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CONSERVATION OF PRUNUS AFRICANA, AN OVER-EXPLOITED AFRICAN MEDICINAL TREE1

by

Ian Dawson, James Were, Ard Lengkeek

International Centre for Research in Agroforestry, P.O. Box 30677, United Nations Avenue, Gigiri, Nairobi, Kenya. Tel.: 254 2 524 000; Fax: 254 2 524 001; E-mail: icraf@cgiar.org


INTRODUCTION
Prunus africana (Hook. f.) Kalkman (Rosaceae) is a geographically widespread tree growing in the highland forest in mainland Africa (Angola, Cameroon, Democratic Republic of Congo, Ethiopia, Kenya, Malawi, Nigeria, Somalia, South Africa, Sudan, Swaziland, Tanzania, Uganda, Zimbabwe) and outlying islands (Bioko, Grand Comore, Madagascar, Sao Tomé) (Kalkman 1965). The only species of Prunus native to Africa, it is a large tree that can grow to more than 40 m in height and a diameter of 1 m. The medicinal property of P. africana bark extract for the treatment of benign prostatic hyperplasia has led to an annual international trade worth approximately US$220 million in the final pharmaceutical product (Cunningham et al. 1997). To supply this demand, approximately 4,000 tonnes of bark is presently collected annually by the felling of trees from natural stands, leading to concerns on the long term sustainability of harvesting and the conservation of the species. The natural resource base is most exploited and under the greatest threat in Cameroon (Cunningham and Mbenkum 1993) and Madagascar (Walter and Rakotonirina 1995). Exploitation is also high, although currently less intensive, in Kenya (Cunningham et al. 1997) and on the island of Bioko (Equatorial Guinea) (Sunderland and Tako 1999). Accurate exploitation figures for other countries are not available, but are considered to be comparatively low (Cunningham et al. 1997). Conservation needs are therefore highest in Cameroon and Madagascar, with less urgent needs in Equatorial Guinea and Kenya.

As a result of over-exploitation, trade in P. africana products is regulated under Appendix II of the Convention on International Trade in Endangered Species of wild fauna and flora (CITES). Prunus africana is listed in the Tree Conservation Database of the World Conservation Monitoring Centre (WCMC, 1999). In addition, the FAO Panel of Experts on Forest Gene Resources lists P. africana as one of 18 top priority species for action in Africa (FAO 1997).

In its work, ICRAF has considered a number of options for conservation based on determinants that impact most decisively on any conservation strategy. Both determinants and options are discussed here.

IMPORTANT DETERMINANTS FOR A CONSERVATION STRATEGY

Biology and ecology
1. Genetic variation

P. africana has a wide but disjunct distribution in highland forest 'islands' across Africa (Kalkman 1965), and genetic variation can be expected to have diverged accordingly. Analysis by Dawson and Powell (1999) using molecular markers (random amplified polymorphic DNA RAPD) indicated this to indeed be the case at the gene level. Analysing 10 populations sampled from Cameroon, Ethiopia, Kenya, Madagascar and Uganda, data revealed most genetic variation among countries (66%, P < 0.001), indicating the importance of regional approaches for conservation. Variation among individuals within populations, and among populations within Cameroon and Madagascar, was also highly significant, indicating the importance of developing genetic management strategies that also take account of genetic variation at a country level. Despite the geographic distance between Uganda and Cameroon, Ugandan material was more similar to west African populations than that from Kenya and Ethiopia (Figure 1). This is consistent with theories by White (1983) relating to historical climate differences and migration corridors during world glacial periods. Data indicated that Malagash populations were most distinct and therefore of particular conservation concern.

Figure 1: Genetic relationships in Prunus africana

2. Reproductive biology
Seed of P. africana is intermediate in nature, which limits ex situ seed storage (Jaenicke et al. 2000; Sunderland and Nkefor 1997). The best conditions for seed storage were obtained when seed from mature (purple) fruit was harvested directly from trees and depulped immediately after collection, followed by storage, without drying, at 5° Celsius. However, even under these conditions, germination was only 35% after 12 months of storage (Jaenicke et al. 2000). Long term seed storage of P. africana as a means of ex situ conservation is therefore not advisable, although short-term storage across planting seasons is possible.

