3.7 Processing and utilization of perennial vegetation in the arid-zone of India

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by
J.K. MAHESHWARI
National Botanical Research Institute, Lucknow - 226 001, India

INTRODUCTION

1. FOREST AND FOREST PRODUCTS IN THE ARID AND SEMI-ARID ZONES OF INDIA

The arid zone of India covers about 12% of the geographical area including 31,900 million km² of hot desert located in parts of Rajasthan (61%), Gujarat (20%), Punjab and Haryana (9%), and Andhra Pradesh and Karnataka (10%). The cold arid tracts are located in the North-West Himalayas, viz. Ladakh, Kashmir, and Lahaul and Spiti (Himachal Pradesh). (See Table 1; Figs. 1 & 2).

In the Indian Desert, 14 major land form units have been identified. The following vegetation types associated with different land forms have been identified and mapped from the Landsat imageries in conjunction with ground survey and photo-interpretation:

i) Euphorbia caducifolia, Acacia senegal community on rocky, gravelly and buried pediments;
ii) Capparis decidua, Zizyphus nummularia, Prosopis cineraria community on flat buried pediments;
iii) Acacia senegal, Calotropis procera, Calligonum polygonoides community on sandy undulating buried pediments;
iv) Acacia senegal, Maytenus emarginatus community on flat buried plateaus and pediments;
v) Capparis decidua, Zizyphus nummularia community on flat alluvial plains;
vi) Prosopis cineraria, Capparis decidua, Zizyphus nummularia community on alluvial plains;
vii) Prosopis cineraria, Acacia nilotica, Salvadora oleoides, Tamarix aphylla community on flat older alluvial plains;
viii) Zizyphus nummularia, Calligonum polygonoides community on sandy undulating older alluvial plains;
ix) Prosopis cineraria, Zizyphus nummularia community on sandy undulating older alluvial plains;
x) Prosopis cineraria. Zizyphus nummularia, Capparis decidua community on sandy older alluvial plains;
xi) Prosopis cineraria, Acacia nilotica ssp. indica, Salvadora oleoides community on younger alluvial plains;
xii) Acacia senegal, Calligonum polygonoides community on dunes;
xiii) Calligonum polygonoides, Zizyphus nummularia, Calotropis procera community on interdune plains;
xiv) Suaeda fruticosa, Salsola baryosma community on saline depressions;
xv) Haloxylon salicornicum, Sporbolus marginatus community on saline depressions, and
xvi) Fimbristylis, Scirpus, Cyperus community on saline depressions (66) *.

The dry deciduous low forest is dominated by Anogeissus pendula forming almost pure stands. The common species are: Acacia leucophloea, Butea monosperma, Bauhinia racemosa, Holoptelea intergrifolia, Moringa concanensis, Wrightia tinctoria, Mitragyna parvifolia, Boswellia serrata, Lannea coromandelica, Sterculia urens, Diospyros melanoxylon and Albizia odoratissima. The thorny thicket represents a degraded stage of the low forest and is composed of species like Aerva javanica, Prosopis cineraria, Capparis decidua, Sericostoma pauciflorum, Acacia jacquemontii, Calotropis procera, Cassia auriculata, Leptadenia pyrotechnica, Lycium barbarum, etc. Some tickets are invaded by an exotic species, Prosopis juliflora. Euphorbia caducifolia, E. nivulia and Dyerophytum indicum are encountered in the rocky habitat. Anogeissus pendula is cut ruthlessly and is so heavily browsed that it almost touches the ground (48). The optimum physiognomic state which the above types reach is a forest, but under the pressure of a high density of human and cattle-goat population, the woodlands often degenerate into thickets and savannahs.

The importance of forests and perennial vegetation to the rural people is mainly three-fold. Forest trees and shrubs provide fuel and other products essential to meet the basic needs of rural households and communities. They provide food and the environmental stability necessary for continued food production. Forests and forest products generate income and employment in the rural community. The major forest products consist of timber, firewood and charcoal. The term Minor Forest Produce (MFP) has long been used to cover a wide range of raw materials other than timber which are derived from shrubs and trees. These include various materials like medicinal and aromatic plants, oilseeds, gums and resins, spices, tanning and dyeing materials, fibres and flosses, canes and bamboos, edible plants, fodder and forage plants, latex-yielding plants, bidi wrapper leaves and many other miscellaneous products. Although individually these products appear of little significance, collectively they are of immense importance to the country. In recent years, the MFP contributed 30-35% of the total forest revenue of the country and formed as much as 70% share of the total export of forest produce. Only one such product, the bidi (Diospyros melanoxylon) leaves creates 20-25 million mandays per year of employment to the rural people. The Minor Forest Produce (MFP) should, therefore, better be called Non-Timber Forest Products (NTFP). The important products obtained from the forest are reviewed in the following sections.

