Part four: Regional reviews and analyses
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An analysis of the role of forestry in combating desertification on a regional basis must necessarily concentrate on its major agents within the regions themselves, bringing to light any recurrent patterns of causes, climate, soils and vegetation types that would prompt the extension of successful measures in one region to assist counter-desertification work in other regions.
Desertification can be described as "the intensification or extension of desert conditions; it is the process leading to reduced biological productivity with consequent reduction in plant biomass, in the land's carrying capacity for livestock, in crop yields and human well-being".
In order to be considered as an effective activity to counter desertification forestry must therefore be seen as a measure to increase biological productivity, to increase plant biomass, the land's carrying capacity for livestock as well as crop yields and improving human well-being.
Basic to the above considerations are the environmental features of climate and soils which provide the conditions under which the necessary counter-measures must be applied and which will largely control the choice of biological material (tree/shrub species and provenances) to be used.
2. ENVIRONMENTAL FACTORS
The climate of areas subject to desertification is a common feature providing a link between different regions. Since most areas of desertification occur in dry lands the degree of bioclimatic aridity as expressed by the ratio of mean annual precipitation to mean annual evapotranspiration (P/ETP) is a convenient index for the above purposes:
Hyper-arid zones P/ETP <0.03
Arid zones <0.20
Semi-arid zones 0.20 <0.50
Sub-humid 0.50 <0.75
Modified by the application of mean temperature in °C for the coldest month of the year:
Warm winter 20 - 30°C
Mild winter 10 - 20°C
Cool winter 0 - 10°C
Cold winter <0°C
as well as by the mean temperature in °C for the hottest month of the year:
Very warm summer >30°C
Warm summer 20 - 30°C
Mild summer 10 - 20°C
Table 1 provides a very brief description of main climatic patterns, soils, vegetation and major land uses by regions.
These general descriptions derived from regional statements and the MAB Map of the World Distribution of Arid Regions as well as the Map of Arid Regions itself when compared with the FAO/Unesco World Map of Desertification, show a very close correlation between the location and extent of areas of existing and potential desertification. This is not surprising when the fragile nature of the arid to semi-arid zone environment is considered as well as the impact of man and his livestock upon it. Added to this the effect of climatic factors of persistent desiccating winds, high evaporation, low variable rainfall and extremes of temperature place a constant stress on both vegetation and soils. These achieve a delicate natural equilibrium which requires little disturbance to cause instability and imbalance leading to degradation.
The regional-descriptions display a number of common factors:
This last feature is particularly marked in Southern Africa, the Americas, the Indian sub-continent and to some extent Australia.
Table 1 provides a very brief description of main climatic patterns, soils, vegetation and major land uses by regions.
|North America||U.S.A. and Mexico||Latitudes 33°N to 45°N with all possible types of dry climate due to extent N/S, mountains and wide longitudinal range. Hyper-arid Great Basin, Mojave, Colorado and Chihuahua. Main divisions and mild winters are hot summers Arizona, S. California; cool winters and hot summers; cold winters and cool summers according to altitude. Precipitation varies enormously from W to E., and is invariably summer rainfall towards the South with some transition regimes towards the West Cost. There are practically no arid/semi-arid regions with cold winters in Mexico, most being mild winters and hot summers. Rainfall is less varied Than in USA.||Soils generally readily erodable, often rocky and poorly developed. The USA dry zones range from woodland in the sub-humid, through scrub formations in the form of thorny steppes. Prosopis is wide spread in the South. The vegetation of semi-arid Mexico are "Matorrales" of open scrub with succulents. Steppe vegetation occurs in the arid parts with either grasses and/or thorny succulent shrubs. Irrigated agriculture has developed in California, but not in the arid regions of Mexico except for a narrow strip in the gulf of California. In dry zones the major general land use in both countries in livestock raising.|
|Latin America||Argentina Bolivia Brazil Chile Paraguay Peru Colombia Venezuela||The driest part of South America is its western part, the main cause being the cold humboldt current. The western region becomes more humid South of Valparaiso while the centre and east become drier under the influence of largely westerly-prevailing winds. Pronounced drought therefore occurs as far as latitude 50°S. Hyper-aridity occurs on the costs of Peru and Chile from the Sechura desert to and including Atacama Desert. Coastal fogs create high atmospheric humidity. Cool winters and hot summers occur in Patagonia.||Very open steppes with Prosopis along watercourses are found in the fog zones near the coast. High altitude zones contain shrubby steppes with summer rains in the north and winters ones in the south. Patagonia contains shrubby steppes. The dry zones of the northern tropical countries carry dense thorny shrubs and "Caatings" with cacti. Livestock raising and graizing are the mainstay of agriculture with some rainfed cereal crops and cotton. Sols are very variable, as could be expected from the size of the region but are often of marine sediment origin on the west coast of the continent.|
|Sahel||Mauritania Senegal Niger Nigeria Chad Sudan Somalia||The arid to semi-arid zones of the Sahel are characterized by warm winters and hot to very-hot summers. Corresponding broadly to the Sahelian "steppes" an the Sudanic wooded savannas. These regions have a rainfall regime with a single July/August maximum. Fewer than 30 rainy days per year occur in the arid areas with 8-11 months dry season. The region is subject to cyclic droughts.||The soils vary from tropical feruginous to feralitic with skeletal gravels, laterites, halomorphic and hidromorphic soils; the vegetation comprises thorny steppes with acacias (A. radiana, A. sengal, A. seyal), Balanites and Ziziphus to Acacia tortilis, A. mellifera and Camiphora in the east. The semi-arid savannas are dominated by Faidherbia, Adansonia, Borassus, Vitellaria and others. Land use predominently pastoral with subsistence agriculture in the drier semi-arid regions merging into cash crops such as ground nuts under moister conditions. Wildlife is a significant natural resource.|
|Africa South of the Equator||Mozambique Tanzania Zambia Botswana Zimbabwe Namibia Angola Lesotho||The driest areas are in the S.W.: hyper-arid with mild winters to arid and semi-arid with warm winters in the NE and mild winters towards the South.||The southern vegetation is steppe merging into tree steppe with thorny species similar to that of the Sahel. Sclerophyllous brush of Ericaceae and Proteaceae corresponds to areas of winter rain in the South. Livestock raising is of prime agricultural interest towards the North and East, wildlife is a significant natural resource.|
|North Africa||Marocco Algeria Tunisia Libya||The zone is characterized by a single winter rainfall maximum and a sharp decline in rainfall southward ranging from semi-arid and arid with almost total summer drought to hyper-arid with mild winters and warm to very warm summers. Inland mountains affect rainfall distribution and allows Saharan conditions to reach a high latitude in Marocco, Algeria and part of Tunisia. The desert influence affects Libya and Egypt.||Wooded steppes of degraded woodlands (Juniperus phoenicea and Tetraclinis articulata) grading further into woody vegetation steppes (Artemisia herbalba and Ziziphus lotus), salt steppes: Fankenia and Sueda; grassy steppes Stipa tenacissima; shrubby steppes: Pistacia atlantica, Argania spirosa. Livestock raising is important but tree crops: olives, figs, apricots, almonds and raised and cereals are grown in the uplands largely and cereals in the lowlands.|
|Near and Middle East||Turkey Egypt Iran Syria/Iraq Lebanon/Israel Jordan Afghanistan Yemen Oman Cyprus||The zone covers 30° of longitude and is of predominantly winter rainfall with hyper-arid areas of mild to warm winters and hot to very hot summers in the South (Saudi Arabia), Arid to semi-arid areas with cool winters to cold winters in the North (Turkey, Syria, Iraq, Iran, Afghanistan)||Various steppe and pseudo-steppe vegetations ranging from high steppes in Turkey (Astragalus + Acantholema) to ephemerals (Egypt), Artemisia herba-alba steppes (Syria, Iraq) to humid steppes (Prosopis stephaniana, Ziziphus lotus) Syria; spiny shrub/grass pseudo-steppe (Capparis, Acacia, Calligonum) Iran; open thumbush steppe (Acacia tortilis) Saudi Arabia, Yemen republics; mid-altitude steppes (Pistacia, Juniperus, Amygdalus) Afghanistan. Irrigation is practised along the Euphrates, the Nile Valley and Israel. Cereals penetrate into the semi-arid but livestock raising and pastoral nomadism is dominant in the arid zones.|
|Central Asia and Pacific||USSR China Mongolia||The cold deserts of the USSR and NW China stretch over 60° of latitude from the Caspian Sea to the Gobi. They are arid to semi-arid with cold winters and hot to warm summers with very hot summers in Turkmenistan. In China a hyper-arid enclave occurs in Sinkiang, the general climate ranging from arid to semi-arid with cold with and mild summers are characteristic of the region from Sinkiang to the Sbantung peninsula.||The soils are largely sands, sandy loams,solanchaks and highly carbonaceous soils with large areas of moving sands and rocky deserts. In land drainage is poor with much infrabed flow and watertables recharged by hill catchments. Waters are highly mineralized. Haloxylon steppes and Artemisia steppes are the 2 main types of vegetation in the Northern deserts. In North West China shrub formation of Haloxylon; Salsola and Nitraria occur where the water table is high and Tamarix, Kalidum and Nitraria where water is saline. Artemisia, Caragana, Hedysarum occur where the rain is the only moisture available with Nitraria, Calligonum and Amnopiptanthus in the Gobi. The dominant land use is pastoral nomadism: sheep, horses, camels. Overgrazing can occur and winds are a problem.|
