Wild populations of the Afromontane forest tree Prunus africana (Rosaceae), known as the African Cherry or Red Stinkwood (sometimes called Pygeum africanum) are currently the sole source of bark and bark extract exported from Africa and Madagascar to Europe. This trade has taken place for nearly 30 years, for production of at least 19 different herbal preparations sold by 23 companies based primarily in Europe, but also in North and South America. These are used to treat benign prostatic hypertrophy (BPH), a common disease in older men. This account provides an interesting case-study of a medicinal species which is in transition from wild harvest to cultivated sources of supply. It also illustrates the ‘ecological footprint’ of Europe on African forests, and upon a medicinal resource within them. Bark exploitation has caused serious damage to wild populations of Prunus africana, including trees inside forests of high conservation value in Madagascar and Cameroon. Because of the difficulty of implementing and enforcing conservation measures or developing local institutions to do so, sustainable bark harvesting of remaining wild stocks by local communities is considered unlikely in Cameroon and in Madagascar. For these reasons, cultivation has been suggested as an alternative source of bark production. This study investigated the economic feasibility of different planting systems (enrichment planting, small-scale farming and plantations) for Prunus africana cultivation. As part of this process, we investigated Prunus Africana bark production and growth rates, finding statistically significant correlations between bark thickness, diameter at breast height (dbh) and tree height. Prunus africana showed rapid growth, reaching 14m high and 37cm dbh in 18 years. Results of a comparison between the flow of costs and benefits from small-scale production of Prunus africana and Eucalyptus camaldulensis show that Eucalyptus camaldulensis cultivation is 30% more profitable than Prunus Africana production. But there are reasons why farmers might rather invest in Prunus africana instead of, or in addition to, Eucalyptus trees: Prunus africana is highly valued as an ingredient in many local medicinal treatments, it is used in making tools such as hoes and axes, and it is a good source of poles and firewood. Moreover, farmers and field observation indicated that with the possible exception of maize, crop yield is not much affected by the presence of Prunus africana in the fields. This contrasts with the depressive effect of Eucalyptus trees on crop yields. In North West Province, Cameroon, at least 3,500 farmers are already planting Prunus africana. Bark price is affected by moisture content, distance from the factory and the monopoly, which the company has had on export of bark and bark extract. This study determined bark moisture content to be 42-50%. In rural Cameroon, intermediaries only pay 70 FCFA (0.14 US$) per kg of Prunus africana bark, equivalent to about US$ 142 per ton of fresh bark. At the factory gate, bark sells for 104-270 FCFA francs per kg (in 1994, 1 US$ = 490 CFA), depending on bark moisture content and quality, equivalent to US$ 212 – 551 per ton. Higher prices were paid for bark in Cameroon in 1994, when an Italian company paid 250 FCFA francs/kg, regardless of bark moisture content (US$510 per ton of fresh bark). In Kenya, the price paid to the exporter was considerably higher (11 French francs (US$ 2) per kg). This is equivalent to a price of US$ 2,000 per ton of fresh bark. By comparison, the price for fresh bark of the black wattle, Acacia mearnsii, which is cultivated for its tannin- rich bark, was US$ 94 per ton. On the basis of this study, we recommend clarification of Cameroon forestry law to enable farmers to sell bark from Prunus africana trees they cultivate, that information on the best methods for Prunus africana cultivation from seed be provided to farmers, more competitive bark prices that reflect the international market value of this product, and the initiation of an out-grower scheme with the involvement of the pharmaceutical company that buys the bark and has a monopoly on the export of bark extract.
Tag: leaf area
Vegetative propagation of Prunus africana: effects of rooting medium, auxin concentrations and leaf area
The region of West and Central Africa is endowed with high-value fruit trees and medicinal plants, which are currently traded locally as well as on regional and international markets. Unfortunately, they are all exploited from the wild and there has been little or no focussed effort to domesticate and cultivate them. Prunus africana is one of these important medicinal plant under domestication. A series of nursery experiments were conducted to assess the effects of rooting medium (sawdust, sand and a 50:50 mixture of sand and sawdust), auxin concentration (0, 50, 100, 150, and 200 µg IBA), and leaf area (0, 5, 10, 20, and 25 cm2) on rooting success of juvenile cuttings of P. africana. The percentage of cuttings rooted was significantly greater (P < 0.05) in sawdust (80%), than in sand alone (72%) or in mixture with sawdust (71%). Leaf area also significantly affected the percentage of rooting. Leafless cuttings did not root and were all dead by week 6, but in leafy cuttings rooting ability increased proportionally with leaf area up to 20 cm2 (79%). Larger leaf cuttings (25 cm2) rooted at the same level as those of 20 cm2. The cuttings with the largest leaves also had the greatest mean number of roots per cutting (14 roots cutting1), while those with the smallest (5 cm2) leaf area produced the fewest roots (5 roots cutting1). The application of auxin (IBA) promoted rooting (P < 0.05) up to an optimum application of 100–200 µg IBA per cutting, but 300 µg was supraoptimal. It can be concluded that P. africana is amenable to vegetative propagation.
Biomass production and allocation in Jatropha curcas L. seedlings under different levels of drought stress
In a greenhouse experiment we applied three levels of drought stress and monitored growth variables and biomass production of Jatropha curcas seedlings propagated from three seed accessions. We determined biomass allocation, allometric relationships and plant traits. Well-watered J. curcas seedlings grew 0.81 0.15 cm day-1 in length and produced 1.49 0.31 g dry biomass day-1. Under medium stress (40% plant available water) the plants maintained a similar stem shape, although they grew at lower rate (stem length: 0.28 0.11 cm day-1; dry biomass production: 0.64 0.18 g day-1). Seedlings under extreme drought stress (no irrigation) stopped growing, started shedding leaves and showed shrinking stem diameter from the 12th day after the start of the drought treatment. The drought treatment did not influence the wood density (0.26 g cm-3). The root/shoot ratio of the wet treatment was 0.27, which is low compared to other tropical trees. Both the biomass allocation and root/shoot were significantly influenced by drought. Plants of the different accessions were uniform in biomass production and plant traits. The allometric relationship predicting total aboveground biomass (B) with the stem diameter (D) (B = 0.029 × D2.33; R2 = 0.89) fits well in universal scaling models in which the exponent is expected to converge to 2.67 at plant maturity. Based on a small validation data set from mature J. curcas individuals this hypothesis could be confirmed. A second regression model predicts the total leaf area (LA) as a function of stem diameter (LA = 2.03 × D2.41; R2 = 0.95). The estimated transpiration crop coefficient Kcb ranged from 0.51 to 0.60 for the well-watered plants.