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3. Land degradation by main type of rural land use in dryland areas
3.2 Land degradation and rainfed agriculture
3.3 Land degradation and irrigated agriculture
3.4 Land degradation and rangeland management
3.5 Land degradation and woodland management
There is both competition and complementarily of land uses in a spatial context. Traditional land users in drylands are often versatile; they adapt to the often very local rainfall variability through year-to-year changes in agricultural practices and herding. The current transformation of communal lands into private ownership, especially when absent ownership is involved, creates a rigidity that is detrimental to such versatile land uses.
Land uses in drylands are very complex, for example, cultivated land is usually grazed between crops. The description below of land degradation aspects in relation to rainfed farming, irrigated farming, rangeland and woodland use, respectively, is therefore a rather artificial undertaking.
There is an acute need for systematic analysis and georeferencing of the various forms of multiple land use in dryland areas, including aspects such as inputs, labour requirements, local redistribution of soil fertility, as a prerequisite for any well integrated intervention to halt land degradation and rehabilitate rural livelihood systems. Each landscape and each occupational system needs its own solution; there is no panacea.
3.2 Land degradation and rainfed agriculture
Rainfed agriculture is practiced in drylands all over the world. It is a major cropping system which provides considerable amounts of crops, particularly cereals and legumes. Lands under rainfed agriculture, although often marginal in some areas, are important land resources and provides livelihood for several social groups and are managed traditionally under complex land use systems.
3.2. 1 Causes
Rainfed arable lands in arid, semi-arid and subhumid areas have been extensively degraded due to population pressure and to the struggle to produce more in order to satisfy growing food needs. Specific causes of land degradation arc inappropriate land-use practices and farming techniques.
- Encroachment of farming into areas where risk of drought is high or on to other marginal lands (see 3.4.3).
- Shortening of cycles in farming. Reducing the fallow period in shifting cultivation in dry tropics.
- Inadequate restitution of plant nutrients to the land.
- Monoculture or lack of adequate crop rotation.
- Clean fallowing and excessive tillage.
- Divorce of arable farming from livestock production.
- Ploughing and planting crops down the slopes in sloping lands.
- Deterioration of terraces and other soil and water conservation structures, (often because of labour shortage, as in areas of strong migration).
Rainfed arable land in the drylands is subject to; range of degradation hazards, including erosion by water and wind, sandblasting of crops and emerging seedlings on arable land and rangeland, deposition of windblown sand, plant nutrient depletion in the soils, surface sealing or crusting, salinization in some areas. These hazards are generally more severe than in more well-watered regions, for several reasons.
During the long dry season, crop residues are exported from the land or ire consumed by livestock belonging to the farmers or to pastoraliste, by wildlife or by termites. This leaves the fields essentially bare to the impact of the early rains, and to wind action during the dry season. Traditional defence to these hazards was by adequate fallow periods.
The soil material eroded by wind or water generally is more fine-grained and contains more organic matter, and the coarser grains are left. Most of the plant nutrients are contained in the fractions of the soil that are lost. The amounts of such nutrient losses may even exceed the amount of nutrients removed in the harvest or in the crop residues eaten and in part removed by the animals.
The year-to-year variability of the rainfall in drylands and of its distribution over the rainy season entail a great risk to the farmer, so that inputs applied at the start of the crop season such as fertilizer, or indeed seed or labour for land preparation, might not be repaid by the crop yield in low-rainfall years.
The consequent tendency to low-input, variable-yield farming systems is a sound economic strategy in principle, and this may work well where land is relatively abundant and where dry season grazing is light, recycles plant nutrients and allows some cover to remain until the start of the next rains. Fig. 4 shows plant nutrient dynamics in mixed farming systems, and demonstrates the spatial interaction between grazing land, rainfed arable land and irrigated land in terms of nutrient depletion, transport by various means, intentional (e.g., by manure from livestock) or unintentional (for example through runoff), and concentration of plant nutrients on the more intensively used land.
In the many places where increasing numbers of people and livestock lead to greater intensity of cultivation and grazing, however, a downward spiral of decreasing soil fertility starts, resulting in low crop yields even in, years with good rainfall. The small amounts of crop residues then provide poor cover, and soil erosion aggravates the nutrient losses.
Silty or loamy topsoils are generally liable to seal or crust under rain impact; especially where organic matter contents are low and where there is little soil cover. Such conditions are aggravated, through excessive grazing on crop residues or grazing land, or through plant nutrient mining, low-input arable farming. The resulting runoff may accelerate removal of plant nutrients and decrease the amounts of moisture available to the next crop or the vegetation, aggravating the downward trend in productivity.
