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2.4 Processing and utilization
1. ECONOMIC USE OF DRY LAND WOODY VEGETATION
Processing and utilization of native woody vegetation is important to the livelihood of the people in arid zones. Fuelwood, charcoal, foodstuffs, tannins and gum, essential oils, pharmaceutical products are only a few of the numerous primary and secondary wood products obtained from woody vegetation. Although called minor forest products, they constitute more than 30% of the total forest revenue (India). In Sudan, collection of gum arabic contributes to some 30% of farm earnings at times when cash is badly needed.
Of the 350 000 plant species that have been described by botanists, only 3 000 are reported to be sources of useful material for people. Less than 100 of these plants are cultivated on a large-scale and none are xerophytic. However, the search for native xerophytic plants of economic value has greatly intensified in recent years.
According to the type of their utilization, non-wood products from dry land vegetation can be divided into the following groups: foliage fruits, tannins, gums and resin, oils, fibres and medicinal.
2. FOLIAGE
Foliage of woody plants is important to arid zone dwellers: that of palms (Phoenix, Hyphaene, Borassus,) for instance, providing raw material for fibres, enclosures, sand-fixing palissades and household articles; that of trees such as Adansonia, Boscia, Cadaba and Balanites providing vitamin-rich food; foliage of Diospyros melanoxylon, Morus alba and Zizyphus mauritiana, raw material for local industry: cigarette making, sericulture and lac respectively.
Nor should the utility of foliage in recycling nutrients, providing shade and reducing wind speed be forgotten; well managed stands of appropriately drought-resistant and palatable deep-rooting woody species also provide valuable aerial fodder resources for long drought periods when surface vegetation disappears.
3. FRUITS
Arid and semi-arid zone vegetation comprizes a wide range of edible fruit-bearing and food-producing species: Phoenix, Borassus, Hyphaene (fruit, edible pollen and nuts); Grewia, Morus alba, Zizyphus, Tamarindus, Ficus carica, Opuntia, Ceratonia and Olea europea (fruit); Pistachio, Prunus amygdalinus, Pinus, pinea, P. cembroides, P. edulis (nuts). Many of the above play a multiple role in dry zone agroforestry systems providing soil cover, wind protection, fuelwood and fodder as well as food.
The production and consumption of fruit in arid zones provides a dietary supplement as well as commercial opportunity. The growing of trees for fruit production encourages the preservation of more or less permanent stands or scattered individual trees in otherwise bare lands. Such trees are often a feature of Sahelian landscapes and form the basis of traditional agroforestry land-use systems still practiced in parts of that region.
3. TANNIN
Tannin is produced from the fruit, bark, leaves and roots of many arid-zone shrubs and trees. The preparation of tannin involves breaking or crushing the tannin-rich material which is then washed and boiled with water. After separation of insolubles the thick, viscous extract is evaporated leaving crude tannin which can be purified by extraction of the crude portion with an alcohol-ether mixture depositing tannic acid. Tannins can be of widely varying chemical structure but are capable of converting the gelatin of hides and pelts into insoluable non-putrefying material, that is: leather. Tannins are readily soluble in water or alcohol giving strongly astringent solutions also useful in medicines. They are used with feric salts in compounding inks of greenish-black to bluish-black colours.
Tannins are either condensed tannins that cannot be hydrolyzed by acids or enzymes, hydrolyzable tennis (allotannins, cafetannins and elagitannins) and unclassified tannins.
The practice of tanning hides and skins is extremely important in arid and semi-arid regions where pastoralism is the main land use and wildlife thrives, if protected or adequately managed. Tanning permits the processing and protection of the locally-produced raw material adding utility and commercial value to a mayor byproduct of meat production.
A large number of arid and semi-arid zone species yield tannin in commercial quantities. For example, from the bark: Acacia nilotica, A. cyanophylla, Eucalyptus astringens, Parkia biglobosa; from the fruit: Calotropis procera, A. farnesiana; from the wood: A. polyacantha, Schinopsis lorentzii; from roots: Punica granatum, Zizyphus spina-christi.
The styptic and astringent properties of tannic acid are useful in the treatment of inflammation, skin eruptions and bowel conditions.