|India and Pakistan||Dry climates in the Indian sub-continent range from the very hot arid to semi-arid region with hot winters and very hot summers of the Indian Peninsula to the mild winters and very hot summers of the arid to semi-arid Northwest. Cold desert areas occur in the high valleys of Kashmir characterised by cold winters and mild summers. The dominant rainfall regime is of summer rain often occurring as late as September/October.||Large alluvial plains are characteristic of Pakistan and areas of sandy soils in the deserts of Pakistan and Rajasthan in in which areas of moving dunes occur. Soils are often of coarse texture and of high pH but nevertheless crops are widely grown in spite of the lack of water. Irrigation is a prominent feature of agriculture in Pakistan and Southern India and occurs in a very localised form in Rajasthan. Pastoralism is a major land use in non-irrigated and drier areas; it is often nomadic but usually combined with grazing on agricultural land. Wind is common, dust storms frequent in season and wind-erosion a feature of Northern areas.|
|Australia||Some 80% of Australia is classified as arid to semi-arid but does not prossess areas of hyper-aridity, the lack of extreme dryness is thought to be due to the lack of high orographic barriers and very cold offshore currents in the extensive surrounding oceans. Rainfall is, however, extremely variable: largely winter rainfall in the South and summer in the North with a transitional zone between the two systems. Winters in the South are mild with warm summers to mild or warm in the North with hot summers. The dry lands of the continent are subject drought cycles.||Soils of arid areas range from sandy, with sand dunes, to stony desert soils based on granites and laterites with smaller areas clay plains and riverine deserts. Extensive areas of solonized brown soils, grey-brown to red calcareous red earths all poor in P and N, also occur. Main vegetation types are: semi-arid low woods; shrub steppe; Acacia shrubland; Eucalyptus shrubland (mallee); Arid hummock grassland; Arid tussock grassland. Pastoralism is the major land use. Sheep mainly in the South and cattle in the North. Relatively small areas of irrigation occur under semi-arid conditions as well as some cultivation of cereals. No clearly definable demarcation between arid and semi-arid areas is possible from classification of ...|
19.9 million km² of the world's arid and semi-arid land surface have been classified as being under very high and high desertification risk. Of this area North and Central America comprises 7.4%, S. America 8.4%, Africa 33.3%, Asia 40.4%, Australia 10.2% and Europe 0.3%. Man's activities-have already had an impact on a signifiant proportion in the more densely populated developing countries of Africa and Asia. Assuming that only 20% has been affected so far, the task of anti-desertification action under PACD would be to stabilize, reclaim or rehabilitate roughly 4 million km² (400 x 10 ha) by appropriate, proven methods.
3. GOALS FOR ARID-ZONE FORESTRY
Regional goals for arid-zone forestry depend on the nature of the resource and the needs of the population.
3.1 North America
In North America the need to develop a variety of wood products and fuelwood from semi-arid zones has been recognized as being necessary to augment current supplies. The application of management for the production of multiple benefits on a sustained yield basis is in the process of evolution but production pressures do not yet appear to require more than planning for rangeland development.
Silvicultural potentials and management systems have yet to be determined. Multiple resource inventories and growth studies are required towards obtaining better data for management purposes.
The use or not of fire as a management tool is also a topic for investigation as well as the management of watersheds and rangelands under joint international (USA/Mexico) planning, programme design and implementation.
3.2 Latin America
The need to fully understand the ecology and nature of arid-zone resources is recognized as well as the need to develop management systems based upon the above data. Work is required to complete the ecological and demographic studies necessary for this purpose.
Emphasis is laid on slowing down and halting the spread of desert conditions through rehabilitation of degraded soils and the need to obtain more reliable information on water resources, climatic patterns and knowledge of arid-zone tree species silvics as well as the genetic improvement of plants and livestock for arid-zone development.
In the Sahel the current goals of arid-zone forestry is to afforest about 3.5 million ha in Senegal by the year 2010 and manage 500 000 ha of forest along the Senegal River. In Niger it is intended to completely rehabilitate about 100 000 ha during 1986-1990. Other needs are recognized for the intensification of research; efficient extension of methods of economizing on fuelwood use; reinforcement of activities in plantation establishment, agroforestry, forest fire management, management of wildlife and natural vegetation.
3.4 Africa South of the Equator
The major goals are to manage natural vegetation and regenerate natural forests while halting their steady degradation. In Ethiopia activity is aimed at the conservation and regeneration of the natural Acacia stands as well as the northern forests of Juniperus.
3.5 North Africa
The immediate goals in North African countries are to supply the needs of expanding populations with adequate fuelwood, roundwood and non-wood products such as honey through the establishment and management of forest resources also aimed at stabilizing the forest environment which provides fodder for livestock. It is also intended to re-establish an ecological equilibrium to balance wood and forage production; protect soils against erosion caused by water and wind; and protect and conserve water resources through measures to counter siltation. Finally it is intended to win the support of local populations for the programmes envisaged.
3.6 Near Fast
The goals of Near East countries envisage the use of trees (both forest and horticultural) to counter the effects of desertification in large-scale, rainfed and irrigated tree planting programmes (Syria, Jordan, Turkey).~ Reclamation of saline land with salt-resistant species is a second objective and the establishment of adequate local reserves of wood and fodder to alleviate pressure on natural resources a third. In order to conserve what is left and halt desert encroachment it is considered necessary to take the nature and ecology of the resource into account in the process of its restoration. Continuation and expansion of soil and water conservation and protection work is also considered essential.
3.7 Asia and Pacific
This region comprises USSR, Australia, India, Pakistan, and China.
In the USSR, arid land stabilization of soil against aeolian erosion, water harvesting and conservation of water resources are essential objectives in supporting irrigated agricultural and pastoral development. In Australia the objectives of management are to improve and maintain the largely pastoral productivity of the arid to semi-arid environments by adjustment of livestock numbers and control/improvement of woody vegetation competing with or supplementing ground forage species. In the Southern and South Western wheatbelts, reclamation of saline lands and measures to counter salinization of agricultural lands is an important activity. Many Australian species are being investigated for possible overseas introduction.
In China, arid-zone management aims at controlling aeolian and hydric erosion through engineering and combined tree planting as well as fixation of sand dunes and protection of cases to promote intensive irrigated agriculture and improve livestock management for food production.
India and Pakistan, on the other hand, are engaged in the selection of multi-purpose tree species and their extension into traditional farming/pastoral systems together with the maximization of benefits to be derived from natural species already present and the species proposed for use. The role of woody species in arid land development and in anti-desertification work has been widely acknowledged and genetic improvement of these is now being sought. Pakistan is seriously involved in the reclamation of saline lands which pose a serious threat to agricultural expansion.
3.8 Overall it can be said that the utility of tree and shrub species for arid land development has been recognized. In more developed countries with low population densities woody cover is also considered an obstacle to optimum ground forage development in the short term. However, arid zone conditions dictate some sort of woody vegetation to provide foliage during drought, cover for livestock and protection against wind. Interest is now being shown in the ecology of natural vegetation, the effects of its removal on a large scale and its preservation and management as opposed to artificial establishment with indigenous or exotic species. Effective soil and water conservation and sand-dune fixation remain a preoccupation while increasing attention is being given to reclamation of areas which have become salinized.
4. EXPERIENCES AND RESULTS OBTAINED
4.1 Natural Vegetation Management
4.1.1 North America
No formal management of semi-arid, arid zone vegetation appears to have been instituted so far, apart from fire prevention and suppression.
4.1.2 Latin America
No formal management systems for semi-arid to arid zone vegetation appear to have evolved yet.
