Bark re-growth and wood decay in response to bark stripping for medicinal use

[摘要] ENGLISH ABSTRACT: Plants have been used for centuries to treat a wide range of ailments in the history of all civilizations. However, a growing interest in medicinal plants requires appropriate management to prevent over-exploitation of target species. The challenge for scientists is to find equilibrium between resource exploitation and the maintenance of viable populations of target species. Sustainability of use requires an understanding of the ecological, economic and socio-cultural aspects of resource use and the interaction between these factors. This research focuses on the ecological and socio-cultural aspects required to underwrite species-specific sustainable harvesting systems for bark used for traditional medicine.The social survey conducted in the form of structured interviews with traditional healers reported 69 plant species used for medicinal purposes in the southern Cape. The results suggested that resource users are aware of the increase in demand for medicinal plants in general, attributing this to an increasing recognition of traditional medicines and increasing prevalence of diseases. Ocotea bullata (Endangered), Curtisia dentata (Nearly Threatened) and Rapanea melanophloeos (Declining), as well as Siphonochilis aethiopicus (Critically Endangered), Elaeodendron transvaalense (Near Threatened) and Cassipourea flananganii (Endangered) that do not occur in the area naturally, were identified as species in high demand for their medicinal bark properties. Given the high demand and concerns about over-exploitation, a need for further ecological research to develop sustainable harvest systems was identified.Two species, O. bullata and C. dentata, were selected from an earlier study on the response of several species to bark stripping, that was confined to a study period of three years after treatment. With this current study tree response to bark stripping and harvesting impact were assessed over a period of ten years to reveal the intra and inter-specific difference of wound occlusion (wound closure through bark-regrowth) and the anatomical decay consequences of bark stripping. This is, to the knowledge of the author, the first study to evaluate the structural-tree pathogen interaction following bark stripping on medicinal tree species in Africa. The results revealed species-specific differences in terms of both wound closure and efficiency in decay containment. O. bullata had a significantly better wound occlusion rate and a lower extent of decay. The relationship between tree diameter growth and the rate of wound occlusion allowedfor the formulation of a preliminary model that will assist forest managers in developing bark harvest systems. Smaller trees showed poor bark regrowth and a significantly higher mortality, which suggest that a minimum tree size for harvesting needs to be stipulated in the harvest prescriptions. In contrast, C. dentata showed a much higher volume of decay within the stem, poor bark regrowth and a significantly higher mortality of bark-stripped trees. In conclusion, the harvesting of bark for C. dentata through bark stripping is not viable, and alternatives should be explored. O. bullata has a much greater potential for strip harvesting, both in terms of bark regrowth and the containment of wood decay following wounding.

[发布机构] Stellenbosch University