Prunus africana - stripping away an essential resource
Prunus africana (pygeum or African stinkwood) is the source of an important drug used in the treatment of prostate conditions common in older men. The drug is almost exclusively extracted from this tree, which is therefore of great economic value to those African countries that export the bark from which the drug is derived. Prunus is found across much of Africa, mostly in montane forest, but its over-exploitation is already causing concern in Cameroon and Madagascar - the origin of much of the exported bark.
When the medicinal value of this bark was first recognised by western pharmaceutical companies over 20 years ago, the trees were harvested in a sustainable manner by removing only a few strips of the bark a time, which allowed the trees to continue growing. But, as the demand increased, it became more common to find trees stripped of all their bark or even felled. This has led to a decrease in mature trees and also to very limited regeneration as the trees that remain are too young to produce seeds. The result is that Prunus is now classified as an endangered species as the destruction, and the pressure on the remaining areas of montane forest, continues.
In an attempt to lessen the pressure, the Cameroon government has banned the exploitation of Prunus in two mountainous regions of the country. Farmers here have now started to plant large areas of the tree to replace the bark they would have harvested from the wild. Although those currently planting Prunus will not begin to harvest the bark until the trees are more mature, the trees will remain a valuable source of income for a long time, provided that the bark is stripped in a sustainable manner.
Despite the efforts to replace felled trees in Cameroon, the best solution may lie in the domestication of the tree for cultivation by farmers. ICRAF says that the tree has high potential for incorporation into agroforestry systems, that it would decrease pressure on natural forests and would preserve biodiversity of the species. ICRAF, with the assistance of UNESCO (United Nations Educational, Scientific and Cultural Organization), has begun a programme to survey the genetic variation of the species in the wild so that it may be possible to select for domestication the populations that produce the most bark - or alternatively, the best bark extracts for medicinal use.
However, to domesticate P. africana successfully, the problems of seed germination have to be overcome. The seed is known to be 'recalcitrant', which means that the majority of seeds will not germinate unless they are planted within a few days of being collected. This has proved to be a particular problem in Madagascar where farmers have limited knowledge of tree planting. Research on the best way to handle seeds and how to transfer that knowledge to farmers are therefore important aspects of the research programme. ICRAF is also working with IPGRI (International Plant Genetic Resources Institute) on ways of extending the life of the seed by using better storage techniques. It is also possible to reproduce the trees vegetatively by taking cuttings.
The market value of the final pharmaceutical product of Prunus africana is currently estimated at US $220 million a year. It is very difficult to synthesise artificially so it is estimated that the market for it should remain stable for at least the next 20 years. With villagers in Madagascar currently receiving about US $0.20 per kilogram of bark, they should look forward to a prosperous future provided that they start planting Prunus as well as felling it. A stable domesticated population of the species would, without doubt, provide a guaranteed income and decrease pressure on a natural resource already under threat.