Although little experience has been gained in natural vegetation management, a diameter limit at 0.25 m above ground level of 4 cm for intention of Guiera and 6 cm for Combretum sp. has been imposed on fire-wood harvesting of stands in the Guesselbodi forest in Niger. Such stands on slopes of 3% or more are subject to mechanical scarification to encourage regeneration.
4.1.4 Africa South of the Equator
No formal management systems identified.
4.1.5 North Africa
System of Holmoak thinning (Depressage de chêne vert) and branch pruning in semi-arid zones combined with controlled grazing off coppice shoots and other vegetation fuelwood harvesting and reseeding with ground fodder species; (Morocco, moister semi-arid zones).
4.1.6 Near East
No formal management systems identified.
4.1.7 Asia and Pacific
Pakistan appears to be the only country with some formal system of management of semi-arid forest types: the tropical thorn forests and dry sub-tropical broadleaved forests are cut on a 30-year coppice-regeneration cycle; A selection system is applied to the latter type, supplemented by enrichment planting when lack of grazing pressure permits.
4.1.8 Lack of knowledge of the ecology and silvics of natural woody species in the various regions together with lack of data on growth and yield makes the expense of application of ad hoc management difficult to justify. Inventory, ecological and growth studies now current, at least in the USA, will help to overcome this barrier. Where demand for forest products such as fodder, fuelwood, charcoal and tannin is strong it is evident that management (whether administered by local communities or the government) should be applied to prevent further degradation of resources and to ensure continued supply of forest products and benefits.
4.2.1 North America
Use of active woody forage species in pastures can be considered as basic agroforestry practice. Demonstration plots have been set up to promote -this.
4.2.2 Latin America
Agroforestry practice is commonplace in humid zones but in arid zones the only examples are instances of retention of scattered native trees on agricultural land growing maize, sorghum, beans, wheat or barley and the planting of fruit trees or retention of native trees of economic potential along gullies and water courses.
Traditional practices exist where useful trees of native species are retained at wide spacing over crop land. This results in an intensive individual tree management system combined with agricultural cropping and grazing. The system is widespread but infrequently used in areas where cash cropping (e.g. ground nuts) is prevalent. An applied agrosilvicultural system uses Faidherbia albida at 10 x 10 m spacing on agricultural or grazing land.
4.2.4 Africa South of the Equator
"Taungya" systems of crop growing with a forest tree crop are said to be in the process of development. Agroforestry systems are being reintroduced in Kenya and Tanzania resulting from research by ICRAF in Nairobi.
4.2.5 North Africa
Planting of horticultural varieties (olives, almonds, figs, apricots, pistachio) and acacias; very frequently A. cyanophylia along soil and water conservation works: contour ditches, gradonis and dry stone contour walls or terraces on agricultural land. Permanent stands of olives at 80-85 trees per ha are sometimes established on sloping land cultivated for wheat in Morocco.
4.2.6 Near East
A number of systems exist usually related to windbreaks of productive species around fields: poplars or mixed fruit-bearing trees and shrubs with Juglans (walnut). As in N. Africa trees are frequently established in association with soil and water conservation engineering works on agricultural land.
4.2.7 Asia and Pacific
Australia and USSR concentrate on windbreak establishment and in Australia native and exotic trees are used on grazing land for drought fodder and cover for livestock. Extension of tree planting is common in some areas for the reclamation of salinized land.
China and India make extensive use of trees on agricultural land for protection and production, less so in the arid zones of China than in India and Pakistan where traditional systems involving the permanent presence (40-80 trees/ha) of lopped Prosopis cineraria and Ziziphus mauritiana on crop land for combined fuelwood/fodder/fruit production purposes exist. In Pakistan, tree planting is closely associated with the already extensive and intensive irrigated agriculture of the Indus basin. Some systems include the planting of wide-spaced rows of Eucalyptus, A. nilotica, or Poplars on irrigated agricultural land for wood production combined with agricultural cropping.
4.2.8 Agroforestry systems embody the broad approach to land use required for successful agricultural production under arid conditions. It is characteristically less popular in developed countries in which land-use objectives are narrower. Common sense, well-established systems incorporating the permanent presence of managed trees on cropland already exist in semi-arid zones of Africa and Asia. There appears to be ample opportunity for the extension of this concept to other regions.
4.3 Sylvo-pastoral systems
4.3.1 North America
Much arid and semi-arid land is regarded as rangeland in North America. Its management in the USA is mainly geared to the reduction of woody vegetation to promote production of fodder grasses combined with the use of fire as a management tool and periodic reseeding to boost fodder volumes. Serious adoption of woody browse for drought fodder has not yet started, possibly awaiting validation of species regarded as useful as supplementary feed for livestock.
4.3.2 Latin America
Grazing is an important land use in areas of natural vegetation in semi-arid zones and a number of useful native species (Prosopis spp. for example) exist which provide a nutritious supplement to livestock feed during the dry season. Work on the rationalization of grazing systems is under way and these envisage use of Acacias, Cactus and Prosopis on pasture land in order to provide fodder and shade.
Natural vegetation is heavily grazed in the Sahel and woody browse provides an important supplement (at least 45%) to livestock diets at the end of the dry season. Nomadism and transhumance are necessary for stock management. No silvopastoral systems appear to have developed specifically apart from burning of dried grass to promote new shoots and lopping of fodder trees.
4.3.4 Africa South of the Equator
No mention is made of any silvo-pastoral systems. The use of fire for regenerating grasses and overgrazing is a severe problem in arid zones. Projects incorporating planting of fuelwood/fodder species combined with water-harvesting measures have revealed opportunities for and means of creating drought fodder reserves. The beneficial effects of protection against overgrazing have been amply demonstrated at Hado in Tanzania.
4.3.5 North Africa
Roughly 75 million ha of semi-arid and arid land are grazed in North Africa, woody species provide an essential part of the fodder consumed. Livestock is managed either under pastoral, nomadic, transhumance or more or less sedentary systems. Woody browse species, Acacia cyanophylla for instance, are widely planted. Attempts to resettle nomads and take the pressure off natural vegetation have given rise to the creation of permanent fodder reserves, and the silvopastoral management of natural vegetation to provide fodder and fuelwood.
4.3.6 Near East
Traditional silvo-pastoral systems exist with the combination of lopped trees (Pistacia spp.) and grazing (Syria). Pasture improvement incorporates the establishment of woody browse as well as reseeding. The arid and semi-arid zones provide a major resource of pastoral land usually managed under pastoral nomadism and transhumance systems.
4.3.7 Asia and Pacific
The dry lands of India and Pakistan are heavily overgrazed although certain traditional systems exist for the retention of lopped trees and shrubs. Integrated pasture improvement has been undertaken comprising the establishment of woody browse (both indigenous and exotic species), and in Pakistan this is accompanied by building-up infrastructure such as stock water points, roads and buildings as well as the control of grazing. In Australia, as in the USA, no well-defined silvo-pastoral systems exist other than those described under 188.8.131.52 apart from the planting of single, grouped, or lines of trees to provide shade or shelter from wind. The USSR has developed restocking of ranges with a mixture of woody (Artemisia spp.) and herbaceous (Salsola spp.) combined with carefully controlled grazing.
4.3.8 The utility of browse is widely recognized in arid to semi-arid regions but its retention for long-term sustainability of fodder production and environmental protection has not been so readily accepted in the developed countries of the various regions. More information is evidently required on the productivity of combined forage/browse systems taking the aspects of other benefits (fuelwood, charcoal, honey, tannins, protection from wind, provision of shade) into account. Control of grazing animals and stocking density emerge as vital components of any successful system.
4.4.1 North America
Afforestation is not allocated high priority in the arid, semi-arid zones of North America. Where it is practiced it involves intensive site preparation with machinery, concentrating on contour alignment of deep ploughing, terracing, pitting and the installation of water-harvesting systems. Planting is carried out and trees may or may not be watered after planting. Both bare-root and container stock are planted.
4.4.2 Latin America
No large-scale planting of arid zones has been undertaken although special planting techniques have been developed for Prosopis tamarugo in the Tamarugal Pampa of Chile. Tree planting for soil protection, fuelwood and fodder has progressed in the semi-arid regions of the Andes using Eucalyptus sideroxylon and Atriplex nummularia. Native species of Pines and Prosopis are generally used as well as Acacia and Atriplex among others, nearly always as containerized stock.