4. GUMS
Gums are typical products of broadleaved trees and shrubs. They are complex carbohydrate derivatives of a polysaccharide nature and are either soluble in water, as in the case of gum arable, or form mucilages by the absorbtion of large amounts of water (gum tragacanth). Their principal use is in foodstuffs by nature of their ability to impart desired qualities to foods by influencing their viscosity, body and texture: most frequently in confectionery food, flavouring and soft drinks. They also have pharmaceutical applications as demulcents, adhesives in pill manufacture and as emulsifying agents. Industrial uses are for adhesives, lithography, paints and inks.
Gums are produced from woody plants either naturally from exudations from cracks in the bark or damage to the bark by insects or animals. Gum flow is also artificially induced by incisions in the bark. The viscous, brittle nodule which forms can be removed by hand.
Gum Arabic is the main commercial gum exudate. About 85% of the world's supply is produced in the Sudan. This gum is mainly obtained from Acacia senegal and some from the related species A. laeta, A. polyacantha and A. mellifera. Production of 40.000 tonnes per year currently exceeds supply.
Other gums are Gum Karaya from Sterculia urens, S. villosa (India), S. setigera (Africa) which provides the raw material for emulsifiers, adhesives, fixatives and laxatives. Gum Tragacanth from Astragalus spp. of Asia Minor is even more valuable. It is a natural emulsifier in food products such as mayonnaise but is now being replaced, because of its high cost, by synthetic fermentation type products. Gums of commercial interest are also obtained from the fruit of the carob (Ceratonia siliqua), Gum Mesquite (Prosopis latifolia) and Indian Squill from Urginea indica.
5. RESINS
Natural resins are distinguishable from gums because of their insolubility in water but because the exudates from so many plants possess this quality, classification of resins is difficult. Resins comprise balsams: resins of a fluid character often used for healing purposes; oleoresins generally from conifers. These are solutions of resins in essential oils; turpentines also from conifers and some broadleaved species; mastics, such as those from Pistachio spp., used in protecting oil paintings; hard resins soluble in alcohol and benzene such as "dragon's blood" and "gambage"; dammars soluble in aliphatic and aromatic hydrocarbons and sandarac, a base for spirit varnishes derived from Callitris and Tetraclinis. Others of the oil-soluble Resin group include Copals, oriental lacquers and substances such as Cashew shell-nut oil and Lac derived from the lac insect.
Resins are generally used in adhesives, paper sizing, surfacing, fixtures for perfumes, in medicines and for the manufacture of synthetic polymers.
The market for natural resins has fallen over the last two decades because of the development of cheaper petroleum-based substitutes as well as synthesised chemicals (perfumery, cosmetics and pharmaceuticals). However, the demand for natural resins still persists in developing countries particularly for those with religious end uses: frankincense, myrrh, olibanum and bdellium from the dry-zone species Boswellia sp. and Commiphora sp., and those used in perfumery: Opopanax sp..
Resin-bearing plants are fairly common in arid zones and the following list provides an indication of their range. USA: Grindelia camporum, Pinus cembroides, oleo-resins for naval stores; Larrea tridentata, resins and turpentines. North Africa: P. brutia and P. halepensis for oleo-resins, Tetraclinis articulate for sandarac. Latin America: Schinus terebinthifolius and Juniperus californica for medicinal resins and oleo-resins. Sahelian Africa: Commiphora africana and Boswellia dalzielii for myrrh, bdellium and frankincense. India: Boswellia serrate and Commiphora urghtii for products similar to those produced by African relatives. Near East: Juniperus macropodia and Boswellia sacra, oleoresins for perfumery and frankincense.
6. OILS AND EXTRACTS
Plants that produce essential oils are very characteristic of dry areas and some have been used since ancient times in the Mediterranean region where the essences of rosemary (Rosemarinus officianalis), thyme (Thymus vulgaris) and lavender (Lavandula angustifolia) have been extracted by steam distillation for perfumery.
Tunisia, for example, produces 120 tonnes per year of distillates from natural aromatic plants of which the greatest proportion is rosemary.