TABLE - 1: AREA UNDER ARID AND SEMI-ARID ZONES IN INDIA

FIG. 1. MAP SHOWING ARID AND SEMI-ARID ZONES OF INDIA

FIG. 2. Map of Lahaul and Spiti district, H.P showing the cold arid zone of Himachal Pradesh, India

1.1 Timber, wood and bamboo resources

The small timber used for making furniture, door and window panels, house construction, agricultural implements, poles for fencing and roofing is mainly derived from Anogeissus pendula, A. latifolia, Zizyphus mauritiana Tamarix aphylla Salvadora persica S. oleoides, Butea monosperma, Boswellia serrate, Gmelina arborea, Prosopis cineraria, Acacia nilotica ssp. indica, A. catechu, A. leucophloea, Balanites aegyptiaca, Tecomella undulate, Cordia dichotoma, C. gharaf, etc.

The wood of Boswellia serrate, Cordia dichotoma, Mangifera indica, Lannea coromandelica and Holoptelea integrifolia is suitable for boxes and packing cases. The species, Boswellia serrate, Tecomella undulate, Wrightia tinctoria and Lannea coromandelica are used for making lacquered toys. The wood of Securinega virosa and Grewia tenax is used for making walking sticks and pencils. The species suitable for matchwood are: Bombax ceiba, Sterculia villosa, Gmelina arborea, Holoptelea integrifolia, Kydia calycina, Garuga pinnate, Hymenodictyon excelsum and Lannea coromandelica. However, the quantity of wood lost owing to lack of seasoning and to biological degradation is appalling.

Bamboos have been called poor man's timber and have been used for making huts, mats, ladders, bridges, fences, tool handles, brushes, pipes, fans, umbrellas, toys, musical instruments, spears, bows and arrows, fishing rods, baskets, flower pots and furniture. Dendrocalamus strictus is the only bamboo which occurs in the forests of Rajasthan, Gujarat and Saurashtra. It has long been recognized as an acceptable raw material for the manufacture of paper.

1.2 Firewood and charcoal

Firewood scarcity is probably most acute today in the countries of the Indian subcontinent. The available information about the firewood resources is somewhat inadequate. In rural India, firewood accounts for 93% of total energy consumption. There is now increasing reliance on charcoal which is produced by the slow burning of wood with a very restricted air supply. However, during conversion of wood into charcoal, heat and smoke are given off in the burning process, and various chemical byproducts are volatilized. Without collecting these chemicals and using normal processing techniques, the efficiency of converting wood to charcoal in only about 25%. This means that about 4 Kcal of wood must be processed to produce 1 Kcal of charcoal. However, charcoal is a product which can be used as a fuel and chemical feedstock (68). Compared to wood, it provides much greater useful heat as well as smokeless burning and produces less pollution. Anogeissus pendula is the principal source of firewood and charcoal; the other species being Prosopis cineraria, Anogeissus latifolia, Salvadora oleoides, Bauhinia racemosa, Acacia nilotica ssp. indica and ssp. cupressiformis, _. leucophloea, A. catechu, A. senegal, Zizyphus_ mauritiana, Gmelina arborea, Commiphora wightii, Capparis decidua, Euphorbia nivulia, Butea monosperma, Calotropis gigantea, Tamarix aphylla and Adhatoda zeylanica. Calligonum polygonoides is also the chief source of fuelwood in the desert region. In Bikaner town, for instance, the fuel of this species accounts for 75% of the total quantity of firewood sold by the villagers (27, 36). The species Kochia indica was accidentally introduced from India to Egypt during the last war and thrives well in desert areas. It is found from Delhi westwards and also in the Deccan Peninsula in the saline soils of Coimbatore, and is locally used as fuel (32).

Fuel is the biggest problem in the cold desert region of Ladakh and Himachal Pradesh. Salix is probably the commonest woody genus in mountainous areas ascending into the alpine zone. The larger woody species are very important in the economy of the villages in the dry inner valleys. Willows and poplars are cultivated in every village for fuel, building purposes and for baskets. Before the winter sets in, caravans of men, women and beasts set out to pick, cut and gather fuel and dung-cakes from the alpine pastures. In Tabo and Poh villages of Spiti, people are axing the fast vanishing junipers. It has been estimated that one-third of the total consumption of firewood per year is met from local shrub and tree vegetation, while two-thirds of the requirements are through dried cattle dung (54).

