Sustainable agricultural resource management requires more than the identification and adoption of measures to control soil erosion. The need is for a holistic better land husbandry approach where the emphasis is on individual rural households and farming communities caring for and managing their available resources for productive purposes. This to be done in a way that enables them to meet their immediate welfare needs (for food, water, fuel, shelter, cash etc) without reducing these resources productive potential to meet future needs and aspirations.
Primary consideration should go to identifying practices that, when adopted, would provide economic benefits (e.g. livelihoods) to the adopters, while sustaining the agricultural resources of the area (eg catchment protection). In addition to identifying agricultural resource management practices for field level implementation, it is equally important to consider whether there is a need to change the policy and institutional environment (and if so how) so as to enable such technological options to achieve their design objective of productive and sustainable agricultural development.
A wide range of technologies that can be used as components of sustainable agricultural systems already exist. Some of these are indigenous techniques that have evolved in different places in response to local agro-ecological and socio-economic conditions (see ASOCON 1990, Kerr and Sanghi 1992 for examples). Others are the so-called `improved' techniques, usually derived from research work undertaken by a wide range of government, non-government and international agencies. Examples can be found in the technical manuals of various soil conservation services, the publications of a number of national and international NGOs, as well as in several FAO bulletins (e.g. Hudson 1987 and Sheng 1989).
Whether an indigenous or research derived technology, it is believed that any measure adopted with the aim of promoting the sustainable use of agricultural soils, will need to serve one or more of the following purposes (after Wood and Humphreys 1982):
When selecting the appropriate technological options for SARM it is necessary to consider (after Douglas 1992):
It is important to remember that while current agricultural and forestry enterprises and management practices may accelerate land degradation, technical remedies will only succeed if they can function within, and address, local socio-economic constraints.
It should also be noted that, however excellent the land management practices may be at the field and catchment level, soils can become completely saturated during periods of heavy and prolonged rainfall (e.g. during the passage of a slow moving tropical cyclone) resulting in high runoff levels and mass wasting in the form of landslides (natural geologic events). With high levels of natural runoff during severe storm events, often concentrated into a single channel, flooding associated with high volume stream flows (with the ability to transport large quantities of sediment), and landslides rapidly delivering large quantities of sediment into river systems, are natural phenomena that can be expected to occur on a periodic basis almost anywhere in the Asia Pacific region. Even in arid areas when rainfall occurs it typically falls in the form of a heavy downpour which may result in rapid and short lived runoff with localised flooding and erosion.
Agricultural resource management has to recognise that various natural denudation processes are at work. Such processes have to be considered as natural hazards, and therefore fixed design constraints when seeking to develop land use management recommendations appropriate to individual areas.
The dominant soil degradation process in the Asia Pacific region is water erosion. Whether or not water erosion occurs at a particular site will depend on the erosivity of the rainfall received, the soil's infiltration capacity and erodibility, slope length and angle, and the amount of ground cover provided by surface litter and growing plants.
Erosivity is a function of the physical characteristics of rainfall. As rainfall intensity increases, so in turn does raindrop size (up to certain high intensities), terminal velocity and kinetic energy. Thus, the higher the rainfall intensity the greater its capacity to cause erosion (Lal 1977, Hudson 1995). There is considerable variation in total annual rainfall between and within the different agro-ecological zones of the Asia Pacific region from close to zero in parts of the Gobi desert to over 10,000mm in parts of the highlands of Papua New Guinea. Irrespective of the area, total annual precipitation typically comes in the form of short duration high intensity rain storms with maximum intensities associated with individual tropical cyclone events and the occasional typhoon. Within the tropics at least some 40% of the annual rainfall can be expected to be received at erosive intensities.5
Rainfall erosivity is a factor that cannot be modified by man's actions. Given that rain will fall at erosive intensities it has to be regarded as a fixed constraint for SARM purposes. The only options open are to reduce its impact by providing protective ground cover through appropriate crop management and revegetation practices. In an agricultural context the aim should be to ensure the least amount of bare soil at the time the most intensive rainfall can be expected. This could be achieved by such practices as mulching with crop residues and improved crop husbandry designed to provide the maximum crop cover as quickly as possible.