Tree planting, either in plantations, in woodlots or as individual trees is very commonly practiced in the Sahelian region. About half the species used are exotics, usually Eucalyptus and Acacia planted out as containerized seedlings of 3-6 months of age or as striplings and stumps of between 8 months to 2 years of age. Spacings are wide, 4 x 4 m and the holes prepared for planting (usually well before planting) are usually large (60 cm³). Timing of planting to exactly coincide with rains is an extremely important factor with regard to subsequent survival. Large-scale irrigated plantations of E. microtheca have been established in the Sudanian sector for fuelwood production. The majority of other planting, however, has a strong community forestry orientation and uses multi-purpose tree species.
4.4.4 Africa South of the Equator
Tree planting, often accompanied by micro-catchment preparation, contour ditching and terracing is on the increase in the region. These plantings have a strong soil and water protection and multi-purpose production bias. Eucalyptus, Acacia, Faidherbia albida, Prosopis sp., Cassia sp., Olea africana and Dodonea sp. play a significant part in these plantings.
4.4.5 North Africa
Afforestation for soil stabilization and protection is considered extremely important and is often carried out in conjunction with soil and water conservation works involving contour ditching, terracing and large planting holes to help absorb and concentrate precipitation close to trees. Conifers (P. halepensis, P. pinea, Cupressus sempervirens) comprise a high proportion of dry-zone planting followed by Acacia cyanophylla and Eucalyptus. However, parallel tree planting on agricultural land employs olives, apricots, almonds, figs, pistachio and carob. Trees are almost invariably planted out as containerized stock although some tentative seeding of conifers is in progress.
4.4.6 Near East
As in the case of North Africa, the Mediterranean and sub-Mediterranean countries of the Near East consider tree planting an essential part of the environmental rehabilitation of arid, semi-arid zones. Large-scale green-belt planting in Syria and Jordan attest to this fact. Tree planting of containerized stock in very dry zones accompanies intensive site preparation often with the aid of machinery: terracing, contour ditching, holes (30 cm³) and watering at least 3-6 times during the first season. National plans for 6 Near East countries envisaged the establishment of 631,000 ha between 1960 and 1980.
4.4.7 Asia and Pacific
In this region tree planting in arid zones assumes a fairly high priority in Australia where trees are established largely for amenity, stock shelter and bare saline land reclamation. Since a wide range of useful native tree and shrub species successfully grow in Australian dry lands, these have been identified, climatically classified and germplasm obtained for possible overseas testing. In the USSR attention has centred on the establishment of woody species in cold deserts in order to provide protection to soil and livestock from wind, and fodder for livestock. These activities are accompanied by either low-height protective fencing or repeated carpet-type chemical-stabilized strips on sandy soil behind which woody and herbaceous species are either planted (high wind velocity) or sown (relatively low wind velocity). Genera established are Haloxylon sp., Salsola sp. When planted, the shrubs are 30 cm high containerized stock, of which the top 1/3 is removed at time of planting.
Dry-land afforestation in China is on a characteristically massive scale, often accompanying soil and water conservation engineering works. Its aim is largely environmental enhancement and conservation or fixation of sand dunes. Detailed site allocation of species is practiced in relation to individual species requirements, growth rates and ability to resist wind and abrasion by wind-borne particles. Pinus, Populus, Tamarix, Ulmus and Salix are frequently used with understoreys of shrubs such as Amorpha fruticans, Hippophae rhamnoides, Capparis spinosa and Nitaria sibirica. The planting of narrow belts in tight grids is often preferred.
In the Indian sub-continent Pakistan is more versed in establishing and managing irrigated plantations but successfully carries out rainfed plantation establishment for which 25 species (only 7 exotic) have been identified. Watering of trees includes "pitcher" irrigation and drip-irrigation as well as direct sowing in micro-basins and the use of cuttings. In India planted species include eucalyptus,.acacias, casuarina as well as a number of indigenous species: Acacia senegal, Albizia lebbek and Tecomella spp. Methods are largely manual and include large pits for planting and watering (roadside plantings, 9 litres/tree/month) and some seeding of Acacia nilotica along local irrigation ditches.
4.4.8 Tree or shrub planting has been widely accepted by most countries as an integral part of dry-land rehabilitation, regarded perhaps as being of lower priority in developed countries where the effects of degradation on human welfare are less dramatic.
Techniques are very similar throughout and refinements such as drip irrigation are in the process of testing and introduction for large-scale work, as they may have an application in the conditioning of tree species to high salt levels and their establishment with the aid of brackish water.
Particular techniques have evolved for the fixation of dunes in cold deserts and their concepts may have some application to similar needs in the North Africa and Near East regions as well as in Latin America. The wider application of effective water-harvesting techniques could expand current plantings into even drier zones than at present with an increasing impact on wind-movement, improvement of soil protection, landscapes and the environment of livestock and humans.
All afforestation in the USSR arid zones is established with the objective of also fulfilling a windbreak function. Fixation of moving sand with Neozin (a mixture of petroleum wastes, sulphite alcohol liquors, cotton tar...) is basic to shelterbelt establishment and provides a cover behind which Calligonum, Haloxylon persicum and Haloxylon aphyllum can be established. These species can also be established by sowing along a series of 5 x 1.5 m wide ploughed strips at 5-8 m spacing.
4.5 Shelterbelts and Windbreaks
4.5.1 North America
The establishment of windbreaks for the protection of agricultural crops is not widely practiced in the arid, semi-arid zones of the USA and Mexico although the influence of their effects has been studied on the "Great plains" of the sub-humid zones to the North. The main species employed are prosopis, acacias, tamarix and eucalyptus often as single rows flanked by shorter trees or shrubs and cut on 25 to 35-year cycles. Their benefits in protecting land against aeolian erosion are already recognized.
4.5.2 Latin America
Windbreaks are of considerable importance on the large plains and windy southern portion of South America. 1.5-4 m high stone and adobe walls are initially established to provide immediate protection from wind in Patagonia and tree and shrub species such as Salix caprea and Sorbus aucuparia planted behind them. In Argentina either eucalyptus with acacias are planted as windbreak species or lombardy poplars and willows, while in Uruguay mixtures of eucalyptus, pines and acacias provide protection on the Atlantic coast.
Protection from dry desiccating winds and windblown sands is important in dry Sahelian countries. Windbreaks of trees such as Azadirachta indica and Acacia or live fences of Euphorbia balsamifera, Commiphera africana-(both established as cuttings), Leptadenia, Tamarix articulata and Bauhinia reticulate provide the type of drought and wind-resistant cover required. It has also been noted that scattered single trees can also significantly slow down wind movement.
4.5.4 Africa South of the Equator
The value of windbreaks in dry zones is acknowledged but further work is needed in selecting species and designing and establishing windbreaks. Species currently used are Eucalyptus spp., Leucaena leucocephala, Euphorbia spp., Cassia siamea and Casuarina equisetifolia.
4.5.5 North Africa
Shelterbelts and windbreaks assume great importance in this region because of the need to fix dunes and protect agricultural lands and human settlements. About 282 000 ha are already under the protection of windbreaks of various sorts in North Africa and further work is going ahead in Morocco. Windbreak specifications are fairly well defined in the Cap Bon area of Tunisia and the main species used are Eucalyptus spp., Acacias spp. and Cupresus spp.
4.5.6 Near East
Irrigated agriculture in Egypt would be inconceivable without the protection of the existing network of Casuarina and Eucalyptus windbreaks to afford protection and supply wood. Windbreaks of poplars and other species are also considered essential for the irrigated agricultural lands around Damascus in Syria. These windbreaks and stands of trees not only provide protection but also substantial profit from the wood products derived from them.
4.5.7 Asia and Pacific
The application of windbreaks for the protection of agricultural crops is highly developed in the dry lands of China in order to protect crops from desiccation and physical damage from wind-blow sand and loess. Width of belts varies from 10 to 15 m and pines, poplars and Ulmus pumila as well as shrubs are used. Eleagnus angustifolia in 180-200 m wide bands is used to provide protection from the salt-laden winds of the "gravel" gobi. These belts are combined with a system of alternating green belts and ditches.
On the Indian sub-continent windbreaks are established in irrigation areas and as roadside plantings. In rain-fed agricultural areas Tamarix and Calligonum sp. are most commonly used, and under irrigation Dalbergia sissoo, A. nilotica, Melia azedarach, Salmalia malabarica and Azadirachta indica. Tree spacings of 2 x 3 m are common as well as 3 to 10 lines of trees.
Shelterbelts in Australia have been shown to improve lamb survival and growth of adult sheep. 12 tree species were identified as being useful.
4.5.8 The need for shelterbelts and windbreaks appears to be widely appreciated in most regions. Their application, however, is not as widely supported as would appear necessary in view of their benefits. Bearing in mind the fact that the beneficial influence of a windbreak covers 15 to 20 times its height, even low hedges would assist in ameliorating conditions for crops or livestock.
