In view of the increasing importance attached to tropical medicinal plants by multinational corporations and some research organisations in industrialised countries, many species face the danger of extinction or disappearance from unscrupulous overharvesting. This threat is very real as evidenced by reported losses of some species in recent times. Most of the depletions are not natural but are a consequence of the heightened interest in screening medicinal plants, largely identified by indigenous communities. Nearly all these plants formed an essential part of health care systems of forest cultures. As ethnobotanical studies provide crucial information about pharmaceutical leads from certain tropical plants, the search and screening programmes have recently concentrated more attention on species with firmly established indigenous medical histories. Expeditionary forces sent to tropical regions to collect samples for screening engage, in nearly all cases, tribal members to harvest the medicinal plants. Tribal members usually have a vast knowledge of forest terrains. With a few dollars in their pockets, hired individuals bring back sackfuls of plant material. The impoverished communities are lured by the dollar to treat harvesting as an important source of income. This gives birth to a new breed of indigenous entrepreneurs inclined to employ local teams or gangs to harvest plants. Screening activities take years to generate tangible results and so overhar-vesting is bound to occur. The rates of harvesting accelerate as the yearning for bigger incomes by the local population increases. To a very considerable extent, the expeditionary forces from industrialised countries have no idea about the degree of damage or threat their activities are posing to plant species. Most collection activities generally proceed under the assumption that plant resources are not endangered through collection. This particular assumption holds true when: (1) indigenous demand for medicinal plants is lower than regenerative capacity, and (2) no export demand exists; but when harvests occur for reasons unrelated to indigenous health requirements, the supply of medicinal plants is no longer non-threatening. Common ownership of forest resources by members of tribal communities also means that access to plant materials knows no defined limits.
For some plants, depending on their biological characteristics, rising demand may catalyse processes of domestic cultivation, thereby increasing supplies. This is contrary to the general run of opinion that surges in demand may lead to depletion of medicinal remedies; but the easy availability of wild stocks may not induce cultivation in the short term. As such, governments are faced with the challenge of monitoring harvesting rates and introducing policy measures to control production.
Drawing from the Ghanaian context, Odamtten et al. (1992) argue that high deforestation rates coupled with rising global demand, will considerably reduce the supply of wild species. A high incidence of bush fires is also expected to worsen the supply problems. The supply factor will not only affect exports, but will also generate adverse consequences for the primary health care system on which a large proportion of the indigenous population depends. The lack of information about medicinal exports is made even more serious by the lack of effective marketing methods, poor packaging arrangements and the limited shelf-life of the products (Heywood, 1991:3). These are areas which demand immediate attention.
The danger of overexploitation is illustrated by the reduction in size of specific medicinal plants. In Ghana, the bark of the Khaya senegalensis has been in high demand for both gum and herbal remedies. The plant is being threatened by extinction (Heywood, 1991:4). A medicinal plant in Cameroon, the Pygeum africanus, was becoming an endangered species. This plant is central in alleviating the urinary problems of indigenous communities (Heywood, 1991: 4). The Cameroonian government introduced a system of regulated debarking (over a limited time scale) to save the plant (Heywood, 1991: 4).
The lack of information can itself weaken regulatory controls. The issue of information is given considerable emphasis by Heywood (1992):
A general problem affecting most medicinal plant species which are used locally is that information on supply and demand is often lacking. We need to know which plants are used, how they are harvested, by whom, how they are traded, whether the supply is sufficient to meet the demand, whether the plants are in or susceptible to cultivation, whether they are endangered in the wild and if so what conservation measures are appropriate
China recognises that the abundant diversity of medicinal plants is a heritage that needs considerable policy support. This abundance can easily lead to scarcity if deliberate programmes for sustainable collection, cultivation and utilisation of medicinal plants are not developed. At the level of collection, a number of important characteristics have been noted. These include the manner of harvesting, stage of growth of plant, parts to be collected, place of collection and amounts harvested. The collection system is driven by conservation ethics, which eschew wasteful methods and bans the harvesting of endangered species (Pei-gen, 1991: 307). China has very harsh laws against infringements of conservation.
Conservation of medicinal plants in China has been extended to imports. A number of crude drugs have been introduced in trials on farms and in botanical gardens for eventual large-scale production. The growth of gene banks to preserve medicinal plants has also been influenced by the conservation ethic. For the time being, considerable emphasis is being placed on the cultivation of the most widely consumed species.1
Cases of species loss and erosion of the genetic base is also reported in India. Most collection activities are undertaken by the indigenous population
1 See Pei-gen, X. (1991), p. 308. Pei-gen states that about 100 medicinal species are already under cultivation in some 460 000 hectares. The cultivation process is being aided substantially by modern biotechnological techniques such as tissue culture.
for economic reasons; given their limited training in collection work, wasteful strategies cannot be ruled out. Some plants are already in short supply, and the destruction of forests, partly as a result of conversion and partly from overharvesting, is likely to accelerate the process of species diminution in the years ahead (Alok, 1991: 299).