In a reforestation context the aim should be to keep to a minimum the area that has to be kept clear to reduce weed competition during tree seedling establishment. Also it is important to recognise when promoting tree planting as a conservation measure that it is the improved groundcover from litter below the trees rather than the tree canopy itself that provides the bulk of the protection against erosion (see box 50).
Soil erodibility is a measure of how vulnerable or susceptible the soil is to erosion. This will depend on the soil's structure and structural stability, texture, organic matter content, porosity, and permeability. Erodibility is initially an inherent property of the soil, but can change as a response to management (Lal 1977, Hudson 1995). A soil's erodibility can be increased or decreased by changes in soil organic matter. Within upland areas, land that has been used for dryland annual crops (particularly shifting cultivation) typically has a low soil organic matter content. When such conditions are combined with coarse topsoil textures and weak surface structure it makes for highly erodible soils. A soil's erodibility can be reduced by management practices designed to raise the organic matter content of the topsoil.
Slope length and angle in the geomorphological sense are unalterable, but their values with respect to erosion can be modified by conservation measures. Effective slope angle can be altered only by terracing. However, the cost of terrace construction and maintenance (especially the labour requirement) is high. A shortage of labour within the household can result in low quality terracing which may actually increase soil erosion, should runoff concentrate at low points. Also, crop yields may be reduced if during terrace construction the original topsoil is removed or buried and crops end up being planted in less fertile subsoil. It is important that any conservation project promoting terracing should have a mechanism for monitoring the quality of terrace construction and maintenance.
Effective slope length can be reduced by conservation measures of the barrier type. These may be physical structures (e.g. earth banks, stone walls, storm drains and cutoff ditches) or biological barriers (e.g. grass strips, barrier hedges). When considering the use of barriers for erosion control a distinction should be drawn between impermeable and permeable barriers. Impermeable barriers are those, such as ditch and bank structures which check all runoff, either by diversion or by retaining it in situ until it can infiltrate into the soil. Permeable barriers are those which allow some proportion of runoff to pass through. Examples of the latter would be contour stone lines, hedges or grass strips.
By allowing some runoff to flow through them, at a greatly reduced velocity, permeable barriers have an automatic safety valve to cope with the occasional storms of very high intensity, which would overtop and destroy earth banks. Hence contour grass strips and hedgerows may be technically suitable alternatives to earth banks in high rainfall areas. Grass strips and hedgerows can also contribute directly to on-farm production by providing fodder, green manure, fuel and mulch.
In semi arid areas crop production is limited by moisture availability. Production benefits may follow the adoption of measures that encourage the conservation and infiltration of rainwater, such as the construction of impermeable cross slope barriers, retention ditches, level and backward sloping bench terraces. However the risk of mass movement increases with increased slope angle, therefore caution should be exhibited in steeply sloping areas, when adopting conservation farming practices that increase infiltration and reduce runoff. Retaining more water in situ may actually accelerate land degradation by mass movement. It therefore must be remembered that not all slopes can be terraced safely, the critical factors being soil type and geological structure and stability. Efforts to introduce terracing on unsuitable slopes can result in catastrophic landslides and mud flows (Hudson 1995).
There are disadvantages to relying on structures alone to solve soil degradation problems because (after Shaxson 1989, Douglas 1991a):
Conservation structures provide a means of dealing with excess storm runoff, but on their own cannot substitute for improved conditions of soil structure and cover in the inter-bank areas. They can be used safely and effectively only in support of better crop and livestock husbandry.
Ground cover is the factor that has the greatest impact on the rate of erosion by protecting the soil surface from the impact of erosive rains. It is also easily modified by changes in land and crop management practice. Cover may be provided by the leaves and other parts of plants growing above the surface (the canopy) or the dead materials deposited on the soil surface below the plants (litter). In a natural system the litter would be composed of leaves, stems, twigs, branches, seeds, fruits etc. In cropping and agroforestry systems the canopy will be provided by the growing crop and the leaves of any woody perennials, while the litter may consist of deliberately applied mulch and/or crop residues.
Perennial tree crops with cover crops beneath have the potential to reduce erosion to a fraction of its rate on bare soil. Hence when planting perennial tree crops, as an alternative to annual crops, consideration should be given to interplanting cover crops. Cover crops should not only be conservation effective, but also offer productive benefits. For perennial cover crops to be accepted by farmers they must be easily propagated, require little management, be shade tolerant (so they will continue to provide surface cover as the tree canopy expands) and have some economic value as a food crop, green manure and/or fodder.