Most firewood is burned inefficiently in open fires, or in smoky stoves without flues or dampers to control the burning. It has been estimated that only 5-10% of the heat released is actually used.

1.3 Gums and resins

Many commercially important gums, mucilages and resins are extracted from forest trees. The gums are used in food, pharmaceuticals, inks, textiles, confectionery, adhesives and many other industries. The resins are used in paints, varnishes and paper industries. These are produced by plants in the form of tears or nodules spontaneously or by making incisions in the bark of the tree trunk. A viscous material comes out at the point of injury to seal off the wound on the trunk. The viscous, clear solution gradually hardens to form a transparent brittle nodule which can be removed by hand. The gums of commercial importance collected from the forest are: Sterculia urens (gum karaya), Anogeissus latifolia (gum ghatti), Boswellia serrata (salai), Commiphora wightii (guggul), and gums from various species of Acacia, including Indian gum arabic from Acacia nilotica ssp. indica and true gum arabic from A. senegal. There are many other trees producing gum such as Azadirachta indica (margosa gum), Cochlospermum religiosum (gum katira), Butea monosperma (pales or dhak), Albizia lebbeck (kokko), Feronia limonia (kaith), Lannea coromandelica (jhingan gum), Prosopis juliflora (gum mesquite), P. cineraria (jand), Soymida febrifuga (rohun), Ailanthus excelsa (maharukh), Pithecellobium dulce (Madras-thorn) and Moringa oleifera (saijan gum).

Commiphora wightii yields a fragrant gum-oleoresin called Indian myrrh, Indian bdellium or guggul, and is used as an incense, as a fixative in perfumery, in medicine and as a substitute for the foreign myrrh. The gum has been found to reduce cholesterol content of the blood and accordingly demand for it is rising. The species occurs in the arid and semi-arid tracts of Rajasthan, Gujarat, Maharashtra and in parts of Karnataka and Madhya Pradesh. The guggul is collected during the months of November - January by making incisions on the trunks of trees. The gum is ready for collection 7-15 days after the first incision. About 200-500 gms. of dry guggul is generally obtained from a plant in one season. The availability of guggul gum is becoming scarce due to indiscriminate felling and exploitation of the plants, and adoption of faulty tapping techniques (6).

The gum oleo-resin obtained by tapping Boswellia serrate, commonly known as Indian olibanum, Indian frankincense or salai-guggul, is at present mostly used as incense and fumigant. The maximum yield of gum oleo-resin is obtainable from the bark portion and hence deep blazing is unnecessary and may also adversely affect the growth of the tree. The tapping operations are generally carried out from November up to end of May. The gum is collected in a semi-solid state and kept in a bamboo basket for up to a month whereupon the fluid portion known as Ras flows out. After this, oil is separated from the raw gum oleo-resin; the latter is dried thoroughly and sometimes treated with soapstone powder to make it brittle. It is then broken into small-sized pieces by wooden mallet or chopper and graded depending on its colour, impurities, etc. The constituents of gum oleo-resin can be separated either by steam distillation or solvent extraction followed by steam distillation. The resin obtained by these processes can be utilized as a substitute for the imported Canada balsam and micro-oil (oil immersion used in microscopy) (30).

1.4 Oilseeds

There are several oil-yielding plants in the country which are used as articles of diet, or for illumination, candle-making, soap-making, and for industrial and medicinal purposes. The oilseeds of tree origin which were hitherto considered unimportant have assumed great importance now because of the increasing demand for oils and fats for various industries.

The oils obtained from forest tree seeds, although characterized by deep colour, unpleasant odour and taste, and large content of free fatty acids which limit their use in the raw state, can be used for other non-edible purposes like making soaps and lubricants, thus lessening the pressure on edible oil for human consumption. The important oilseeds of tree origin are sal (Shorea robusta), mahua (Madhuca longifolia), neem (Azadirachta indica), karanja (Pongamia pinnata), khakan (Salvadora oleoides), kusum (Schleichera oleosa), etc. (Tables 2 & 3). It is estimated that at present hardly 2-3% of the seeds are processed. The total annual production of oilseeds is about 10 million tonnes, which if properly tapped and processed can substantially increase the supply of non-edible oils (34,35).