4.6 National Parks
4.6.1 North America
National parks in dry zones are considered not only useful for conservation but also as units for monitoring regional desertification as influenced by man's activities. Wilderness areas are considered an essential component for strict conservation of the 2.9 million ha of the 11 national parks and reserves in the dry-land areas of the USA, 10 are "wilderness" units covering 1.4 million ha.
4.6.2 Latin America
The situation concerning national parks in arid and semi-arid areas is not clear. There are about 45 reserves and national parks in dry land areas of 7 countries: Argentina, Bolivia, Brazil, Chile, Ecuador, Peru and Venezuela covering some 3.27 million ha of the continent. The largest proportion of this area occurs in Bolivia (38%) and Venezuela (39%) and the smallest (<1%) surprisingly in Chile which has more than 12 million ha of parks in other climatic zones.
The Sahel contains some 8.5 million ha of national parks and game reserves covering extensive areas. Senegal's national parks and reserves comprise 26%, those of Sudan 23% and Mauritania 17%: 66% of the total area, attesting governments' interest in conservation. Population pressure on some of these reserves is likely to be severe, particularly in Senegal and the Sudan.
4.6.4 Africa South of the Equator
Wildlife is abundant in the region with more than 30 species of large mammals and at least 200 wildfowl species. These animals are managed in reserves 75% of the area of which occurs in arid to semi-arid zones. National parks and fauna reserves cover 43.88 million ha in 9 countries with arid to semi-arid zones. The reserves are designed to conserve plant and animal species, protect certain types of vegetation and landscapes and to retain breeding conditions for wildlife.
4.6.5 North Africa
The region possesses 4 national parks, 3 nature reserves and 3 wildlife reserves in Libya, Algeria and Tunisia. These have been selected to conserve flora and fauna and certain zones of particular scenic, botanical or historical interest. The total for the countries of the region comprises 431 500 ha.
4.6.6 Near East
5 countries of the Near East Region (Egypt, Iran, Oman, Saudi Arabia and Turkey) possess national parks in dry lands covering about 3.7 million ha of which by far the greatest proportion have been established in Iran (83%). The parks were created to preserve the land, landscape and wildlife species of the various countries. Considerable pressure is, however, exerted by local populations living in adjacent degraded environments to exploit these protected areas for their daily needs.
4.6.7 Asia and Pacific
The Asia and Pacific region is well endowed with national parks and reserves of different types established in dry lands. India has established 9.15 million ha, Pakistan 7.74 million ha, the USSR 1.12 million, Australia 14.37 million and China and Tibet 1.38 million. The reserves were selected on the basis of scenic merit, historical and/or biological significance and in some cases (Australia) because unused land was available. Constant pressure is exerted by rural populations on many of the reserves in the more densely populated parts of the region in Pakistan and India.
4.6.8 A rough total of 96.47 million ha has been reserved in the arid to semi-arid lands of the world's major regions, that is 2.6% of the 3 764 million ha of the world's arid, semi-arid and sub-humid zone surface likely to be affected by desertification. It is suggested that this proportion could be increased in order to provide a better monitoring of the effects of man's activities on the arid and semi-arid zone environments as well as reference points for the assessment of further degradation or rehabilitation of degraded arid lands.
4.7.1 North America
Wildlife strategies in North America are structured on management to obtain optimum levels of big game production for hunting in season and under licence. This form of utilization takes 15 to 25% of the large wild animal population and it is possible that an even larger proportion of small game is taken as they form a "buffer" group when large game is scarce. Greater attention is being paid to the preservation of endangered species and to the non-game aspects of species in relation to their role in the overall functioning of ecosystems. In semi-arid zones the greatest hunting pressure is on the Pinyon-juniper and Madrean evergreen (Encinal) woodlands.
4.7.2 Latin America
In the arid to semi-arid zones of Latin America parks have been established (see section 4.6) for the conservation of flora and fauna. Legal protection is well defined and generally total but incursions of grazing livestock and damage by fire is fairly common. Protection of wildlife within parks appears well assured and the habitats of important species such as the Vicuña (Vicugna vicugna) and Guanaco (Vicugna guanicoe) plus a wide variety of bird life, reptiles and insects are well protected. As in Africa it is beginning to be realized that the local fauna are best adapted to and are the most efficient users of marginal conditions. If appropriately managed they can contribute significantly to the diets of rural people in arid lands on a sustainable basis.
Meat from wildlife provides an important contribution to the diets of rural dwellers with access to game. Wild animals are one of the most important renewable resources of arid zones because of their high degree of adaptability to available fodder and browse, resistance to disease and low water requirements. Despite restrictions on hunting in the 280 310 km² of parks and reserves in the Sahel, poaching is rife and provides meat for the poorest elements of the community. Unfortunately, commercial incentives promoted by local, urban-based and international demand have placed even greater harvesting pressure on the now increasingly limited resource. The concept of game ranching, investigated in the Sahel, offers scope for the introduction of a system with significant utilitarian and conservation propensities. The mobilization of local support for conservation policies is essential and wildlife extension is an important field for future development.
4.7.4 Africa South of the Equator
Wildlife and protected area management are important components in natural resource management in Africa South of the Equator: Wildlife is harvested through cropping schemes, game ranching, wildlife farming, subsistence wildlife utilization (frequently poaching), and safari hunting. Wildlife is a prominent aspect of drier and more open areas of the region and 524,000 km² of land in the region have been set aside as parks and reserves for the propagation, protection, conservation and management of vegetation and wild animals". Other features of resource usefulness in arid and semi-arid zones are (1) wildlife-based tourism: a strong foreign-exchange earning industry and (2) the conservation of genetic resources.
4.7.5 North Africa
The predominantly dry zones of North Africa are under heavy grazing pressure, disturbing the habitats and competing with surviving wildlife for food. The wildlife resource is very impoverished but some action is being taken to restock reserves, with partridges, for instance (Morocco). Partridges are being raised in farms for this purpose and then released. Wild boar is plentiful in forest areas because of religious objections to its consumption although some hunting is conducted. Hunting of game species is seasonally controlled and largely administered by forest services whose lands often provide the necessary habitats for game animals and birds.
4.7.6 Near East
In many parts of the region wildlife habitats have been overgrazed and virtually destroyed through the activities of humans and their domestic animals. Some significantly large reserves, however, still exist in Iran. A number of species such as the wolf, the Anatolian leopard, the oryx, the addax and the Syrian wild ass have become endangered and various antelopes and gazelles very rare. Only the wild boar thrives in the thickets of forest reserves owing to religious objections to its consumption.
4.7.7 Asia and Pacific
In some parts of the region control of wildlife expansion has been necessary because of its successful competition with livestock and impact on the environment (kangaroos and rabbits in Australia). However, in other parts of the region, notably China, India and Pakistan the competition from man and his livestock has degraded habitats and seriously reduced wildlife numbers to the verge of extinction. A large area of national parks and reserves still exists in India and Pakistan but many appear to be severely affected by the intrusion of livestock although poaching itself may be minimal. Present policies are aimed at conserving game and promoting tourism. Little progress has been made towards game farming (crocodile for instance) or game ranching although pioneer work has been carried out and techniques suggested in both fields.
Although no details are available of wildlife management or conservation in dryland China, similar lands and conditions in the USSR provide environments for antelopes, foxes, wolves and gophers, the latter being hunted for their pelts. Hunting is regarded as a special aspect of the economy and is given due development attention. This entails the decreeing of hunting seasons and shooting quotas and the recording of animals shot. Two million tarbagan marmot skins, tens of thousands of fox pelts and thousands of wolf pelts are procured annually while desert antelopes are hunted for meat and pelts.
4.7.8 Wildlife can be seen to be a valuable resource in arid areas because of its adaptability and ability to thrive under harsh conditions. Its protection is important from the aspect of conservation of gene resources and tourism but its rational management and harvesting also provide development opportunities for more efficient use of vegetation and the consequent supply of protein to rural populations. The purposeful allocation of land for wildlife either as special reserves or in the form of shared use of arid-zone pasture in the Asia Pacific region is a subject for careful consideration of its socio-economic conservation and environmental implications.
