Land resources and human populations are not evenly distributed across the earth. A result of this uneven distribution is that the way in which steeplands (typically characterized as slopes greater than 20%) are used varies considerably in different countries and regions. In countries with a large amount of prime agricultural land and a relatively low population density, such as the United States, Canada and Australia, steeplands are regarded as unsuitable for agriculture. Such lands are often managed so as to maintain the original forest cover, with an emphasis on watershed protection and recreational use. In contrast, arable land is a scarce commodity in many densely populated mountainous regions such as Nepal, Mexico, Rwanda, and Haiti. Consequently, large areas of steeplands in these countries have been cleared of their original forest cover, and are being used for crop and/or livestock production. Shortage of fuelwood has become a serious problem for the rural population.
People cultivating steeplands often have no alternative resource for producing food. Many poor peasants depend on steeplands for their subsistence needs, and many countries rely heavily on steeplands to meet their basic food needs. For example, USAID (1980) documented that steepland farms produce 75% of the staple grains consumed in Honduras. Subsistence necessities and socio-political pressures make it impractical to expect that governments will remove farmers from steeplands in the foreseeable future. In fact, the reality is that rapid expansion of agricultural activity on steeplands is likely to continue. The rapid rate of deforestation and conversion of steeplands for agriculture during recent decades, and the projected trends in tropical and subtropical regions, have become an international concern (FAO 1982, 1990; Moldenhauer and Hudson 1988, Aldhous 1993). Land tenure inequity exacerbates the effects of population pressure. In some regions, governments often view disbursement of land title in uplands as a mechanism to placate the land needs of the rural poor. In many instances, unstable land tenure is also the root cause of farmers' inability and unwillingness to risk investment in soil conservation (Pla Sentis 1992).
Soil erosion is the most significant ecological restriction to sustainable agricultural production on steeplands. Unsustainable practices on steep slopes pose a series of problems, such as flood and siltation, for downstream portions of the watershed (Gray and Leiser 1989, Thurow and Juo 1995). Measured rates of soil losses of 100 - 200 mt/ha/yr have been reported in many cultivated steepland areas (Primentel et al. 1995). High intensity monsoon rains, combined with the runoff energy that can be generated on steep slopes, contribute to high erosion rates. Forests, which originally provided cover of most steepland sites, help to protect the soil by dissipating raindrop energy. After forests were cut and replaced with cassava or groundnut in Ivory Coast, Africa, erosion increased from 0.05 mt/ha/yr to 750 mt/ha/yr (Roose 1988). However, in densely populated regions, the cutting of wood for fuel and the use of crop residues as cooking fuels by smallholder farmers also contribute significantly to soil degradation on steeplands. For example, approximately 60% of crop residues in China and 90% in Bangladesh are removed and burned for fuel each year (Wen Daznog 1993 in Pimentel 1993).
This paper reviews promising old and new soil and water conservation technologies for steepland farming. Selected success stories are briefly described to illustrate that productivity of some steeplands can be maintained when appropriate technologies are combined with responsible and dedicated human effort.
Principles and Approaches
The management of steepland for farming essentially involves implementing practices designed to retain soil on the hillside. This requires that several erosion processes (interrill erosion, rill erosion, and mass wasting) be controlled. Interrill erosion, caused by raindrop splash, is basically controlled by maintaining cover on the soil which will intercept and dissipate the energy of a raindrop before it strikes the soil. Rill erosion, caused by runoff, can be controlled by managing the soil to foster a high infiltration rate. This may be achieved by land alternation that reduces the length and/or degree of slope, or by obstructing or impounding overland water flow. Mass wasting is caused by the increase in topsoil weight when the topsoil becomes saturated, thus creating a situation where it will be pulled downslope by gravity. Mass wasting may be controlled by tying the soil in place with deep-rooted plant species, or by installing physical barriers such as rock walls with foundations dug into the hillside.