Furthermore, Lozoya (1992) emphasises the need to introduce legislation to achieve conservation. In Mexico, he observes, medicinal plants are drawn from the wild. No cultivation programmes have been organised. Collection expeditions have been driven purely by economic motives, the result of which has left many useful medicinal species endangered or extinct. The case of Mimosa tenuifiora is particularly relevant. Immediately after receiving media coverage, many Mexicans tracked into the forests to harvest the bark which they sold to pharmaceutical companies. With no conservation policy as a guide, the destruction of Mimosa tenuifiora was almost total. By the time legislation was introduced, ecological damage was extensive. In some areas, the loss was complete. This case illustrates that government intervention is necessary if medicinal plants are to survive in their ecological niches.
Under specific proprietary conditions, conservation of medicinal plants can in part be effected through germplasm exchange. The exchange of germplasm has two important consequences. First, it guarantees the continuation of research. Second, it adds to the stock of ex situ conservation. The first of these is reinforced by stock from the wild as well as from botanic gardens and gene banks. Costs of supply will depend, among other things, on expenses incurred in conservation and cultivation.
A significant exercise in the conservation of medicinal plants in Rwanda can be gauged from the backyard cultivation of a popular herb called Tetradenia riparia. It is common knowledge and the practice among households to use the plant extract to treat a wide array of diseases such as malaria, coughs, diarrhoea, fevers, muscle aches and headaches. The leaves have been used after harvesting as a pesticide on beans, and some of its extracts have been studied for insecticidal properties to protect potatoes. These developments have activated considerable interest in conservation of medicinal plants. As the research programme is being extended to cover many more plants, the issue of conservation may well become an important national question in the years ahead. It is vital for Rwanda to put together indigenous knowledge within her borders, and treat it as a vital national asset. Otherwise resources such as these will end up in the same way as endod.
In some important respects, the conservation of tropical medicinal plants is both a multidimensional and a multicausal problem. Many factors impinge on the success or failure of biodiversity conservation, most of which act simultaneously. Two key aspects have been mentioned by some writers that could influence the enhancement of biodiversity conservation. One concerns the incentive to create an economic value for tropical medicinal plants by investing in drug development programmes with potential financial spin-offs. For instance, it has been noted that pharmaceutical firms have not been part of the programme to save tropical forests largely because financial and institutional incentives are lacking. The second component hinges on the relaxation of the drug approval process by the US Food and Drug Administration (FDA). Presently, FDA requirements insist on new drugs being single molecular entities and pure isolates that have been completely elucidated. The trial drug must also pass the clinical tests of efficacy and safety. Plant-derived concoctions, however, are whole crude extracts containing many molecular compounds. The extracts are therefore dismissed by the FDA unless all constituents in the mixture are examined according to the standard set criteria.
Such programmes will hinge on the supply factor.2 Padoch et al. describe the impact of commercial exploitation on the supply of two medicinal plants in Indonesia, both of which reveal contrasting possibilities in policy interventions. The first, referred to as gaharu in the native dialect, has been used for centuries to treat pregnancy and childbirth problems in Southeast Asia, China and the Middle East (Pardoch et al., 1991:325). Despite its wide distribution, it does not grow abundantly. One of its chief biological characteristics is that it has a low regenerative capacity; a whole tree has to be brought down to obtain the remedy. This problem is compounded by the fact that collectors have to travel far and wide to gather sufficient commercial quantities. The supply of the product is not, therefore, continuous. As such, the traded products are subject to major price fluctuations. This high demand, coupled with conditioning factors such as sparse distribution and low regeneration, has led to depletion of the gaharu species in a number of wild areas. Its great market potential and biological characteristics have neither elicited nor galvanised collectors to cultivate the species. The policy requirement for endangered species of this kind is certainly different from wild stocks that are in abundant supply and of high regenerative potential.
2 A precedent of this kind (which caused major hold-ups) can be drawn from a research programme on HIV vaccine development. A critical shortage of chimpanzees has led to delays in trials on AIDS vaccines. The challenge stock, even though only small quantities are needed per trial, is only economical to prepare if production is carried out in batches. The cost of chimpanzees is rising, and chimpanzees themselves are becoming rare and endangered. The import ban imposed by the USA is adding to the difficulties of challenge stock preparations. The supply issue is thus having a limiting influence on the vaccine development programme. For a fascinating overview of the question, see Cohen (1991).
This is true of the kayu putih, the second species in Indonesia described by Pardoch et al. The authors did not specify the range of ailments kayu putih was capable of treating; they did, however, indicate that it has considerable medicinal significance, can resprout rapidly, and is not subject to a specific ecosystem niche. These idiosyncrasies have made the medicinal plant amenable to cultivation, and it is grown widely. Undoubtedly, policy interventions for this plant differ markedly from those for the first.3
Multitudinous forces have tended to conspire against the conservation of plant biodiversity. Denial of access to tropical genetic resources would smother innovation. Unrestricted access to plants of medicinal value would trigger their destruction and extinction. It is only through regulated access that the ambitions of innovation and conservation can be achieved simultaneously.
In some countries, a respectful policy of re-orientation towards traditional medicine has rejuvenated peoples' appreciation of herbal remedies, which in time, led to a substantial increase in demand. This phenomenon triggered human waves of wildstock over harvesting, the aftermath of which was a bitter legacy of deforestation and the erosion of species diversity.4 Legislation has since been enacted in some countries to stem the activities of unsustainable collection. The legislation is said to support a programme of exports for which the exporter must obtain proper documentation about source (herbal gardens) of harvest (Lokubandara, 1991: 244).
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