4.1. Impacts of Land Competition
4.2. Impacts of Competition for Crop Residues
4.3. Impacts on Socio-economic Factors
4.1.1. Impacts on vegetation
4.1.2. Impacts on wildlife
4.1.3. Impacts on soil conditions
4.1.4. Impacts on water resources
Of particular concern is the extension of cropping into marginal lands and fragile ecosystems. Traditional land use systems, especially in sub-Saharan Africa, tend to encourage cropping because rights to land are gained by cultivation not grazing. As a consequence, grazing areas will be reduced and since the more productive rangelands are usually converted into cropping, so the productivity of the remaining grazing resource is also likely to be lower.
Any displacement of grazing land, including fallows, following an expansion of cultivation would be aggravated if existing stocking rates were maintained or actually increased as a result of the ownership of more livestock. The consequences of this would be overstocking. The likely negative environmental effects would then be similar to those experienced in extensive pastoral systems, when animal numbers exceed the optimum carrying capacity. In practice, although stock numbers determine current crop-livestock interactions, competition for land between crops and livestock does not limit the stocking rate until relatively high human population densities are reached (McINTIRE et al., 1992). Land competition is strongest in highland areas, e.g. sub-Saharan Africa, because population densities and stocking rates are already high.
The decision to expand cultivation in the pastoral areas of China has had an enormous impact on the resources available for use by traditional pastoralists (LONGWORTH and WILLIAMSON, 1993). In the Chifeng City Prefecture of the Inner Mongolia Autonomous Region, for example, 21 percent of the total rangeland in the prefecture was lost to agricultural production between 1953 and 1979. However, the real reduction in pasture resources is likely to be considerably greater for a number of reasons. First, the rangeland brought into agricultural use would almost certainly have been the more productive, better quality grasslands. Secondly, the official statistics relating to the area of land reclaimed only included currently farmed areas. Large amounts of poor quality rangeland destroyed by cultivation, which are no longer cultivated, were not recorded in the official statistics. Thirdly, official figures may understate the actual area of agricultural land successfully cultivated and converted from rangeland. Furthermore, the destruction of rangeland is not specifically confined to land reclaimed for agricultural use. In most cases, pastures surrounding the newly developed agricultural areas become severely degraded. Arable farmers also keep small ruminants which intensively graze the surrounding rangeland adding to the increased grazing pressure.
A further example of major land degradation, initiated by an expansion of cropping, is given by TREACHER (1993) for the rangelands (steppe) of Syria, where 75 percent of the sheep population is kept. A key influence at the start of the process was the introduction of tractors in the 1950s which allowed easy cultivation of the steppe, particularly in the areas of higher rainfall and better soils. In the 1960s, the drilling of new wells allowed grazing in areas which were formerly protected for long periods through water shortage and inaccessibility. Then, the purchase of water-tankers permitted richer flock owners to graze even more remote areas for longer periods. Flocks could also be moved rapidly by lorry to good grazing areas, and the pressure on the remaining steppe increased. This was further intensified by the progressive abandonment of tribal control of steppe and the transfer to individual ownership. Despite measures introduced by the Syrian Government to prevent further degradation, the process has continued. Since about 1970, there has been a steady expansion of sheep numbers and an increase in demand for barley as feed. The area of barley has increased and further intensified the grazing pressure in the decreased area of steppe. Palatable bushes have been overgrazed and disappeared, and unpalatable ones used for fuel. Speculative barley-growing financed by urban investors has accentuated the degradation process. This example shows the complexity of the linkages involved as cropping extends into grazing areas. Whilst the ratio of grazing to arable land gives a measure of this encroachment, the quantitative impact on the environment will depend on local vegetation and soil conditions etc., and the indicators must take these into account.
An increase in irrigated cropping systems has resulted in many areas in a decline in land productivity through salinisation and waterlogging. REPETTO (1987) refers to FAO estimates that half of the worlds irrigated land is so badly salinised that yields are affected, with 1-1.5 million hectares of prime land becoming salinised annually. Salinisation is a problem in irrigated systems in South Asia, Central Asia, West Asia and North Africa, North America and Eastern China. High water tables markedly concentrate salts in the root zones. In India and Pakistan, where irrigation has been practiced without adequate provision for drainage, water tables have risen to within a few metres of the surface across broad zones. Providing drainage can add substantially to water resource project costs. The process of salinisation can be controlled through a variety of methods including improvements in the efficiency of water application and conjunctive use of ground and surface water supplies. Although salinisation is not an effect of the integration of livestock with cropping, salt concentrations in soils and the quality of water used for irrigation need to be taken into account, and indicators developed for these systems (Sections 6.2 and 6.3).
