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HISTORICAL CONTEXT
The process of degradation of sensitive environments leading to desertification is as old as agriculture itself. The European colonization of North America and Australia has, for example, over the space of only a few centuries set in motion processes of soil deterioration, environmental degradation and desertification not experienced during the hundreds of thousands of years existence of their aboriginal hunter/gatherer human populations.
The world became aware of the causes of desertification and the role played by human populations in its expansion after the Second World War, when the consequences of desertification were brought into sharp focus by the Sudano-Sahelian drought of 1968 to 1974. This catastrophe clearly exposed the basic processes of environmental degradation which gave rise to the accelerated and massive disruption of the socio-economic conditions of the countries concerned.
At least seven international conferences sponsored by the United Nations Organization were held between 1972 and 1979 dealing either directly or indirectly with various aspects of the desertification process. The most important of these as far as desertification was concerned were the UN Conference on the Human Environment of 1972, the UN Conference on Desertification (UNCOD) of 1977 and the FAO World Conference on Agrarian Reform and Rural Development (WCARRD) of 1979.
The United Nations Plan of Action to Combat Desertification (PACD), adopted by the UN General Assembly in December 1987 arose directly out of UNCOD and provided UNEP with a mandate to organize and coordinate action with a view to eventually controlling desertification world-wide by the year 2000. Three immediate actions were recommended under PACD:
(i) The creation of government institutions to combat desertification at national level.
(ii) The convening of conferences, seminars and workshops at regional level as well as the conduct of inter-regional studies to establish regional training centres by Regional Economic Commissions. These commissions would also organize and coordinate the implementation of trans-national projects to combat desertification.
(iii) The promotion of participation of UN Agencies and Organizations by UNEP through a plan of action based on requests for assistance received from governments. UNEP would also undertake joint planning with other agencies to formulate specific actions, mobilize finance and coordinate projects to counter desertification.
By 1979 it was recognized that the main factors causing desertification were due to human pressure on sensitive environments, largely in arid, semi-arid and sub-humid zones. This pressure of man's activity results in the widespread removal of vegetation through overgrazing, clearing, fuelwood harvesting and the recurrent lighting of fires to promote green shoots for livestock. These activities, in turn, give rise to erosion by wind and water, loss of soil productivity and a general trend to agriculturally exploit increasingly marginal and desertification-prone lands. Added environmental stress was also caused through inefficient irrigation resulting in loss of productive land through waterlogging, alkalization and salinization. Overall environmental consequences included depletion of wildlife and degradation of plant and animal genetic resources.
MAJOR FACTORS CAUSING DESERTIFICATION
Analysis of the country reports reveals that desertification can occur under, and is often caused by, seven sets of conditions.
(i) Overgrazing
Desertification occurs under pastoralism in the arid and semi-arid lands of Asia, (USSR, Pakistan, Afghanistan, Iran, Iraq, India and China). This is a phenomenon also prevalent in the Sahel, North Africa, East Africa and Southern Africa as well as the drier zones of Latin America. Nor is it confined to developing countries as desertification caused by pastoralism and overgrazing is common in North America and Australia where local vegetation has been over-exploited. Overgrazing by domestic livestock can be exacerbated through competition from wildlife: Installation of watering points can result in the explosive increase in drought-resistant wildlife (Australia; kangaroos) and insupportable additional stress can be placed on natural regeneration of woody plants as well as the removal of herbaceous ground cover (Australia; rabbits) by exotic animals which have become feral. Severe degradation of soil and vegetation can occur around inadequately spaced watering points by high concentrations of grazing animals during droughts. These result in decertified patches, a common enough occurrence in many dry lands.
(ii) Types of livestock
Certain types of livestock, goats for instance, can be particularly destructive of vegetation in dry lands if pastured in excessive concentrations. Legislation has been brought against these (Algeria) and the race has been genetically modified (Syria) to minimise damage to browse species.
(iii) Shifting cultivation
Removal of protective vegetation occurs when the rotations of shifting cultivation become excessively short owing to high population density. This phenomenon is more characteristic of the higher rainfall zones but can occur under sub-humid conditions (Sahelian Africa, India, South Eastern Asia and certain parts of Latin America). Due to the climatic and edaphic nature of these areas, loss of protective cover almost certainly leads to wind erosion, loss of productive soils, and desertification.