Few studies on the reproductive biology of P. africana have been conducted. According to studies by Munjuga et al. (2000) the species is predominantly outcrossing. Flowering and fruiting in a given population may be spread over a relatively long period of time, with stigma receptivity of individual flowers short (Munjuga et al. 2000). Combined with the frequent low density, patchy and unusual size class distribution of P. africana in forest (Ewusi et al. 1992; Ewusi et al. 1997), these observations raise concerns regarding effective population sizes of exploited natural stands and their long term reproductive viability for in situ conservation.

3. Ecosystem function
The Afromontane forest 'islands' or other highland forests which P. africana inhabits, have been classified as being important conservation targets (Davis et al. 1994). According to Thomas and Cheek (1992), 42 plant species are strictly endemic to Mount Cameroon. Bwindi Impenetrable Forest in Uganda is one of the most diverse forests in East Africa and contains half the world's endangered mountain gorilla (Gorilla gorilla beringei) population (Cunningham 1996; Wild and Mutebi 1996). Kakamega Forest in Kenya is considered to be the eastern edge of the Guinea-Congolian Forest block and as such is considered of particularly high conservation value (Kokwaro 1988).

Although the situation varies greatly with location, these forested areas are often under threat from agricultural clearance because they coincide with regions of high population density (Cunningham 1996; Cunningham et al. 1997; Watts and Akago 1994; Wild and Mutebi 1996). Other activities may further contribute to the degradation of these highly diverse forests. The possible keystone function of P. africana within these forests in maintaining their integrity is therefore a key consideration. However, although the fruit of P. africana is eaten by a number of threatened bird and mammal species (Cunningham and Mbenkum 1993), none of these appear to be critically dependent on P. africana, but appear to be generalist frugivores that may feed off a number of plants. Moreover, the density of mature P. africana trees in forest is generally low (Ewusi et al. 1992; Ewusi et al. 1997; Nzilani 1999), suggesting that the quantity of fruit produced is limited and unlikely to compose a large part of the diet of bird and mammal species.

The most important impact of P. africana harvesting on the ecosystems in which it occurs may be indirect. According to the Bioko Primate Protection Programme (BPPP), in 1997, new access routes opened into the forest of Pico Basile on Bioko to harvest P. africana. These gave bush meat hunters easier access to the habitat of a seriously threatened endemic subspecies of the primate Preuss's guenon (Cercopithecus pruessi insularis), which has contributed to its endangered status (BPPP 1999). In Cameroon, the Fon of Banso considered that commercial harvesting of P. africana bark had aggravated forest clearance by changing local perceptions of forest use, from being a community resource to an asset to be exploited for personal gain (Cunningham and Mbenkum 1993).

Policy and regulation
1. International

Internationally, the main regulation that influences the development of conservation strategies for P. africana is CITES. Listing of P. africana on Appendix II of the Convention indicates that trade in both wild and cultivated material must be licensed at export and import. However, a difficulty in implementation has been the identification of P. africana products in international trade, which has lead to unreported export and, particularly, import of P. africana (Cunningham et al. 1997). An additional difficulty is based on the fact that some countries have not to date nominated National CITES Authorities.

2. National and local
In the countries where exploitation is highest, Cameroon and Madagascar, a number of national regulations address the harvesting of P. africana bark (reviewed by Ndibi and Kay 1997 for Cameroon; Walter and Rakotonirina 1995 for Madagascar). Regulations of the two countries differ widely, however, with the Malagash framework in particular being considered inadequate from a sustainable use perspective. Conservation activities in Madagascar could therefore benefit if harvesting regulations were adapted which were more in line with those applied in Cameroon.

However, also in Cameroon, it seems as if the regulations for sustainable harvesting are not always well understood. For example, harvesting licences specify that bark should only be stripped from one quarter of the standing trees, but the level of tree mortality and rate of bark recovery following present practices remain a concern (Sunderland and Tako 1999; Cunningham and Mbenkum 1993; Ewusi et al. 1992). Inadequate inventory data on the size of populations is an additional constraint to the possibilities to determine sustainable harvesting levels (Ewusi et al. 1997).