The processing of oilseeds is carried out in bullock-driven wooden ghanis (kohlus) and powder-driven ghanis (rotary mills). The ghani is a familiar feature of the rural landscape contributing to village economy. The ghani (kohlu) is devised on a pestle and mortar rotating system driven by a pair of bullocks. In semi-urban areas, where electricity is available, most of the bullock-driven ghanis have been replaced by motorized rotaries for crushing oilseeds. These rotaries take less space than the ghanis. The seeds of Butea monosperma, Celastrus paniculatus, Jatropha curcas, Malloutus philippensis, Mangifera indica, Moringa oleifera, Holoptelea integrifolia, Annona squamosa, Sapindus mukorossi, Balanites aegyptiace, Prosopis cineraria, Boswellia serrate, Wrightia tomentosa, Peganum harmala, Citrullus colocynthis, etc. also yield oil, but many of these are not being exploited on a commercial scale. (19).

TABLE - 2 POTENTIAL AVAILABILITY AND UTILIZATION OF MINOR OILSEEDS
(Quantity in tonnes)

TABLE - 3 ESTIMATE OF NEEM SEED PRODUCTION

* (Source: Directorate of Oilseeds Development, Hyderabad)

1.5 Essential Oils

Many forest plants are a source of essential oils of commercial importance. The manufacture of essential oils, attars and perfumed waters has been carried out in India since time immemorial and from cottage-scale, it gradually became an industry. Several aromatic plants have been developed for commercial production in the country. The palmarosa oil is obtained on distillation of the flowering shoots, leaves and overground parts of Cymbopogon martini) var. "motia" which containes a high percentage of geraniol (75-90%). The other form "sofia" yielding ginger grass oil fetches a low price due to its low percentage of geraniol (40-45%). Vetiver oil is obtained from the roots of Vetiveria zizanioides (khus) found wild in several parts of India. The species can be grown in almost every kind of soil including saline and alkaline soils with a pH range of 8.5 to 10.1 (22). The oil obtained from the aromatic species of Cyperus scaraiosus (nagarmotha) and _ rotundus is known in trade as cyperol oil or oil of cyperiol. The oil is used as a fixative by Indian perfumers for flavouring of tobacco and scenting of soaps (61). Rose oil is obtained from the scented flowers of Rosa damascena (Damask rose). The other products made from rose flowers are rose water, rose attar, gul-roghan (hair oil), gulkand and pankhuri (60). The species Inula racemosa has gained some prominence as an aromatic plant and is now grown on a small scale in the cold arid habitat (3000-3500 m.) of the Northwestern Himalayas.

The essential oils are volatile with steam and hence hydrodistillation, i.e. distillation with the help of water, is employed for extraction. The distillation is generally done at the site of plantation. At the National Botanical Research Institute, Lucknow, a field distillation unit has been developed and is used for the distillation of rose oil (60). The main drawback of the conventional (Deg type) technique which is extensively used for water distillation of flowers and seeds is the overheating of the plant material leading to deterioration in quality of the resultant products. The national Botanical Research Institute, Lucknow has developed an apparatus, especially suited for small-scale manufacture of attar and perfumed water. Its double cooling system allows proper condensation of vapours and as the danger of charring the plant material is minimized, the quality of oil and perfumed water is high (Fig. 3).

1.6 Tannins and Dyes

The fruits, barks and leaves of many forest trees are used for tanning of hides and skins in the cottage and small-scale industries. Among the species that can be utilized in tanning industry, mention should be made of babul (Acacia nilotica ssp. indica) pods and bark, wattle (A. mearnsii) bark, avaram senna (Cassia auriculata) bark, axlewood (Anogeissus latifolia) bark and leaves, Indian laburnum (Cassia fistula) bark, Indian redwood (Soymida febrifuga) bark, arjun (Terminalia arjuna) leaves, bark and fruit, bahera (T. bellirica) fruit and bark, sain (T. alata) bark, ghatbor (Zizyphus xylopyrus) bark and fruit, jawasee (Alhagi pseudalhagi) ak (Calotropis procera) garar (Cleistanthus collinus) fruit, leaves and bark, and pomegranate (Punica granatum) root and fruit rind. The green bark can advantageously be used for tanning or extract manufacture within 48 hours of its stripping but it is mostly impractical. The dark red colour of the infusion is attributed to oxidation caused during drying by enzymes contained in the material. This can be effectively checked by treating the bark with sulphur dioxide or a solution of sodium bisulphate. The tanstuffs should be perfectly dried before storage, otherwise if the fermentation starts the colour and quality is seriously affected (18).

Dyestuff is obtained from the flowers of Butea monosperma and Nyctanthes arbor-tristis (orange-coloured floral tubes); fruits of Mallotus philippensis and Kirganelia reticulate; leaves of Wrightia tinctoria and Lawsonia inermis (henna), and plants of Striga gesneroides.