Eucalyptus oil is steam-distilled from fresh eucalypt foliage obtained from felled trees or cultured coppice shoots. Eucalyptus oils are useful for medicinal purposes (inhalants, embrocations, soaps, gargles, sprays and lozenges), industrial uses (disinfectants, solvents, synthetic thymol and menthol) and perfumery (eudesmil, geranyl acetate, citronella!). The dry-zone species E. astringens, E. leucoxylon, E. melliodora, E. occidentalis and populnea are known to produce oils with commercially high proportions of cineole, geranyl acetate (E. marcarthuri) or citronella! (E. citriodora).
Other oils include those of lauric acid from Salvadora oleoides which provides a substitute for coconut oil; vetiver oil for perfumery from Vetiveria zizanoides; palmarosa oil from Cymbopogon martini var. motia for geraniol; perfumery oils from Rosa demascena and Inula racemosa; zachun oil for soapmaking from Balanites aegyptica fruit; karite butter from the fruit of Butyrospermum parkii; jojoba oil from Simmondsia chinensis, a substitute for whale oil; lubricating oil from Jatropha curcas and medicinal oils and waxes from Quillaja saponaria, Tabebuia toxofora and Pilocarpus jaborandi. Euphorbia anti-syphilitica is another species producing a white wax, a substitute for beeswax while the guayule, Parthenium argentatum produces a latex similar to rubber.
7. FIBRES
Dry land woody species offer considerable scope for the extraction and use of fibres for cordage, ropes and handicrafts. The date palm, Phoenix dactylifera is one such species. It is estimated that about 150 million Phoenix dactylifera can be found in the Near East and North Africa and these also form a potential source of fibre for paper manufacture.
Borassus aethiopium and Hyphaene thebaica provide fibres from pounded leaf petioles from which fibres are manually separated and used for cordage, strings or raw fibres for binding and the manufacture of domestic articles and handicrafts.
In Latin America, Yucca carnerosana, Agave lechuguilla and Agave sisalana are important producers of fibres in dry lands. Agave sisalana, the producer of sisal and a non-wood plant of the Amarillydaceae family, is planted in the drylands of Brazil at a density of about 5.000 plants per hectare, yielding around 30 leaves per plant per year. The dried sisal fibre, about a% of the weight of the green leaves, is principally used for the manufacture of baler twine and also rope, cordage and hand crafts (such as macrame). It is also excellent for paper suitable for thin printing papers, bible papers, cigarette papers, bank notes and tea bags. It can be blended with other pulps for newsprint, wrappings and tissue paper.
In India, fibres are produced from the inner bark of the climber Bauhinia vahlii (ropes for domestic purposes); the bark of the shrubby dryland plants Calotropis gigantea, C. procera ssp. hamiltonii and Leptadenia pyrotechnica also yield fibres useful for weaving string and nets.
Esparto grass or alpha grass, Lygeum spartum and stipa tenacissima provide important resources of fibre in North Africa yielding 0.2 to 0.7 tonnes per hectare for a paper industry absorbing about 250 000 tonnes of pulp per year. They also provide material for handicrafts in the form of baskets, woven mats and screens. Paper made from esparto is smooth with a soft surface possessing excellent printing qualities especially suitable for illustrations and colour with a high dimensional stability.
8. MEDICINAL
Possibly 80% of the world's rural populations are reliant on medicinal plants to maintain their health and to cure their ailments. At the present time a list of over 400 species of medicinal plants has been prepared from 64 flowering plant families found in arid zones.
These plants contain a wide range of chemical substances and are very varied in their effects and uses. An idea of this variety can be obtained from the following list:
For instance, diosgenin for wounds and stomach ailments can be obtained from Agave sisalana; steriodal saponins and sapogenins useful as anthelmintics and purgatives from Balanites aegyptica; glycosides and calotropin with strong cardiotonic action from Calotropis procera; the alkaloid artemitin, a potent stimulant, from Artemisia absinthium; astringent, carminative resins from Commiphora nukul; the cardiotonic, antiseptic and analgesic stachydrine and other compounds from Capparis decidua; ephedrine, a bronchodilator, from Ephedra sinica; hyoscyamine producing atropine for ophthalmology from Duboisia leichardtii; astrogalin, rutin and cardiotonic glycosides from Nerium oleander.