Strong horizontal winds can cause both damage to vegetation and soil erosion. Such winds are a feature of the arid and semiarid zones of in Asia and Australia. They are also a feature of coastal areas in both Asia and the Pacific that lie within the typhoon belt. Wind erosion can be expected when the following conditions occur:
Such conditions are a feature of North West China and Northern Mongolia where the climate is characterised by low ,and very seasonal, rainfall and frequent strong winds. Once the original natural vegetation of the steppe has been removed by ploughing then the soils are particularly susceptible to wind erosion due to their light topsoil textures (typically fine sandy loam to loam). The risk of wind erosion is highest in spring, prior to the onset of the summer rains, due to the combination of strong winds, dry topsoil and poor vegetative ground cover.
In addition to the problems of wind erosion, the strong dry winds, combined with low humidity, that are a feature of the climate in the arid and semi arid zones of Asia and Australia can adversely affect crop production by:
Wind erosion is restricted to dry soils,6 and the amount is dependent upon wind velocity and ground roughness. Control measures can therefore be directed towards changing one or more of these factors, that is by maintaining soil moisture, reducing the wind velocity, or increasing soil roughness.
The planting of windbreaks would assist in reducing wind velocity, which in turn would reduce the ability of the wind to dry out the topsoil. Not only would windbreaks serve as a wind erosion control measure, but they would also improve the micro-climate for crop production. In addition should there be any risk that irrigation would lead to waterlogging and salinization of the upper soil layers, then the planting of trees, in the form of windbreaks, would provide a means of counteracting this. The roots of mature trees can pump water at depth and thus would help in re-establishing a downwards water circulation in the soil.
For shelter belts or windbreaks with a height of less than some 10 m, a velocity reduction of more than 20% can be obtained up to heights of half the height of the belt and up to distances 15-20 times the height of the belt. Higher belts have relatively less effect. A key requirement of a windbreak is that it must not block the wind velocity. If the wind is blocked it causes serious turbulence just behind the belt. Hence a porous belt (one that the wind can flow through) has much more effect than a very dense one (one that wind has to go round or over). The best effect is obtained with a belt of medium density and a dynamic porosity of about 40-50%.
Shelter belts require good care and maintenance as openings in a belt give rise to higher wind speeds. This can be the case in old belts with heavy trees and a lack of undergrowth. The adverse effect of openings in dense belts is still worse (jet formation). These streams cause locally increased wind erosion or damage to vegetation. The same applies to both ends of a shelter belt. A belt should therefore not be ended abruptly, neither should part of a dense shelter belt be cut off; instead, porous ends should be maintained.
In deciding on the location and extent of shelter belt planting it should be borne in mind that; a) a second belt gives less protection than the first most windward one; and b) shelter belts have the disadvantage of contributing to an irregular windspeed pattern over the field. When a regular decrease in wind velocity is required trees and bushes (for fruit, green manure, fodder, fuel etc) could be spread evenly and in small groups, planted in a variety of agroforestry systems, over the country. An increasing surface roughness and, consequently, a decrease in wind velocity will then result.
Land that has been adversely affected by waterlogging and salinisation can, at a cost, usually be restored to a productive state. This requires improved drainage to lower the water table, correct application of irrigation water with good drainage to ensure a downward flow of water to leach salts from the surface horizons and the application of gypsum to the topsoil to improve the physical structure.
Chemical degradation, specifically in the form of acidification and nutrient decline, is a problem in parts of the Asia Pacific region. Soils derived from non volcanic parent materials are generally naturally acidic and low in weatherable minerals. Past misuse may make a poor situation worse. In particular failure to replenish the nutrients lost by leaching and their removal in harvested products (including the collection of grasses, litter and brush from forest areas for fodder, fuel and livestock bedding) can lead to the steady impoverishment of the nutrient status of agricultural and forest soils.
Nutrient deficiencies cannot be made up solely by the addition of composite chemical fertilisers. The highly acidic nature of many soils means that elements such as phosphorus are rapidly fixed and unavailable to plants. High rainfall when combined with coarse textured and very porous soils results in soluble elements like nitrogen being rapidly lost by leaching. Nutrient deficiencies are best overcome by the application of organic manures supplemented with chemical fertilisers. Liming, to reduce soil acidity is generally not a cost-effective option for small-scale farmers in the tropics (Young 1976). Currently the only practical way to ameliorate soil acidity would appear to be the addition of large quantities of organic manure, complemented by a change in the type of fertiliser used (e.g. calcium ammonium nitrate instead of sulphate of ammonia).