Katha - The extraction of cutch and katha from the heartwood of Acacia catechu (khair) has been carried out in India by boiling in water from very early times. The chief constituents of the heartwood are: catechin (katha), catechu-tannic-acid (cutch) and kheersl. Katha is widely eaten with betel leaf (Piper betle) in the Indian subcontinent. Cutch is used as a dyeing and preserving agent, particularly for canvas, sails, marine fishing nets and in oil-drilling operations. At present, two methods are being used for manufacturing katha, viz. (i) Bhatti katha, crude katha or desi katha by traditional or country method, and (ii) factory method. Though there are about a dozen factories in the country which manufacture katha, the bulk of the material is produced by the traditional "country method inside the forests (15).

1.7 Fibres, mats, baskets and tattles

The forest vegetation offers great scope for the extraction of fibres and manufacture of cordage and ropes. The fibres are extracted from a number of wild species, namely Bauhinia vahlii (Malu fibre), B. racemosa, Butea monosperma, Calotropis gigantea and procera ssp. hamiltonii, Crotalaria burhia (sannia), Girardinia heterophylla, Aerva javanica and A. pseudotomentos, Bombax ceiba, Helicteres isora, Leptadenia pyrotechnica (khimp), Phoenix sylvestris, Sida rhombifolia, etc. Among the grasses growing in the forest, the root fibre of Elyonurus royleanus is used for making weaver's brushes. Imperata cylindrica, Vetiveria zizanioides and Typha angustata are used for making sirkis, fans and mats. The species Aristida setacea, A. adscensionis and Eremopogon foveolatus along with twigs of Tamarix and Crotalaria are used for making brooms. The twigs of Alhagi pseudalhagi are used for making baskets and tattles.

1.8 Indigenous herbal drugs

A number of medicinal plants grow wild in the region and are used as such or after trivial processing in the Ayurvedic, Unani and Siddha systems of medicine, particularly in the rural areas. In the cold arid tracts of Ladakh, the Amchi system of medicine has been in vogue for the past several centuries. The local doctors or "Amchi" use a variety of herbs in the treatment of common human diseases. The Ladakh region is a cold desert but certain areas seem to be rich in herbal drugs like Ephedra gerardiana, Physochlaina praealta, Hyoscyamus niger, Podophyllum hexandrum and Orchis latifolia (65). After collection, the herbal drugs reach the crude drug market from where they are marketed to various parts of the country to be used for manufacture of proprietary medicines or used by the physicians of indigenous systems of medicine or in home remedies. The collection of herbal drugs has long afforded a gainful occupation for many people in the rural areas. The processing of herbal drugs in traditional phytotherapy includes simple operations such as preparation of powders, pills, lotions, decoctions, arrack or liquid extracts. Ashwagandha (roots of Withania somnifera) is an important cash crop, cultivated in western Madhya Pradesh and Nagaur district of Rajasthan. The yield of dry roots ranges from 3 to 4 quintals/ha. Ferula narthex and F. jaeschkeana occur commonly in Ladakh, kh, and a gum-resin, the asafoetida of commerce (heeng) is obtained by incision and a gum-resin, the asafoetida of commerce (heeng) is obtained by incision from the living rhizomes and roots of F. narthex. The indigenous plants of E. narthex give a fairly good yield of the gum-resin which forms a good substitute for the imported commodity, mostly from Afghanistan.

FIG. 3 FIELD DISTILLATION UNIT FOR ROSE OIL AND ROSE WATER

1.9 Fodder trees and grasses

The practice of collecting leaves and grasses both for cattle fodder and for use as bedding in cattle sheds has been prevalent since time immemorial. A large number of trees, shrubs and bushes are heavily lopped for cattle fodder in the region, e.g. Acacia nilotica ssp. indica, Prosopis cineraria, P. juliflora, Zizyphus nummularia, Pithecellobium dulce, Calligonum polygonboides, etc. The fodder grasses relished by livestock belong to Bothriochloa pertusa, Brachiaria ramosa, Cenchrus ciliaris, Lasiurus ecaudatus, Panicum turgidum, Sehima nervosum, etc.

1.10 Subsidiary foods and wild edible plants

Famine is often a serious challenge to the people inhabiting the Great Indian Desert. There are many plant species that are used in times of scarcity as emergency or famine foods (e.g. Cenchrus biflorus, Acacia Leucophloea, Citrullus colocynthis, Madhuca longifolia, Prosopis cineraria); vegetables (e.g. Prosopis cineraria, Capparis decidua, Euphorbia caducifolia, Caralluma edulis); and fruits (e.g. Zizyphus nummularia, Z. mauritiana, Diospyros melanoxylon Rhus mysorensis, Glossonema varians, Ephedra foliate).