4.8 Conservation of vegetation, soil and water resources
4.8.1 North America
Baseline inventories of arid to semi-arid zone vegetation continue in the region but are of increasing scope in order to provide information for broader land-use objectives. Hydric erosion is not considered a serious problem overall and attention is being given to fire prevention and suppression as fire is considered a major cause of erosion. Control of aeolian erosion is practiced on a limited scale usually by establishing a cover of wind-resistant shrubs such as Larrea tridentata, Baccharis sarothroides and Atriplex canescens. Attention is also given to the reclamation of land disturbed by mining through revegetation and supplementary irrigation with such species as Citus crispus and Purshia glandulosa. Since demand for water in arid zones exceeds the output techniques of water harvesting, waste disposal and water salvage are being applied and a handbook of water harvesting techniques published and circulated. This advocates measures such as covering areas of ground with plastic, leading runoff into lined tanks provided with floating anti-evaporation rafts. Watershed management is practiced widely in order to minimize erosion, increase yields of water and reclaim degraded watersheds. Efforts are made in arid areas to avoid adverse impacts of man-made structures and overgrazing. Relationship of vegetation cover to water yield is also being studied and vegetation composition and structure duly adjusted.
4.8.2 Latin America
Decrees have had to be issued to protect certain vegetation types from virtual extinction due to overcutting: Prosopis tamarugo and P. atacamensis in Northern Peru for instance, with subsequent artificial re-establishment of more than 35 000 ha. The application of remote sensing has assisted the work of classifying the vegetation of arid-zone areas and thus permitted improved development. Afforestation of severely degraded vegetation in the Brazilian "Caatinga" is another example of conservation of vegetation and soil resources.
Protection against hydric erosion of soil is serious in the higher rainfall areas and in coastal drylands affected by floods due to poor soil and water conservation in the interior.
Aeolian erosion is a major problem in the arides zones of Patagonia where average wind velocity is 35 km/hour attaining levels of 200 km/hour. Establishment of windbreaks is necessary. Sand-dune fixation is currently applied in Chile with the aid of woody plants: Ammophylla arenoria, Ambrossia chamissanis and Acacia cyanophylla.
The arid zones of Latin America have been submitted to strong population pressure and require irrigation in order to support agriculture. Drip irrigation is an important advance in this respect in the field of water conservation. Another approach has been to develop the use of drought-resistant species to which the genus Prosopis provides an important contribution. Water harvesting is another development under investigation as well as the desalinization of water and the recycling of polluted town water for agricultural use.
Watershed management is considered essential in dry lands and the use of productive tree species plays a major part together with the establishment of soil and water conservation works and the rehabilitation of the vegetation of degraded areas. Studies are also required in the effectiveness of trees to substantially add to the soil water regime by condensation of atmospheric moisture in cloud and fog zones.
Formal conservation of vegetation and soil and water resources in Sahelian regions follows the well-established pattern of: protection from grazing and exploitation through establishment of zones of protection; application of proven methods of water collection and watershed management. The major factor in conservation is to relieve the constant pressure of livestock and human activities of fuelwood collection, charcoal burning and periodic burning of vegetation.
Measures are also applied to protected areas to reduce erosion by water and wind: contour ditching, ridging, construction of gradonis, gully plugging and so on, allied to tree planting and the management of surviving areas of natural vegetation. The encouragement of traditional practices of intensive individual tree retention and management would also be useful on agricultural land together with amenity tree planting and the establishment of hedges of drought-resistant species: Jatropha curcas, Euphorbia sp., Azadirachta indica, etc.
4.8.4 Africa South of the Equator
The developing countries of this region appear to have carried out considerable development work in the application of soil and water conservation works combined with tree planting, often with the assistance of food aid. Advances have been achieved in the establishment of sub-surface dams and water harvesting combined with the establishment of fuelwood/fodder reserves for semi-nomadic tribal groups (Kenya). It is in this region that research is being conducted into agroforestry systems which assist in stabilizing shifting cultivation, thereby relieving the pressure on land and vegetation.
4.8.5 North Africa
A great deal of progress has been made in this region by the development and widespread application of soil and water conservation works combined with forest and fruit tree planting as well as fuelwood/fodder species. 593 000 ha of such soil and water conservation measures have been applied in 3 countries of the region. Work has been assisted by the fact that traditional water harvesting, spreading and conservation systems have been working and used in hill areas since ancient times.
Measures to counter erosion by wind have been applied in areas of sandy soil using both mechanical and vegetative methods, employing inert material of shrubs and reeds (Arundo donax) as well as palm fronds and also mulching with fronds of palms, branches, synthetic fibres and chemical products such as URESOL. These are nearly always accompanied by planting of trees and shrubs such as Tamarix, Calligonumm Acacia cyanophylla, Eucalyptus spp. and Prosopis juliflora. Roughly 101 000 ha of sand-dunes have been fixed to date and 182 000 ha protected by mechanical methods with palissades. integrated management of watersheds has been seriously undertaken in Morocco where 878 000 ha of watersheds are under progressive management of which 570 000 ha have been studied and worked on. Watersheds serving dams have been selected as priority subjects for management in Tunisia.
4.8.6 Near East
Countries of the Near East region have tackled the problem of grazing control and the genetic improvement of goats to reduce damage to natural vegetation (Al-Sham) breed). In addition, in situ conservation of remaining woody vegetation is being attempted. Soil and water conservation work is largely based on mechanical site preparation with contour furrowing, ditching, terracing, ridging and ploughing combined, as in other regions with planting of conifers: P. brutia, P. halepensis, P. pinea and Cupressus sempervirens and fruit trees. (almonds, figs, apricots). Sand-dune fixation is an extremely important component of anti wind-erosion work in this region. Work carried out includes spraying of oil-derived fixatives in addition to the selection of tree species suitable for fixation of dunes under arid conditions. These include Acacia cyanophylla, certain eucalyptus, Tamarix gallica, T. aphylla in the Near East, Tamarix laxa and T. leptostachis in Afghanistan. Not only the fixation of dunes but the management of forested dune areas has been studied. Water harvesting for runoff agriculture on the basis of diversion of water from natural catchments and its sub-surface storage have been achieved following the guidelines of well-established traditional practices. Other techniques have been developed such as the creation of artificial catchments and storage of water collected from the roofs of houses as well as the use of polluted town water and sewage for agricultural purposes together with salt water irrigation and desalinization of ground and seawater.
4.8.7 Asia and Pacific
Australia has made advances in the field of intensive land-use systems surveys and analyses based on low-level aerial photography and related ground truth for the conservation and development of forage vegetation resources. LANDSAT imagery is used to prepare maps for determination of conservation status and various programmes have been developed for land-use evaluation and planning (SIRO-PLAN and LUPLAN).
The other countries of the region are more preoccupied with soil and water conservation; India, Pakistan and China in particular. The countries practice a wide range of soil conservation work using manual and mechanical engineering works: contour ditching, furrowing, ridging to conserve soil, together with associated planting of trees.
Water conservation is also important and the USSR has developed the system of natural and artificial takyr catchments capable of yielding 5 000 to 35 000 m³ of water per km² under semi-desert conditions. This water recharges ground water reserves and is also tapped for human consumption: fresh water "lenses" are created underground, floating on sub-surface saline resources.
Reclamation of saline lands and prevention of salinization is another preoccupation of the countries of the region. Salt resistant species are being intensively investigated, some provenances of Eucalyptus for example are being subjected to tissue culture in Australia in order to develop particularly resistant strains. In India and Pakistan particular techniques such as drainage, ditching and the planting of salt-resistant species such as A. nilotica, Prosopis juliflora, Salvadora persica and others is being undertaken.
Sand-dune fixation is also well developed particularly in the USSR and China where special tree, shrub and grass combinations are used: species such as Artemisia halodendron, Salix flavida, Lespedeza dahurica and Caragona microphylla. In China strategies such as 'block in front and pull from behind are successfully applied for sand-dune fixation with belts of Salix cheilophila and Artemisia ordosica on the lower windward side of dunes complemented with the planting of grass in the depressions.
Reclamation of degraded land is variously tackled in the region by stock exclusion, type pitting', ploughing and water ponding of scalded areas (Australia) and in Pakistan saline water is used for first raising and then irrigating trees.
4.8.8 Techniques of conservation of soil, water and vegetation resources are already well developed in the Asia and Pacific region. There appear to be opportunities for the transfer of certain concepts particularly in the realms of water harvesting and fixation of wind-blown sand and soil.
Desertification caused by over-irrigation with resultant salinization is another recognized phenomenon requiring the refinement of water-management prescriptions as well as remedial measures to reclaim salinized lands in certain countries of the region.
Applied conservation boosts the productivity and ensures the sustainability of resources in arid and semi-arid zones. However, its application requires compromises between social and purely technical conservation interests because of the rearrangements of people and rights to resources that are necessary. The application of the concepts and techniques of conservation depends on political processes which demand comprehensive ecological, technical, financial, productive and social justification for their successful implementation.