Conservation technologies can reduce soil and nutrient losses, and in this way preserve water holding capacity and soil fertility, and make possible sustainable crop production. In many instances, the use of conservation technologies may increase crop yields by 50% (Pimentel et al. 1995, Siebert and Belsky 1990). It should be pointed out that climate and soil data are needed to determine suitable soil conservation measures. They include
- Amount, intensity and frequency of rainfall,
- Amount and frequency of runoff,
- Infiltration rate,
- Soil water storage capacity, and
- Soil profile characteristics (Hudson 1981).
Soil conservation practices fall into three general categories, as briefly described below:
In steepland farming, physical structures such as rock barriers, contour bunds, waterways (diversion ditches, terrace channels and grass waterways), stabilization structures (dams), windbreaks, and terraces (diversion, retention and bench) are often necessary (Morgan 1986, Bennett 1970). The construction of physical structures is often labor intensive, since steep slopes make construction difficult. Since building these structures is usually labor intensive, both construction and maintenance require long-term collaborative effort by farmers, the local community and the government.
An effective way to control erosion is to maintain a year-round vegetative cover which dissipates the erosive energy of rain. Seedbed preparation techniques such as minimum tillage and residue mulching can also help achieve this objective. Leguminous cover crops such as mucuna ( Mucuna utilis) can provide cover and fix nitrogen, thus making it also useful as a green manure. Vegetative barriers using grasses or trees planted along contours can be as effective as physical structures in controlling soil erosion. They can be established by farmers for little or no cost. Trees and grasses can also be harvested periodically for fuel and fodder. Often it is useful to combine vegetation conservation measures with physical structures, such as planting useful trees along the downslope side of rock barriers. Once established, the trees can strengthen the stability of the rock wall.
Integrated Watershed Management
A watershed, large or small, with its drainage patterns and different soil and land types, is a logical planning and management unit for agriculture and forestry. Land use activities within a watershed are such that if the upland portion is being misused and degraded, this may disrupt the stability and productivity of the lowland portion of the watershed as well. Downstream consequences of poorly managed uplands include stream siltation, exaggerated swings between flooding and low streamflow, and increases in soluble N, P and heavy metal loading of downstream aquatic ecosystems. For this reason, small-scale approaches to land use and management may be successful in the short run, but the long-term ecological stability and economic potential of the entire watershed may be undercut if interdependent elements of the landscape are overlooked. Thus, to insure long-term viability of downstream agriculture and urban development, it is necessary to invest in vegetation and physical measures in the upstream land use systems that can prevent degradation. However, the planning and design of agricultural watersheds must be a multidisciplinary effort. Past experience in the United States and other industrialized countries has shown that long-term commitments from land users, local communities and most importantly, technical and financial support from government agencies, are critical in the successful implementation of watershed management programs.
Physical and Vegetative Measures for Steeplands in Humid Regions
Physical structures are usually constructed along contours across the slope. They are used to reduce the steepness and length of a slope, and to intercept surface runoff and convey it to a stable outlet at a non-erosive velocity (Morgan 1986). Physical measures, particularly various forms of terracing designs, have a long history of use by agricultural societies around the world. The earliest are found in China, dated to around 2000 BC (Troeh and Thompson 1993). Early civilizations which used terracing methods were generally characterized by the need to farm sloping lands, and by an abundant supply of human labor. In the Yangtze Valley, in the twelfth century A.D., the Mongols forced the Chinese population living in the northern plains to retreat southward to the mountains, where they began to farm on steep slopes by constructing terraces. In the Philippines, Java, Sri Lanka and India, farmers have been building terraces for over 200 years (Bennett 1970). In Yemen, terraces 1.5 to 5 m high have been continuously cultivated for 3000 years (Vogel 1987). These techniques were passed on by the Arabs to Spain in the tenth century. Terracing and large-scale irrigation structures were used before 360 AD in Antioch, Syria, and supported a population of 400,000 at that time (Bennett 1970). Knowledge of terracing and irrigation was introduced into Greece by 600 AD (Bennett 1970). The pre-Inca culture Chavin, of South America, dated to 900-200 BC, built terraces on mountain slopes and constructed raised fields for intensive cultivation and sophisticated irrigation and drainage systems (Burger 1992). About 1 million ha of land was terraced in Peru under the Inca empire, of which about one third is still in cultivation today (Denevan 1985, cited by Lal 1990). Williams (1987) estimates that these terraces are retained by 3 billion square meters of rock wall that would have required at least 4 million person-years of labor for construction. This system is clearly a result of careful planning and design, as plots of considerable size were developed at the same time, requiring the very sophisticated organization of human labor.