1.11 Tendu leaves

The leaves of tendu (Diospyros melanoxylon) are most widely used as bidi (country cigarettes) wrapper. The collection of bidi leaves and making bidis is a labour-intensive cottage-scale industry. The leaves of the following species are also used locally: D. exsculpta, Bauhinia racemosa, Holarrhena pubescens, Artocarpus heterophyllus, Careya arborea and Cordia dichotoma. The good-quality leaves are produced from coppice shoots and root suckers. Normally, the leaves of new flush in the month of April and May are plucked and made into bundles of 50 leaves each called 'Paula". These are dried in the sun and packed in gunny bags for export.

1.12 Lac

Lac is one of the most important forest products of tribal areas. It is a resinous secretion formed as a protective covering on the bodies of larvae of an insect, Laccifer lacca, living parasitically on the juicy twigs of certain plants and sucking their juice. The important host plants are kusum (Schleichera oleosa), pales (Butea monosperma), ber (Zizyphus mauritiana), ghont (Z. xylopyrus) and pipal (Ficus religiosa). The collection of lac is made in the months of April and May, and it can provide supplementary income (9).

1.13 Honey and beeswax

Honey is a sweet viscid liquid elaborated by various species of honey bee through nectar collected by them from flowers. It is a natural unrefined food consumed as such, and is mostly used in the indigenous systems of medicine, as also as an oral tonic. The species Apis indica is the only one suitable for bee keeping in the country. Some of the important nectar and pollen plants are: Acacia senegal, Azadirachta indica, Gmelina arborea, Melilotus alba, Parkinsonia aculeata, Pongamia pinnata, Prosopis cineraria, P. glandulosa, P. juliflora, Tamarindus indica, Zizyphus mauritiana and Z. nummularia.

Beeswax is a secretion from wax glands located in the abdomen of worker bees. It is used in wax polishes of different types, dressing and waterproofing leather goods and for making candles and moulds. It is also used in dental and electronic industries.

2. NEW TECHNOLOGIES FOR PROCESSING AND UTILIZATION OF PERENNIAL VEGETATION

2.1 Energy forests

Wood is the dominant domestic fuel for rural people in developing countries. Although many people think of wood as a fuel of the past, it is rapidly emerging as an important source of energy for the future. The dependence on fossil fuels could be reduced by harnessing "Wood Energy Systems" systematically and scientifically. Whereas in the past wood fuel has been gathered mostly from natural stands, in the future it must come increasingly from plantations. The technologies are becoming available for harnessing the sun to produce sunfuels as alternative supplements to fossil fuels. New silvicultural and forest management systems have to be developed with a view to maximizing net primary production. The concept of energy plantations involves the use of selected strains of tree species grown on a short rotation system. The system should permit a harvest at least every two years of biomass for conversion into fuels. The harvested biomass may either be burnt as a direct energy source or by further processing converted into liquid or gaseous fuels.

Technological research for more effective use of plant biomass than direct burning deserves special attention. The possibility of the utilization of firewood of Prosopis for wood-fired steam power plants, otherwise called "dendro-thermal power plants" has been explored. It has been observed that small wood-burning power plants can play an important role in rural electrification, and the residues from processing plants can provide low-cost fuel for agro-industrial operations (56). Energy farms are still in the conceptual stage in India and require further research. The major sources of biomass and the technologies available for converting it to a variety of gas, liquid and solid fuels are shown in Fig. 4 (2,43).

2.2 The improvement of wood-burning stoves

The common type of Anghiti or Chulha (wood stove) used in Indian villages has a heat utilization efficienty of 13.5% which is very low. The improvement of wood-burning stoves is, therefore, of particular importance because of the low thermic yield usually obtained from the fuel by traditional methods. It is technically feasible to save one-third or more of fuel and hence to lower fuelwood requirements by this amount, by using stoves that are better designed and better used. The wood stoves commonly used in India have been recently improved from the point of view of energy conservation, combustion improvements and smoke reduction (9). These have been found to reduce the consumption of fuelwood for cooking up to about 70%. The improved crematoria also save as much as 40% of the fuel need. The considerable saving of fuelwood could also be achieved by improved processing techniques like briquetting. Thus, the use of improved forms of wood-burning appliances alone might do more and cost less to arrest deforestation than would huge expensive reforestation programmes. The final answer is probably a combination of reforestation, energy plantations and better wood-fired cooking stoves (9,56).