In a small proportion of the drylands, groundwater occurs at depths of only a few meters. There, the natural vegetation has root systems with very different depth distributions, and thus draws moisture from a great range of depths. Salts tend to be distributed throughout the rooting zone, and seasonally fluctuate in depth and concentration. Where such land is cleared and used for arable crops, initially these may use less water, and that mainly from the upper soil layers. In these conditions the groundwater table may rise gradually, until capillary rise brings the groundwater within reach of the crop roots and eventually, within reach of the surface. Then, the upper soil layers rapidly become saline, and crop yields fall or the crop fails.
Traditional defense against this dryland salinization (differing from that under irrigation) has been the planting of tree lines or groups of trees in sufficient number to keep the groundwater level down by the increased transpiration and water uptake through their deep root systems. Areas with such hydrological characteristics thus provide loot}! a hazard of salinization and the opportunity to combine arable or grazing use with wood production.
3.2.3 Measures for land degradation control in rainfed agricultural areas in drylands
The conservation and rehabilitation of rainfed agriculture areas in drylands should be part of a holistic approach to sustainable agriculture and rural development (see: 4) or through improving land use and agricultural techniques; participation of land users at all stages of planning and implementation, training and research and adoption of legal measures.
Actions aimed at improving land use at national level include:
making an inventory of national land resources;
assessing potentials and constraints in dryland farming and identifying agricultural options to safely increase cropping intensity and yields, decrease risks and' offering other advantages while reducing land degradation;
studying the reasons behind poor land use, including land tenure-based problems, pricing of agricultural goods, subsidies, taxes, laws and social customs;
encouraging farmers to adopt more sustainable forms of land use, including contingency crop planning in the case of droughts.
Improving agricultural techniques should cover biological (agronomic) techniques and mechanical measures. Biological techniques such as: improved and diversified farming systems with appropriate inclusion of livestock, multipurpose tree and shrub, arboriculture, including adapted fruit trees; improved crop rotation; shelterbelt establishment, revegetation of watersheds, sand dune fixation, supplementary irrigation. Mechanical techniques include improved land preparation methods, soil and water conservation techniques, water harvesting, etc...
Where water is available, even in small amounts, from groundwater or from runoff captures in farm ponds, for example, the irrigation of a small proportion of the land can drastically improve the resilience of farm families against droughts by the increased food and feed security. At the same time, the productivity increase would lower the pressure on the rainfed land from livestock and thus allow some more cover to be retained on the soil. These favourable consequences would only materialize, however, where the increase in productivity is not immediately overtaken by increases in human and livestock populations.
For effective participation of land users in all stages, the role of governments must change from that of implementor to facilitator. The ideal programme for improved land management is one in which land users plan and implement solutions for their own benefit.
National training and research institutions need. to be strengthened to support development in rainfed agriculture, in drylands and land use planning.
Legal measures may need to be adopted to provide a sound framework for land use planning; they should take into account effective traditional land rights and aspects of collective land management. i
Legal limits may be needed to cultivation by tractors ploughing in marginal lands, which are ecologically better suited for grazing.
Land tenure systems which are incompatible with the introduction of improved agriculture and land management need to be reviewed.
3.3 Land degradation and irrigated agriculture
Irrigated agriculture represents the most intensive and productive forte of primary land use in arid regions and serves as a vital supplement to crop production in arid and semi-arid zones to satisfy the growing food needs of the increasing population
Many irrigation projects, past and present, are severely affected by secondary salinization or sodication and waterlogging. Secondary salinization of soil is the main degradation process in arid and semi-arid areas.
As soil science develops, the causes and mechanisms of salt accumulation have been better understood. However, in spite of a better knowledge of the phenomenon, the processes of salinization and sodication have not been arrested. Even today. they keep expanding in new irrigated areas and continue to cause considerable damage to the developing world economy. Between 20 and 30 million hectares of irrigated land are today severely affected by salinity with a resulting loss of agricultural production.
The main cause of secondary salinization is inadequate drainage and excessive water application which cause the groundwater table to rise close to the surface and the consequent evaporation of water rising by capillarity. The phenomenon is aggravated by the salinity of the irrigation water: the higher the salt content of the irrigation water the more severe the risk of salinization.
As long as the water table is deep and the moisture cannot come up through capillary flow to the soil profile, even saline groundwater does not cause salinization. But one effect of irrigation in poorly drained areas is to cause the groundwater level to rise so high that it can reach the surface layers and cause salinization even where good quality water is used to irrigate. This rise is often underestimated because the water table may be at great depths (10-20 m below the surface) before the implementation of an irrigation scheme.