Apart from the development of regulations and quotas for harvesting to ensure sustainability, their enforcement is often difficult. In areas where P. africana is currently exploited harvesting regulations are not consistently adhered to, due to lack of awareness and resources, and institutional weaknesses (Cunningham et al. 1997; Ndibi & Kay 1997; Mbenkum and Fisiy 1992). In Cameroon, for example, at least 900 tonnes of bark is reported to have been harvested illegally around Mount Cameroon between 1994 and 1996, when export licences were awarded to 3 Cameroonian entrepreneurs to fulfil a large order for bark export to Italy (Cunningham et al. 1997). In Madagascar, almost all bark is reportedly harvested illegally (Walter and Rakotonirina 1995), and includes harvest in protected areas (Ian Dawson, personal observations).

In Cameroon, where welcome recent moves have been taken to issue a much-reduced quota for bark collection from the Mount Cameroon area, it will be important to ensure that resulting sustainable harvesting will not be counteracted by increased illegal exploitation (James Acworth, Mount Cameroon Project, personal communication).

Thus, even when regulations exist to promote the sustainable management of P. africana from wild populations, such formal regulations alone are unlikely to be effective in ensuring conservation of the resources. As a result of verified problems, there have been recent moves, promoted by European countries, to place P. africana on Appendix I of CITES, which prohibits all commercial trade (Nouhou Ndam, Mount Cameroon Project, personal communication).

Community management issues
Local human communities are an important determinant in the success of conservation efforts, as they are often involved in harvesting P. africana bark and can derive long-term benefits from sustainable utilisation strategies. One of the strongest efforts to encourage community participation in the sustainable management of P. africana has been made in Mount Cameroon, where the company handling and exporting bark signed special agreements with two villages in 1997 for the sustainable management and production of P. africana (Laird and Lisinge 1998). Elements of the agreement included payment of relatively high prices per unit weight of bark to villagers, and the training of collectors in harvesting techniques. Prescribed harvesting involves no cutting of trees, and is monitored by a committee.

Community management of forests can help overcome difficulties in enforcement of regulations (Ndibi and Kay 1997). However, since approaches to forest resource use differ widely among communities, even within a region (Watts and Akogo 1994), the involvement of communities in conservation efforts has to be location-specific rather than prescriptive. This makes the development of management plans a lengthy process and, often, longer than the window available for effective conservation action.

Markets and economics
As the world population ages, the demand for treatments for benign prostatic hyperplasia (BPH) is likely to increase. Coupled with trends toward the use of herbal products, the future world demand for P. africana bark may increase considerably (Simons et al. 1998). In this context, unless alternative sources of bark can be developed through cultivation, or alternative remedies for BPH are found, natural stands of P. africana are in danger of depletion. In fact, a number of other herbal remedies are used to treat BPH, and these may become more popular if the available stocks of P. africana continue to decrease (Cunningham et al. 1997).

The collection of bark provides a relatively small return to harvesters compared to profits of the companies marketing the product (Simons et al. 1998). However, the poverty of collectors and lack of alternative sources of income mean that they will make considerable efforts to harvest trees. In Madagascar, for example, villagers are willing to walk long distances (for several days) into the forest to harvest bark of P. africana (Walter and Rakotonirina 1995). Only extremely remote populations of the species are likely to be not viable economically for harvesting purposes.

OPTIONS FOR CONSERVATION

Forest
In the context of the presently high levels of illegal harvesting without management, in situ conservation of P. africana in countries where the species is widely exploited will be possible only in very limited cases, in which strict monitoring of harvesting can be assured, strong community involvement in sustainable harvesting can be sustained, or trees are too inaccessible to exploit. Although traditional community beliefs connected with forest conservation are being eroded (Cunningham and Mbenkum 1993), in specific cases they may form a basis for in situ conservation efforts. For example, in Embu District of Kenya, over 250 sacred groves of forest have been identified in land otherwise cleared for agriculture. Many of these groves contain P. africana (Meru Traditional Healers Group, personal communication). The utility of these groves for conservation purposes depends on their size and isolation from each other, but remnant P. africana trees on farmland are expected to provide a degree of gene flow between small natural groves, which may allow population viability to be maintained (Ard Lengkeek, personal observations).