Where soils have been overcropped and overgrazed they are likely to be deficient in the biological processes needed to both maintain their physical structure and to supply essential nutrients to plants. Although soils originally under forest or grassland cover may start with a relatively high organic matter content, following years of misuse this may be reduced to a very low level. Organic recycling practices (composting, burying crop residues, green manuring and the application of animal manures) will improve soil structure, and thereby root penetration and erosion resistance; augment cation exchange capacity; and act as a store of nutrients, that can be slowly converted to forms available to plants.
Physical degradation, especially loss of topsoil structure following cultivation, is a concern as it reduces the ability of the soil to withstand erosion. Sealing and crusting of the topsoil can occur where ground cover is insufficient to protect against the impact of raindrops. Both compaction and crusting may be problems in areas heavily trampled by livestock. Subsoil compaction may occur following a switch from livestock to machines for ploughing and other cultivation operations. Compaction, sealing and crusting will reduce infiltration thereby increasing runoff and the likelihood of water erosion. The only realistic option for improving topsoil structure is through the raising of organic matter levels either by digging in organic manure, or by growing a grass or herbaceous legume cover crop (pasture). This may also reduce the risk of sealing and crusting. It is better to prevent compaction from occurring in the first place, by controlling livestock movements and regulating grazing, as corrective measures (e.g. deep ripping by tractor) are likely to be costly and, in hillside locations, technically difficult. In severe cases it may be necessary to `close' an area and rely on the regrowth of the natural grasses, shrubs, and trees to slowly restore the soil's physical condition.
As indicated above there are a range of agronomic techniques that can be used to improve the biological, chemical and physical properties of the soil which will all have an impact on fertility. In particular soil organic matter can be replenished by incorporating crop residues, animal manure, green manure and compost. Nutrient levels can be replenished and topsoil structure restored by the use of short, medium or long term fallows (e.g. bush fallow, enriched bush fallow or grass/pasture leys). Nitrogen levels can be replenished with the aid of N-fixing rhizobium and scope may exist for using mycorrhiza to improve the efficiency of extracting available phosphorus and other soil nutrients. Mineral fertilisers and lime can be used to provide nutrients and improve soil chemical properties.
Balanced and efficient fertiliser application provides a means to compensate for the greater removal of soil nutrients that goes with increased yields (FAO 1991d). Fertiliser efficiency can be improved by reducing nutrient losses between each application and uptake of the nutrients by the plant. Much can be done to minimise nitrogen losses by good management: maintenance and enhancement of soil organic matter, control of irrigation, timing and splitting fertiliser applications to suit the needs of the crop, and the deep placement of fertiliser. Possibilities are also offered by coating urea granules to control the rate of dissolution in the soil and by the addition of chemicals which reduce the activity of nitrifying organisms. The efficiency of phosphatic fertilisers can also be enhanced by careful placement and timing of application.
Whereas there are technical options for improving the efficiency of fertiliser application, inorganic fertilisers should always be seen as a supplement to, not a replacement for, better use of on-farm organic matter resources (recycling of crop residues and animal manure, compost, green manure, agroforestry etc). Improved on-farm organic matter management is therefore the most critical factor in fertility management. It should however be emphasized that there is a limit to the quantity of nutrients that can be supplied from purely on-farm sources, as what is not there in the first place cannot be recycled. The original source for phosphorus, potassium, and the secondary and micronutrients is rock weathering. If the soil parent material is low in these elements then, however closed the soil-plant system may be, it cannot become richer without external inputs. Likewise even on soils initially rich in these elements, nutrient deficiencies will occur if they are removed in the harvested products faster than they can be replaced by the process of natural weathering. Nitrogen on the other hand originates from atmospheric fixation and can be increased in situ by biological means.
