PLANT GUMS, RESINS AND ESSENTIAL OIL RESOURCES IN AFRICA: POTENTIALS FOR DOMESTICATION
D. O. LADIPO |
The forests of Africa are full of plants and particularly tree species that people within and around them utilise for various purposes. Gum, resin and essential oil-producing plants form part of these important species (see Fig. 1). Extraction from wild sources still forms over 95% of the total production but deforestation is causing great concern as genepools are becoming smaller and smaller with the imminent threat of severe genetic degradation or extinction in the case of some of these relatively wild species. Genetic resources collection and conservation has commenced in some cases but the full potentials of these products are still to be realised, despite their immense socio-cultural, economic and scientific importance. Leakey and Izac (1996) in considering the domestication and commercialisation of non-timber forest products enumerated some evolutionary steps which extends from raw extractivism of wild products to biotechnology. In the case of gums, resins and essential oils, markets are available, so the development of commercialisation does not feature here although we may need to help market expansion in future. From the wild to the semi-domesticated stages, farmers themselves have exerted some selection pressure based on acquired experiences in the field including markets, local or international. This is indigenous knowledge (IK). Domestication is not a new phenomenon. It is an old process which started very many centuries ago for many plant species. Simon (1996) suggested that it must be seen as a continuum — from ‘unmolested or unmodified state’ to management of trees in forests (in-situ) to cultivation of semi-domesticated to monocultural plantations of advanced generation breeding lines.
The definition of Harlan (1975) simplifies it as it says, "to domesticate is to naturalise to human conditions and this involves human-induced changes in the genetics of a plant". This paper reviews present efforts and identifies needs and potentials for the change in genetics’ or genetic improvement of gum, resin and essential oil plants in Africa to facilitate full domestication.
The vegetation of most African forests has been subjected to uncontrolled exploitation (IUFRO 1989) for many decades. In the drier Sahelian areas where many gum-and tannin-producing species abound, annual fires and droughts have also increased in severity and frequency in the past 2 decades, causing significant changes in local ecologies and vegetations. This has resulted in serious loss of genetic resources and the creation of a poor socio-economy for the rural poor who depend on these trees or their products for survival.
| Acacia senegal A. albida A.dudgeoni A. farnesiana A. hockii A. polycantha A. nilotica Burkea africana Albizia zygia Combretum nigricans Spondias mombin Sterculia setigera Stercula tragacantha Albizia adianthifolia Anogeisus leiocarpus Balanites aegyptica Cola gigantea Dialium guineensis Diospyrus mespiliformis Entada africana Hidegardia barteri Piptademiastrum africanum Entandofragma spp |
Allanblackia parviflora Amphimas pterocarpoidas Berlinia grandiflora Copaifera salikounda Daniellia thurifera Garcinia kola Zanthoxylum xanthoxyloides Nauclea latifolia Pseudospondias microcarpa Pterocarpus ernaceus Carapa procera Ceiba pentandra Tetraplaura tetraptera |
Ocimum gratissimum Piper guineensis |
Figure 1: Inventory of Native Gum, Resin and Essential Oil Producing Plants
Apart from deforestation which has resulted in loss of vital germplasm, Africa is not politically stable and many wars which are fought on the continent contribute to loss of genetic resources either in the field or in storage.
Can genetic resources be safely stored in Africa now? Yes, but duplicate copies need to be put away (IPGRI) for security. As deforestation and change in conditions continue, we will continue to lose vital germplasm, resources that are the building blocks for future development. IUFRO (1989) recognised this problem and suggested conservation and research on some multipurpose trees with DANIDA's contribution for seed storage. In Nigeria, this project did not take off, but the document is still available and can be useful. IUFRO (1989) suggested immediate effort on genetic improvement and the development of effective silvo-pastoral management systems for these continually degraded and stressed natural woodlands.
FAO (1980) proposed a project in Senegal and Sudan, among other countries, for collection of the genetic resources of some tree species including Acacia nilotica, A. tortilis, Prosopis spp and the well-known gum-producing tree, Acacia senegal. The collection areas in these countries were identified and the taxonomic status of the species and their variants determined. This project commenced a significantly robust and soundly scientific approach to saving the continually degrading genepools of these species. Table 1 shows the state of field plantings of some gum-producing species, particularly A. senegal, in many countries in Africa.