The process of upward capillary flow depends on the balance between rainfall and evapotranspiration and on the hydraulic conductivity of the soil which is a function of its structure and texture. The minimum depth at which the water table must toe kept so that the velocity of the capillary flow be less than 0.5 mm/day is called the critical depth. This is in the order of 1 m for the loamy or sandy soils and 1.5 m for other soils.
Secondary salinization and sodication and waterlogging in irrigated areas in drylands cause many serious environmental and socio-economic problems such as: reduction in crop yield and abandonment of irrigable lands; decreasing income of the farmers; proliferation of water-borne diseases.
3.3.3 Combating land degradation of irrigated land in dry areas
Considering the importance of irrigation in achieving sustainable agriculture and rural development in drylands, it is essential to prevent and control waterlogging, secondary salinization or sodication in irrigation schemes by: improving irrigation and drainage systems; improving irrigated farming systems to increase productivity in a regular and sustained way; and through improvement of the socio-economic and health conditions of people dependent upon irrigated agriculture.
Combating land degradation in irrigated lands should be conceived in an integrated approach to sustainable agriculture and rural development in drylands.
Prevention and reduction of the salinization in connection with irrigation should focus on the following actions:
- ensure that new or rehabilitated irrigation projects have adequate drainage
- implement groundwater monitoring and water balance studies to predict drainage requirements and implement conjunctive use of ground and surface water,, where feasible, to prevent or correct waterlogging,
- establish pilot drainage projects in waterlogged and salinized areas to verify design and effectiveness of materials, demonstrate the effect of drainage on productivity, and train personnel in operation and maintenance of drainage systems,
- monitor groundwater salinity and improve groundwater management where excessive groundwater abstraction results in salt water intrusion into the aquifers from the sea or from nearby saline aquifers,
- monitor soil and water salinity in problem areas and adopt appropriate water, soil and crop management practices to overcome the problem.
3.4 Land degradation and rangeland management
3.4.1 Main types of pastoral systems in drylands
The following three main types of pastoral systems are practiced in arid and semiarid areas in the world:
a) the nomadic/transhumant pastoral system. There are two kinds of nomadism: true nomadism (more of less continuous movement of livestock with no set pattern) and transhumance (livestock movement along more predetermined routes leading from the wet season grazing lands in the arid zone to fallow lands in the semi-arid agricultural zone in the dry season).True nomadism usually involves the herding of drought-hardy camels, goats and sheep, in some cases, with a few cattle, a way of insurance against drought.
b) The sedentary livestock raising system. It is practiced by farmers who are mainly concerned with rainfed cropping in semi-arid areas, but keep some animals, grazing them on fallow lands and communal village grazing lands. Usually only limited areas of pastures are available within easy reach of villages, so these are used quite intensively and suffer considerable
There is a symbiotic relationship between farmers and nomads, in which meat and milk are exchanged for grains and legumes, and fallow lands are grazed by nomadic herds in return for the fertilizing value of the dung and also for cash and other goods.
c) Cattle and sheep ranching are the typical kinds of cattle pastoral system in the drylands of developed nations such as USA and Australia. The development of lucrative markets in some developing countries such as Nigeria and Ivory Coast has encouraged some trials to establish cattle ranches in the Sudanan and Savanna zone.
3.4.2 Common features in rangeland degradation
The continuing or accelerating course of rangelands degradation shows common features, including:
- deterioration in the quantity, quality and persistence of native pastures, generally associated with a diminution of plant cover, but also with invasion by shrubs of low pastoral value; frequently unpalatable and of little economic value or practical use.
- structural changes in the plant cover, notably the loss of shrubs and trees, partly through browsing. but also through gathering of fuelwood and clearing and burning for agriculture: this increases the exposure of the soil surface to accelerated water and wind erosion, removal of fertile top soils and loss of nutrient and seed stores and may eventually lead to the exposure of barren, locally hard-setting subsoils which resist revegetation. The range rehabilitation in this case becomes critical or impossible, with a definitive loss of many plant species, which could be of great value in the future;
- changes in soil surface conditions, notably compaction through trampling by livestock, leading to deterioration in soil - plant - water relationships and reduced germination rate, particularly of the palatable species;
- additional processes of sand drift siltation, leading to further further destruction of the vegetation and commonly to deterioration of surface and shallow groundwater supplies.
The pattern of such changes varies with the movements and concentration of grazing animals, with seasonal conditions and with the varying vulnerability of the land itself.