(iv) Harvesting pressure
High population pressure and excessive harvesting of the natural vegetation for industrial and domestic fuelwood, wood for building materials and artifacts, and the collection of non-wood raw materials for medicines, extracts, fibres and food can cause desertification. This is a phenomenon often observed in pert-urban lands in developing countries and is particularly marked in the Sahel, India, Sudan and Somalia.
(v) Agricultural expansion into marginal dry lands
The expansion of agriculture into marginal dry lands, occasioning the clearing of large tracts of natural vegetation and excessive cultivation, can destabilize the equilibrium of the environment and result in erosion by wind and water. (Morocco for instance). In some areas the removal of deep rooted tree cover can allow saline water tables to rise, resulting in salinization and loss of productive lands (South and South Western Australia, North Africa, Sudan). Commercial pressure to grow cash crops on a large scale can also result in serious degradation of soils through loss of structure and erosion (Senegal; groundnuts. South and South Western Australia; wheat).
(vi) Inefficiently managed or incorrect irrigation practices
The introduction of irrigation into the arid regions of many countries has caused the loss of large areas of formerly productive lands through waterlogging and salinization (Afghanistan, Pakistan, Syria, China, USSR). This degradation is caused not by the process itself but by its incorrect or careless application, and measures are now being successfully applied for the reclamation of some areas (Pakistan, China, USSR).
(vii) River diversion
Specific up-stream actions such as the excessive drawing off of water or diversion of river systems can induce shortages of water for irrigation of dry lands and intrusive estuarine salinity with consequent desertification and loss of productive lands.
Each factor mentioned above can have an independent effect but their influence on the environment is often felt in conjunction with different combinations of other factors in greater or lesser degrees depending on local traditions, customs, industries and population pressure.
FORESTRY IN COMBATING DESERTIFICATION
The major types of forestry-oriented activities to overcome desertification and to rehabilitate decertified land arising out of the previously listed sets of conditions are:
The following conclusions can be derived from the foregoing under the headings which are listed above:
(a) Management of Natural Vegetation
Natural vegetation provides not only soil cover, protection from erosion, and control of the levels of sub-surface saline water tables but also a resource of wood, fuelwood, forage and non-wood forest products. In zones of low and uncertain rainfall, agriculture is risky and gives way to grazing as a subsistence and economic form of land use. Stress additional to that of direct cutting and gathering results in the disappearance of surface vegetation. Good management systems aim at the preservation of native perennial cover to create a stable and yet productive environment.
Both developed and developing countries have come to recognise the wisdom of the above practice although the clearing of drought-hardy woody vegetation still occurs in pasture improvement programmes involving the seeding of herbaceous species. The rehabilitation of degraded natural vegetation shows that strict protective measures can have impressively beneficial effects.
Few formal silvicultural systems exist for the management of dry land woody vegetation. The depressage de chêne vert of Morocco and the coppice-rotation system of dry thorn forests of Pakistan are examples of some systems that do occur, but these are very much in the minority.
The specific knowledge of silvics, mensurational methods, growth rates and yield seriously hamper the management planning of natural vegetation although ad hoc restrictive imposition of rotations systems appears to be effective.
Programmes of enrichment to boost the content of palatable species and overall productivity are also hampered by lack of knowledge of natural species behaviour, phenology, characteristics and regenerative capacity.
Ecological studies have commenced in the USA and are a component of UNEP policies to combat desertification. The involvement of local populations in management planning and execution is essential for the success of future schemes.
(b) Agroforestry Systems
Traditional systems in arid lands often involve the permanent retention of scattered multi-purpose trees as cover and a source of various fruits, fibres, energy and fodder on agricultural lands in arid zones (Latin America, Sahel, India, Pakistan). In some cases this involves the artificial establishment of multi-purpose trees or shrubs such as acacias and Atriplex (North Africa, Sudan).
The establishment of horticultural and other multi-purpose species (figs, pistachio, apricots, almonds, olives and carob as well as Acacia cyanophylla) is frequently a feature of soil and water conservation works on sloping lands in agricultural areas. The presence of these species materially contributes to production and environmental protection. Similarly, windbreaks of multi-purpose species comprising poplars, eucalypts, walnuts, pines and cypresses contribute to supplying the timber, fuelwood and fodder needs of inhabitants of Near-Eastern countries.