In 1988, FAO developed a project plan for many dryland MPTs (see FAO Project GCP/RAF/234/FRA), for Tanzania and many other African countries.
| Table 1: Some Records of past general or
provenance trials on some gum producing tree species in Africa (Modified after IUFRO, 1989) |
||
| Species | Year planted | Location (Country) |
| Acacia senegal | 1973 — — 1974 1975 1976 — |
Nigeria Mauritania Niger Senegal Senegal Senegal Sudan |
| Parkia biglobosa | 1977 1984 1991 1986 |
Burkina Faso Burkina Faso Burkina Faso, Nigeria Mali |
This plan recommended the following steps:
a) Genetic resources collection (ex-situ and in-situ)
b) Genetic resources conservation
c) Provenance trials, progeny trials and eventual breeding
It also suggested clonal development and selection based on robust clonal trials and then the establishment of clonal seed orchards. The species listed included Acacia senegal, obviously because of its importance for the production of gum arabic. Considering that gum arabic was mainly collected from the wild, FAO (1988) reported that in Tanzania only 40 kg of seed was demanded while for Azadiracta indica, demand was 600 kg per annum. This shows the low level of planting practiced for most of these MPTs. In A. senegal, five provenances were identified (Arusha, Singida, Ilangani, Tabora and Mbinga) in this proposal.
A network of 14 countries (2 regions) was suggested, and it covered Burkina Faso, Cameroon, Chad, Ethiopia, Gambia, Kenya, Mali, Mauritania, Niger, Nigeria, Senegal, Somalia, Sudan and Tanzania. Twelve of these countries were involved in the network suggested by IUFRO (1989) on Acacia senegal (see Table 2).
On IUFRO’s (1989) request, countries suggested the species in which they were interested but this process was probably wrong. It is thus valuable that a preference survey on gum, resin and tannin including essential-oil bearing trees be carried out in each of the countries.
| Table 2: Status of in-country activities in breeding and related research (Modified after IUFRO, 1989) | ||||||
| Country | Biology of tree spp |
Clonal and Progeny |
Seed Ordered dev. |
Veg Prop |
Tissue Culture |
Conserve |
| Burkina Faso | x | x | x | x | — | x |
| Cameroon | — | x | — | x | — | x |
| Chad | — | — | — | x | — | x |
| Ethiopia | — | — | — | — | — | x |
| Gambia | — | — | — | — | — | x |
| Kenya | x | x | x | x | x | x |
| Mali | — | — | — | — | — | x |
| Mauritania | — | — | — | — | — | x |
| Niger | — | x | x | x | — | x |
| Nigeria | x | x | x | x | x | x |
| Senegal | x | x | x | x | x | x |
| Somalia | — | — | — | — | — | — |
| Sudan | — | — | — | — | — | — |
| Tanzania | x | x | x | x | x | |
Many plants produce gums. Various presentations at this meeting have already described gum-producing trees and mentioned the various types which include: Gum karaya (Sterculia gum), S. villosa, Gum arabic (Acacia senegal gum), A. senegal, Gum combretum (Combretum gum), Combretum nigicans; and Gum talha (Acacia gum), A. seyal and A. sieberiana. The situation is the same with resin and essential-oil producing plants (Fig. 1).
Where many plants are involved in the production of useful products, we need to go through various processes in order to get to the priority species and goals of producing improved products (Fig. 2). It is vital that a list of wanted species and traits be generated for each country. This process of species prioritisation is well documented by ICRAF (Jaenike et al., 1996) and can help to identify priority species in each of the countries.
Booth and Wickens (1988) described non-timber uses of selected arid zone trees and shrubs in Africa. They provided a clear account of the uses and the environmental needs of various multipurpose species, including those of Acacia senegal. Their account on A. senegal has provided the synthesis of information critically needed for developing a viable approach to the genetic improvement and domestication of this species.
Besides, it is important that the criteria for consideration be identified and discussed with farmers, users and in this case by foreign industries that use them and know what product consumers need. In the case of gums, the involvement of the FAO/WHO Expert Committees on Food Additives is vital. The support of the US National Academy of Sciences will also be invaluable so that the desired traits are considered for research, and followed strictly. Acacia senegal (the gum arabic producing tree) will be used as an example here. However, for a multipurpose tree such as Acacia senegal, desirable tree criteria may include: fast growth, drought resistance, high gum yield, production of high quality non variable gum, and resistance to pests and diseases.
The process of genetic improvement will continue to follow the pattern described in Fig. 3, where range-wide germplasm collection and conservation will be carried out and inherent variability fully identified and captured. Genetic resources collection will follow the recommendations of FAO (1988), based on prior and adequate eco-geographic survey. Accessions will need to be duplicated at various locations to prevent loss in Africa as a result of constant instability.
STAGE I
(Identification Stage)
Proceed to Stage II
Figure 2: Processes involved in obtaining priority species and determining goals of producing improved products
The next phase (Phase III) will include the process for carrying out actual genetic improvement (see Fig. 4). It will need to first review and evaluate the values in the works already carried out in these countries. For example, in Tanzania, where provenances have already been identified and work on them planned and carried out, breeding and selection can proceed. Selection should be carried out at this stage together with all other support activities such as vegetative propagation which can result in early clonal trials. The development of seed orchards to ensure seed supply for commercial planting and the production of high-quality gums or other products as may be the case should also be fully considered. The final phase (Phase IV) will be the integration of the materials produced from the processes described in Figures 2 to 4 into appropriate production systems. In this case, institutions such as ICRAF and National Research Systems, (NARS), including NGOs can proceed to work.
STAGE II
(Genetic Improvement)
Figure 3: The process of genetic improvement
Phase III
* Further breeding to solve specific problems (pests, diseases, etc.)
Figure 4: A regional Research Approach (West and East/South) for A. senegal
The improved materials produced will have to be integrated into a viable production system. Wiersum (1996) suggested the consideration of tree morphology. He suggested that this will need to be manipulated as it is a major component of the plant’s ability to produce in its immediate environment. Wiersum (1996) was referring to the integration of these trees in agroforestry systems and for this, his assertions are viable.
This phase (Fig. 5) as suggested in the present paper will, however, consider in addition to agroforestry system, the intensive monoculture production systems which have so far been practiced in Africa with Acacia senegal, in its present small trial plantings.
Phase IV
(Production System)
Figure 5: Integration of improved materials into a viable production system
It is common to consider seed orchards mainly as reliable sources of seed for afforestation, such orchards are also established to make genetic management of forests possible. Good "seed production areas" can as well be useful if careful selection of individuals with desirable heritable traits is made from parent trees or stands in the forest.
Through mass selection, genes can accumulate if reselections are confined to stands generated by such selections in the previous generation but this process can be saddled with various problems. Therefore, a strict program for seed orchard development in order to ensure the continued supply of quality seed for development is suggested (Ladipo et. al. 1993).
Recent regional efforts on some Multi-purpose tree species such as Parkia biglobosa (EEC) and Milicea excelsa (ITTO) show that it is possible and productive to take a regional rather than a national approach to research on genetic improvement and domestication. Using Acacia senegal as an example, a 14 country collaboration (Table 2) is recommended. For ease of research management, a West and East/South Africa approach for research collaboration is suggested but full exchange of germplasm between both zones (East/West) is required and exchange of expertise between the groups (sub-regions) will also be encouraged. The present collaborative suggestion is presented in Figure 6. It is important to consider this, because in the past, lack of sufficient research collaboration caused major deficiencies in research approach. Particularly, there has never been sufficient exchange or interaction between researchers or experts within the continent or within regions. This has caused a lot of duplication and waste of funds, which could have been better used to further research.
With the efforts of the FAO, and IPGRI and other international agencies or organisations, these problems can be solved as they will act as "links-men" and the proper potentials inherent in these vital non-wood forest resources adequately realised.
Training is needed in order to allow proper research development. On this issue, the need to identify the key areas of research requiring immediate training or support is thus vital. Although this paper has dealt with Acacia senegal , as an example, the process for domestication suggested above can be applied to other species such as those producing resins or essential oils.
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INDIGENOUS KNOWLEDGE AND ITS APPLICATION IN RESOLVING CONSERVATION AND UTILISATION PROBLEMS
EDMUND
G.C. BARROW, |
Arid and Semi-Arid Lands occupy extensive areas of Africa, up to 80% in the IGAD countries and between 30 and 90% in other African countries. Our knowledge base for such lands is woefully lacking. Emphasis has been placed on technological fixes to what are, more often than not, social issues . Land conversion and excision to seemingly more productive land uses, such as irrigation and dryland agriculture is preferred to improving natural resource management. Change has been externally imposed, thereby ignoring the wealth of local knowledge and management experience which exists across the drylands of Africa. By ignoring that knowledge base, through external interventions, education systems which favor others, are being marginalised from their better lands. This perpetuates a neo-colonial and paternalistic perspective derived from agrarian and industrial-based "modern" society, and is probably the single most important contributing factor to the demise of the ASALs, their perpetual famine dependency.
To understand the ASALs we must understand how people survive and thrive, why they do what they do, and what mechanisms both technical and social they have put in place to make use of the limited resource base they have at their disposal - a resource base limited by the unforgiving climate. This is a wide subject, encompassing an understanding of pastoralism, dryland natural resource management and conservation . For this presentation focus is going to be placed on how and why people inhabiting the drylands of Africa conserve, use and manage trees, with a particular emphasis on the topic of this conference.
Pastoralism is based on risk spreading and resilience - two interdependent factors
vital to sustainable management of natural resources in such harsh environments, yet two
factors which are misunderstood and misrepresented. For successful dryland natural
resource management, risk spreading, mobility and resilience need to include some or all
of the following attributes:
All detailed studies of uses and perceptions of trees by rural people, especially those in the drylands, show that there is an extensive ethnobotanical knowledge, with a keen appreciation of species' properties . Trees are used for a wide variety of purposes, and nowhere more so than in the drylands where woody vegetation survives better, and produces more in the drier times. This detailed and extensive knowledge about individual tree species and their management is reflected in their people’s life styles, and the extent of their dependence on trees. There is ample evidence across the drylands of Africa that many different tree species in different systems have been deliberately managed by the local people.
Some tree species are more important than others since they can survive and produce
well even through the long dry seasons when they are particularly important, including
drought times. Indeed, the woody vegetation may constitute the most valuable resource that
such arid and semi-arid lands areas have and within such areas riverine forest and other
rich patch areas of vegetation may be the most important . This knowledge reflects the
life styles and the extent of their dependence on the woody vegetation including
Dryland natural resource management strategies have evolved so as to make optimal use of a wide range of opportunities which mitigate risk and improve resilience. A range of livestock species, a wide array of food species available at different times of the year and the use of natural products for trade among other factors, contribute to this. Yet many of these production strategies are not recognised, not valued, and there are continued attempts to substitute them.
For dryland natural resource management to be important and develop, it has to have value, economic value at a local and national level. However, this value has to be balanced with risk and resilience. Livestock have an obvious and important value. However, the value of other natural products may be locally, but usually are not nationally, understood. To regain some of its viability, the gross pastoral product has to be better recognised, improved economic options need to be in place for the production and marketing of pastoral products and national governments must facilitate the enabling environment pastoralism so badly needs. Not to do so, will perpetuate the expropriation of the most productive drylands, denigration of pastoralism as a land use, and continued famine and aid dependency in the vast drought-prone lands of Africa.
The role of gums and resins is one component of a number of non-timber forest products, which if integrated and balanced with other opportunities for dryland management, can contribute to the economic well-being and long-term viability of such areas. There are well documented examples of the use of gums and resins in Africa, some of which are being presented in these proceedings . The trick is not to ignore local knowledge, but to understand it so as to be able to assist in adapting and improving it; not to ignore local land-use systems but to strengthen and support their integrity; not to bypass local social structures, but understand and provide synergy for them; and not to substitute or expropriate, but to enable local ownership.
If this workshop is to have impact on dryland natural resource management, it is going
have to
If we cannot start to improve dryland natural resource management, by acknowledging and valuing the wide range of economic options including those from livestock, produce from wild plants and trees, limited cropping, conservation, and tourism; by ensuring that an enabling policy environment is in place; and by building on the potential and opportunities found in the local knowledge base, then the plight of the drylands can only worsen - a plight not of existing land users’ making, but externally, and maybe unwittingly, driven by national governments and donors.
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Barrow, E. G. C. (1996). The Drylands of Africa: Local Participation in Tree Management. Initiatives Publishers, Nairobi, Kenya.
Chambers, R., A. Pacey, et al., Eds. (1989). Farmer First: Farmer Innovation and Agricultural Research. London, Intermediate Technology Publications.
Eckholm, E. and G. Foley (1984). Fuelwood: the energy crisis that won't go away. London, Earthscan.
Ecosystems, L. (1985). Turkana District Resources survey 1982-1984. Nairobi, Report for Republic of Kenya, Ministry of Energy and Regional Development, Turkana Rehabilitation Project: 261.
Ellis, J. E. and D. M. Swift (1988). "Stability of African pastoral ecosystems: alternative paradigms and implications for development." J. Range Management 41(6): 450-459.
Forestry Department Turkana district, (1989). Draft forestry policy and guidelines for Turkana district. Based on the recommendations from district, divisional and location seminars on forestry and woody management for chiefs, leaders, elders, women and extension agents. Lodwar, Forestry Department, Turkana District.
Gerden, C. A. and S. Mtallo (1990). Traditional Forest reserves in Babati District, Tanzania. A study in human ecology. Uppsala, Sweden, Forestry Trees and People and Swedish University of Agricultural Sciences - International Rural Development Centre Working Paper 128: 50.
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Leach, G. and R. Mearns (1988). Beyond the woodfuel Crisis. People, Land and Trees in Africa. London, Earthscan.
Rochleau, D.and F. Weber (1988). Agroforestry in Dryland Africa. Nairobi, ICRAF Science and Practise of Agroforestry.
Seif el Din, A. G. (1987). Gum Hashab and land Tenure in Western Sudan. Proceeding of International Workshop on Tenure Issues in Agroforestry. J. B. Raintree. Nairobi, ICRAF and Land Tenure Centre.
Seif el Din, A. G. (1987). The natural regeneration of Acacia senegal (L) wild. Khartoum, University of Khartoum.
Weber, F. and M. Hoskins (1983). Agroforestry in the Sahel. A concept paper based on the Niamey Agroforestry Seminar, 23 May to 9 June 1983. Virginia, Department of Sociology, Blacksburg, Virginia Polytechnic Institute and State University.
INDIGENOUS KNOWLEDGE AND UTILISATION POTENTIALS OF SELECTED GUM, RESIN AND OIL PLANT SPECIES OF TANZANIA
F.B.S. MAKONDA and
R.C. ISHENGOMA |
This paper discusses indigenous knowledge and utilisation potentials of selected plants of Tanzania, producing gums, resins and oils. The selected gum producing plant species include Acacia senegal, A. seyal, A. spirocarpa and A. tortilis whose 60% of the produce is used in the food industry. The resin plants are Pinus elliottii, P. patula and P. caribaea whereas selected oil plants include Allanblackia stuhlmanii, A. ulugurensis, Adansonia digitata, Eucalyptus spp. and Jatropha curcas. Studies on uses of such products in other African countries have been included in this paper for comparison and reflection of the potential uses of Tanzania's forested land.
Tanzania (mainland) has an area covering 88.6 million hectares; almost 50% of this area is covered by forests and woodlands (MLNRT, 1989). Only 0.3% of the forested area is covered by plantation forests, with the rest being natural forests. The distribution of the vegetation cover is: Woodlands (42,891,000 ha), Mangrove forests (80,000 ha); and Forests other than mangroves (1,400,000 ha) to give a total of 44,371,000 ha.
Many of the Tanzanian indigenous and exotic tree and shrub species found in these forest types are potential producers of gums, resins and oils. These forest resources contribute to the livelihood of mankind by providing Non-Wood Forest Products (NWFPs) of various sorts including gums, resins and oils. The pharmaceutical, fragrance, food, agricultural, epoxy resin and coating uses are constantly searching for such natural products from plants. Developing countries should use their forest resources to raise their GDP. In Peru, for example, NWFPs yield 90% of the use potential (Statz, 1997).
Humankind has always depended on plant products by utilising indigenous knowledge on forest resources use. Lewington (1990) documented that the inhalation and fumigation of the body with smoke from the burning of fragrant plant materials is one of the oldest uses of plants by humans. Another major use of plants is medicinal. Kasparek (1997) added that at least 35,000 plant species are used worldwide for medicinal purposes.
Because of their number, versatility, end use variation, dissimilarities of the producer base and resource richness, NWFPs represent one of the most challenging product groups from a marketing point of view (Lintu, 1995). For example, out of 3,000 essential oils known, approximately 300 have a commercial importance (Lintu, 1995).
Many authors have documented African indigenous knowledge on the utilisation of plant gums, resins and oils. In South Africa, for example, the Zulu use Sclerocarya birrea oil in preservation of meat and massaging the skin as a cosmetic (Taylor et al., 1995). Maliehe (1995) reported that the oil of Ximenia americana is used as a cosmetic as well as for softening leather. According to FAO (1983), the kernel of X. americana yields 40 - 50% oil and the shell yields 5.9% fat. Lewington (1990) and Axtell and Fairman (1992) documented that the yellow oil obtained from Balanites aegyptiaca seeds in Sudan and Chad is used as a type of soap and is also edible.
Concerning plant gums, the uses vary between places. In Cameroon, for example the gum of Canarium schweinfurthii is used medicinally to dress wounds and as a cure of round worm and colic ophthalmia (Songwe, 1994) but in Geita Tanzania the use of this gum is in rituals only, in petty gold mines (Makonda, 1997).
Mwamba (1995) in his report for Zambia's resin-, gum- and glue-yielding plants, indicated that while Acacia polyacantha can yield gum used for dyeing and tanning, Albizia adianthifolia yields sassa gum which is used for cosmetics and book binding while Piliostigma thonningii yields gum which is used for caulking boats.
Some of the traditional uses of these products have been copied by industrial manufacturers. The resins from Commiphora myrrha and C. abyssinica, for instance, are used in some cosmetics and perfumes as well as pharmaceuticals in Sudan (Lewington, 1990). The same author added that gum karaya exuded from Sterculia sp. is an important dental fixative in the west. This product, together with gum arabic, is among the six important Indian gums (Soni, 1995).
Chemical analyses may promote some of the forest products. Mushove (1995) gave an example of the oil extract of Tegetes minuta (Mexican marigold), an obnoxious weed to have anti-nematode qualities and is used in organic agriculture. Zimbabwe is reported by this author to be the largest exporter of T. minuta oil in Africa.
The objectives of this paper are:
Acacia spp
Gum arabic is the most important gum in Tanzania. The product is tapped from acacia trees in unmanaged natural forests mainly in Shinyanga, Dodoma, Singida and Tabora Regions. Practically, gum arabic is obtained from Acacia woodland species but species of importance include Acacia senegal (true gum arabic) and A. seyal. The gum is only collected from a few species and active tapping is still more limited.
Contrarily, in Sudan, where almost 90% of the world market supply of gum arabic comes from (Awouda, 1976) acacias are grown as part of an agrosilvipastoral system and these produce 70% of Sudan's gum arabic (Jamal and Huntsinger, 1993). The figures for Sudan's exported gum arabic were at 56,000 tons in 1966 (Pollath, 1972). The annual production of gum arabic has been reported by Tanzania Bureau of Statistics (1994) to stand at 1,000 tonnes out of which 50% is exported. The export was at a peak in 1990 when 740 tonnes were exported. Constraints to expanding the market in Tanzania include an unstable world market prices of the product and failure to meet quality requirements for export trade. However, Anderson (1993) reported that gum arabic and gum karaya meeting international specifications have commercial demand at competitive prices. Moreover, information about the resource and present collection practices to be able to assess the potential for gum collection is inadequate.
Statz (1997) reported that 55 - 60% of gum arabic is used in the food industry. Traditionally, gum arabic is an important food for pastoralists and hunters.
Resins of potential development include turpentine and rosin which is obtained by tapping pine trees. Tanzania has 80,000 ha of industrial softwood plantations which form sources of resins. The species grown are Pinus elliotti and P. caribaea. The major potential sources of supply are within Sao Hill in Iringa, Buhindi and Rubya in Mwanza, Rondo in Lindi, Matogoro in Ruvuma, Ruvu in Coast region, Rubare in Kagera and Ukaguru in Morogoro.
These sources have not yet been tapped and the potential economic value is not yet recognised. Makupa (1995) reported that all commodities which are partial derivatives of turpentine and rosin consumed by various industries in Tanzania are imported and most of them could be substituted if the existing sources in Tanzania were exploited. The greatest single use of rosin in Tanzania is for sizing in paper production (Makupa, 1995). Other uses of oleo-resin are in the paint and varnish industry as a solvent and thinning agent, in the manufacture of adhesives, printing inks, rubber products, greases and lubricants.
Potential oil plants in Tanzania include Allanblackia stuhlmanii, A. ulugurensis, Adansonia digitata, Eucalyptus globulus, E. maidenii and E. regnans and Jatropha curcas.
Allanblackia spp.
Allanblackia stuhlmanii and A. ulugurensis are found growing naturally in montane forests of the East Usambaras and Uluguru. Nuts of these species yield an edible fat used locally for cooking, lighting and as a liniment.
Mugasha (1980) observed that a good A. stuhlmanii tree can produce up to 300 fruits in one fruiting season. According to Glendon (1946 cited by FAO 1983), sun-dried nuts of A. stuhlmanii contain 51% fat. In Kenya, the nuts are used in the manufacture of the famous cooking fat "Kimbo".
Adansonia digitata
Tanzania has vast areas with baobab (Adansonia digitata) growing in natural habitats in such regions as Dodoma, Iringa, Singida and Shinyanga. The tree is well known throughout the country for its fruits which are traded for making juice that has a similar taste to that of Tamarindus indica fruits. The adansonia fruits and juice are locally known as "ubuyu".
Nkana and Iddi (1991) reported that, in Dodoma the seeds of baobab are used locally as a source of cooking oil. These seeds contain 37% edible oil (FAO, 1988a; 1988b) which could be extracted easily using modern technologies. To date, there are not any efforts made by government authorities concerned to utilise these resources.
Eucalyptus spp.
Tanzania has several plantations of Eucalyptus species. The large ones are found in Arusha, Mbeya and Iringa. Essential oils that can be extracted from eucalyptus include cineole, citronellal, phellandrene and piperitone which find uses in pharmaceutical and perfumery compounds.
The blue gum trees (Eucalyptus globulus and E. maidenii) produce cineole from their leaves that is used in medicine for treating nose and throat disorders. The local uses of eucalyptus oil in Geita district was reported by Makonda (1997) where eucalyptus leaves are smoked to repel mosquitoes and also as a cure for yellow fever. Kiwalabye (1995) documented that in Uganda, Eucalyptus citriodora leaves are used in the treatment of cough.
Extraction of eucalyptus oils from plantations would improve profitability of primary forest activities and provide employment to local people. However, as for resins, the actual production of eucalyptus oils in the country has not yet been developed. The trees are only used for poles, posts and pulp.
Jatropha curcas
Jatropha curcas is widely planted in Tanzania as hedges for home and farm protection. It is also planted in graveyards for demarcation. The seeds of this plant contain 35% non-edible oil (Henning, 1997). In Geita District, Tanzania, the oil is used for lighting and the sap from leaves and twigs is used for cleaning tongues particularly in children (Makonda, 1997).
Henning (1997) documented that in Mali, Jatropha oil is used as fuel in pre-combustion chamber engines and in manufacturing of soap. This technology could also be imported to Tanzania, which does not produce mineral oil. The Jatropha oil would form a substitute for diesel, to save some foreign exchange and also provide raw material for manufacture of soap and boost the local economy of rural women in particular.
The forests of Tanzania are a great reservoir of gum, resin and oil plants which have been neglected. Important information about these products is lacking and so the products are greatly under-valued and under-utilised.
These products are of social and economic importance; they provide employment and income opportunities and are potential foreign exchange earners.
To benefit from these resources the following actions are recommended:
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