Thus the maintenance of soil fertility calls for the adoption of what has been termed the integrated plant nutrition systems (IPNS) approach (FAO RAPA 1993). According to FAO's perception "IPNS aims to foster the maintenance of soil fertility and of plant nutrient supply to an optimum level for sustaining crop productivity through optimization of the benefits from all possible sources of plant nutrients in an integrated manner. Such systems seek to maximize the efficiency of plant nutrient supply to the crops through proper association of local and external sources of plant nutrients and to ensure the sustainability of agricultural growth through improvements of the soils production capacity. IPNS, in providing timely and sufficient plant nutrient supply to the crops, according to the targeted yields, and in reducing as far as possible plant nutrient losses in the cropping system, may reduce significantly the needs for mineral fertilisers applied to produce a better financial return from limited investment in external inputs".
Thus IPNS involves a holistic farming system nutrient `balance sheet' approach that seeks to improve the exploitation of on-farm sources of nutrients (e.g. through better integration of crops, livestock and trees), supplementing these as and when necessary with nutrients obtained from off-farm sources (forest litter, animal manure collected or purchased from commercial livestock producers and purchased inorganic fertiliser). The aim is to ensure that whatever nutrients are lost during the cropping cycle (by leaching, oxidation and removal in harvested products etc) should be replaced in ways (e.g. fallowing, incorporation of crop residues, application of organic/green manures and chemical fertilisers) that are both economically viable and socially acceptable.
In arid and semi-arid areas water management calls for techniques that will harvest, store and/or spread water with the aim of concentrating moisture locally within a catchment, for the purpose of crop production (e.g. earth and rock bunds, graded channels, rock weirs etc). In slightly higher rainfall areas where moisture may still limit crop production the need is for techniques that will hold rainfall in situ, reduce the velocity of any runoff, and promote infiltration (e.g. hill side ditches, retention terraces, stone lines, tied ridges, planting pits, earth basins, vegetative strips etc). In humid high rainfall areas the need is for techniques that can utilise the available water (eg level paddy rice terraces), control and safely dispose of excess rainfall (e.g. graded terraces and waterways) and drain soils that would otherwise be prone to waterlogging and possible mass movement (e.g. graded hillside ditches and drainage channels).
Methods for controlling soil temperature are primarily aimed at reducing extreme temperatures at the soil surface or within the topsoil that would otherwise limit crop production. In lowland arid and semi arid areas the sun shining on to bare soil can raise surface temperatures high enough to kill germinating plants. Mulching with stones or vegetative materials will not only conserve moisture but insulate the soil surface against extreme temperatures. The shade provided by the canopy of growing plants will also help. In Papua New Guinea the composting of fresh vegetative material in large planting mounds raises soil temperature and allows sweet potatoes and other crops to be grown at altitudes that would otherwise be too cold (Wood and Humphreys 1982). Mulching is also used for protecting sensitive plants from damage by ground frost.
The land use practices of rural households are strongly influenced by the policy environment in which they operate and it is therefore important to look not only at field level technical options but also potential options at the policy level. The first requirement is to identify those elements of the existing policy environment (prices, markets, subsidies, extension messages etc) that will influence agricultural, and forestry land use practices, and to review their effect on natural resource sustainability.
It is necessary to distinguish between those influences that conform to the stated goals of government policies and those that relate to problems in implementation, as the actual results of a particular policy may be quite different to the stated goals. For instance in the Philippines the proclamation of protected watersheds has on occasion ended up inadvertently increasing social inequalities by imposing costs on resource poor hill farmers for the benefit of better off lowland irrigated farmers. Also even where government agencies may have formulated the right agricultural and forestry development policies they typically lack the manpower and financial resources to implement them.
Issues that are likely to be considered in the formulation of macro-level policies that will influence agricultural resource management plans will include:
The promotion of development activities within a specific area may require micro-level changes in the policy environment. Key policy design issues that may need to be considered are as follows:
SARM embraces both the bio-physical and social science disciplines and is multi-sectoral in nature. This raises the need for co-operation between different interest groups (farmers, foresters, ranchers, energy users etc) and technical specialists (natural resource scientists, social scientists, engineers etc) in the planning and implementation of development programmes. At the government level success will depend on the favourable resolution of a range of institutional issues. This will include appropriate mechanisms for inter-departmental co-operation, and the co-ordination of activities undertaken by different government line agencies. Success will also depend on the availability of the necessary manpower with appropriate disciplinary skills, and effective extension research linkages in both the forestry and agricultural sectors.
