Prunus africanum / Pygeum africanum
Prunus africana (Hook. f) Kalkman (aka Pygeum africanum Hook.) is a montane forest species occurring naturally from Ethiopia in the north, down to South Africa, as far west as Nigeria and as far east as Madagascar (Cunningham and Mbenkum, 1993). It is an evergreen, mid-to-late successional species that can attain a height of 45 m. It is found only above 1000 m altitude and hence is confined to isolated populations that form a wide but disjunct distribution. Among the 200-plus species in the genus Prunus, it is the only one native to Africa. European interest in the species began as early as the 1700s when medicine men from Natal tribes in South Africa related to early settlers the palliative effect of pygeum bark on bladder pains. Similarly, Bakweri peoples on the slopes of Mount Cameroon revealed to colonists that they had used the bark of Prunus to treat "old man's disease" for centuries (Mbai, 1998). Despite the clearly African derived indigenous knowledge it was a French en trepreneur, Dr. Jacques Debat, who lodged the first patent for pygeum bark extract in 1966 (Cunningham and Mbenkum, 1993). Today it is no longer one of nature's secrets, with thousands of Internet addresses advertising its merits.
When people first started to collect bark of the species they did so in a sustainable way. Small pieces or panels of bark were removed and the standing trees could easily regenerate the removed portion (Eben-Ebai et al., 1992). PlanteCam-MediCam (a company that evolved from Laboratoire Debat) and others have made a real effort in Cameroon to train bark collectors to ensure sustainable bark collection. The recommended procedure is to remove bark from opposite quarters of the trunk from about 35cm above ground level to the height of the first branch. After seven to eight years, the bark regrows to allow the alternate quarters to be removed. This provides a mean bark yield of 55 kg per tree with a range from 38-74 kg (Macleod, 1987). Such practices, however, were destined to be replaced as larger and larger quantities were sought and when recently licensed entrepreneurs entered the picture (Sunderland and Nkefor, 1997). In an unpublished report from Mount Oku, Mbenkum and Fisiy re cord the presence of 8,000 dead but standing trees, while at Mount Kilim it was observed that 80 percent of mature trees die as a result of poor harvesting techniques.
In the past 10 years, the annual harvest of P. africana bark has risen to approximately 3,500 tons, of which the majority comes from Cameroon (2,000 tons) and Madagascar (600 tons) (Dawson, 1997). The rise in the annual quantities harvested has been most marked in Cameroon where according to official figures only 200 tons were harvested in 1980 but by 1991 this had peaked at 3,100 tons (Cunningham and Mbenkum, 1993). Most worrying is that a large proportion of this comes from destructive harvesting of the entire bark of a tree through felling (Mbai, 1998). The remaining fragmented populations of P. africana are at best under threat of genetic erosion and at worst liable to extinction (Walter and Rakotonorina, 1995).
Such is the concern for its survival that trade in the bark of P. africana has been added to Appendix II of the Convention in Trade in Endangered Species (CITES) -- trade in both wild and captive bred/artificially propagated specimens is allowed but subject only to licensing.
Laws are one thing and enforcing them is another. In one month alone (July 1996) on Mount Cameroon, a dedicated but under-resourced Provincial Delegation of the Environment and Forestry seized 100 tons of illegally collected bark (Mbai, 1998). Ndibi and Kay (1997) provide a comprehensive review of the regulatory policies and their effectiveness in Cameroon. According to these authors, anomalies exist which have hastened the exploitation of the species. For instance, export licenses were given to operators who did not have exploitation permits, and who subsequently carded out large-scale illegal harvesting on Mount Cameroon. This encourages destructive harvesting by engendering the attitude in others that "well if I don't cut the tree down and only strip bark it then I won't be able to come back again in seven years because someone else will have cut the tree down." These attitudes are hard to reverse although one successful participatory initiative by the Mount Cameroon Project (MCP), based at Limbe Botanic Garden, involves the custodians of the resource, namely the local communities (Glyn Davies, MCP, Limbe, Cameroon).
CHEMISTRY AND PHARMACOLOGY
What is the magic of pygeum bark that has led to its near extinction? From chemical and pharmacological studies the efficacy of pygeum is believed to be a synergistic effect of a cocktail of a number of known and unknown compounds (Legramandi et al., 1984; Waterman, 1994; Bassi et al., 1987). On the list of knowns are: (1) phytosterols (e.g. beta-sitosterol), which have anti-inflammatory effects by interfering with the accumulation of pro-inflammatory prostaglandins in the prostate; (2) pentacyclic triterpenes (ursolic and oleanic acids), which have an anti-edema or decongesting action; and (3) ferulic esters (n-docosanol and tetracosanol), which reduce prolactin levels and block accumulation of cholesterol in the prostate (significant because prolactin increases uptake of testosterone by the prostate and cholesterol increases binding sites for DHT) (Murray, 1995). Lipophilic extracts from dry, powdered bark are obtained through chloroform extraction and standardized to 12-13 pe rcent total sterols (as beta-sitosterol).