Sheng (1977) described eight types of land treatment structures which are essentially all reversed-slope benches. Some are continuous, and some discontinuous. They differ in width to suit different crops and slopes ( Fig. 1(14)). These various categories of physical structures are briefly described below:
These are a series of level or nearly level strips running across the slope, supported by steep risers. The reverse slope of a bench is 5%, and the slope along the contour or horizontal is less than 1%. Bench terraces can be used for upland crops on slopes of up to 47% (25Â°). Where machinery is used, bench terraces are the most common technique for land modification. The possible width of the terrace without excavating into subsoil or rock is a function of both soil depth and land slope.
These are a discontinuous type of narrow (about 2 m), reverse-slope benches built across the hill slope in order to break long slopes into many shorter ones. The ditches are used to drain runoff and as roads. The width of the cultivable strips between two ditches is determined by the slope of the land, as well as by the type of crop grown. This land treatment can be applied to slopes of up to 47% (or 25Â°).
These are small round benches in which individual trees or perennials are planted. They can be used in dissected terrain and on shallow soils. Generally, they are supplemented by hillside ditches, orchard terraces and cover crops on steep slopes.
These are a continuous type of narrow terrace (1.75 m wide) which is used on steep slopes of up to 58% (30Â°). The spacing is determined by the planting distance between the trees. As orchard terraces are usually used on steep slopes, the space between two terraces should be kept under grass or a legume cover crop. Tree crops should be planted in individual basins in the spaces between the terraces. One terrace can accommodate two lines of trees.
These are bench terraces which have to be built over a period of several years, to minimize the cost of labor or energy. Normal bench terraces are staked out, but to begin with only one out of three is built. All terraced and unterraced spaces are planted in crops. The benches will intercept runoff from slopes above and reduce erosion.
These are similar to intermittent terraces, except that the spaces between the two terraces are used to plant semi-permanent or tree crops. The farmer can use the terraced land either for annual crops, or for tree crops.
These are constructed initially with contour bunds (or rock retention walls) 50 cm high on slopes over 12% (7Â°), and on soil with good infiltration. They are designed and constructed in such a way that the lower bund is level with the mid-slope between two bunds, so that a natural terrace will form after a few years of cultivation.
A unit hexagon is a special arrangement of a farm road that surrounds a piece of sloping land with discontinuous terraces, thus making the land accessible to four-wheel tractors. The hexagonal connections of roads enable each terrace to be entered at an obtuse angle. This land treatment is designed primarily for mechanized operations of orchards or annual crops on larger blocks of sloping land with a gradient of up to 20Â°.
Vegetative barriers may be the most cost-effective means of soil and water conservation on small farms. This is especially so when the costs of constructing bench terraces are high, or soils are not suitable for mechanical treatment.
Grass strips planted along the contour lines can also achieve a terracing effect. Deep-rooted grass species such as vetiver ( Vetiveria zizanioides) and elephant grass ( Pennisetum purpureum) are commonly used for such a purpose. Vetiver grass has long been used with success in India and Fiji. It was, however, once rejected as a soil conservation tool in Indonesia and Haiti, because the market price for essential oils derived from vetiver roots encouraged people to uproot the plants and make erosion worse (NRC 1993). Recently, the World Bank has been promoting the use of vetiver barriers as a soil conservation measure through an international vetiver network.