In arid zones the practice of agroforestry provides a buffer against the effects of irregular and unpredictable rainfalls and economic fluctuations through a regular, reliable supply of alternative products useful for humans and livestock. This reduces pressure on local resources and promotes sustainability of production.
(c) Sylvopastoral Systems
Pastoralism is the major land use in most arid zones, and, although productivity is low, the extremely large area that is involved (45 million Km²) provides a significant contribution to world food supplies. Population densities, although generally low, are relatively high in Iran, Pakistan and India. Some areas: Afghanistan, Pakistan, North Western India, the Near East and North Africa have been continuously inhabited for over 5 000 years during which time the natural woody vegetation has always provided browse for grazing animals.
In the USA and Australia more attention is paid to herbaceous feed. In Sahelian countries browse is said to provide at least 45% of the livestock feed at the end of the dry season.
Strategies for the reclamation of degraded rangeland involve absolute protection. Manipulation of grazing through "deferment" systems (Australia), which make use of observed ecological reactions of browse species to grazing pressure in determining frequency and periodicity of grazing, can improve range production. When coupled with dry-season burning of spinifex this can promote the development of edible perennial browse. In general terms control of grazing is a required component of sylvopastoral systems, with or without fencing to exclude livestock, and reseeding or other types of pasture enrichment with browse species. More attention is now paid to mechanical drill reseeding of mixtures of browse and cover species combined with exclusion of rabbits with special fences and destruction of warrens in order to rehabilitate degraded lands (Australia).
Sylvopastoral systems also include the establishment of multi-purpose trees to provide shelter to stock from very hot, dry, or very cold winds as well as strong insolation. Establishment of browse and also herbaceous species is also successfully practiced in the dry lands of the USSR. Special water harvesting techniques such as the creation of microcatchments can assist the concentration of annual precipitations as low as 100 to 150 mm into the planting sites of shrubs and trees, thereby assuring a high level of survival under arid conditions.
It is now generally accepted that the major task of combating desertification is social and not technical: the need to motivate local populations, often nomadic in inclination, to help themselves. The creation of the necessary institutions and infrastructure to support such action is another essential component for success.
(d) Afforestation
Afforestation under arid conditions generally requires the supplementary application of water to promote adequate initiaI tree and shrub survival and growth. This water can be supplied from tanks transported by vehicles, from reservoirs and irrigation systems supplying water through channels, pipes and flooding or through pipes and drip systems. Another method involves the capture and concentration of precipitation through water harvesting systems using microcatchments, contour berms, contour ditches, pitting and roaded catchments.
Afforestation is recognised as one of the effective methods of rehabilitating degraded lands. Tree planting and agroforestry can be successfully applied when combined with water harvesting in areas of extremely low precipitation, below 150 mm, but dryland farming with water harvesting and spreading is only economically feasible in areas where annual rainfalls exceed 250 mm with true rainfed agriculture becoming feasible in zones with annual precipitations above 300 mm.
7% of the world's land area (9.2 million km²) is salt-affected with 3% being dominantly saline or sodic. Rehabilitation of such lands requires the successful reestablishment of vegetation cover using salt-tolerant species and strict protection from grazing or other harvesting. Malcolm considers that the cost of using nursery-raised plants is prohibitive for large areas and that careful site preparation, direct seeding and protection from animals is more economically feasible. The reclamation of large areas of saline areas appears possible and could eventually significantly boost land available for agriculture. At the very least the revegetation of such areas could reduce the level of saline water tables, and the transport of saline wind-borne particles and run-off, as well as providing forage and cover for domestic animals and wildlife, fuelwood, non-wood forest products and improved landscapes.
Rainfed afforestation
Successful rainfed afforestation using drought-resistant tree species has been undertaken in parts of the Sahel (Cape Verde Islands, Burkina Faso, Niger), North Africa (Tunisia, Morocco, Algeria, Libya), the Near East (Israel, Syria, Jordan), and advances are being achieved in developing techniques of mechanically sowing mixtures of tree and shrub species in the dry land areas of South Australia.