There is no doubt that the market for herbal treatments for urological and prostatic problems is lucrative. In 1994, German men spent US $150 million for this purpose alone with a large proportion of this being P. africana-based products (Gruenwald and Buttle, 1996). In the U.S., where P. africana use is more limited, a survey of Health Food Stores revealed that saw palmetto accounts for 4.4 percent of all sales of herbal products (Brevoort, 1996). The OTC trade in Prunus remedies is currently estimated at US $220 million annually. (Cunningham et al., 1997).
With a rising incidence of prostate problems, an aging population, and growing confidence in natural medicines, some companies believe the market for Prunus remedies could double or triple in the coming decade. Assuming this demand profile is accurate, from where will future stocks of Prunus be supplied? All of the bark currently harvested comes from wild populations although many observers consider production to have peaked in Cameroon and Madagascar. While moderately sized natural stands still exist in Democratic Republic of Congo, Kenya, and Uganda, these could easily be exhausted within 5-10 years. Cultivation appears to be the only long-term solution.
The earliest recorded attempt at cultivation is a 0.4 hectare block established at Ngong in Kenya in 1913 (Forest Department Inventory, Kenya). Interestingly, this trial plantation as well as 64 others established in Kenya during the period 1914 to 1992 (total 628 hectares) were planted for timber production and not bark extraction. Prunus africana produces a high-value, quality hardwood (specific gravity 0.75) exported for veneers and paneling (Brown, 1978). Farmers also value it for axe handles, agricultural implements, and construction because of its durable nature (Simons, 1996). Reliable timber trade figures for Prunus are scarce. In Kenya, Leakey (1995) reports a nine-fold increase in timber production (mostly from wild stands) during the decade leading up to 1993 to reach a volume of 170,000 m3 (cubic meters; timber is measured by volume not weight).
The suitability for Prunus, africana to be grown in plantations in East Africa was not matched in Cameroon experiences. This can largely be attributed to the low altitude at which it was planted, where a wood boring beetle larvae (Cerambycidae) attacked 87 percent of trees (Cunningham, 1995) in contrast to the 9 percent of trees attacked at higher altitudes (2,300 m). The real tree-planting surge in Cameroon, however, is happening on farms. Cunningham (1995) estimates that about 3,250 small-scale farmers in Cameroon are planting seedlings of P. africana. A serious constraint faced in the expansion of on-farm tree planting is seed availability. Here a key difficulty is the recalcitrant nature of seed. Further, although a large tree can produce up to 20 kg of seed (5,000 seeds per kg), this fluctuates widely between years. The seed shortage is likely to be exacerbated in future years as sizes of natural populations of trees diminish. Since the approximate time to the first floweri ng and fruiting is 15-20 years, establishing reliable seed sources is an urgent priority.
Raising awareness about the need for seed provision and other activities as part of a wider domestication effort has been a long but fruitful process for the WWF/UNESCO/Kew People and Plants Initiative. In this regard, most credit should be accorded to Alan Hamilton and Tony Cunningham. For a medicinal species that involves impoverished farmers, deteriorating rainforests, international regulation and big business, it would be unusual if there were not conflicts. Certainly mutual suspicion of private sector companies between conservation, research, NGO, and policy groups is evident. On the brighter side, companies are appreciating the need to be more ethically and environmentally minded. The attendance by industrial representatives (e.g. Jean-Francois Colas, Industrial Director, Groupe Fournier) at a recent workshop in Nairobi (March 1997) demonstrates a positive and changing philosophy. From the industrial point of view, the Prunus market is mainly about economies of scale, pro fitability, pseudo-monopolistic control and the sustainability of the supply of raw material. Price paid to bark collectors is likely a lower priority but one that will need greater attention as more material is sourced from farm sources. The prospect for farmer interest groups to collectively market their produce, perhaps with a "green label," may result in greater returns to rural communities.
What one considers as equitable returns to the various actors involved in the product marketing chain (i.e., those with tree tenure rights, harvesters, transporters, middlemen, processors, exporters, governments where bark originated, and pharmaceutical companies) will depend on one's perspective. Little reliable data are available on margins and mark-ups. The crudest calculation of worth is to divide the annual OTC figure (US $220 million) by the yearly harvest (3,500 tons), which gives a value of US $63 per kg of bark. It is easy to point the accusing finger at the most obvious actors, the pharmaceutical companies, but this tendency has led to their reluctance to get involved in open forums. In this regard, PlanteCam deserve praise for venturing out into the foray of criticism (fair and unfair) against them.
