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The source of a popular medicine for treating prostate disorders has been caught in a muddle that extends from the hills of central Africa to the halls of Brussels.
At the center of this tale: tree bark.
Prunus africana — more widely known as African cherry — is a remarkable tree. Related to the common rose, this large tropical tree is also called African stinkwood, on account of its pungent bark. It is found only in high-conservation value montane forests in Africa and Madagascar.
Extracts from its bark are used as an herbal remedy for benign prostate hyperplasia (BPH), an enlargement of the prostate gland that affects many middle-aged men around the world. There now are at least 40 brand-name products using P. africana bark extract; in 1997, the over-the-counter retail value of the trade in P. africana herbal preparations was estimated to be US$220 million a year and may be even higher today. In the past 40 years, P. africana bark harvest has shifted from subsistence use to large-scale commercial use for this growing international trade.
Growing concerns about the sustainability of bark harvest led to P. africana being listed in Appendix-II of the Convention on International Trade in Endangered Species (CITES) in 1995. Twelve years later, the European Union banned the importation of wild harvested bark from Cameroon, due to the overwhelming evidence that it was highly unsustainable. However, based on pressure from the private sector and from the Cameroon government, the ban was lifted in 2011, and quotas have been established for the major producing regions.
The rationale for the lifting of the ban was based primarily on “Management Plan for Prunus,” a report published by the UN Food and Agriculture Organization and commissioned by the Cameroonian government, with participation from several research organizations including the Center for International Forestry Research (CIFOR). But senior scientists within CIFOR, as well as staff at a major donor organization, have since expressed concern that this plan did not take into account the complex ecology of the species, and that it overestimated the potential for bark supplies from cultivated sources.
Weak governance and vested interests in the profits from Prunus bark suggest that there is some way to go to ensure that the wild harvesting of the species can be considered sustainable, according to scientists with knowledge of the report. There also are concerns about commercial bark harvest due to the biology of this typically long-lived tree species. For example, where no exploitation takes place, the annual mortality of P. africana trees larger than 10cm in diameter at breast height (dbh, a typical measure of tree size) is very low (around 1 percent per year). Due to commercial bark harvest, death rates of P. africana trees larger than 10cm dbh in commercially harvested wild populations can be 50 to 100 times higher than the natural mortality rate in montane forests in Cameroon.
This case holds lessons about policy development, forest governance and trade, one researcher says.
“The challenge is to get the balance right between commercial demand for the bark, local people’s livelihoods and the resource itself,” said Terry Sunderland, a Principal Scientist at CIFOR. “And this is where there remains a major gap between policy and practice.”
Can wild harvest continue?
P. africana is threatened not just by unsustainable exploitation, but overall habitat loss due to forest clearing. In the central highlands of Ethiopia, for example, forest cover has been reduced from 35 percent to 40 percent cover at the turn of 19th century to less than 2.8 percent now. Forest loss in the Prunus africana-producing countries of Kenya, Uganda, Cameroon and Madagascar has also been high.
Is wild harvest the right path for the future? If experience from other commercially harvested medicinal bark holds any lessons for Prunus africana, it is doubtful. Unlike P. africana, most bark-producing tree species in international trade have made the transition from wild harvest to production from cultivated sources in plantations or agroforestry systems. Cameroonian farmers have been planting trees, but mortality rates are high and the majority of the planted stock is not sufficiently mature for commercial exploitation, Sunderland said.
Despite these factors, some international organizations still see the sustainable harvest of Prunus africana as a model that can be applied elsewhere. If this is to occur, it is essential that widely expressed concerns about inventory and management recommendations are placed on a firm evidential basis, CIFOR’s Sunderland said, to avoid a situation where disputed studies condone continued exploitation within globally significant forest conservation areas.
Research efforts are now under way to determine the way forward for the exploitation of Prunus africana, taking into account the biology of the species, harvesting quotas, governance and benefit-sharing arrangements and international law and policy.
The next stage, Sunderland says, is to determine what is actually happening on the ground with the current phase of bark harvesting and to try to gauge the impacts on both the species and the livelihoods of those involved. This information then will be fed directly into the policy processes that affect the controls on the harvesting of the species, not only in Cameroon but throughout its range.
This scenario, one expert says, illustrates how forestry can contribute to human well-being regardless of geographic location and beyond conventional forest concerns. “It is a good example of why we should acknowledge forestry across the sustainable development agenda, rather than confining it to isolated forest goals or targets,” said CIFOR Director General Peter Holmgren. In the case of Prunus africana, the trees provide considerable health values. “We don’t want to jeopardize these benefits from forests,” Holmgren said. “In this case, a comparatively rare product can generate profound health impacts, depending on how the forests are managed.”
“Situations like this show the need for a more holistic management approach that crosses borders and stakeholder groups — and which is bound together by policies based on the best available evidence.”
For more information about this topic, contact Terry Sunderland at email@example.com.