At the community level programmes to promote sustainable agriculture and forest management may call for co-operation between different social and ethnic groups within the same locality. They may also have a direct or indirect impact on the activities of other local interest groups such as logging companies, traders, and large scale commercial plantations. Success in resolving conflicts of interest within rural communities (e.g. between groups of lowland and upland farm households) will depend to a large extent on the existence, strength and organizational structure of local people based institutions. Where such institutions do not already exist considerable time and effort may need to be devoted to training and organization within local communities in order to establish the necessary peoples' organizations before participatory planning can begin.
The following are some key institutional considerations related to SARM planning.
Differences in strategies, approaches and even technical methods between government departments and donor agencies may lead to duplication of effort, and confusion or resentment on the part of land users. There must be an institutional framework that enables different development support agencies to collaborate, and operate, in an integrated manner rather than compartmentalised on a geographic area (e.g. private agricultural land, Forest land or local government administrative boundaries) or disciplinary interest basis (crops, livestock, trees, soil conservation, irrigation, energy etc).
Government programmes should acknowledge the presence and the potential of Non Governmental Organizations (NGOs), many of which may often have comparative advantages when it comes to contact with natural resource users at the local level.
Community level `peoples' organizations can provide a forum, not under direct government control, in which local peoples' wishes can be articulated, problems analyzed, plans formulated, and agreements reached on how particular interventions are to be implemented. Management of such organizations should be in the hands of responsible, responsive and respected leaders. Such organizations may require external assistance (e.g. training of leaders, information, `seed' money) before they can be self sustaining.
If governments are to provide the back-up services that rural communities need to plan and implement their own field solutions they will need to strengthen the relevant development support institutions. It will not be enough simply to provide more finance and personnel (welcome though that would be). What is needed is to reorientate the training, extension and research programmes of these institutions to the realities of small-scale farming, and the opportunities for bottom up participatory planning, and implementation, of development activities .
SARM requires an integrated extension message. This requires close cooperation between the various subject matter specialists, and extension services responsible for crops, livestock, horticulture, forestry etc. Agroforestry, by definition requires the integration of the traditional disciplines of agriculture and forestry. Different subject matter specialists should combine their recommendations to enable generalist agricultural extension workers at the grass roots level to present a `holistic' land husbandry and conservation-with-production message.
Training is a vital ingredient of SARM programmes at all levels. It is necessary not only for programme personnel but also for the participating land users. Developing skills amongst the beneficiaries not only `demystifies' technology, but also acts as a powerful incentive to increased involvement in conservation-with-production activities. Promoting a participatory approach to SARM requires changes in current training approaches and curricula so as to create new attitudes, skills and awareness within professional people. Changing from a top-down to bottom-up approach creates retraining needs at all levels.
Research should be conducted in an inter-disciplinary manner and include specialists from both the natural and social science disciplines. Priority should be given to `on-farm' research and participatory technology development and address the specific constraints and opportunities of the catchment. Any necessary `on-station' research should be formulated in response to problems and concerns identified at the farm/field level.
There are a wide range of design considerations that will need to be taken into account when formulating SARM proposals. These will vary depending on the sectoral nature of the particular proposal and will embrace a variety of different policy, technological and institutional factors.
The small-scale farming sector: Development proposals to improve the productivity and sustainability of the small-scale farming sector should take as their starting point the indigenous agricultural knowledge of the existing farming communities, the agro-biodiversity of their farming systems, and the variety of agro-ecological niches exploited. The development of new and improved agricultural resource management technologies will therefore require:
Farmers rarely adopt complete technological packages, rather they tend to select from an array of recommended technologies and practices those perceived as most appropriate to the conditions in which they operate. The aim of any SARM programme should therefore be to provide farmers with the basic principles (eg contour planting, use of hedge rows and other cross slope barriers, rotations, ground cover etc.), offer a range of locally appropriate options that match the different agro-ecological niches exploited (eg several alternatives rather than a single recommended practice), and provide the necessary support services (nurseries, credit, technical advice etc). Leaving farmers free to choose and experiment and in so doing put together their own farming package based on their individual needs. Technologies intended to improve the productivity and sustainability of small-scale farming systems should ideally be:
In addition to the above points the following are key design considerations with regard to the promotion of sustainable and productive small-scale farming systems:
Commercial farming sector: The commercial farming sector within the Asia Pacific region differs from the small-scale farming sector in that agricultural production is geared to producing commodities for sale rather than meeting subsistence needs. Whereas the small-scale farming sector is increasingly entering into cash crop production there are very few small-scale farming households who would not seek to meet some, if not all, of their subsistence food needs from their own on-farm production.