However, in some situations, a loss of the rangeland resource due to the expansion of cropping can be compensated for by an increased availability of crop residues, the development of zero-grazing systems and the planting of high-yielding improved forages on reduced land areas or in backyard production systems. This has occurred in parts of the East African highlands with the use of Pennisetum purpureum and multipurpose trees.
Overgrazing decreases the productivity of grasslands and changes floristic composition, with losses in plant diversity and desirable species. Successional changes in the vegetation usually result in perennial species being replaced by annual or ephemeral herbs, and palatable shrubs and trees by more xeric vegetation dominated by spiny or succulent species. Areas devoid of vegetation appear that are vulnerable to water and wind erosion.
There are numerous examples in the literature of adverse successional changes in vegetation as a consequence of overgrazing. In West Africa, BREMAN and CISSE (1977) have noted the disappearance of the perennial Andropogon gayanus in overgrazed Sahelian pastures, and its replacement by short-lived legumes and unpalatable annuals. In South-East Asia, FALVEY and HENGMICHAI (1979) found that pastures of Imperata cylindrica were invaded by unpalatable broad-leaved species of Eupatorium when grazing pressure was increased. Overgrazing in three areas of the Western Ghats in India resulted in the elimination of dominant grasses such as Themeda triandra, Themeda quadruvalis, Pseudanthistiria heteroclita, Heteropogon contortus and Anthraxon meeboldi (BHARUCHA and SHANKARNARAYAN, 1958). They were replaced by less palatable species of Aristida, Dicanthium and Eragrostis, and the useless weed Blumea eriantha. As well as stocking intensity, differences in grazing system can also influence botanical composition (BOGDAN and KIDNER, 1967; WALKER and SCOTT, 1968). Control of stock numbers and grazing management can often reverse these adverse successional changes. The positive impact of protection from free grazing on vegetation changes and erosion in arid and semi-arid areas of North-West India is described by KUMAR and BHANDARI (1992).
Changes in plant communities or single species can, therefore, be used as indicators of range trend and condition to detect local environmental impacts of a decreasing grazing to cropping ratio. These are quantified in Section 6.1.
In theory, the multiple use of grasslands by grazing and browsing animals is a sound ecological system that can be highly productive per unit area of land, because different animal species are at most only partially competitive for food when supply is abundant. This argument is relevant to the utilisation of grazing resources by both wildlife and domestic livestock. In sub-Saharan Africa, where the wildlife endowment is particularly unique and diverse, WINROCK INTERNATIONAL (1992) concluded that wildlife and domestic livestock were compatible in most rangelands across all agro-ecological zones. For example, in Zimbabwe (formerly Rhodesia), eland were found by LIGHTFOOT and POSSELT (1977) to be well adapted to complement cattle in the low and middle veld, where their preference for browse was important for the utilisation and control of woody plants. Similar observations were made in East Africa by SKOVLIN (1971).
However, the expansion of cultivation and high livestock densities are resulting in the displacement, fragmentation and reduction in wildlife populations through changes in, or the destruction of, habitats and competition for diminished grazing and water resources. On the other hand, wildlife are blamed for transmission of diseases to cattle, destroying crops, breaking fences, damaging irrigation ditches and for predation.
Although protected areas exist, these only cover roughly four percent of land in sub-Saharan Africa. Even protected areas are now subject to encroachment by arable farming and domestic livestock. MONDAY and INFIELD (1993) studied the effects of increased human and livestock activity in the Lake Mburo National Park in Uganda. Originally a well-balanced Themeda- Acacia association, overgrazing and trampling by cattle, accentuated by burning, resulted in the invasion of well-drained hillsides and hilltops by Acacia hockii, which formed dense, inaccessible thickets. The proportion of Cymbopogon nardus increased dramatically and this grass, with a high content of essential oils, was grazed neither by domestic animals nor wildlife. In the valley bottoms, unpalatable sedges and Sporobolus pyramidalis dominated. The diversity of both flora and fauna has been reduced, and the incidence of erosion has increased. Some large mammals are now extinct in the reserve and populations of other species are much reduced. The authors of the survey concluded that the greatest threat to wildlife in this park came from overstocking.