4.9 Conservation of genetic resources
Conservation of genetic resources can be practiced in situ, that is, as part of a viable natural ecosystem. This is the most desirable method provided that the area can be fully protected. Little is known about the minimum area needed, but one large reserve in the centre of a range of species is less likely to be effective than a series of smaller reserves sampling the range of variation.
Ex situ conservation: the establishment of artificial stands outside the natural geographic range but with good prospects of long-term conservation, is a promising method of gene-pool conservation. Combinations of both _ situ and in situ conservation could be the solution to conserving some species.
Appreciation of the concepts and application of the techniques of genetic resource conservation vary from region to region as is shown below.
4.9.1 North America
A number of arboreta, botanical gardens, museums and collections of plant and animal species are maintained under government or private sponsorship. In addition, the national parks, wilderness areas and biosphere reserves in the arid regions of the South Western United States and Northern Mexico provide the most extensive system for the conservation of genetic resources of both plant and animal species. These areas also provide suitable control sites for ecological investigations into the impact of human modifications on genetic resources.
4.9.2 Latin America
The network of national parks in the region provides at least a basis for the selection of areas to be protected for in situ conservation purposes. More attention is being given to the collection of seed of dry-zone species and their inclusion in an FAO/IBPGR project for the provenance testing of useful arid-zone tree species. Endangered species of animals and plants have been identified and measures have been taken for their protection, among them being: Caesalpinia spinosa, Gorbiera hygrometrica and certain species of Prosopis such as P. atacamensis. In Peru an area of 180 000 ha containing the mayor proportion of Peruvian arid-zone species has been declared a national forest (Bosque Nacional de San Ignacio).
Very little mention has been made in available documents of genetic resource conservation activities in this region. The FAO/IBPGR/UNEP (now FAO) Project on Genetic Resources of Arboreal Species for the Improvement of Rural Living in Arid and Semi-Arid Areas has promoted collections of seed (intended for provenance testing and ex situ conservation) in the Republic of Sudan and in Senegal.
4.9.4 Africa South of the Equator
No mention of genetic resource conservation has arisen out of the available documentation on arid zones. However, it can be presumed that the large area under national parks and game reserves has provided at least a base for the selection and protection of appropriate areas for in situ genetic resource conservation of both wild animals and vegetation.
4.9.5 North Africa
No mention of conservation of genetic resources was made concerning the countries of this region although the creation of national parks and their protection could be considered a first step in this direction.
4.9.6 Near East
The FAO/IBPGR/UNEP project mentioned in paragraph 4.9.3 has organized collection of seed of arid-zone species in the People's Democratic Republic of Yemen where the in situ conservation of the genetic resources of Prosopis cineraria is in the process of being organized. No other formal steps appear to have been taken apart from the creation of national parks in certain countries of the region.
4.9.7 Asia and Pacific
Certain countries of the region are fully aware of the implications and needs of genetic resource conservation. Australia is possibly a leader in this field and has accumulated and stored data on computers in order to provide information on precise location for those wishing to sample the range of variation of a given species. India is a participating country in the FAO/IBPGR/UNEP arid land species project mentioned previously. Again, the large area of dry lands under national parks in the region offers opportunities for the selection, protection and preservation of certain samples for in situ genetic resource conservation.
4.9.8 It is apparent that the importance of genetic resource conservation has not yet been recognized in many countries. Extension in this field is necessary in order to promote acceptance of the concepts and stimulate appropriate action. The arid zones are possibly those zones of the world under the most severe environmental pressure and zones in which species are most likely to become extinct in a relatively short time unless appropriate action is taken. Adaptation and improvement of tree and shrub species of arid zones could have a lasting impact on their productive capacity and utility to man.
4.10 Processing and utilization
The occurrence of desertification implies that people should change their ways to fit in with their environment; whereas development demands that the use of resources must be reorganized with the aid of newly-available technologies to fit people's expectations. The fragile nature of the arid and semi-arid zone environments means that they react adversely to single-objective intensive land-use activities such as might occur under the heading of "development". If the user is to attain sustainable production it is preferable to spread the burden of cropping over all the components of the environment: soil and various layers of the vegetation that cover it, in much the same way that a combination of wildlife species can make continued long-term selective use of the ground cover and browse. Excessive harvesting and cropping pressure on one component results in its degradation, throwing the rest of the system out of balance and making it susceptible to desertification.
Dry land environments are capable of sustained production albeit at a modest or low level. Not only does the environment provide fodder but various other products such as wood for energy, domestic use, and a host of non-wood products useful to human beings in their daily lives. The following chapter provides examples quoted from country reports and studies of dry-zone vegetation. Some of the products and processes are treated in greater detail in Section 2: Update of Recent Developments.
4.10.1 North America
The North American approach to the utilization of dryland vegetation is generally more industrially-oriented than in other regions and the harvesting of trees in "woodland" types are considered suitable for the manufacture of particle board. Other uses include charcoal, fence-posts, limited sawn products from Prosopis spp., edible nuts form Piñon pine:
(Pinus edulis in the North and P. cembroides in the South), and oleoresins from tapping Pines and Junipers. Other non-wood products such as rubber can be obtained if required from Parthenium argentatum, oil from Simmondsia chinensis (the jojoba) and Lesquerella fendleri; resins from Grindella camporum and Larrea tridentata; fibres from Agave lechugilla and A. sisalana. The Mexican pharmacopoeia names a wide variety of species from arid lands with medicinal uses such as Agave sisalana, for the extraction of diosgenin.
4.10.2 Latin America
The inhabitants of arid and semi-arid zones in Latin America make wide use of the species available to assist them to survive under frequently harsh conditions. Harvesting of wood for fuelwood and charcoal is common, particularly those of high density and therefore high calorific value: Prosopis tamarugo, Acacia caven for instance and. Quillaja saponaria for handicraft manufacture. A list of 107 woody species was drawn up by the author of the basic document for the Latin America region, indicating uses such as charcoal, construction, parquet, turnery, posts and cabinetmaking. A very wide range of forage-producers has also been identified among them, being members of the genus Prosopis, Leucaena leucocephala and Caesalpinia ferrea. 54 species are actually listed indicating the portion of the plant palatable for livestock and suggested method of processing (if required). "Industrial" use of dryland species included the extraction of tannins, oils, gums, waxes, resins and sugars. 54 species have been listed such as Tabetuia carariba for tanning, Copernica cerifera for oils and waxes, Euphorbia xanti for gum and Hymenea coubaril for resin. Considerable importance is also given to the medicinal properties of arid-zone plants and their contribution to the evolution of the Latin American pharmacopoeia. The names of 29 species have been provided together with the part of the plant used. Among them are Larrea tridentata and Quillaja saponaria. Finally, food and fruit-bearing arid-zone species such as Carica chilensis and Erythrina velutina are listed amongst 31 species providing edible matter.
The difficult living conditions, erratic rainfall and periodic droughts of the Sahelian countries require a broader base than provided by purely agricultural products to supply the necessities of life, if not survival itself. Fuel for cooking is a primary need for the processing of food which would otherwise be indigestible and therefore not nutritious. The excellent work by Von Maydell (1983) "Arbres et Arbustes du Sahel" gives details of over 100 species, illustrating them, describing them and their uses for wood, fuel, forage, apiculture, medicines, gums, tannins, colouring matter, mineral salts and fibres as well as their potential use for amenity purposes, soil improvement and protection. The notable fact is that all the species listed are known and used more or less intensively by Sahelian populations. Some of them are purposely retained on cultivated land and are intensively managed as individual trees under traditional agroforestry systems. The arid and semi-arid zone tree species and shrubs are too numerous to list here and examples are given in Section 2. A major tree crop is gum arable, largely collected from natural and planted stands of Acacia senegal, also a useful producer of wood and forage (both as foliage and fruits) as well as honey-bearing flowers.
4.10.4 Africa South of the Equator
No broad information was available for dry-zone woody species in this region although local uses must be made of them other than those of charcoal, fuelwood and forage, tannin, gum arabic and the resin myrrh. Tannin would appear to be of particular importance in view of the need to process hides produced by wildlife harvesting. Attention is drawn to FAO Forestry Paper No. 44/1 Food and fruit-bearing Forest Species (examples from Eastern Africa) describing 40 wild species of which some occur under semi-arid to sub-humid conditions providing food, wood, sometimes fodder, fibre and medicines. This is another collection of monographs on tree and shrub species known and widely used by local people as supplements to their diets and providing raw material for their day-to-day needs.