Alley or Hedgerow Cropping
Fast-growing, deep-rooted legume trees such as leucaena ( Leucaena leucocephala) have been planted in double or single rows in Indonesia and the Philippines by small-scale farmers on sloping lands to control erosion (Lungren and Nair 1985). Food crops are then planted in the alleys between the trees. Periodic pruning is needed to prevent shading of the food crops by the tree canopy. Once established, the trees facilitate terrace formation within the alley ( Fig. 2(13)). Alley cropping as a technique for nutrient recycling and soil conservation has been developed at the International Institute of Tropical Agriculture (IITA) in Nigeria. The system can sustain maize and cowpea yields and maintain soil fertility on the highly erosive Alfisols in the humid and subhumid transition zone of West Africa (Kang et al. 1985). Moreover, the leguminous trees fix atmospheric nitrogen, cycle mineral nutrients from the subsoil, and produce fodder and fuelwood (Kang et al. 1991).
Several legume trees have been used for this purpose, including leucaena, gliricidia ( Gliricidia sepium), and flemingia ( Flemingia microphylla). For the tree species to control erosion and runoff effectively, it must be fast-growing, deep-rooted, and have vigorous regrowth after pruning.
Alley widths of 4 m and 6 m have been used for alley cropping with leucaena, which is pruned periodically so that it does not shade the annual crop planted in the alley. The prunings are returned to the soil surface as a mulch to prevent erosion, and as a green manure for the annual crop planted between the alleys. Juo et al. (1994) reviewed published results on the effect of alley cropping on soil erosion as influenced by different soil types. As Table 1(10) shows, the tree alleys, once established, could effectively control soil erosion at the three erosive sites. On the Andisol site, on the other hand, there was no measurable erosion either under the alley treatment or from the tilled control.
Planting grasses, shrubs or trees along terrace edges stabilizes terrace structure, and can provide other benefits such as fuelwood, nitrogen fixation and forage. Combining physical structures with multi-use vegetation planted to stabilize the physical structures is a common conservation practice.
Surface Drainage Measures
Fig. 3(12) shows that there are three essential components of surface drainage systems on sloping lands. These include diversion or cut-off drains to protect the arable land from runoff flowing down from higher ground, graded channel terraces to lead runoff away at a non-erosion velocity, and a channel to take the water down the slope at a non-erosive velocity (Hudson 1988). In humid regions, the surfaces of drainage ways are usually protected by planting them with suitable grass species.
A critical part of the design is to estimate the maximum rate of runoff that the system should accommodate. With the exception of the United States, few countries in the world have accumulated sufficient soil and climate data to construct reliable and accurate tables or design charts. Moreover, most published runoff prediction methods were designed for large, mechanized farms, or for small watersheds under mixed use on gentle slopes. Data on catchments of less than 5 ha of arable land with different types of terracing on slopes greater than 15% are scarce. A preliminary study of such an area has recently been completed at a steepland site in southern Honduras (Smith 1997).
Physical and Vegetative Measures for Steeplands in Drier Regions
Generally, rainfall in arid and semiarid regions is characterized by high intensity (i.e., >50 mm/hr) and short duration. Under such circumstances, cultivation on steep slopes is not always possible. Instead, surface runoff from the bare or sparsely vegetated steep slope should be harvested for irrigating the crops planted in the valley bottom. Common land treatments for agriculture in this type of environment often include diverting runoff to crop fields in the valley bottom, and constructing various types of microcatchment on the slopes to reduce runoff and increase infiltration. The improved soil moisture regime thus enhances the growth and establishment of trees, shrubs and grasses inside and around the microcatchments.
In arid areas (i.e., areas with an annual rainfall below 200 mm), it is best to encourage and collect the runoff from a barren catchment area, and lead it to a cropping area in the valley bottom (FAO 1987, Hudson 1988, Finkel 1986). Surface runoff in a small watershed is encouraged by shaping the catchment and by removing the surface stones. Such water harvesting technique is known as `runoff farming', and was practiced many centuries ago in the Negev Desert (Evenari and Koller 1956). Level terraces were constructed in the valley bottom. These water-spreading terraces are known as "limanim", from a Greek term for port. The water filled the first terrace, and was then drained off at the side through a stone weir or over a low gabion into the field below. Similar water harvesting techniques were found in many parts of North Africa and other drier region of the world, and are still being used today.