In West Africa, an increase in cultivation, the utilisation of woodlands by Sahelian cattle and hunting has caused fragmentation of wildlife populations and an appreciable reduction in numbers. Under these conditions, there is competition for forage resources and water, especially in the dry season. Only elephant and giraffe are free from competition due to a capacity to browse above a height of 1.75 m, the upper limit for cattle. BIE (1991) concluded that the introduction of livestock into areas occupied by wild ungulates had serious negative effects on the composition of wildlife communities and that the cultivation of food crops was incompatible with the conservation of large ungulate populations in this region. Overstocking not only caused a decrease in forage availability, but altered the composition and structure of the vegetation. It would appear that the ecological carrying capacity of West African savannas is lower than in comparable ecosystems in East or Southern Africa. West Africa is less diversified in its vegetation due to differences in soil nutrient status, and the Harmattan winds from the Sahara Desert place an extra physiological stress on ungulates in the dry season.
Similar conflicts have taken place outside Africa. For example, ALEEM (1978) found that overgrazing and wood cutting caused a deterioration in vegetation, increased soil erosion and habitat destruction in the Chitral Gol Game Sanctuary in Pakistan. The wild goat (the Markhor), a key species in this location, was particularly under threat from domestic goats and sheep which grazed plants preferred by the Markhor.
It is worth mentioning briefly that the use of herbicides in arable farming and the use of pesticides for the indirect control of animal diseases (e.g. spraying to reduce the numbers of tsetse flies to counter trypanosomiasis) could also have negative effects on the populations and diversity of fauna.
Although changes in wildlife numbers and species diversity are obvious indicators of the effects of livestock, these are of concern at a global rather than local level. Indicators for these changes are being developed in the Wildlife Diversity Impact Domain study.
The hooves of livestock not only have direct effects on plant growth, but influence indirectly soil structure by pulverisation and compaction of the surface. Treading, which causes a packing of soil particles and a loss of the larger pores in the soil mass, results in an increase in bulk density. This, in turn, reduces aeration, moisture infiltration and retention, and drainage. Resistance to root penetration increases and biological and chemical activity in the soil decreases. Gaseous composition of soils is also affected. Treading increases run-off and erosion, which are both positively correlated with bulk density. Erosion leads to losses of dissolved nutrients in surface run-off or overland water flow, and transport of nutrients adsorbed or chemically-bonded on soil solids. Thus, erosion contributes to a decline in soil fertility. Soil particles reaching drainage channels cause sedimentation of water courses downstream reducing the capacity of dams and reservoirs. Increases in annual stocking rates and grazing pressure accentuate these effects, whilst stall-feeding animals in confinement would eliminate them.
In the grasslands of the Western Ghats in India, BHARUCHA and SHANKARNARAYAN (1958) found that both mechanical and chemical composition of the soil were markedly altered by trampling and overgrazing. Clay content, which forms the bulk of the colloidal complex of the soil and from which nutrients are available to plants, ranged from 50-69 percent in undergrazed areas compared to only 8-36 percent in overgrazed parts. Soils in the latter areas were sandy, due to depletion of vegetation by overgrazing, and the appearance of bare ground where the clay content was seriously eroded. With changes in mechanical composition, moisture content also varied, and average contents were more than 50 percent lower in the overgrazed areas compared to those that were undergrazed. Organic matter levels and base exchange capacities also declined significantly in the overgrazed parts. Total exchangeable bases and exchangeable calcium contents followed a similar trend.
FULS (1992) studied the influence of patch overgrazing on soil conditions and range hydrology in the semi-arid climax grasslands of Southern Africa. Long-term patch overgrazing resulted in vegetation retrogression, soil compaction and the loss of substantial quantities of topsoil. Soil moisture decreases of up to 60 percent were observed in the degraded patches.
Changes in the physical and chemical properties of soils from both cropped and grazing land can be used as indicators of the effects of a decreasing grazing to cropping ratio on the environment (see Section 6.2). Indicators are also included for irrigated systems.