The commercial farming sector is typically characterised by the use of improved hybrid varieties or clones grown as mono-crops. These may be annual crops such as maize, wheat, soya beans, ginger, taro and squash or perennials such as sugar cane, tea, coffee, oil palm, coconuts and rubber. In the Pacific the commercial farming sector is primarily geared to producing commodities for export, whereas in Asia, due to the higher population, it may be producing for both the domestic and international markets. Livestock ranching and large scale poultry, piggery and dairy enterprises, for both the domestic and export markets, are likewise a feature of the commercial farming sector in the region. The importance varying from country to country but representing a significant proportion of the agricultural exports from countries such as Australia, New Zealand and Vanuatu.
When seeking to promote the commercial farming sector the following are some key design considerations in the context of SARM:
Tree planting in rural areas may involve farmers integrating trees into their crop and livestock production systems (agroforestry), the establishment of woodlots on an individual or community basis (social forestry), or as a large scale reforestation exercise (plantation forestry).
Agroforestry is commonly advocated as a land use practice to be promoted in the context of SARM. However agroforestry is not one discrete land use practice, but a collective name for land use systems where woody perennials (trees, shrubs, palms, bamboos etc) grow on the same land management unit with agricultural crops and/or animals. This can be either in some form of spatial arrangement or in a time sequence. To qualify as agroforestry, a given land use system must permit significant economic and ecological interactions between the woody and non-woody components.
In many upland development and catchment management programmes the agroforestry component turns out to be little more than orchard development or reforestation by rural households. The emphasis is almost exclusively on supporting the tree planting component with little, if any, extension assistance provided for any food crops that the households may interplant with the trees.
The term agroforestry covers a large number of separate land use practices involving a wide range of different woody species, crops and/or livestock. These may be traditional land use practices or research derived technologies. There is no one practice that can be termed agroforestry. Hence it is a mistake to specify agroforestry as a component of a SARM programme without making it clear as to what is actually involved. The following design issues will need to be considered when selecting an agroforestry option:
"Forestry for local community development", "community forestry" or "social forestry" are alternative terms for programmes designed to assist rural communities and individuals to better meet their needs for tree products - fuel, timber, poles, food, fodder etc. Social forestry usually focuses on the planting and raising of trees and shrubs (afforestation) on a communal or individual basis. It may also involve rural communities in managing and exploiting local natural woodland and forest areas. A basic feature of recent social forestry programmes is the active involvement and participation of the beneficiaries in the forest management process.
Participatory social forestry calls for quite radical changes to conventional forestry practices. Particularly in terms of selecting what to grow, how to organise planting and management and what form government involvement and support should take in situations where foresters have a supportive rather than executive role. The following design issues will need to be considered when formulating social forestry proposals:
Reforestation, particularly in upland and highland areas, frequently takes the form of plantation forestry. That is the planting of one, or a limited range of, tree species on an extensive basis. Key design considerations related to plantation forestry are as follows:
Within much of the Asia Pacific region a significant proportion of the tree products used by rural communities come from the remaining, and rapidly dwindling, natural forests. Where there are patches of natural forest (virgin or secondary regrowth) it would be necessary to consider how best to maintain and enhance the resource. The following design considerations should be considered when formulating natural forest management and/or protection proposals:
Changes in land use and the vegetative cover can be expected to have an impact on the natural hydrological cycle within individual catchments. Whether this is a negative or positive change will depend on the nature and objectives of the water management practices followed. The following are some of the key water management design considerations that should be taken into account in SARM programmes:
22 Research work in a number of tropical countries suggests that intensities of less than 30mm per hour are virtually non-erosive, with intensities of 30-60mm per hour, some 10% of rainfall will be erosive, once the intensity reaches 100mm per hour, all rain is erosive. Such conditions can be expected to apply within much of the Asia Pacific region.
23 Only dry soil blows, and any soil will be unmoved by wind while its surface is moist, Hudson N.W. 1981. Soil Conservation. Batsford London.