Obviously, bark harvesters cannot expect to get US $63 per kilo. In addition, however low the current price they receive, it is still a strong incentive to continue in this activity. Dawson (1997) reports from Madagascar that villagers residing at forest margins receive US $0.20 per kilo for delivered bark. In Cameroon, in 1997, licensed harvesters were paid 170 CFA (US $0.35) per kilo at the PlanteCam factory gate (Gerard Del Vechio, General Manager, PlanteCam). PlanteCam stresses, however, that the buying price does not represent the sole investment in villagers on Mount Cameroon by the company since they have been involved in training bark harvesters, providing seedlings, and community development projects. In Kenya in 1997, bark was typically bought from an entire tree on site (personal communication; Jonathan Leakey, sole exporter in Kenya to Groupe Fournier). A tree with 100 kg of bark fetches about 2,500 Kenya Shillings (US $40), equal to about US $0.40 per kilo. After ad ding the costs for reconnaissance, transportation, administration, obtaining CITES permits and containerization, Leakey maintains a profit is made on the price (US $2 per kg) he sells to Groupe Fournier, but it is not exorbitant.
One kilo of bark produces approximately 5 g of dried extract. Tadenan and other products with a similar concentration of extract (50 mg per capsule) sell for between US $0.30 and US $0.80 per capsule. One can derive 100 capsules (50 days' worth of treatment) from a kilogram of bark. The most expensive product found during a cursory search of the Internet was from Life Health Inc (Ohio, USA). This might be expected given their more expensive processing to a liquid extract (steeped in distilled water and grain alcohol for two to six weeks, cold-pressed and filtered). In this product, 28 g of bark (presumably containing an equivalent of 140 mg of powdered extract on three capsules) cost US $5.50. It was revealed during another Internet search that one company (Sequential Healing Health Services, North Carolina, USA) no longer sold Prunus extract with the explanation "because of the severely endangered status of the pygeum tree, tablets are no longer carried."
As for the conservation of the species it is clear for Prunus that it will not become extinct. However, total loss, or at best genetic erosion, of specific populations has already occurred. It is likely that useful genetic variation has been lost with these local extinctions due to the pronounced intra-specific variation in the species as revealed by DNA-based molecular markers (Barker et al., 1994; Dawson and Powell, in press). Clearly, the top priority for domestication of P. africana is collection of germ plasm from extant stands. The International Centre for Research in Agroforestry (ICRAF) together with its national partners (Kenya Forest Research Institute -- KEFRI; Institut de Recherche Agronomique et Development -- IRAD) has, with modest funding from UNESCO, carried out germ plasm collections in Kenya (2 populations) and Cameroon (3 populations). These have been planted out in large blocks to serve as conservation stands, comparative trials, seed orchard and selection ga rdens for sexual or vegetative propagation. They have also been planted in farmers' fields as part of a participatory domestication effort. The traits for improvement in the species logically center around yield (quality, amount, timing, etc.). These traits are in urgent need of assessment to determine the genetic control and expected gains from selection.
Palevitch (1988) questioned the scope for genetic improvement of secondary metabolite yield in medicinal plants, citing low heritability due to strong environmental influences. This conflicts with a report by Ohlendorf (1996) who described the process of domesticating a medicinal tree species (Duboisia) which until the late 1950s was largely collected from the wild. In this instance, a large pharmaceutical company (Boehringer Ingelheim) took the bold decision to support silvicultural and tree improvement research, which has resulted in enhanced alkaloid content (scopolamine, hyoscyamine), ease of vegetative propagation, elevated alkaloid yield and increased hardiness. In Prunus, environmental influences (temperature, light, altitude, soil) will partly determine the potency of the bark but genetic differences are also likely. For example, PlanteCam researchers are able to distinguish bark from the northern and southern slopes of Mount Cameroon (personal communication; G. Del Vec hio, General Manager, PlanteCam, Cameroon). One source has high docanosol levels and low beta-sitosterol levels, and the other the reverse.
What may be biologically possible in terms of genetic improvement (e.g., clonal development through vegetative propagation with rooted cuttings) may not be economically profitable for farmers or industry. Economic and marketing analyses are urgently required to back up the enthusiasm being generated about Prunus domestication. The fact that Prunus appears to perform better under an inter-cropped situation than in plantations (Bahiru Duguma, IRAD/ICRAF Project, Cameroon, personal observation) is encouraging for rural development, and it is here that greatest efforts should be focused with a need for extension materials. Declining natural populations and concerns over local extinctions may be a passing problem with P. africana if continued collaborative efforts result in policy reforms and greater on-farm cultivation.
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By A.J. Simons and Z. Tchoundjeu