In high population areas of sub-Saharan Africa, for example, the increased use of land for arable farming will lead to the intensification of milk and meat production on small farms (WINROCK INTERNATIONAL, 1992). Under these conditions, the feeding of livestock in confinement with cut-and-carry forage is likely to be of increasing importance. High livestock densities in small compounds will pose problems of water pollution, sanitation and hygiene. Resource-poor farmers are unlikely to be able to afford investments in infrastructure that will be required to satisfy minimum safety standards. The greatest risks are expected to be in the peri-urban areas and in densely-populated highland areas. Increased use of artificial fertilisers and eroded plant nutrients also lead to water pollution, with enrichment of nitrates in surface-water. Other sources of pollution in surface and ground-water are faecal micro-organisms, herbicides and pesticides.
The nitrate content of water and the presence of micro-organisms that are a human health hazard would be two measurable indicators of the impacts of increased confinement of livestock on water quality, and are quantified in Section 6.3. Indicators for irrigated systems are also included.
Crop residues may be used for livestock food or as mulch, compost and windbreaks. In Europe and the Southeastern USA, residues have been burnt before establishment of the next crop, resulting in considerable aerial pollution. Any reallocation of residues away from soil conservation purposes could have negative environmental implications. STANGEL (1993) has reported that, in sub-Saharan Africa, substantial amounts of crop residues (and manure) are being put to non-farm uses such as energy and building rather than being returned to the soil. In the semi-arid West African tropics, BATIONO et al. (1993) have concluded that soil fertility can only be maintained through efficient recycling of organic materials in combination with chemical fertilisers and the use of nitrogen-fixing species in rotations. The various uses of crop residues and competition amongst the various uses needs to be addressed according to the authors.
Experimental data are available from India (BALPANDE et al., 1991; VERMA et al., 1992), South America (SANCHEZ and BENITES, 1987; BRAGAGNOLO and MIELNICZUK, 1990) and sub-Saharan Africa (PICHOT et al., 1981; BATIONO et al., 1989), which illustrate the effects of crop residues on soil properties and crop yields. The principal benefits of using crop residues for mulch have been summarised by SRIVASTAVA et al.(1993):
· Mulching conserves soil and water through improvements in soil structure and macroporosity; increases infiltration rates; decreases losses due to run-off and evaporation; and reduces raindrop impact, soil splash and water erosion. Most of the rain falling directly on bare, crusted soil is lost by surface run-off and evaporation. Consequently, crops suffer from frequent and severe drought even during the wet season. Mulching with crop residues can conserve water in the root zone, increasing crop growth and yield.Crop residues can also be effective in reducing wind erosion. Water is the major erosive factor in most areas where agriculture is practised. However, as climate becomes more arid so wind erosion becomes more important, particularly where soils are loose and sandy, vegetation cover sparse and wind velocities high. Two processes are involved in wind erosion. Firstly, saltation lifts coarse particles into the air and deposits them 1-2 m down-wind. Secondly, finer particles are lifted into the air and deposited considerable distances away in dust-storms. Wind erosion is most effectively controlled by reducing wind velocity at the soil surface or creating a non-erosive soil surface (SRIVASTAVA et al., 1993). Standing vegetation is a more effective barrier against wind erosion than the same quantity of vegetation lying flat on the soil surface (FRYREAR, 1989). Thus, the collection of crop residues or their utilisation in situ by livestock, would mean that it would not always be possible to leave vegetation standing for extended time periods, thus exposing the bare soil to wind erosion in the dry season.
· Mulching increases soil organic matter levels and enhances soil fertility through the addition of plant nutrients contained in the biomass. Cereals add cations such as potassium, calcium, and magnesium. Legume residues also supply nitrogen.
· Mulching moderates soil temperature. In regions such as the Sahel, seedling mortality is high due to excessive soil temperatures. Mulch applied at rates of between 4-6 t/ha can reduce soil temperature by 15-20°C.
Although in regions such as sub-Saharan Africa there is potential conflict between the use of crop residues for livestock feed and mulching, the fact that livestock almost exclusively eat the leaves and leaf-sheaths would allow the stems to be used as a surface mulch or incorporated into the soil.
As mentioned in Section 3.3, crop residue utilisation is unlikely to be useful as a measurable indicator of direct environmental impact at local level.