However, since rainfed afforestation in arid zones is not very productive, it is not allocated high priority in the arid and semi-arid zones of North America. In other areas special techniques have been developed for the establishment of Prosopis tamarugo (Chile) and large-scale tree planting for soil protection, fuelwood and fodder has progressed in the semi-arid zones of the Andes. Large-scale green belt planting of a variety of useful species is being undertaken in Syria while dry land afforestation is practiced on a massive scale in China with the major objective of controlling wind erosion. The USSR is also undertaking the reclamation of large areas of unstable soil using artificial fixatives for moving sand and the establishment of halophytic shrubs and herbs. Considerable extension effort is being expended on tree planting for salt land reclamation of degraded semi-arid wheat lands in the Australian States of Victoria and South Australia. Long lists of suitable trees and shrubs are being circulated to advertise their availability in government-run nurseries.
Irrigation can clearly increase the capacity of land to carry agricultural and tree crops in arid zones and thereby augment the population density to around 250 per Km² from a non-irrigated maximum of about 10. Tree growth rates can attain commercially feasible levels under these conditions (Sudan, Syria, India, Pakistan).
However, the attendant serious problems of waterlogging: around 25% in the 16 million irrigated ha of Pakistan; and salinization, around 4% of irrigated land in Pakistan; provide adequate justification for intensive programmes of land rehabilitation. Pakistan has opted for the engineering/ mechanical solution of tubewell construction and operation to reclaim the above lands and no mention has been made of the possibility of afforestation. In Southern Australia, however work is proceeding on determining the technology of reclaiming salinized land through the successful establishment of fast-growing tree crops on otherwise unproductive sites using drip irrigation to leach mounded tree planting and establishing salt-resistant eucalypts, Melaleuca, and Casuarina.
India is pioneering work in the irrigation of agricultural crops; saline water of Ec 9-12mmhos can be used for continuous irrigation of a certain type of millet.
Sand-dune fixation
Another widespread use of trees and shrubs is for the stabilization of sand dunes. Work in the People's Republic of China demonstrates a wide range of concepts and techniques such as the establishment of particularly wide belts of trees and shrubs to reduce the sand content of desert winds; systems of multiple belts and ditches; purposeful variation of rows of species of varying final height potential in order to enhance roughness, cut wind velocity and wind-borne particle content; variation of species and combinations of species to match different sites; planting on the windward side of dunes in order to reduce their height; planting tall cuttings on the lee side depressions of dunes in order to block their advance and gradually level them off; combinations of lower windward side planting combined with later shrub planting to consolidate levelled areas; stabilisation of lower dunes with tree, shrub and grass mixtures. A wide range of woody species are used in different parts of the country, such as: Salix cheilophylla, S. matsudana, Populus simonii, Artemisia ordosica, Amorpha fruticosa, Lespedeza sp. dahurica, Caragona microphylla, Tamarix chinensis, Halostachys spp., Astragalus adsurgens and many others.
The USSR has also developed concepts and techniques of mechanical protection ranging from fences to carpet-type strips to retard sand movement, all combined with the establishment by seed and vegetative material of Haloxylon and Salsola spp.. Fixative petro-product wastes such as Neozin, sulphite-alcohol slops, and cotton tar are also used in combination with seedling establishment. Species such as Haloxylon persicum and H. aphyllum are commonly used. The radical improvement of desert pastures is being achieved without irrigation and through site-improving treatments such as rough ploughing for the establishment of man-made shrub pastures using pelleted seed mixtures of Haloxylon, sage brush, Russian and sow thistles and Salsola ritcheri.
(e) Shelterbelts and Windbreak Establishment
As described under the section covering afforestation, considerable practical advances have been achieved in China and the USSR where large areas of decertified land are being reclaimed by the systematic establishment of shelterbelts in addition to the protection and expansion of productive oases.
In areas where the effects of wind are severe, such as the southern tip of Latin America, mechanical means such as stone or adobe walls are used as initial protection for planted trees and shrubs. Windbreak establishment on sandy, dry coastal areas of tropical countries use screens of Casuarina (Senegal for instance). In Morocco, Tunisia and other North African countries chequerboard and dune-top installation of palissades is common in combination with the establishment of windbreaks to fix moving sands. In the Sahel the establishment of windbreaks is not as common as the retention of scattered trees and shrubs which also serve to combat the effects of wind. The People's Democratic Republic of Yemen and particularly Egypt recognize the value of windbreaks to agricultural crops in extremely dry climates, while in Syria windbreaks provide protection as well as fruit, fodder, fuelwood and income from timber.