Fig 4 CONVERSION TECHNIQUES FOR PRODUCING FUELS FROM BIOMASS

2.3 Biodung as fuel and fertilizer from forest weeds

Efforts have been made to produce a replacement material by fermentation of aquatic and terrestrial plants for use as fuel, fertilizer and biogas plant feed. This is the simplest possible technology and production process which is within the reach of the poorest. The plant species used as experimental material belong to Eichhornia crassipes, Pistia stratiotes, Salvinia molesta, Lemna trisulca, Ipomoea pestigridis, Typha elephantine, Leucaena leucocephala, Ipomoea aquatica, Brachiaria mutica, Cyperus rotundus, etc.

The mass-scale utilization of the process has been started in 10 villages of Divi Taluka in Andhra Pradesh for production of biodung cakes. The experiments with dry biodung for biogas production are considered as significant. If biogas can be obtained from the dried fermented mass in sufficient quantities, then it would mean that the dried cakes can be manufactured in large quantities during the post-monsoon period when forest weeds are abundant and transported like coal to places where they are required, particularly to the arid areas having little vegetation (8).

2.4 Gums and resins

Plant gums are carbohydrate polymers of various structures, and are used as suspending and dispersing agents, as body builders and as adhesives for various applications. These resources should be looked upon as renewable sources of energy through production of chemicals and semi-synthetic polymers. The gums obtained from seeds, husks, tubers and roots constitute the largest class. These gums include various carbohydrate polymer types, namely glucans, glucomannans, galactomannans, and complex acidic polysaccharides. The seeds of Crotalaria, Cassia, Indigofera and Sesbania have been found to be rich in gums. Tamarind kernel powder obtained from the seeds of tamarind (Tamarindus indica) by a process of roasting followed by grinding and winnowing is being manufactured in India and is mainly used as sizing material in various industries. Dhaincha gum obtained from the seeds of Sesbania bispinosa has been found to be a potential source of cheap galactomannan gum. In recent years, a gum used in textile sizing has been extracted from Indian squill (Urginea indica) found in the hilly regions of Rajasthan and in the salt range of Punjab. The bulbs are cut into small pieces and after drying pulverized to a creamy white powder. However, the utilization of gum resources has so far been rather limited (64).

2.5 Oils, hydrocarbons and petro-plants

As a part of the current drive for maximum and optimum utilization of all the possible byproducts from forest-based industries, many new materials have already attracted attention. A typical example is non-edible oilseeds from forests. For fuller utilization of non-edible oilseeds from certain trees (Madhuca longifolia, Azadirachta indica, Pongamia pinnata etc.) in the forest, very attractive schemes have been launched by the Khadi and Village Industries Commission. India produces 7.8 million tonnes of mangoes every year. Mango kernel has a fat content of 6-12% on dry weight basis, which can be obtained by solvent extraction and acetone fractionation to segregate the solid fraction. Mango kernel fat has been found to be a good substitute for cocoa butter fat in the confectionery industry. The seeds of the common weed, Cleome viscosa, growing all over the barren lands and forest areas, have an oil content of 26%. The oil is rich in linoleic acid (70%) and can be safely used for edible purposes. At present, coconut oil is being utilized to meet the demand for lauryl alcohol. However, Salvadora oleoides growing in the arid tracts of Rajasthan and Gujarat contains 35% lauric acid and could be tapped as an alternate source (58). The pods of the common hedge plant, Pithecellobium dulce, yield lecithin and saponin, apart from fat (50). The non-edible oilseed resources of forest origin can be profitably utilized, both for fat and protein, and products of pharmaceutical and industrial interest.

Oil and hydrocarbon-producing plants are especially attractive as future sources of energy and chemicals. The arid land vegetation has the potential to provide new and important sources of oil or rubber. Nearly 400 species belonging to six laticiferous families, viz. Euphorbiaceae, Asclepiadaceae, Moraceae, Apocynaceae, Convolvulaceae and Sapotaceae have been surveyed in India and are being investigated as potential biocrude feedstocks. The promising candidate species are: Argyreia nervosa, Baliospermum montanum, Calotropis gigantea, C. procera, Cryptostegia grandiflora, Euphorbia trigona, E. neriifolia, E. nivulia, E. royleana, E. tirucalli, Hemidesmus indicus, Pedilanthus tithymaloides and Pergularia daemia. The present thrust is towards a survey of the nature and yield of oils from hydrocarbon-producing plants, identification of plant species suitable for cultivation on marginal lands, and development of techniques and equipment for processing plant oils and hydrocarbons for fuel (23, 27).