In semiarid regions (i.e. areas with a mean annual rainfall of 200 to 800 mm), sloping lands are generally used for natural or managed pasture and fuelwood production (Reij et al. 1988). Microcatchments of various types can be built to reduce and collect runoff and increase infiltration along the slope. These microcatchments commonly consist of triangular and semi-circular or crescent-shaped earth bunds constructed along the contour line ( Fig. 4(10)). Water is impounded behind the bunds to the level of the contour, and eventually overflows to spread down into the next lower tier of the bunds. The radius of the semicircle and the dimension of the triangle are determined by the ratio of catchment area to cultivated area, and by the distance between rows (Finkel 1986).
In drier regions, vegetative barriers are generally used in combination with mechanical land treatments such as microcatchments. Once the tree and grass species inside and around the microcatchments are established, a combined system of land treatments can increase infiltration and control erosion. In West Africa, it has been demonstrated that the semicircular microcatchment not only collects runoff, but also gathers nutrient-rich dusts and seeds during wind storms, thus enhancing the establishment of natural grasses, legumes and other species inside and around the microcatchments (Manu et al. 1990). Drought-tolerant trees, such as Acacia holosericea and Prosopis africana, have been used to rejuvenate over-grazed lands in the semiarid tropical regions. Furthermore, grasses, trees, or other perennial species planted as vegetative barriers can also be used as fodder and fuel. In view of the increasing shortage of fuelwood and forage in the drier regions, especially sub-Saharan Africa, better management is needed of the vegetative cover of land degraded from decades of over-grazing and fuelwood collection.
Watershed Management: A Holistic Approach
As mentioned earlier, poorly planned land use activities in the uplands may adversely affect the productivity and environmental quality of the lowland portion of a watershed. In spite of numerous historical lessons, massive soil erosion from deforestation and subsequent land misuse continue to take place, as can be seen in available aerial surveys of different parts of the world. Curiously, the first major soil conservation movement in the United States did not take place until the 1940s. This led to the establishment of the first national Soil Conservation Services (SCS) in the early 1950s. To help with the formulation of sound land use policies, large quantities of climate, soil, hydrology and crop performance data have since been collected to facilitate the development of the Erosion Productivity Impact Calculator, otherwise known as the EPIC Model. Forest vegetation has since been restored to degraded upstream catchments such as those of the humid eastern and southeastern United States. The Conservation Reserve Program (CRP) has since been implemented to encourage farmers either to put marginal lands under long-term fallow, or to use improved soil management practices such as minimum tillage.
Watersheds cannot be improved by land users and local communities alone. Such programs require external financial and technical assistance for planning, design and construction of the necessary physical structures. It needs the active participation of water engineers, soil scientists, agronomists, forest and livestock managers and extension specialists (Hudson 1981). All of the physical and biological land treatment technologies described earlier will be needed to design and implement the various land treatments and farming practices. In most developing nations, the lack of climate, soil and hydrological data, particularly for small watersheds, constitutes a major obstacle to water planning and design. Information on land tenure, and on both traditional and improved farming systems, are also needed to justify initial investment for land treatment structures and irrigation facilities (Pereira 1989). Moreover, national planners should give equal importance to the restoration of small eroding catchments, and the protection of less disrupted ones.
Ideally, the steepland portion of watersheds should be left in forest or other forms of natural vegetation. Where the soil and climatic conditions are suitable, well-designed and carefully managed upland modifications such as the paddy rice terraces built on steep slopes in northern Luzon of the Philippines, and in Java and Bali of Indonesia, have proven to be ecologically sustainable for many centuries without disrupting downstream farming activity and water quality. On the other hand, there is abundant evidence that human activity has caused irreversible hydrological and land degradation in numerous large and small watersheds. Recent examples are the severely degraded steeplands in Haiti and Madagascar.