3.4.3 Main causes of rangeland degradation in dry areas
Overgrazing is a major cause of rangeland degradation in drylands leading to desertification, as it has been proved by different studies and observations in the world. Overgrazing results when livestock density becomes excessive and too many animals are grazed on the same area of rangeland, leading to the degradation of vegetation, soil compaction, wind and water erosion. When there is heavy pressure on rangelands, the animals consume palatable vegetation faster than it can regenerates, and eventually only inedible or no vegetation remains. With degraded plant cover, soil erosion becomes serious and any chance of restoring the range becomes remote because of massive top soil loss. Livestock density can rise in four main ways: first, herd sizes are allowed to grow too large during wet years to be sustained by the limited pasture growth in the dry years. In the dry years, pressure is reduced, although it always remains greater than the carrying capacity of the range. Second, the area available for grazing decreases as nomads are displaced by farmers growing crops. Third, livestock becomes concentrated around villages by nomad resettlement schemes and along herding routes made popular by the sinking of boreholes. Fourth, traditional controls on the grazing of rangelands break down. But the most common cause of overgrazing is the growing of herd sizes within a given area. In the Sahelian rangelands, by 1980 numbers of small livestock have surpassed those of the first-drought years of the late 1960s. Growing markets and marketing systems, linked with rising meat consumption by urban population, are likely to maintain this pressure of livestock numbers on the grazing lands in many of the worse-affected dry rangelands.
The growing size of herd in dry rangelands is caused by many factors:
the growing human population in dryland developing countries;
the changes in the economic circumstances of nomads, lead to greater emphasis on the role of livestock. From the nomad point of view, increasing the size of his herd is the only way in which he could save for the future
market forces at home and overseas have caused livestock numbers to rise in many dry rangelands. In response to growing urban markets, new commercial forces have linked inappropriately with traditional attitudes to livestock numbers as wealth, prestige or drought insurance, to accentuate further the recent inordinate increases in grazing pressure. Such forces have arisen just when the social structures within which traditional systems are embedded are themselves. undergoing change and breakdown through modernization and mobilization of the society;
the introduction of better veterinary care for livestock has considerably decreased mortality rate;
in some cases, governments have provided feed-grains at heavily subsidised prices. This has allowed maintaining stock numbers through the dry season far in excess of the range carrying capacity. Until the heavy subsidization of food-grain ceases, there is little hope of improving range conditions in these cases.
b) Encroachment of rainfed agriculture in rangelands
At national levels in developing countries, particularly in Africa and Middle East, traditional pastoral societies have commonly lost their relative influence within the new national states of the drylands, where political and economic powers tend to be in the urban and agricultural sectors. It is in this context for example that a marked recent encroachment of rainfed cropping into the better pasture land can be understood as a response to newly created national policies for increased food production and increased emphasis on cash crops as producers of foreign exchange. Thus valuable grazing lands have been lost and important traditional exchange relationships between pastoralists and farmers have broken down.
This type of range degradation is widespread in the Near and Middle East and in Africa, particularly in East and South East Africa where agriculture and pastoralism in the past were in balance with environmental conditions; rangeland degradation seems only to have been considered a serious problem at a few specific cases. The accelerated rangeland degradation should be considered in part as a reflection of unequal economic development and of inequality of access to resources, at national and local levels linked with poverty and inadequate management and poor infrastructure.
In Rajasthan, India, the erect of arid land used for rainfed cropping almost doubled from 30% to 60% between 1951 and 1971 at the expense of the grazing lands.
c) Deforestation also causes a decline in the fodder content of rangelands. Although we might think of shrinking rangelands merely in terms of a reduction in the areas of grass available for grazing, as far as livestock is concerned, rangelands are three dimensional assemblies of fodder, in which grasses, shrubs and small trees are all valuable food sources.
d) Frequent drought
The frequent drought in many parts of the world's drylands and notably In Africa is a prominent factor which has contributed to range degradation. The crisis in the pastoral production systems of the Sahel in the early 1970s shows the great repercussion of this sequence of dry years on rangeland degradation.