4.3.1. Land competition
4.3.2. Competition for crop residues
4.3.3. Competition for labour availability
An expansion of the cultivated area could deny pastoralists access to traditional dry-season grazing resources. For example, the fadama (wetland patches) of Northern Nigeria are important grazing areas for Fulani pastoralists. Access to this land is becoming increasingly restricted as agriculture expands as a result of government and donor-sponsored development schemes that have encouraged wheat production and the use of pumps for irrigation (KOLAWOLE, 1991). The author does not comment whether the crop residues are made available to pastoralists, but this seems unlikely given that the cultivators themselves are often raisers of livestock. In The Gambia the expansion of rice production in swampy areas has replaced an important source of dry season grazing which is leading to increased pressure on rangelands (RUSSO et al., 1986). In Zambia increasing competition is reported between herders and rice farmers for access to wetlands (KOKWE, 1991). Agricultural use of bas-fonds in Burkina Faso has severely reduced the availability of grazing for pastoralists (HOTTINGA et al., 1991). The loss of wetland grazing is of crucial importance to pastoral groups as these areas remain productive throughout the dry season and are considered as key grazing resources. There is also a danger that the expanding frontier of cultivation will also increase pressure on these resources from the livestock of cultivators which will be herded away from farms during the growing season.
Therefore, the effect of diversification which is a rational response by cultivators to prevailing economic conditions is the increased marginalisation of pastoralists which probably forces them to over-exploit their grazing resources, resulting in environmental degradation and a reduced capacity of rangeland to maintain livestock. In the longer term, these groups may be forced to adopt a similar strategy to the mixed farmers, where this is technically feasible. Only the most arid regions that are unsuitable for any cultivation will remain as extensive livestock-producing areas.
A knock-on effect of competition between herders and cultivators will be additional pressure from migratory livestock producers on areas protected for wildlife or the maintenance of endangered species and habitats such as National Parks and game reserves. During periods of drought, conflict may develop between protected area managers and herders seeking grazing. These areas are potentially valuable not only in terms of the maintenance of biodiversity, but are also important to the national economy, generating income from the tourist industry.
Therefore, changes in the relative prosperity of herders and farmers can be used as socio-economic indicators of increased competition for land. The potential economic impact of increasing settlement, grazing and cultivation of protected areas (National Parks etc.) can be assessed by calculating the actual use value (PEARCE and TURNER, 1990) (see Section 7.4.1).
The major responses of farmers to land competition between crops and livestock (i.e. between cultivators and herders) has been the intensification of production and the use of more labour per unit of land, greater quantities of fertiliser and manure, higher yielding varieties, and more careful use of crop residues as livestock feed. These changes postpone conflicts between cultivators and pastoralists although increasing population growth may eventually result in the adoption of mixed farming by both groups (McINTIRE, et al., 1992) except under arid conditions unfavourable to crop production. In the absence of yield-enhancing technology the development of conflict is likely to occur that much earlier in the development process.
McINTIRE et al. (1992) assessed the reallocation of crop residues within crop-livestock systems in three African countries. They concluded that reallocating crop residues from animals to crops would not be efficient in two of the three sites analysed because the opportunity cost of the loss of livestock fodder was too high. At the third site the opposite occurred because the maintenance value of crop residue used as livestock fodder was lower, and could be sacrificed to expand crop production via mulching. Thus, the economics of reallocation are very much dependent upon the availability of other sources of animal feed. Under humid African conditions, where livestock densities are lower as a result of disease challenges (trypanosomiasis), the use of residues for mulch is more likely and will have little effect upon livestock production.
It appears that as crop-livestock farming expands at the margins of crop cultivation and natural pasture so there is increasing competition for the use of crop residues between mixed farmers and pastoral groups. Traditionally, in much of West Africa pastoralists have depended upon the availability of crop-residues for dry season grazing. In return farmers benefited by having dung deposited on their fields. These reciprocal arrangements are breaking down as cultivators diversify into animal production and adopt draught animal power for cultivation. Consequently, pastoralists are increasingly denied access to these crop residues forcing them to seek alternative fodder sources and contributing to over-exploitation of range resources. The increasing privatisation of crop residue resources and the development of trade in these products will indicate their increasing scarcity (see Section 6.4).
