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Chapter VIII. Non-wood forest products
1. Introduction
2. Foliage and fruits
3. Tannins
4. Gums
5. Resins
6. Oils and extracts
7. Fibres
8. Medicinal plants
Utilization of native woody vegetation is important to the livelihood of the people in arid zones. Foodstuffs, tannins and gum, essential oils, pharmaceutical products are only a few of the numerous non-wood products obtained from woody vegetation. Although called minor forest products, they are of vital importance to the people and often constitute an important part of the total forest revenue.
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 and fruits, tannins, gums and resins, oils and extracts, fibres and medicinal plants. These products are reviewed in the following sections.
The 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 palisades 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.
The utility of foliage in recycling nutrients, providing shade and reducing wind speed should not be forgotten; well-managed stands of appropriate drought-resistant and palatable deep-rooting woody species also provide valuable aerial fodder for long drought periods when surface vegetation disappears.
Arid and semi-arid zone vegetation comprises 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.
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 insoluble 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.
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 materials adding utility and commercial value to a major 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 astringent, 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 inflammations, skin eruptions and bowel conditions and thus form an important principle in the action of many medicinal products.
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 arabic or form mucilages by the absorption 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 can be removed by hand.
Gum arabic is the main commercial gum exudate. This gum is mainly obtained from Acacia senegal and some from the related species A. laeta, A. polyaccantha and A. mellifera.
Other gums are gum Karaya from Sterculia urens, S. villosa (India), and S. setigera (Africa); they provide 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 obtainable from the fruit of the carob (Ceratonia siligua), gum Mesquite (Prosopis latifolia) and Indian Squill from Urginea indica.
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 and in medicines. Other resins for religious end uses include: frankicense and myrrh, from the dry-zone species Boswellia spp. and Commiphora spp.
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 articulata for sandarac. Latin America: Schinus terebinthifolius and Juniperus californica for medicinal resins and oleo-resins. Sahelian Africa: Commiphora africana and Boswellia dalzielii for myrrh, and frankincense. India: Boswellia serrata and Commiphora urghtii for products similar to those produced by African relatives. Near East: Juniperus macropodia and Boswellia sacra, oleoresins for perfumery and frankincense.
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 officinalis), thyme (Thymus vulgaris) and lavender (Lavandula angustifolia) are extracted by steam distillation for perfumery.
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 E. populnea are known to produce oils with commercially high proportions of cineole, geranyl acetate (E. marcarthuri) or citronellal (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 soap making 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, Tabeluia toxofora and Pilocarpus jaborandi. Euphorbia anti-syphilitica (Figure 8.1 and 8.2) is another species producing a white wax, a substitute for beeswax, while the guaynle, Parthenium argentatum produces a latex similar to rubber.
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.
Figure 8.1 Euphorbis antisyphilitica (Candelilla)
Figure 8.2 Extraction of wax from Candelilla
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 (Figures 8.3 and 8.4) 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 dry lands 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 6 per cent of the weight of the green leaves, is principally used for the manufacture of baler twine and also rope, cordage and handicrafts (such as macrame). It is also excellent for paper suitable for thin printing papers, cigarette papers, bank notes and teabags. 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 spp. 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 pulp. 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.
Possibly 80 per cent of the world's rural populations are reliant on medicinal plants to maintain their health and to cure their ailments.
Medicinal plants contain a wide range of chemical substances and are very varied in their effects and uses. For instance, diosegenin for wounds and stomach ailments can be obtained from Agave sisalana; steroidal 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 opthalmology from Duboisia leichardtti; astrogalin, rutin and cardiotonic glycosides from Nerius oleander.
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 the preparation of powders, pills, lotions, decoctions and liquid extracts.
Figure 8.4 Extraction of fibre from Agave Lechuguilla