Glycerine is in short supply in the country. The minor oilseeds of tree origin, especially those of neem (Azadirachta indica), karanja (Pongamia pinnate) and mahua (Madhuca longifolia) can be utilized for distillation of fatty acids and glycerine. The technology is based on the hydrolysis of the fat, separation of fatty acids and concentration of mother liquor by evaporation which gives 70-80% crude glycerine. It would be desirable to set up mini-oil mills and fat-splitting plants for production of fatty acids and glycerine, as shown in Figs. 5-7.

2.6 Katha and cutch

The indigenous country method for extraction of katha inside the forests is not at all sound since the total recovery is hardly 50% of what could be achieved under controlled conditions of factories. Moreover, cutch is not recovered at all in the indigenous method, while it is isolated in full in the factory method. However, the main disadvantages of the factory method are:

FIG. 5 MINI OIL MILL: Flow diagram

FIG. 6. MINI FAT SPLITTING PLANT: Flow diagram

FIG. 7 FATTY ACID AND GLYCERINE DISTILLATION PLANT: Flow diagram

(i) the factories are situated at fixed places, which are sometimes far away from the Khari forests and the wood has to be transported over long distances, and

(ii) large capital outlay is required for the establishment of the -factory.

The factory method has been improved at the Forest Research Institute, Dehra Dun, by:

(i) use of copper, alluminium or stainless steel vessels in place of earthen pots,

(ii) use of open evaporating pans of copper for the concentration, and

(iii) filtration of the separated katha by small hand worked filter-press.

These measures involve some initial capital expenditure on the replacement of fragile earthenware equipment, better quality of katha and recovery of cutch (10).

2.7 Tannins

Tannins form an important group of silvichemicals which can be easily tapped from forest resources. Recent studies aimed at the development of potential alternative sources of tannin from Gujarat forests indicate that the leaves of Diospyros melanoxylon, Largerstroemia lanceolata and Woodfordia fruticosa inflorescence and young branches of Tamarix ericoides, and fruits of Terminalia bellirica possess more than 10% tannins and, therefore, are considered to be rich sources (7).

2.8 Vegetables raw material for steroid and drug industries

Diosgenin, a major raw material for commercial steroid production, can be converted into a variety of corticosteroids, cardiovascular drugs and steroidal hormones used for antifertility preparations, especially oral contraceptives. An alternative to diosgenin as raw material is solasodine found in some indigenous or naturalized species of Solanum (e.g. S. indicum, S. incanum, s. viarum, S. nigrum, S. elaeagnifolium and S. surattense). Diosgenin has recently been isolated from the flowers of Lycium barbarum growing in the Indian arid zone (51). The desert date, Balanites aegyptiaca contains steroidal sapogenins in the seed and pericarp, and could also be utilized as a source of diosgenin (24).

Guggals, the gum-resin of certain trees, are advocated for the treatment of rheumatism and obesity in important treatises of ayurveda. A new drug under the brand name Sallaki, prepared from salai-guggul (gum-resin of Boswellia serrate), has been put on the market. Sallaki is highly effective in the treatment of rheumatoid arthritis.

Sannosides are commercially prepared from the foliage and pods of Cassia angustifolia (Tinnevelly senna) cultivated in Tamil Nadu, Karmataka, Andhra Pradesh and Gujarat. India is the largest supplier of leaves and pods to the world market. An allied species, C. acutifolia (Alexandrian senna) is under experimental cultivation in India. The leaves of C. italica growing wild in the arid tracts of Western Rajasthan contains 1.25 to 2.98% total sennosides on dry weight basis (25,59).

2.9 Barks

The barks of certain species of Terminalia (T. arjuna, T. alata, T. bellirica) have been found to be a potential source for oxalic acid and tannins. Large quantities of oxalic acid are consumed by the textile and pharmaceutical industries. The raw material is available in plenty and can be utilized for the manufacture of tan extract and oxalic acid (5).

2.10 Activated carbon - a potential product of forest and rural industries

Activated carbon industry is of recent origin in India. There are plenty of suitable and cheaper raw materials for the manufacture of activated carbon from raw material of tree origin available in forests, viz. wood, nut shells, bar, twigs and leaves. The production of activated carbon mainly consists of two steps: carbonization followed by activation. In modern industry, activated carbon is accepted as an efficient tool in refining, purifying, bleaching and decolourizing a variety of chemicals. It is used on large scale in the manufacture of vegetable oils, pharmaceuticals, liquors, food products, petrochemicals, etc. The industry can, therefore, be very favourably considered as part of the current schemes for increasing the employment potential in rural areas. It may, in fact, serve as an example of optimum blending of labour-intensive traditional practices with modern technology (29).

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