A review of recent literature has shown that the following factors are important in the planning of watershed management (Gil 1979, Meijirink 1988, Pereira 1989, Thurow and Juo 1995)
- It requires close collaboration among farming and non-farming communities, government agencies and research institutions;
- Appropriate incentives must be provided to local farmers if the improved practices involve changes in traditional land use;
- Initial investment from local and national governments is needed for conservation measures and public education;
- Economic incentives must be created through greater transfer of resources from downstream to upstream, in order to improve upstream conservation measures;
- Impact assessment must emphasize the long-term benefits rather than the short-term gains.
- With regard to the design and management of watershed activities, knowledge of the following elements are essential:
- Physical attributes, including topography and soil type, rainfall characteristics, drainage pattern and downstream sediment transport rates;
- Natural vegetation and its distribution;
- Land use and land tenure,
- Social and cultural characteristics of local communities,
- National land use policies, and
- Potential collaborating technical institutions and government agencies.
Where baseline data are readily available, Geographic Information Systems (GIS) and Global Positioning Systems (GPS) could be efficient and accurate tools for soil conservation planning, on both a watershed and farm level. For example, GIS can be used to locate various land treatment practices and identify users in watersheds. Assessment can then be made to indicate to what extent the watershed has been treated to an acceptable level. The GPS can be used to design mechanical or vegetative terrace systems, and assist individual land users in whole-farm soil conservation treatment (ICIMOD 1996, Juhl et al. 1997).
In general, individual farmers or land users within a watershed are interested in maintaining the profitable production of annual crops from the land which they cultivate. Although there has been increasing awareness of the need for a holistic approach to land use and management, success stories are still scarce. This is partly because of difficulties encountered in cross-agency collaboration, especially in case of large watersheds where national or local administrative boundaries may not coincide with watershed boundaries. Furthermore, conflicts of interest between upstream and downstream communities hinder the implementation of sustainable management policies and practices.
The beneficial effect of forest in regulating runoff and erosion in the steepland catchments is well-known. For example in Japan, the upper reaches of river basins are generally steep, and heavy rainfall is common. Forests in these areas are protected for water conservation. Such protected forests constitute about one-third of the total forest area in the country. Forest owners are informed about areas where tree harvests are permitted, provided that regulations on the size and age of trees are observed (FAO 1976). Such policies are derived from quantitative data of soil loss under different forest cutting patterns, as shown in Table 2(13). Downstream irrigation facilities are generally developed with investment from the national governments or local sources. Economic incentives are also provided by the government, to encourage sound land-use practices among both upstream and downstream land users.
Unfortunately, because of a lack of sound land-use policies and the necessary technical and financial resources, integrated watershed management remains mainly an academic exercise in many developing nations today. In small watersheds, most of the success stories are concerned with commercial plantations where both technical and financial resources are readily available. The large tea and coffee plantations in Kenya and Sri Lanka are among the best examples.
Where land resources are limited, both intensive and extensive livestock production can be a major problem in watershed management. In Africa, overgrazing on hillsides is a major cause of sheet and gully erosion. In Latin America, on the other hand, cattle ranches often occupy large areas of fertile flat land, while staple food crops such as corn, sorghum and beans are grown on hillsides by smallholders. Here, social and cultural traditions prevent any major changes in farming systems in the foreseeable future.
Useful Lessons Learned
Humans beings and land have been involved in a conflict of interest ever since farming and herding began (Lowdermilk 1953, Juo and Wilding 1997). In terms of soil and water conservation, history reveals numerous human failures and few success stories. The two most reported ancient success stories are the steepland rice terraces of northern Luzon, in the Philippines, and the runoff farming in the Negev Desert.
