their adaptation to the biotic and abiotic conditions in the humid tropics [Loker, 1989; CIAT, 1991]. Recent research from the Peruvian Amazon has demonstrated the ability of farmers to establish improved forage legumes on their farms without the use of external chemical inputs [Loker et al., 1991]. These onfarm trials indicate their Stylosanthes guianensis cv. Pucallpa, and Desmodium ovalifolium (CIAT 350), can be readily established by farmers in existing slash and burn systems in a manner compatible with local labor availability and without external inputs. Persistence of these species is still under investigation, but preliminary results indicate that either or both can be maintained under moderate grazing by farmers without the addition of external chemical inputs. Another key difference with the traditional system is evident in Time-2. During the period of crop growth and initial grazing, the farmer allows the selective regeneration of trees - approximately 50-100 trees per hectare. These trees are not planted, they regenerate naturally, and therefore represent a free good for the farmer. It is also not essential that the trees by commercially valuable. Their role in the system is to recycle nutrients and maintain soil structure through root action and eventually to contribute to soil regeneration through burning. However, it is expected that some portion of the regenerating trees will be commercially valuable species common in secondary forest such as Guazuma crinita, G. ulmifolia, Jacaranda copaia, Cordia aiIiodora and Schizolobium spp. Their regeneration would allow the possibility of harvesting some portion of the trees for commercial sale at the end of the cultivation cycle. Grass-legume pastures would persist under these conditions creating a type of 'grazed fallow' with a stocking rate of two Animal Units per hectare for four years with no fertilizer and annual or biannual weeding (the norm in the region). During the fifth and sixth years carrying capacity of the 'grazed fallow' is reduced to 1 AU/ha to compensate for yield reductions expected under a more shady environment (Time 3). After'six years of grazing the land is taken out of production and further regeneration is allowed to proceed possibly with oversowing of Pueraria phaseoloides or another rapidly growing, high Nfixing legume to facilitate recovery (Time 4). It is projected that sufficient
238 biomass can be accumulated in a three year period (in addition to the biomass accumulated in the trees that have been allowed to regenerate over six years) to provide adequate site recovery for the successful cultivation of annual crops. Szott et al. [1987b] report that trees are able to shade out grasses after three years in natural fallows in Yurimaguas. Thus a three year fallow should also suppress weedy growth, another essential function of the fallow period in slash and burn systems. At the end of the fallow period any commercially valuable tree species are harvested before the plot in burned and the cycle begins again with the planting of crops and pastures. This system relies on the N-fixing and nutrient cycling capacity of the new pastures, which should allow farmers to intensify management and realize substantial increases in productivity while avoiding soil degradation [Toledo et al., 1982]. The system requires minimal change on the part of the farmer. The main technological innovation is the use of acid-tolerant crop varieties (where available) and the establishment and management of improved pastures species. The feasibility of establishing and managing multi-species grasslegume pastures under low-input conditions on farms has been demonstrated. Other changes in the model proposed here are minimal, principally involving a reduction (though not elimination) in the use of fire, something that again is within the capacity and experience of local farmers. The system appears to be economically viable. It allows a 50 ha farms to maintain 48-58 head of cattle and produce annual crops on 4 to 5 ha of land every year. (Farmers in the Pucallpa region of the Peruvian Amazon currently clear about 4-5 ha per year for planting annual crops [Loker, 1993].) The system is also sustainable; the 1-6-3 crop-pasture-fallow cycle permits these levels of production to be maintained on a 50 ha farm indefinitely. How does this system compare with other agroforestry systems described for the humid tropics? The system is similar to that described by Peck and Bishop [1992] for the Ecuadorian Amazon and analyzed economically by Ramfez et al. [1990, 1992]. The system described by Peck and Bishop includes cattle, but relies more heavily on coffee production and the sale of hardwood timber as income generators. The system described here relies more heavily on cattle production for income generation. The Peck and Bishop model uses only one forage legume species (D. ovalifolium) and thereby does not capture the benefits of using a more diverse pasture flora that increases productivity and enhances sustainability. It is also not clear to what extent the Peck and Bishop model relies on natural regeneration of trees in pastures versus planting of trees in pastures. Convincing Amazonian farmers to plant trees is problematic due to constraints on labor availability. The model described here is based exclusively on natural regenerative capacity of the humid tropics and attempts to harness and improve the successional process to intensify production. Also, the Peck and Bishop model was developed in the perhumid Napo region of the Ecuadorian Amazon which precludes the use of burning. The model described here is appropriate for regions with seasonal rainfall that predominate in the Amazon Basin [Cochrane et al. 1985]'.
239 Many of the same differences can be noted in comparing, this model with other attempts to intensify slash and burn systems (e.g. the work of Staver [1989] in the Palcazu Valley and Sanchez and collaborators in Yurimaguas [Benites, 1990; Szott et al.1987a] both in the Peruvian Amazon.) These experiments did not include a grazing component and focus on the use of one or two N-fixing species for improved fallows in rotation with annual crops. These experiments demonstrate the difficulty in besting Nature's regenerative capacity and the importance of including a woody component in improved fallows. The model presented here attempts to create a synergism between the processes of Nature and human management, enriching naturally regenerating fallows with a variety of herbaceous and shrubby forage legumes and putting the fallow to economic use via grazing. In short, the model proposed here, while untested in the field, 2 holds out great promise as a LISA agroforestry system that is compatible with the humid tropic ecosystem, is adoptable by farmers and includes both annual food crops and cattle - predominant components of many current production systems in the Amazon Basin. Colonists rely on annual food crops for feeding themselves and their families, for feeding their domestic animals and for sale in the market. For many farmers in Amazonia, cattle form the primary link to the market and are a ready source of cash income either periodically (when sold for beef) or on a continuing basis (through the sale of dairy products). As currently practiced, cattle raising is not an ideal land use because its negative impacts on system sustainability undermine the long-term economic viability of farms. The negative ecological impacts of cattle have led some to advocate their removal from the Amazon region. But until viable alternatives are developed that fulfill some or all of the same functions in the household economy, research on sustainable production systems that include cattle should go forward. Sustainable production systems that permits the intensification of land use on already cleared land, together with policies that halt or slow down the opening of new frontier areas, are the best hope for slowing deforestation and conserving the forests of the Amazon Basin.
Acknowledgements Research in the Peruvian Amazon was carried out under a post-doctoral fellowship provided by the Rockefeller Foundation with additional support from the Centro Internacional de Agricultura Tropical (CIAT) and in collaboration with the Peruvian Instituto Nacional de Investigaci6n Agraria y Agroindustrial and the Instituto Verterinario de Investigaci6n en Trdpico y Altura. I have benefitted greatly in discussion of these ideas with Carlos Ser~, Jos6 Toledo, Ratil Vera and Keneth Re~tegui of CIAT's Tropical Pastures Program. I alone am responsible for the ideas presented in this article.
240
Notes Estimates of liveweight gain in the Pucallpa region vary from 200-450 grams/animal/day depending on the state of the pasture, health of the animal and other factors. Milk production in dual-purpose cows averages about 2.5 liters/animal/day. Field testing of this model was cut short by political violence in the study region in 1989.
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