The value of windbreaks in irrigated lands, roadside plantings and rain-fed agricultural areas is recognized on the Indian sub-continent and the use of shelterbelts in Australia has been demonstrated to improve the development of adult sheep and the survival of lambs under arid conditions.
The practical value of shelterbelts is now more widely recognized but still not appreciated in many developing countries where details of design and species composition in relation to the types of protection required are not known. The economics of windbreak establishment in terms of improved crop performance and the added value of products which can be derived from windbreaks themselves require extension to areas where protection from wind is essential. This information is now available from a recent FAO forestry publication. "Conservation Guide ND 15 - Brise-vent et rideaux abris avec référence particulière aux zones sèches", 1986.
(f) Creation of National Parks
National parks are important in assisting the conservation of genetic resources and as such provide a reservoir of species for the selection of useful drought and salt-resistant varieties. Their creation is an essential component in combating desertification as they provide reference points for monitoring the advance of deserts on a regional and national scale.
Roughly 97 million ha of national parks and reserves have been established in the world's arid to semi-arid and sub-humid lands under threat of desertification, that is, about 3% of these areas. Those of North America comprise 3%, Latin America 3.4%, Sahel 8.8%, North Africa 0.1%, Southern Africa 45.5%, Near East 3.8% and Asia/Pacific 35.4%.
(g) Wildlife Management
Wildlife provides a valuable supplement to the diet of rural populations of arid lands in several developing countries in which it abounds. The presence of wild animals, however, often imposes an added environmental stress on rangelands for which they often successfully compete with domestic livestock. Wild animals constitute an important renewable resource which can be productively managed but requires protection against commercial harvesting pressures and destructive competition from land owners favouring livestock expansion - both of which threaten some wildlife species with extinction.
Wild animals provide the basis for foreign exchange-earning tourist industries and are an important subject for the conservation of genetic resources.
Incomes from wildlife management and rational harvesting are particularly important for the drier lands of Central, Eastern and Southern Africa as well as parts of the USSR. Strategies for the shared use of land by domestic livestock and wildlife have been advanced in Africa and are being tested together with the possibilities of game ranching.
(h) Watershed Management
Because of their unleached soils, warmer climates and high degree of insolation, arid lands are recognized as having a high productive potential if water, the limiting factor, is supplied. The supply of this water generally depends on the rainfall and on the nature and state of the watersheds and catchments which trap and release it.
Heavy population pressure and exploitation of catchment areas for grazing, fuelwood harvesting and cultivation results in "flashy", short-lived supplies of water, poor filtration, loss of soil through erosion and downstream damage through floods, siltation and water-borne diseases due to disrupted stream flow.
Some productive dryland areas such as those of the Karakums of the USSR are dependent on supplies of water from impervious, man-made or natural "Takyr" catchments which annually supply 35 cu Km of fresh water for 3.1 million Km² of arid land.
These catchments build up fresh groundwater reserves which supply the needs of livestock grazing on sagebrush and thistle associations ocurring with or without ephemeral grasses.
The management of watersheds is a multidisciplinary science in which forestry and range management play a most significant role in protecting undegraded watersheds and in rehabilitating those suffering desertification from over-exploitation.
The combination of soil and water engineering works and the planting of multipurpose tree species is a feature of many North African and Near East countries suffering from high population pressure and irrational exploitation of resources under arid to semi-arid conditions. The above combination of treatments is also applied to an increasing extent in mountainous parts of India and Pakistan. Extensive watershed protection measures of this type have also been applied in Southern Africa. In general, the excessive harvesting of fuelwood and overgrazing is a major problem in watersheds of developing countries, requiring strict rotational controls of both activities as well as the establishment of alternative supplies of fuelwood and fodder to relieve the pressure on the natural vegetation.
Control of wildfire, another seriously destructive agent, is also necessary in order to preserve vegetation and encourage the growth of natural regeneration. Such control is difficult to achieve because of the use of fire by pastoralists to clear brush and promote green shoots of perennial forage grasses.
Contour cultivation, strip cropping and strip fallows are practices more commonly applied in developed countries but these are gaining acceptance in developing countries where agricultural machinery is generally used for soil cultivation.