In general terms, livestock production requires a fairly constant supply of labour throughout the agricultural seasons, whereas crop production has marked peaks and troughs for labour demands. Some seasonal unemployment or underemployment is, therefore, inevitable unless, for example, hiring of labour is possible to account for the needs for planting and harvesting of arable crops. However, the relative importance of crops or livestock to a farming system is not only governed by labour availability but also by the relative profitability of each enterprise and the effect of this profitability on labour productivity. If livestock have a comparative advantage labour is likely to be redirected to livestock production.
Crop-livestock interactions and the relative importance of each enterprise are affected by labour availability and the seasonal nature of labour requirements for each activity. Crop-livestock farmers in developing countries must have slack resources if they are to incorporate additional activities in the production process. Even if new activities such as animal traction or the incorporation of manure are profitable, they will not be adopted if they require incremental labour that is not available on the farm or cannot be purchased. This explains the use of techniques that, although technically inferior, require less labour. For example, the use of paddocking of animals on arable fields for manuring, which although less technically desirable than composting or incorporation, will often be the only realistic method of manuring for the farmer with limited labour. Fallowing is the least labour-intensive method of maintaining fertility and is, therefore, the most appropriate technique where land is abundant and labour scarce. At low population and land cultivation densities, animals graze pasture at lower stocking rates. This practice has high land inputs and low labour inputs per unit of output. As farming intensity increases, fallowing no longer remains a viable means of maintaining fertility as there is insufficient land. Thus, the addition of manure, legumes and chemical fertilisers, irrigation and modern varieties replace fallows as a means to maintaining output.
As agriculture becomes more intensive and returns per unit of land are increased so labour intensity increases. For example, sown forages are almost unknown in semi-arid environments as natural pasture and crop residues are cheaper, particularly in terms of the labour required for their use. As more profitable commodities are produced by the farming system (e.g. milk) so it becomes economically feasible to invest labour time in the production of forage.
The question facing the crop-livestock farmer is how best to deploy available labour resources. Under most conditions few farmers will forsake crop production, which guarantees their subsistence, for additional livestock production where markets are weak. Increased investment in livestock production will only occur where markets are guaranteed or complementarity between crop and livestock production is enhanced (e.g. animal traction). Crop production for subsistence and sale remains the primary objective of rice-based farming systems in Asia, although livestock production is important and integral to rice production. Intensive ruminant production is unlikely to replace rice production in the foreseeable future in the absence of mechanised methods of tillage.
Labour productivity is generally increased with the use of draught animals for tillage which should, in theory, release labour from field operations to alternatives such as more intensive livestock production and non-farm income-earning opportunities. However, in practice, McINTIRE et al. (1992) observed that, despite labour savings per unit of land cultivated, labour use per farm actually rises in sub-Saharan Africa as the area cultivated increases. Therefore, mechanisation does not generally release labour for other farm operations or non-farm activities. Mechanisation may actually increase labour demands for weeding and harvesting if these operations are not mechanised (harvesting rarely is), creating further labour bottlenecks.
It is impossible to attribute environmental degradation to the allocation of labour resources in a mixed farming system. There is one case where attempts by farmers to overcome labour shortages in crop production may have detrimental environmental effects. The introduction of draught power to African farming systems has been viewed as a means of increasing labour productivity by reducing the labour requirements for land preparation and weeding operations. Generally, the introduction of the technique has led to increases in the area cultivated which in turn has implications for the long-term fertility of the land (MUNZINGER, 1982).
The allocation of labour within crop-livestock systems in unlikely to have a direct environmental effect. However, the need to allocate increasing quantities of scarce labour to livestock is often a direct consequence of environmental degradation. As pasture resources become degraded so it is necessary for crop-livestock farmers to travel greater distances to find suitable pasture. This activity often takes place during the growing season and restricts the availability of labour for crop production. Therefore, the movement of animals over greater and greater distances by agro-pastoralists not only has an effect upon the availability of meat, milk and manure but also has implications for the availability of labour for crop production. Accordingly, distances travelled to pasture will be an indicator of the availability of grazing and the quality of pasture. The consequences of the need to travel increasing distances will be shortages of labour for crop production, increasing dependence upon female labour, less manure for crop production and declining or seasonal availability of meat and milk for household consumption and sale.