4.10.5 North Africa
Attention in this region appears to be centred on extractives: essences from aromatic plants such as rosemary (Rosmarinus officianalis), extraction of tannins and the industrial use of alpha grass (stipa tenacissima) for paper pulp. Food products are obtained from the seed of pines P. pinea, P. halepensis and P. brutia; gum sandarac from Tetraclinis articulate and in sub-humid areas cork from Quercus suber, which provides the raw material for an ancient and well-established industry. Fuelwood and charcoal are high-priority forest products, the harvesting pressure on which has been purposely relieved by a reduction in the price of kerosene (Algeria, Syria). Forests and shrub-lands are regularly grazed and provide fodder from a wide variety of browse species. Beekeeping is a profitable occupation, dependent on both indigenous and exotic cultivated horticultural and forestry species.
4.10.6 Near East
There is generally no advanced forest industry in the dry lands of this region. Poplars are grown under irrigation for paper pulp, local sawnwood and plywood manufacture but the major forest crops are fuelwood, fodder and charcoal. Other non-wood forest crops include gum arabic (Acacia senegal), and resins from Astragalus sp. A wide range of horticultural species are grown under semi-arid and irrigated conditions such as olives, stone fruits (apricots) Salvadora sp., figs and recently on an increasingly large scale the grape vine. Nuts such as pistachio and almond are also commonly grown and the date palm (Phoenix dactylifera) plays a prominent part in the desert diet, culture and handicrafts. Medicinal products are collected from wild plants of the Mediterranean flora but the products of the tropical flora such as Commiphora sp. and Calotropis sp. are better known.
4.10.7 Asia and Pacific
The region boasts a wide and intensive processing and use of products from arid and semi-arid lands. India and Pakistan probably lead in this regard as their dry-land population densities are among the highest in the world and every available source of useful raw material is used. Fuelwood harvesting, charcoal burning and overgrazing are serious causes of desertification but local traditional agroforestry systems could apparently, if practiced in a more widespread way, provide some help in this sphere. Products obtained from natural vegetation include aromatic essences, oils, gums, resins, spices, tannins and dyes, fibres and flosses, weaving materials, edible fruit and plants, latex, leaf wrappers for local cigarettes and honey in addition to small timber for agricultural implements, utensils, furniture, handicrafts and village house construction. Medicinal plants are very commonly collected and used such as Ephedra gerardiana and Hyoscyamus niger from the cold, dry regions of Ladakh or Withania somnifera from Rajasthan. These also provide opportunities for commercial collection and sale of raw material. China, too, has a very large pharmacopoeia derived from herbal drugs but no details are available from the presented papers of this or of the dryland products of vegetation in the USSR.
In Australia dry lands produce fuelwood, posts for fencing (some 20 to 30 million per year), charcoal, tannins and some eucalyptus oil which used to be extracted under fairly primitive conditions. Honey is another important product of semi-arid woodlands containing honey-producing species such as Eucalyptus melliodora. Medicinal products (Atropine for instance) can be extracted from certain dry-zone species such as Duboisia.
4.10.8 The use of non-wood products: forage, extracts, medicines and so on, is far more intensive in developing countries and could in itself pose a problem for the conservation of genetic resources in cases where plants may be uprooted in the process of harvesting. There is no doubt that the collection and processing of non-wood products provides a valuable contribution to life in arid zones of developing countries and efforts to improve and augment resources are worth considering in the general effort to re-establish vegetation cover.
The collection and processing of raw material from arid-zone vegetation is much more contentious in developed countries concentrating more on wood products for industrial and farm use. However, the recent energy crisis and growing appreciation of conservation needs has focussed attention on latex-producing species for energy production and other arid-zone species of industrial potential such as jojoba (Simmondsia chinensis) as a substitute for whale-oil.
5. GAPS AND SOME ISSUES
The preparation of country or regional reports has permitted the evaluation of current measures to combat desertification, revealing shortcomings in data bases and activities. These are now identified on a regional scale:
5.1 North America
Although vegetation surveys and analyses of increasing scope and complexity are being conducted, there is as yet no reliable and comprehensive data on arid-zone species growth rates and productivity upon which to base management strategies and prescriptions. Further information is also needed on silvics of major species, growth rates under different conditions of site, and the determination of rotations of the ecological units for which management is intended.
5.2 Latin America
There appears to be a demand for the collection and synthesis of general information on arid lands covering most aspects of the environment (climate, soils, vegetation, topography). An important innovation is the conscious inclusion of the need for more comprehensive and precise information on the human and livestock components of the environmental set-up under both rainfed as well as irrigated conditions, for evaluation/planning purposes.
Countries of the Sahelian region have found that there are gaps in the knowledge and records of work carried out in the past in order to provide guidelines for the future. This is particularly true for techniques of natural vegetation management to which the need for the determination of the silvics and soil/site relationships of local species is also added. In addition there is a need to determine and develop methods of wildlife management to suit local conditions as well as studies and field work to refine soil and water conservation techniques towards adapting them specifically to the Sahel, including the preparation of a simple and effective fire danger rating system. There also appears to be a need for further and more intensified research into tree improvement including provenance testing.
5.4 Africa South of the Equator
Although not expressed in the regional review, there is a great deal of activity in the region in the identification of old and the development of new agroforestry systems which could be applied more or less generally within the region itself and spread to others. This also applies to wildlife management because of the importance of the wildlife resource in this region.
Possibly the major gaps are in the development of extension systems with which to effectively transfer new technology and influence local populations to accept ideas in wildlife management and agroforestry and participate in useful and gainful new activities.
5.5 North Africa
Countries of the North African region require a synthesis of present knowledge on sand-dune dynamics and techniques of sand-dune fixation, pasture improvement and refinement of afforestation techniques to better suit their conditions.
Appropriate information is sought on the selection and processing of raw material for non-wood products as well as the improvement of wood processing and the development of artisanal industry to add value to locally-produced raw materials.
Further work is required on the delimitation of forest lands, phytoecological inventory of alpha grass (Stipa tenacissima) areas and anthropological/sociological studies to assist in technology transfer and land husbandry. There is also an urgent need for a regional documentation centre for the collection and dissemination of appropriate technical information on desertification.
5.6 Near East
In this region there is a need to collect, consolidate and then disseminate information on the physical environment of the arid and semi-arid lands of the region.
Up-to-date data on the region's physical resources are also required together with information on the relationship between human populations and the surrounding natural ecosystems.
Standards of training and teaching institutions in the region also need to be determined (and possibly standardized).
5.7 Asia and Pacific
The countries of the Asia and Pacific region still appear to need further information and experience on tree planting practices and establishment procedures (methods of sowing and planting) as well as management of large-scale tree-planting activities. Another common need is for information on the productivity of natural and exotic tree and shrub species. Other important needs are for land-use and rangeland inventories and assessments including those of arid-zone vegetation and research into weather patterns in order to improve prediction of future events. Where sand-dune fixation is a particular problem, information is required on the root development of the various species already used or of potential value for this purpose. The problems of salinity and waterlogging and optimum irrigation regimes have yet to be successfully tackled in areas where irrigation is practiced on a large-scale. Further, there is a need for information on salt-tolerant species as well as a techniques for reclaiming saline lands.
A wide variety of other needs have also been expressed including promotion of awareness, extension methods, technical training, selection of species, tree improvement, rangeland rehabilitation and analyses of the productivity of traditional and proposed agroforestry systems.
5.8 With the exception of a few countries the main gap in activity appears to be the lack of application of anti-desertification measures on a large-scale and even in this sphere some of those countries involved feel the need for organizational and procedural improvements. The demand for various kinds of information is extremely broad and indicates the urgent need for some form of centralized collection, analysis and dissemination of information to assist researchers and practioners both on a regional and global level.
Land use and vegetation surveys as well as silvics of arid-zone species and related growth/productivity studies are essential components in the design, planning and implementation of natural vegetation management and agroforestry systems. Assistance in and coordination of land-use studies of arid lands is important for the formulation of strategies to counter the spread of desertification.
Climatic studies and methods to predict drought or wet cycles would be of immeasurable assistance in forward planning, funding and implementing measures to relieve hardship and reduce damage to arid-zone ecosystems (reduction of livestock stocking ahead of dry cycles, for instance).
Information on useful tested arid-zone species and provenances is another general need as well as the genetic improvement of indigenous species to improve their resistance to disease and drought and to increase their productivity. A species such as Prosopis cineraria is a case in point.
Finally, in the case of developing countries the need has been expressed for appropriate training in skills required for anti-desertification work as well as the need, at least in the interim development period, to strengthen the institutions involved in the above work and the extension services that are required to carry the message of systems and techniques to be applied.
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