Rice Terraces of Northern Luzon
In a part of northern Luzon with suitable soils and rainfall conditions (i.e., appropriate intensity and distribution), spectacular rice terraces have been built over a period of several thousand years (Conklin 1981). This is probably one of the most sustainable steepland systems of rice cultivation. Such manually constructed rice terraces are widely found throughout the humid regions of southeastern Asia and southern China. The success of this type of land modification has been attributed to the small scale of land clearing and the construction of terraces, mainly by manual labor. Large areas of terraces and drainage systems were built little by little over a long period of time, so that soil loss was minimized.
Runoff Farming in the Negev Desert
In arid regions, the ancient runoff agriculture practiced by the Nabatean people (200 B.C. to 630 A.D.) in the Negev Desert is an example of a unique system of agricultural exploitation in a desert environment (Evenari and Koller 1956). In this case, the steeplands were left bare to encourage runoff during the brief, intense rainstorms characteristic of the region. Small "catchment runoff farms" were constructed in catchment areas located on slopes and in cultivated areas in the drainage bottomlands below the catchments. The ratio of catchment to farm plots varied according to the amount of runoff. The farm plots were constructed with rock dikes across the water courses, thus accumulating and conserving soil inside the plots. The catchment slopes were modified to maximize runoff. Stone conduits were built to carry water to various parts of the bottomland farm plots in needed amounts ( Fig. 5(14)). The cropping systems varied according to the size of the watershed and its drainage channels. Records show that a variety of crops were grown, including barley, wheat, legumes, grapes, figs and dates. The success of this system seems to be the result of relatively simple technological manipulation of the natural landscape in a manner that deals simultaneously with the problems of both water and nutrients (Cox and Atkins 1964). Unfortunately, the agrarian Nabatean civilization was destroyed about 700 A.D. by the invading Moslem Arabs, resulting in a subsequent change from permanent agriculture to nomadic herding.
Tea and Coffee Plantations
In recent times, the most notable successes in steepland use and management have been the tea and coffee plantations on steeplands throughout tropical and subtropical regions. The tea plantations in Sri Lanka, Kenya and Taiwan, and the coffee plantations in Java, Colombia and Jamaica, are among the many good examples. Most of these plantations are on welldrained soils. Tea is better adapted to acidic soils (Ultisols), while Arabica coffee requires high base status Alfisols and Andisols. In most instances, land was cleared manually in small parcels to minimize soil erosion. Bench terraces were constructed along contours, either manually or mechanically. Large-scale land clearing using heavy machinery was usually avoided. The fields were then gradually expanded to cover a larger area over a period of several years. In areas with intense rainfall, a cover crop is established immediately after land clearing to protect the soil surface. Dirt roads are aligned along topographic crest lines to allow easy access to tea or coffee gardens. Surface drainage systems are constructed to dispose of the runoff at a non-erosive velocity. Mulches are used, especially in newly planted plantations.
Rock Retention Walls in Venezuela and Honduras
Over the last three decades, considerable efforts have been made by national governments and international donor agencies to implement soil conservation programs for steepland farming in South and Central America. The USAID-sponsored rock retention wall projects in the Andes highlands of Peru and Venezuela, and on the hillside farms of Guatemala and Honduras, are among the most notable efforts. In areas where rocks of various sizes were readily available in farmer's fields, rock retention walls or rock barriers were built along the contours at intervals of 10 to 40 meters. They were made by skillfully stacking the rocks to form a firm barrier that would break the downslope flow of water and retain soils eroded from uphill (Williams and Walter 1988). The result was the evolution of terraces over a period of several years or more. Such techniques had been used by the Inca people in ancient times for terrace construction (Williams 1987). The obvious advantage of this technique in comparison with conventional bench terracing is the reduction in the labor needed for earth moving. Moreover, the many large rocks and boulders scattered over the slopes would make the operation of large earth-moving equipment extremely difficult.
Rock retention walls in large areas of intensively cultivated slopes in Venezuela and Honduras were constructed during the 1980s by mobilizing local populations through a government-sponsored "Food for work" program. Subsequently, the rock terraces were reinforced by planting useful trees which could be used for fuel and fodder. Corn, sorghum and beans are the major crops grown on the small hillside farms (Thompson 1992, Sierra 1996).