In most areas, P. africana does not appear to be a keystone species within the ecosystems in which it occurs. Therefore, in situ management strategies should focus on conservation of representative forest blocks rather than on the management of P. africana. However, where specific interventions can be undertaken to promote the recovery of P. africana populations in harvested areas, these should include opening the canopy around, and clearing the undergrowth beneath, seed bearing trees (Ndam 1998).

Enrichment planting and plantations
To date, successful plantations and enrichment plantings have been primarily limited to Kenya, where P. africana has been planted by the Forest Department for timber production. Although these stands provide a useful resource also for bark harvesting, they are of limited utility for conservation as they are often of unknown origin and as they may have a narrow genetic base. However, their success indicates that planting efforts could be successful also in Cameroon and Madagascar. Proper attention should be given to site choice and tree management practices, in addition to the origin and genetic variation of the reproductive materials used. Well managed plantations could serve as ex situ conservation stands, and as sources of planting material for future reforestation and on-farm cultivation.

In areas in Madagascar where natural stands are particularly threatened and a forest management culture is not well developed (Walter and Rakotonirina 1995; Dawson 1997), establishing ex situ conservation stands should be a priority. In cases where harvesting has removed all mature trees from natural tree populations, vegetative propagation techniques, such as cuttings and grafting, may be used to safeguard genetic resources of Prunus africana (Jaenicke et al. 2000).

Small-scale farmer cultivation
According to Cunningham (1994; 1996), the conservation of Afromontane forest can be improved through providing opportunities for small-scale farmers to cultivate useful forest products outside of protected areas. Trees planted on-farm can be an important genetic resource if attention is paid to the origin and genetic variation of the cultivated material. As natural forests contract as a result of agricultural expansion, the management of farmland also for the conservation of biodiversity becomes increasingly important. Research indicates that, in some areas, the number of trees planted on small-holder farms has increased together with human population density; natural forest has been cleared, however, more trees have been planted on-farm to compensate this loss (Arnold and Dewees, 1995; 1998). Agroforestry may be a particularly appropriate method for conservation in highland areas of Africa where high population density and the pressure on natural forests are especially high. In areas of exploitation, this system of "conservation through cultivation" is likely to be more effective than attempting to sustainably manage P. africana within natural forest.

In Cameroon, where considerable planting of P. africana by small-scale farmers has already taken place (Cunningham et al 1997), measures are currently underway to assess the current genetic base of material planted by farmers, using RAPD analysis (Ian Dawson, unpublished data).

Despite the merits of on-farm tree planting, there are serious constraints for its expansion. First, the intermediate nature of seed (Jaenicke et al. 2000) limits seed availability. Second, although a large tree can yield large quantities of seed, seed yields fluctuate widely between years. Seed shortage is likely to be exacerbated in future years as the size of natural populations of trees diminish. Since the approximate time to the first flowering and fruiting in P. africana is 15-20 years, the establishment of seed stands is an urgent priority, as is the further development and adoption of vegetative propagation practices (Jaenicke et al. 2000). Other difficulties with cultivation include the relatively long time scale until bark harvesting is possible (approximately 15 years after planting), access to markets for bark from cultivated trees, and policy issues concerning tree tenure (Simons et al. 1998).

CONCLUSION
Although Prunus africana is heavily over-exploited in parts of its range, it is not in danger of extinction at the species level. However, certain tree populations are being depleted, and valuable genetic resources may be lost.

While there is an urgent need to conserve P. africana, the distribution, biology and current and future use of the species are insufficiently known. It will not be possible to determine the optimal approaches for conservation, as there will not be the possibility to determine the impacts of alternative conservation strategies. Thus, approaches for conservation will likely be influenced largely by institutional and individual perspectives, rather than being based on scientific facts (Cunningham 1996).

In this context, approaches for the conservation of P. africana must be kept flexible and diverse. Although efforts should focus on a number of approaches, planting by small holder farmers perhaps holds the most potential both for P. africana and other Afromontane trees, as natural forest cover continues to contract.

1Received June 2000. Original language: English. This article was adapted from a chapter of a forthcoming monograph on Prunus africana being published by the University of Bangor under an UK Department for International Development initiative.

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