Effective watershed management requires the active cooperation of populations resident in or around the catchment area, and greater attention is now being paid to involving these rural people in watershed management activities. Examples of this cooperation are to be found in Morocco, Tunisia and parts of the Caribbean.
(i) Conservation of Genetic Resources
The conservation of genetic resources aims at the wise utilization of existing resources with a view to improving them to meet actual or potential needs for goods and services.
The process of desertification resulting in the total loss or serious decline in productivity of large areas of land directly erodes the habitats and plant and animal populations of arid lands, narrowing the genetic base of many drought-resistant species affected in the process.
The particular value of conservation of genetic resources to forestry in combating desertification is the purposeful exploration, evaluation and conservation in situ or ex situ of drought-resistant tree and shrub species which are useful in enhancing the productivity of arid lands. Such species are also useful for reclaiming degraded, decertified lands in the above regions. Developed countries have created reserves for gene resource conservation and in many developing countries this function is indirectly assumed by national parks, nature reserves and wildlife reserves. Endangered species of animals and plants have been identified world-wide, also providing a starting point for conservation action on a national basis. The FAO/IBPGR project for Genetic Resources of Arboreal Species for the Improvement of Rural Living in Arid and Semi-Arid Areas has promoted collection of tree and shrub seed for provenance testing and ex situ conservation in the developing countries of Africa, the Near East, Southern Asia and Latin America which possess substantial arid zones.
(i) Processing and Utilization
Arid lands require the land user to spread the burden of cropping and vegetation use broadly over all the various components of the environment: the soil and the various types of vegetation that cover it as well as the other life-forms such as wildlife, thus avoiding intensive single-objective exploitation that could disrupt the delicate ecological balance that exists. Permanent disruption of the balance promotes degradation and gives rise to ultimate desertification, whereas rational and careful use promotes the sustainability of the system employed.
The North American region is more oriented towards industrial-type products and harvesting of sawn and round timber, fibres (Agave sisalana), oils (Simmondsia chinensis) and resins (Grindella camporum).
In developing countries the accent is more on fuelwood, charcoal, small wood for handicrafts, fibres for domestic wares, tannins, foodstuffs such as honey, fruits (Ficus, Zizyphus), karite butter (Butyrospermum), gums (Acacia senegal); medecines: scoparone (Artemisia scoparia), diosgenin (Balanites roxburghii); aromatic essences (Rosmarinus); resins (Boswellia and Astragalus).
Appreciation of the value of the plants yielding the above products tends to promote conservation of useful shrub and tree species which are often incorporated into traditional agroforestry systems (Sahel). Unfortunately, excessive harvesting pressure can also result in the loss of vegetation cover and ultimate site degradation. Knowledge of the particular utility of species can promote their selection for tree planting and agroforestry programmes aimed at the reclamation of decertified land.
Major Gaps in Knowledge Required for Successful Management of Dry Lands, Understanding of Desertification and Reclamation of Desertified Land
The following important gaps and constraints to progress have been revealed through study of the foregoing papers and country reports:
(a) Climatic
(b) Ecological
(c) Technical
(d) Sociological
(e) Economic
Forestry vs Desertification in the Rural Development Context
The case for campaigns against desertification have been largely ecological while the case for development is primarily economic and social. Development is usually implemented according to economic, social and political criteria. There is, however an intimate relationship between desertification and development. Desertification implies that people must change their ways to fit in with nature; development implies that the use of resources must be reorganized with the aid of newly-available technologies to fit people's expectations.
Forestry is an ecologically-based science. Its approach in the past has been ecologically biased and action has been taken with this orientation. However, it is beginning to be realised that the inhabitants of dry lands had already, through force of necessity, developed ecologically viable systems which have become modified or abandoned through external commercial pressures as well as through explosion of human and livestock populations.
The above systems applied on a small scale by family or tribal groups in the past still apply but may require modification in practice to fit in with the increased demands on the environment. Rationalization of practice is sought, not necessarily fundamental change, implying that past systems must be closely studied to analyse their benefits. Any proposed changes must be carried out with the full cooperation of the family, tribal or community units involved if action is to be taken on a sufficient scale to make an impact on resolving the problems of desertification.