In addition to the above, tentative findings from a study of over 100 compounds from desert plants at the University of Arizona show that two plants, namely Caesalpinia gilliesii and Bursera microphylla, have components that show promise for the treatment of cancer. The collection of herbal drugs has long afforded a gainful occupation for many people in the rural areas and the processing of herbal drugs in traditional phytotherapy includes simple operations such as preparation of powder, pills, lotions, decoctions, liquid extracts.
Furthermore the search for, discovery and analysis of useful plant-derived chemicals also provides important information on "templates" upon which the manufacture of artificial derivatives can be based, such as the development of steroidal hormones from diosgenin. Plants in arid zones appear to be rich in complex chemical constituents and could well provide a useful resource for further work in the above field.
9. UTILIZATION OF WILDLIFE
Wildlife has been, and still has the potential to be, one of the most important resources of arid regions, providing a significant source of protein for pastoralists and marginal cultivators, particularly in times of drought or livestock disease. Wild animals have distinct physiological and ecological advantages over traditional domestic livestock species.
In more favourable years wild animal meat may supplement and add variety to staple diets.
To a much lesser extent in some localities, skins and animal trophies have been processed to meet the demand of tourism through local crafts and rural industries.
9.1 Processing of meat
The meat acquired by subsistence hunters is either fresh or preserved by drying and/or smoking for later consumption. When large animals are killed, the reduction in weight of the meat by drying is an important consideration in relation to transport back to the village by head load. After evisceration, small animals are often dried and smoked whole, whereas larger ones are cut up into strips to facilitate drying.
Smoking is also employed to reduce wastage due to decomposition. This is usually achieved by cutting the meat into long strips and exposing these on racks in the smoke of a slow fire. The construction of a simple smoke house, using locally-made bricks, greatly increases the efficiency of the smoking process and allows some control of the temperature.
An improvement in the keeping of meat is achieved by the addition of salt but unfortunately subsistence hunters can rarely afford to buy salt and if they can, are unable to carry enough into the field. Heavy salting and drying to produce "charqui" as in South America, has been tried with some success in Mozambique, but the product, although almost completely impervious to insect, bacterial or fungal attacks for months, proved less attractive to African consumers than plain dried smoked meat. Furthermore, it requires lengthy soaking in water before consumption.
9.2 Preparation of skins and trophies
Skins are prepared using special cutting patterns which differ from one species to another. For crocodile, for instance, skin is removed by Making a longitudinal cut on the back, while for zebra this cut is made on the belly. When the skin has been removed, meat and fat are scraped from it. The skin is then stretched, salted and dried in the shade. The tanning process is usually carried out by local enterprises and treated skins are used in the manufacture of many leather-based items.
Trophy horns and skulls are prepared and preserved by boiling to remove all meat and fat.
10. GAPS AND ISSUES
10.1 Woody vegetation
Processing and utilization of forest vegetation is perhaps of greater importance than increasing production. Processing remains, however, in many cases very wasteful. In this context, considerable improvement is necessary to avoid wastage of the resources. For instance, current practices for the processing of gums are wasteful. Inadequate protection of logs and wood chips from decay and insect attack add to vegetation degradation. In the case of extraction of oils and resins, operations could be improved to reduce losses and waste. The use of products for home consumption or their further processing for sale could also be improved and further developed. Further investigation of energy-rich latex-producing species, their genetic improvement and improved processing of extracts as well as further search, analysis and classification of arid-zone species producing useful chemical compounds are also needed.
The range of forest products is enormous and there is an urgent need for systematic processing and utilization research and improvement of technology for rural cottage industries.
The main problems of processing and utilization of dry land woody vegetation products stem from:
Many potential project activities could be initiated in this area such as:
i) Improved processing and utilization of natural vegetation, including the design of suitable tools and small items of machinery suitable for the processing of the types of vegetation existing in marginal areas. More specific activities could include improved technology for:
ii) Compile literature: collect publications, including special monographs about useful shrubs in all regions and countries.
iii) Market studies: present demand for various products, structure and pattern of consumption.
10.2 Wildlife utilization
The utilization of wildlife resources can make a useful supplementary contribution to integrated programmes for combating desertification. The resource, however, has been seriously depleted in many areas and if the utilization of wildlife resources is to become a more widely accepted and adopted activity in arid zones, research and development should focus on the following areas: