An Africa-wide overview of medicinal plant harvesting, conservation and health care

An Africa-wide overview of medicinal plant harvesting, conservation and health care

A.B. Cunningham

WWF/UNESCO/Kew People and Plants Initiative
P O Box 42
Betty's Bay 7141
South Africa

Abstract

This paper gives an overview of medicinal plant harvesting for the commercial trade in traditional medicines, and its relevance to medicinal plant conservation and the self-sufficiency of traditional medical practitioners. The most vulnerable species are popular, slow reproducing species with specific habitat requirements and a limited distribution. Although in theory sustainable use of bark, roots or whole plants used as herbal medicines is possible, the high level of input of resources in terms of money and manpower required for intensive management of slow-growing species in multiple-species systems is unlikely to be found in most African countries. Cultivation of alternative supply sources of popular, high conservation priority species outside of core conservation areas is therefore essential. Commercial cultivation of high conservation priority species is not a simple solution and at present unlikely to be a profitable exercise for most species due to slow growth rates and low prices paid for traditional medicines. These slow-growing species are a priority for ex-situ conservation and strict protection in core conservation areas. However, the high price paid for some species does make them potential new crop plants for agroforestry systems (e.g. Warburgia salutaris, Garcinia kola, G. afzellii, G. epunctata or agricultural production (e.g. Siphonochilus aethiopicus) and pilot study commercial production is warranted. The following regions are considered to be priority areas for co-operative action between health care professionals, farmers, horticulturists and conservation biologists: West Africa (Guineo-Congolese region), specifically Ghana, Nigeria and Côte d'Ivoire; East Africa (Kenya, Tanzania, Ethiopia) and south-eastern Africa (Swaziland, South Africa). These are all rapidly urbanizing regions with a high level of endemic plant taxa. The most threatened vegetation types are Afro-montane forest, coastal forests of the Zanzibar-Inhambane regional mosaic and those in the Guineo-Congolese Region.

Introduction

This paper is based on a series of surveys undertaken in Africa during 1986-1989, in order to develop a conservation policy on the herbal medicine trade (Cunningham, 1988a, 1990, 1991, 1993). All of these drew on the local knowledge of traditional medical practitioners (TMPs) and herb traders, and concentrated on commercially sold species in setting priorities for medicinal plant conservation and resource management. From these studies, it was clear that medicinal plant species gathered for commercial purposes represent the most popular and often the most effective (physiologically or psychosomatically) herbal remedies. From historical records it is also clear that the majority of species that were popular in the past are still popular today (e.g.Erythrophleum lasianthum, Cassine transvaalensis, Alepidea amatymbica and Warburgia salutaris in southern Africa). Commercially sold species thus represent a "short-list" of medicinal plants used nationally, as many species that are used to a limited extent in rural areas are not in demand in urban areas.

In most cases, non-sustainable use of favoured species results from commercial harvesting to supply an urban demand for traditional medicines after clearing due to agricultural or urban associated development had already taken place. The widespread commercial harvesting and sale of the same genera and species throughout their distribution range is also significant (e.g.Solanum fruits, Erythrophleum bark, Abrus precatorius seeds, Myrothamnus flabellifolius stems and leaves, and Swartzia madagascariensis roots).

Herbal medicine sellers are familiar with the species which are becoming difficult to obtain (because of limited geographical distribution, habitat destruction or over-exploitation). Their insights, coupled with botanical knowledge of the plant species involved, their ecology and distribution, therefore provide an essential source of information for cost-effective surveys (Cunningham, 1991). What is needed is a common methodology applied on the basis of ethnobotanical surveys of markets, as suggested by the IUCN Species Survival Commission Medicinal Plants Specialist Group (MPSG, 1996).

Akerele (1987), Anyinam (1987), Good (1987) and others have pointed out that there is a need, through training and evaluation of effective remedies, to involve TMPs in national health care systems as they are an important and influential group involved in health care. Sustainable use of the major resource base of TMPs - the medicinal plants - is therefore essential.

A hidden economy: dynamics of the commercial trade in medicinal plants

Stimulated by high population growth rates, rapid urbanization, rural unemployment and the value placed on traditional medicines, the national and regional commercial trade in traditional medicines is now greater than at any time in the past. Due to diversity of species used and intertwined religious and socio-economic issues, sustainable use of traditional medicinal plant resources is also the most complex African resource management issue facing conservation agencies, health care professionals and resource users. International export trade also occurs, but is focused on a limited number of species. Constructive resource management and conservation action therefore has to be founded on a clear understanding of the key factors driving medicinal plant use. Where over-exploitation of medicinal plants occurs, it has arisen through three main factors:

Firstly, there has been a decline in the area of distribution of natural vegetation that was, or would have been the source of supply of traditional medicines. An extreme example of this isMonanthotaxis capea, which formerly was harvested for its aromatic leaves for a trade from Côte d'Ivoire to Ghana but is now extinct in the wild after the forest reserve in which it occurred was declassified and cleared for agriculture. In addition, supplies of herbal medicines to TMPs are affected by competing uses such as timber logging (e.g. Pericopsis elata in Côte d'Ivoire,Pterocarpus angolensis in Zambia and Malawi), commercial harvesting for export and extraction of pharmaceuticals, (e.g. Griffonia simplicifolia and Prunus africana), and use for building materials and fuel. A growing demand is thus placed on fewer resources, ultimately threatening those within conservation areas.

Secondly, Africa has the highest rate of urbanization in the world, with urban populations doubling every 14 years as cities grow at 5.1% per annum (Huntley et al., 1989). A large proportion of the urban African population consult traditional practitioners due to the widely held belief that good health, disease, success or misfortune are not chance occurrences, but are due to the action of individuals or ancestral spirits. The urban demand for traditional medicines thus generates a species-specific informal trade network which can extend across international boundaries.

Thirdly, in African countries with large urban populations, medicinal plant use has changed from being a purely specialist activity of traditional medical practitioners to one involving an informal sector group of medicinal plant gatherers. Unlike the rural TMPs who gather medicinal plant material in small quantities, the prime motivation of the commercial gatherers is an economic one. This results in disregard for traditional conservation practices where they exist and an opportunistic scramble for the last bag of bark, bulbs or roots. High rates of unemployment and low levels of formal education (and therefore a low chance of access to the formal job market) have given rise to a flood of popular medicinal plant material to supply the urban demand, keeping prices low and volumes sold high. In the case of medicinal plants harvested and exported for the pharmaceutical industry, prices are also kept low through agreements on prices that do not take resource replacement costs into account.

Urban migration of traditional medical practitioners

A high level of expectations, high unemployment rates, a psychologically stressful environment, and often crowded and unhygienic living conditions are a feature of many urban areas in Africa. Labour migrancy also creates the need to maintain relationships with wives, or find new partners in the urban environment. Under these circumstances, it is therefore not surprising that many of the traditional medicinal plant and animal material sold in urban markets has symbolic or psychosomatic value for luck in finding employment, guarding against jealousy when a person has a job whilst their peer group are unemployed, or love-charms and aphrodisiacs to keep a wife or partner. It is also not surprising that employment options for TMPs increase, as a declining medical : total population ratio is a feature of rapid urbanization. In Lagos, Nigeria, for example, the number of medical doctors increased five-fold since 1955, yet the medical doctor : total population ratio in 1975 was 1:5,000 compared to 1:2,000 in 1955, as provision of western-type medical facilities could not cope with the rapidly growing urban population (Udo, 1987).

Traditional medical practitioners are therefore attracted to urban centres where employment can be rewarding, and studies in Dar es Salaam (Tanzania), Ibadan (Nigeria), Lusaka (Zambia), Kinshasa (Zaire), Kampala (Uganda) and Nairobi (Kenya) have shown that "urban centres are viable and vigorous areas of traditional medicine" (Good & Kimani, 1980). In Zimbabwe this is clearly shown by the higher ratio of TMP : total population in urban areas (1:234) compared to rural areas (1:956) (Gelfand et al., 1985). This is not always the case, however. In the rural area of Kilungu district, Kenya, rural populations of TMPs averaged 1:224 (herbalists 1:665; traditional birth attendants 1:1640 and diviners also 1:665) while in urban Mathare, the overall ratio was 1:883 (Good, 1987). Rapid urbanization and greater demand for traditional medicines result in an increase in harvesting of medicinal plants from rural areas, a depletion of the rural resource base where certain species are vulnerable to over-exploitation, and consequent problems for primary health care. The same applies to harvesting of medicinal plant material for export and processing into modern pharmaceuticals.

Sustainability and effects of harvesting

It is generally accepted that for any resource, a relationship exists between resources stock, population size and sustainable rate of harvest. Low stocks are likely to produce small sustainable yields, particularly if the target species is slow-growing and slow-reproducing. Conversely, large stocks of species with a high biomass production and short time to reproductive maturity could be expected to produce high sustainable yields, particularly if competitive interaction is reduced by "thinning". There is also a clear relationship between the part of the plant harvested, harvesting method used, and the impact of these on the plant.

Traditional medicinal plants

Demand for fast-growing species with a wide distribution, high natural population density and high percentage seed set is easily met, particularly where leaves, seeds, flowers or fruits are used. The common sale and use of medicinal plant leaves as a source of medicine in Côte d'Ivoire (and possibly other parts of West Africa) is therefore highly significant as it differs markedly from the high frequency of roots, bark or bulbs at markets in the Southern African region. Throughout Malawi, Mozambique, Zambia, Zimbabwe, Lesotho, Swaziland and particularly South Africa, herbal material that is dried (roots, bark) or has a long shelf-life (bulbs, seeds, fruits) dominates herbal medicine markets. In comparison, six sellers in Abidjan, Côte d'Ivoire, primarily sold leaf material (20-41 species), followed by roots (1-16 species), bark (0-8 species) and whole plants (0-3 species) a situation that was typical of the 111 traditional medicine sellers. The exception in Côte d'Ivoire are sellers bringing material from Burkina Faso and Mali, who sell more root and bark material. The situation with chewing stick sellers in Côte d'Ivoire and other parts of West Africa is somewhat different however, as stems and roots are the major plant parts used, with consequent higher impact on favoured species.

Despite limited information on population biology of medicinal plants, it is possible to group target plant species according to demand, plant life-form, part used, distribution and abundance (Cunningham, 1988a, 1991). Of little concern to TMPs or conservation biologists are the large category of traditional medicinal plants where there is no threat at all, and demand easily meets supply due to (a) unpopularity of the species; (b) low human population densities and low demand in relation to wild stocks; (c) lack of development of a commercial trade to urban areas, in which case only a selective harvesting is done by TMPs and not by commercial gatherers; and (d) a situation where demand is high, and commercial harvesting takes place, but supplies meet demand as the species concerned are abundant, widely distributed and the impact of harvesting is low (due to the resilience of the plant source, rapid growth and reproductive rates or the use of leaves, seeds or fruits rather than bark, roots, bulbs or the whole plant).

From a conservation viewpoint on an Africa-wide scale, there are two categories of medicinal plants that are of concern. Firstly, where slow growing species with a limited distribution are the focus of commercial gathering with demand exceeding supply. The consequent expansion of gathering to further and further afield (as incentives to collect are covered by rising prices for the target species) results in the species being endangered regionally, with widespread depletion of rural resource bases of TMPs (e.g. Warburgia salutaris in East and southern Africa;Siphonochilus aethiopicus in Swaziland and South Africa). Endemic species with a very localized distribution are a particular problem. Southern African examples of this are Ledebouria hypoxidoides, an endemic of the eastern Cape region, South Africa, where herbalists were observed removing the last bulbs from the type locality near Grahamstown (F. Venter, pers. comm.) and Mystacidium millari, also a South African endemic which is threatened due to harvesting and commercial sale as a traditional medicine in the nearby city of Durban, South Africa (Cunningham, 1988a). Secondly, where a species may be popular, but not endangered due to its widespread distribution, but where habitat change through commercial harvesting is cause for concern. Trichilia emetica and Albizia adianthifolia for example, are not a high species conservation priority in southern Africa, although they are a popular source of traditional medicines. However, ring-barking in "conserved" forests and consequent development of canopy gaps (which change forest structure and can lead to influx of invasive exotic species) is of concern in forest habitat conservation.

Both problems affect protected area management, as core conservation areas will ultimately become the focus of harvesting efforts for favoured species if they are no longer available elsewhere.

Quantities in local or national trade

Information on the quantities of plant material being harvested or sold (whether for the local trade as traditional medicines, or for export and extraction of active ingredients) is sparse. Apart from placing the quantities required from cultivation into perspective, it is also of little relevance unless expressed in terms of impact of the species concerned. In South Africa, harvesting from wild populations of certain species is on a scale that is cause for concern amongst conservation organizations and rural herbalists, and a listing of priority species is available (Cunningham, 1988a). The same concern also applies to some chewing stick sources (e.g. Garcinia afzelii in West Africa. The only quantitative data on volume of plant material sold locally is from South Africa (Cunningham, 1990, 1993; Osborne et al., 1994; Williams, 1996). The scale of this trade is such that it can have an immense impact on wild populations. Stangeria eriopus cycads collected from the wild, for example, which are sold at a rate of over 3,000 per month, are also sold in the city of Durban, South Africa as an intelezi (protective charm), posing a conservation problem which Osborne et al. (1994) have termed "an enigma of the South African situation to which it is difficult to find a solution".

Table 1. African medicinal plant species in international trade showing quantities traded, exporting and importing countries. Percentage of total demand are given where posssible.
  

Family species	Part used	Export country	Year	Quantity Traded in tons/yr	Import country and % of demand imported		Source Of collec- tion*	Refe rence**
AnnonaceaeDennettia tripetala	?	Ghana					w	1
Apocynaceae Hunteria eburnea Rauvolfia vomitoria	bark root	Ghana Zaire Rwanda  Mozambique					w c	1
Strophanthus gratus	fruit	Cameroon	1985-86  1990-91	1.1	Luxembourg  Belgium (38%)		w	8
Strophanthus kombe	fruit				Italy (23%) Holland (13%)  Germany (12%)  France (11%) Spain (2.4%)		w	3
Tabernaemontana elegans	seed	Mozambique	1981	0.6			w	9
Voacanga africana	seed	Cameroon  Côte d'Ivoire	1985-86  1990-91		France		w, c	3
Voacanga thouarsii	seed	Cameroon					w, c	1, 2, 5
Combretaceae Terminalia sericea	bark	Mozambique		24-25	Germany ?		w	9
Euphorbiaceae Ricinus communis	seed	Mozambique	1982	50			n	9
Fabaceae Duparquetia orchidacea		Ghana					w	1
Griffonia simplicifolia	seed	Ghana  Côte d'Ivoire, Cameroon		75-80	Germany		w	1, 2, 5
Physostigma venenosum	fruit	Côte d'Ivoire, Nigeria					w	1, 2
Liliaceae Gloriosa superba	seed	Mozambique	1981	0.1				9
Menispermaceae Jateorhiza palmata	root root	Tanzania Mozambique		0.7-24			w	4 9
Pedaliaceae Harpagophytum procumbens	root	Namibia  Mozambique  Botswana	1981	200  9	Germany (80.4%)  France (12.8%)  Italy (1.5%)  USA (1.0%)  South Africa (1.2%)		w	4, 9
Harpagophytum zeyheri	root	Namibia  Mozambique  Botswana					w	4
Ochnaceae Brackenridgea zanguebarica	bark	Mozambique	1981	0.1			w	9
Rosaceae Prunus africana	bark	Cameroon  Madagascar  Kenya, Zaire  Uganda	1995	3190	France  Italy  Spain		w	3, 6
Rubiaceae Corynanthe pachyceras	?	Ghana					w	1
Pausinystalia johimbe	bark	Cameroon	1985-91	286	Holland (65%)  Germany (18.3%)  Belgium/Luxembourg (10.9%)  France (5.9%)		w	3, 5, 8

*Source of collection: w = wild; c = cultivated; n = naturalised

**References: 1. Abbiw (1990); 2. Ake Assi (pers. comm.); 3. Cunningham & Mbenkum (1993); 4. Nott (1986); 5. J. Seyani (pers. comm.); 6. FAO (1986); 7. Catalano et al. (1985); 8. Seme (1989); 9. Atal (1993).

Quantities in international trade

An average of 25% of prescription drugs sold in the USA during the period 1959 - 1973 contained active principles still derived from higher plants (Farnsworth & Soejarto, 1985) significantly overlapping with plant sources used in traditional medicine. Farnsworth (1988) for example, points out that of the 119 chemicals derived from higher plants which are used for modern pharmaceuticals on a global scale, 74% have similar or related uses in traditional medicine. Like the trade in traditional medicines to cities however, neither the impact of harvesting nor the cost of replacing these resources seems to have been taken into account. For this reason, even when the technology for chemical synthesis is available, it can be cheaper for pharmaceutical companies to extract the active ingredients. In the mid-1970s, for example, the cost of producing reserpine by chemical synthesis was $1.25 per g, compared to $0.75 per g by commercial extraction from Rauvolfia vomitoria roots (Oldfield, 1984). If replacement costs and sustainable use were taken into consideration, this may not be the case.

While data on the quantities of raw material harvested for export are limited, even less data are available on the environmental impact of harvesting. From what little evidence is available, it is clear, however, that large quantities of material are collected from the wild (Table 1) and that harvesting can be very destructive (Cunningham and Mbenkum, 1993). For example, Ake-Assi (pers. comm.) reports that although only fruits are required, commercial gatherers in Côte d'Ivoire chop down Griffonia simplicifolia vines and Voacanga africana and V. thouarsii trees in order to obtain the fruits. Concern has been expressed about a similar situation in Indonesia (Rifai and Kartawinata, 1991).

Sustainability and the impact of commercial harvesting

Due to the number of species involved and the limited amount of information available on biomass, primary production and demography of indigenous medicinal plants, no detailed assessment is possible of sustainable off-take from natural populations. Even if these data were available, their value would be questionable due to the intensive management inputs required for managing sustainable use of vulnerable species in cases where demand exceeds supply. What can be done is to identify the categories of medicinal plant species that are most vulnerable to over-exploitation by combining the insights of herbal medicine sellers with our knowledge of plant biology and distribution (Cunningham, 1990).

The most vulnerable species are the popular, slow-growing, slow-reproducing species with specific habitat requirements and a limited distribution. Although in theory sustainable use of bark, roots or whole plants used as herbal medicines is possible, the high levels of money and manpower required for intensive management of slow-growing species in multiple-species systems are unlikely to be found in most African countries. Cultivation of alternative supply sources of popular, high conservation priority species outside of core conservation areas is therefore essential. However, commercial cultivation of high conservation priority species is not a simple solution and, at present, unlikely to be a profitable exercise for most species due to their slow growth rates and the low prices paid for traditional medicines. These slow-growing species are a priority for ex-situ conservation and strict protection in core conservation areas. However, the high price paid for some species does make them potential new crop plants for agroforestry systems (e.g. Warburgia salutaris), Garcinia kola, G. afzelii, G. epunctata) or agricultural production (e.g. Siphonochilus aethiopicus), and pilot study commercial production is warranted. Priority regions for co-operative action between health care professionals are considered to be the rapidly urbanizing areas with a high level of endemic taxa, particularly West Africa (Guineo-Congolese region), specifically Ghana, Nigeria and Côte d'Ivoire; East Africa (Kenya, Tanzania, Ethiopia) and south-eastern Africa (Swaziland, South Africa). Most threatened vegetation types are Afro-montane forest, coastal forests of the Zanzibar-Inhambane regional mosaic and those in the Guineo-Congolese region.

Commercial gatherers of medicinal plant material, whether for national or international trade, are poor people whose main aim is earning money, and not resource management. Unsustainably high levels of exploitation are not a new problem, although the problem has escalated in regions with large urban areas and high levels of urbanization since the 1960s. Prior to 1898, local extermination of Mondia whitei had been recorded in the Durban area of South Africa due to collection of its roots for commercial sale. By 1900, Siphonochilus natalensis (now considered synonymous with Siphonochilus aethiopicus) had disappeared from its only known localities in the Inanda and Umhloti valleys due to a trade to Lesotho (Medley-Wood & Franks, 1911). This occurred despite a traditional seasonal restriction on harvesting this species. By 1938, all that could be found of Warburgia salutaris in Natal and Zululand was "poor coppices, every year cut right down to the bottom" (Gerstner, 1938). With these few exceptions, most botanical and forestry records reflect the impact of commercial collection of Ocotea bullata bark due to the importance of this species for timber (see Cunningham, 1993). The situation would appear to be similar in Kenya, where Kokwaro (1991) records that some of the largest Warburgia salutaris and Olea capensis subsp. welwitschii trees have been completely ring-barked and have died as a result. Heavy commercial exploitation of Prunus africanatrees has devastated populations in Cameroon (Cunningham & Mbenkum, 1993) and Madagascar (Walter and Rakotonirina, 1995). In Zimbabwe, due to the high demand and limited distribution of this species, the situation is worse, and all that remains of Warburgia salutaris wild populations are a few coppice shoots. In Côte d'Ivoire, Garcinia afzelii is considered threatened due to harvesting for the chewing stick trade (Ake-Assi, 1988). Destructive harvesting of Griffonia simplicifolia, Voacanga thuoarsii and V.africana fruits (for the international pharmaceutical market) through felling of the plants bearing them is also of concern. In Sapoba Forest Reserve, Nigeria, despite traditional restrictions on bark removal, Hardie (1963) observed how the trunk of a large Okoubaka aubrevillei tree (a very rare species in West Africa) "was much scarred where pieces of bark had been removed". There appears to be nothing published on the current status of this species. Botanical records are scanty, particularly for bulbous or herbaceous species, where little remains to indicate former occurrence after the plant has been removed. It would therefore be useful to carry out damage assessments for exported species such as Okoubaka aubrevillei, Garcinia afzelii and G. kola in West Africa (Ghana, Côte d'Ivoire, Nigeria) and Warburgia salutaris in Kenya, Tanzania and Zimbabwe, and assessments of the impact of Pausinystalia johimbe bark harvesting in Cameroon and Griffonia simplicifolia in Ghana.

Field observation has shown a high level of damage to Prunus africana populations in north and west Cameroon (Cunningham and Mbenkum, 1993). In South Africa, bark damage assessments using a 7-point scale (Cunningham, 1990) were carried out for key "indicator species" (medicinal plants chosen for their relatively slow growth rate). Information was also recorded on popularity as a source of traditional medicines, scarcity. Bark damage assessments confirmed most of the observations of herbalists and herb traders (Cunningham, 1988a, 1990), the exceptions being species that were scarce not because of over-exploitation, but due to limited geographical distribution in the region, such as Acacia xanthoploea andSynaptolepsis kirkii. They also demonstrate the very different situation to customary subsistence use, and this fact needs to be taken into account in legislation covering protected area management where conservation of biotic diversity is a primary objective. Although the degree of bark damage varies, the level of damage at all sites where commercial gathering takes place is high and involves mainly trees in the larger diameter size classes. What is significant is that extensive damage has taken place in State Forest, which is theoretically set aside for maintenance of habitat and species diversity (Cunningham, 1988a, 1990). In the Malowe State Forest, Transkei, South Africa, if coppice stems of less than 2cm diameter are excluded, then the level of damage to Curtisia dentata and Ocotea bullata trees encountered amounted to 51% and 57% of trees with more than half the trunk bark removed. All Warburgia salutaris trees found outside strict conservation areas in Natal were ring-barked, and many of those inside conserved areas had their bark removed as well.

Even fewer data are available on the impact of harvesting bulbs, roots, or whole plants although local depletion of Stangeria eriopsius, Gnidia kraussiana and Alepidea amatymbica is known from Natal, South Africa. There has also been a marked reduction in the number of the Afro-montane forest climber Dumasia villosa, which is sold in large quantities in herbal medicine shops (Cunningham, 1988a). In northern Namibia, Protea gauguedi populations have become locally extinct despite attempts at protection by the conservation department. It is worth noting that this has taken place in response to demands placed by a local trade in an area where urban centres are small. Commercial harvesting of Harpagophytum procumbenstubers in Botswana removed up to 66% of plants (Leloup, 1984). In Namibia, however, this species was not considered threatened as the 200 tons exported per annum only represented 2% of the total stocks (de Bruine et al. (1977) as cited by Nott, 1986).

Increasing scarcity of popular species is accompanied by an increasing prices, which in turn provide greater incentives to harvest remaining stocks. The effects of this are firstly, decreased self-sufficiency of traditional medical practitioners as local sources of favoured species decline, and secondly, higher prices which people have to pay for those species. As demand is one of the root causes of over-exploitation, the most popular and effective species are most vulnerable.

Conservation through cultivation as an alternative

Provision of an alternative to over-exploitation of traditional medicinal plants through

cultivation was suggested over 50 years ago in South Africa for scarce and effective species such as Alepidea amatymbica (Gerstner, 1938) and Warburgia salutaris (Gerstner, 1946). Until six years ago, no large scale cultivation had taken place. There are two main reasons for this, and both are applicable elsewhere in Africa: (i) a lack of institutional support for production and dissemination of key species for cultivation; and (ii) the low prices paid for traditional medicinal plants by herbal medicine traders and urban herbalists.

If cultivation is to succeed in providing an alternative supply source to improve self-sufficiency of TMPs and take harvesting pressure off wild stocks, then plants have to be produced cheaply and in large quantity. Any cultivation for meeting the urban demand will be competing with material harvested from the wild that is supplied onto the market by commercial gatherers, who have incurred no input costs for cultivation. Prices therefore increase with scarcity as the transport costs and search time increase for the long-distance trade. At present, low prices (whether for local or international pharmaceutical trade) ensure that few species can be marketed at a high enough price to make cultivation profitable. Even fewer of these are in the category most threatened by over-exploitation.

In all cases where cultivation has taken place, whether in Europe, Asia or Africa, the crops chosen are those yielding good economic returns or a high level of resource returns (e.g. multiple use species for fruits, shade and medicinal properties). These are either fast growing species, or plants where a sustainable harvest is possible (e.g. resins (Boswellia), leaves (Catha edulis)).

With few exceptions, prices paid to gatherers are very low, bearing no relation to annual sustainable off-take. In many cases, they are collected from open access, rather than limited access or privately owned sites. To make a living, commercial medicinal plant gatherers therefore "mine" rather than manage these resources. If cultivation of tree species is to be a viable proposition or an income-generating activity, the flood of cheap bark/roots "mined" from wild stocks should be reduced through better protection of conserved forests in order to bring prices to a realistic level. Alternatively, wild populations will have to decline further before cultivation becomes a viable option.

Cultivation for profit is therefore restricted to a small number of high-priced and/or fast-growing species such as Warburgia salutaris, Alepidea amatymbica, Cassia abbreviata,Haworthia limifolia and Siphonochilus aethiopicus in southern Africa and Garcinia afzelii and Monanthotaxis capea in West Africa.

Although a few of these species are threatened in the wild (e.g. Garcinia afzelii and Warburgia salutaris), low prices ensure that few slow-growing species are cultivated. With the declining economic state of many African countries, it is unlikely that subsidized production of these species will occur, and collection of seed or cuttings for establishment of field gene banks (for recalcitrant fruiting species) and seed banks must therefore be seen as an urgent priority.

Strong support and commitment are necessary if cultivation is to succeed as a means of meeting the requirements of processing plants for pharmaceuticals (whether for local consumption or export) or urban demand for chewing sticks and traditional medicinal plants. If cultivation does not take place on a large enough scale to meet demand, it merely becomes a convenient bit of "window dressing" masking the continued exploitation of wild populations. The regional demand for Scilla natalensis in Natal, South Africa is 300,000 bulbs/year, which are at least 8-10 year old from the wild. On a 6-year rotation under cultivation at the same planting densities as those used by Gentry et al. (1987) for Urginea maritima, 70 ha would be required (Cunningham, 1988a). Due to their slow growth rates, the rotational area required for tree species would be far greater, the total area being dependent on demand.

The success of cultivation also depends on the attitude of TMPs to cultivated material, and this varies from place to place. In Botswana, TMPs said that cultivated material was unacceptable, as cultivated plants did not have the power of material collected from the wild. Discussions with some 400 TMPs in South Africa over a two-year period showed general acceptance of cultivated material as an alternative. Similarly, TMPs in the Malolotja area, Swaziland accepted cultivation as a viable alternative. In both countries there is a tradition of growing succulent plant species near homesteads to ward off lightning. Similarly, in Ghana, West Africa, plants of spiritual significance such as Datura metel, Pergularia daemia, Leptadenia hastata andScoparia dulcis are tended around villages. Therefore, although little is known about attitudes to cultivation of medicinal plants in West Africa, it is possible that TMPs would be in favour of cultivation of alternative supply sources.

A good model to follow may be the Thailand example where (i) a project for cultivation of medicinal plants of known efficacy has been initiated in about 1,000 villages (ii) traditional household remedies, with improved formulae, are produced as compressed tablets packed in foil and distributed to "drug co-operatives" set up through a Drug and Medical Project Fund in more than 45,000 villages as well as in community hospitals (Desawadi, 1988). Wondergem et al. (1989) have already drawn from the Thailand experience in making recommendations regarding primary health care in Ghana.

References

Abbiw, D.K. 1990. Useful Plants of Ghana. Kew, UK; Royal Botanic Gardens. 337 pp.

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