Drought also hit the herd hardly: 39% of Niger's cattle and 10% of its sheep and goats were lost between 1970 and 1974. In the worst affected areas, mortality was much higher. However no advantage was taken of these losses to reduce livestock number to more sustainable levels which amplified the impact of drought on rangeland degradation.
e) Sedentarization of nomads
Many governments are encouraging nomads to settle. Unfortunately, the settlement of nomads, whether voluntary or enforced, breaks up large herds into smaller units which become concentrated around villages and cause degradation of rangelands. Overgrazing around settlements is likely to become a much more serious problem in the future as the inevitable trend towards nomad settlement continues.
f) Introduction of new technology
The potentially harmful consequences of the introduction of new technology into traditional rangelands without the support of appropriate management controls is well exemplified by the provision of permanent bore-holes in rangelands which were formerly used only seasonally, or of stock-water supplies beyond the forage capacity of the rangelands.
g) Large cattle ranches in developed nations can also suffer. from degradation. One cause is the coincidence of wet periods with low market prices: this encourages owners to keep cattle until prices improve and therefore to overstock their ranches. In the USA, more than half of the privately owned rangelands are producing forage at half of their potential or less because of overgrazing and consequent soil erosion.
h) Breakdown of social control
Extensive grazing in rangelands in dry areas, particularly in the Near and Middle East, North Africa and in the Sahel, has been possible for many centuries only because of the rigid social control exerted by the nomads themselves over the movements of their animals. These controls have now broken down, more as a result of outside influences than any other cause (digging of wells; crop cultivation; loss of social control on grazing and growth of a new social class of livestock merchants breaking down the traditional kinship links between nomadic pastoralists; private appropriation of what had previously been communal resources; fencing of rangelands; private boreholes from which water is sold to pastoralists, etc...
i) Government-imposed or abandoned policies
Government-imposed policies and actions resulting in the abolition of the traditional administration system without providing effective alternatives, aggravate conflicts between tribes and distort the tradition al laws governing communal grazing, thus inflicting drastic deterioration on the rangelands. In some cases, policies imposing northern limit of given commercial agricultural practices have been rendered obsolete through lack of enforcement, thus encouraging further encroachment on pasture lands.
3.4.4 Trend in rangeland degradation
The new assessment of the world status of desertification uncle taken by UNEP in 1990 1991 shows that the largest area of degraded rangelands lies in Asia, followed by Africa, while the percentage of degraded rangelands is similar in both these continents. About 3,333 million hectares of rangeland or nearly 73 per cent of this total area in the world's drylands (4,556 million hectares) are affected by degradation, mainly by degradation of vegetation, which, on some 757 million hectares, is accompanied by soil degradation, mainly erosion. It shows an increase of some 233 million hectares in comparison with the 1984 assessment, approximately 7,5 per cent. It is safe to assume that the situation has not changed significantly since 1984, but remains very unsatisfactory with a tendency towards worsening.
There is no reliable global data on actual losses of rangelands and their conversion into agricultural land, wasteland/bad land/desert or urban land.
3.4.5 Management of degraded rangelands in drylands
Rehabilitation of degraded rangelands should be based on sound ecological and integrated management of natural resources.
This calls for thorough understanding of the interferences which range ecosystems can tolerate without suffering irreversible depreciation and understanding of the exploitation that they can sustain without losing their continuing function of producing the required resources.
However, ecological and integrated management of degraded rangelands should be supported by adapted technology. economic planning. legal social and financial measures and improved institutions.
In rangelands areas, there is a need for legislation based on traditional land use rights and obligations in order to assign more secure legal land rights to groups of people who have been able, in the past, to manage rangelands without too much irreversible degradation, but who now are under increasing threat from outsiders. In many such areas, "land grabs" by outsiders are proceeding at an alarming rate.
Rehabilitation of degraded rangelands in dry areas cannot be expected to be economically remunerative in the short term. But in terms of stability and security for the immediately affected population, and the effect on regional security. climate change and biodiversity. the social dividends resulting from improved rangelands use are surely positive.
Improving farming in the sedentary zone is as crucial to arresting rangelands degradation as controlling grazing is. Agricultural progress and intensification in irrigated agriculture as well as rainfed farming are essential not only to provide food, employment and income to the increasing populations, but also to halt the uncontrolled spread of cultivation onto pasturelands.
Drought and dry season feed reserves are priority items of livestock production, but can cause overstocking and destruction of rangelands if purchased feed is used to maintain excessive grazing pressure on rangelands. Reserves are therefore best organized on the basis of what can be produced within the one management unit. Government subsidies on feed brought into drylands are especially destructive for the rangelands.
Livestock marketing is an important option for both increasing returns to producers and reducing grazing pressure on rangelands. Special arrangement should be made for marketing animals during drought, ideally before animals loose too much condition and value.
Veterinary services are a necessary adjunct to marketing and, if available where and when required, make it possible for rangelands pastoralists to secure reliable subsistence from a small number of animals.
Technical interventions in livestock and range improvement and management: forage shrub and tree planting, reset ding, breed improvement, water development should go together with establishment of the institutional framework for research and training in range management.
Most projects and national training institutions should devote sufficient time to interact and exchange knowledge with the pastoral communities and avoid approaching these communities as the object of development.
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