Natural Forest Reserves and Ecotourism in Costa Rica
Over the past few decades, the rate of deforestation in Central America has been among the highest in the world. National and international efforts to reverse this trend have been most successful in the mountainous country of Costa Rica. Large forested steepland areas have been purchased by government and private organizations for use as national parks and wildlife sanctuaries. Costa Rica now has 30 large national parks, biological reserves and wildlife refuges. Altogether, these comprise about 27% of the total land area of this small mountainous country in Central America (Janzen 1983, Harber 1993). Ecological tourism (or ecotourism) has become one of the nation's major foreign exchange earners in recent years. Although the creation of the nation's parks and protected areas began with a handful of fervent local and foreign naturalists, the successful nation-wide implementation of conservation measures has been attributed to the following factors:
- Relatively low population pressure;
- A high literacy rate (over 90%);
- The fact that there are very few foreign-controlled, large commercial cash crop plantations; and
- Public education which has placed a strong emphasis on conservation of the nation's forest and wildlife resources.
The impact of agricultural activity on steeplands has become a major concern throughout the world, particularly in areas with a high population density. A critical problem confronting both developing and industrial nations is the rapid deterioration of soil and water resources as a result of non-sustainable agricultural practices. Although some steeplands have been used successfully for tree and annual crop production, large areas of land are currently at risk because of intensive use and lack of conservation measures. If one defines "land at risk" as land where human and/or livestock populations exceed the carrying capacity of the land under current levels of technology and management (FAO 1982), then large areas of steeplands throughout the world risk irreversible degradation unless urgent action is taken to reverse this trend.
In order to address soil conservation on steeplands, it is important to understand the linkages within a watershed, and how conservation farming in upland systems affects the system as a whole. We also need to understand the trade-offs and decision-making process of both upland farmers and downstream residents. Most research on soil erosion and erosion control has been done on flat or rolling land with a maximum slope of less than 20%. Research on steepland has been neglected, in part because these lands are marginal for agricultural production. Unfortunately, this lack of research does not mean that this land is not being used or cultivated.
The likehood of expansion of agricultural activities on tropical steeplands makes research a pressing need, specifically focusing on steeplands as an integral part of each watershed, and studying steeplands within the context of the landscape in which they exist. In fact, steepland destabilization has been demonstrated to have a cascading effect, making their management a keystone factor in ecosystem and watershed integrity. Using watersheds as a planning unit can alleviate the cost of upland soil and water conservation activities by taking into account the benefits of such programs to downstream users (FAO 1990, Aldhous 1993, Thurow and Juo 1995).
The use of a watershed approach as a basis for planning and management is essential to achieve sustainability. Although technologies for conservation and management of steeplands are well-demonstrated and well-documented, farmers and local communities in many developing nations have few or no resources for conservation measures. Thus, national and international assistance is needed to restore, manage and conserve these endangered steeplands, to the benefit of both upstream and downstream human communities, as well as the natural ecosystem.
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Index of Images
Figure 1 Cross-Sectional View of Eight Types of Bench Terraces
Figure 2 The Concept of Alley Cropping on Sloping Lands
Figure 3 Surface Drainage System Constructed Mechanically on Sloping Lands
Figure 4 Schematic Drawings Showing Semicircular and Triangular Microcatchments
Figure 5 A Schematic Diagram Showing the Design of Rock Barriers Used to Spread Water in Large Shallow Wadis Onto Lateral Portions of the Flood Plain in Runoff Farms of the Nabateans in the Negev Desert. Redrawn from Evenari and Koller (1956).
Table 1 Effect of Five or More Years Old Alley Cropping with Various Woody Species on Soil Erosion
Table 2 Soil Loss under Different Forest Cutting Patterns on Experimental Plots of 30 Years Old Japanese Red Pine (Plot Size 40M Long and 20M Wide; Slope 30Â°) in Okayama Prefecture, Japan (Annual Rainfall 740 MM).
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