Summary 1.The growing interest in medicinal plants from both international industry and local markets requires management of tree bark harvesting from natural forests in order to prevent inappropriate exploitation of target species. This study was designed to determine the bark re-growth response of a selected number of medicinal tree species as a basis for the development of an optimal bark harvesting method. 2. In 2004, bark was harvested from 925 trees belonging to 12 species in 38 sites in a dry forest in Benin, West Africa. Two years later, the response of trees to bark harvesting was examined with respect to re-growth (edge or sheet), development of vegetative growth around the wound, and the sensitivity of the wound to insect attack. 3. Two species, Khaya senegalensis and Lannea kerstingii , showed complete wound recovery by edge growth. At the other extreme, Afzelia africana , Burkea africana and Maranthes polyandra had very poor edge growth. M. polyandra showed good sheet growth, whereas the other 11 species had none or poor sheet growth after total bark harvesting. In contrast, partial bark removal allowed better sheet growth in all 12 species studied. 4. Insect sensitivity was species-specific. Insect attacks were negatively correlated with nonrecovered wound area, but there was a marked species effect for the same rate of regeneration. L. kerstingii and K. senegalensis had very good and similar re-growth, but L. kerstingii was very susceptible to insect attack, whereas K. senegalensis appeared to be very resistant. Only a few individuals developed vegetative growth, and each tree usually developed only one or two agony shoots, but there was no significant difference between species. 5. Synthesis and applications . This is the first study to provide data on the ability of trees to close wounds after bark harvesting in West Africa. We report large variability in the response of different species to our bark harvesting technique, and identify just two out of the 12 study species as suitable for sustainable bark harvesting. Based on our results, we developed a decisional step method to help forest managers select the best techniques for managing medicinal tree species as an alternative to bark harvesting, for example, coppice management, harvesting leaves instead of bark, stand establishment, and collaboration with timber companies.

The phenomenon of distinct, absent or indistinct growth rings is a highly variable feature used for wood identification and a wide range of tree-ring studies. Causes for its variability are not yet fully understood. There is also a lack of consensus within the scientific community about how distinct and indistinct tree rings should be defined and classified. We use a selection of 103 Central African rainforest trees to analyse the anatomy of growth-ring boundaries of 103 Central African rainforest species and assessed the influence of the climate, tree organ and leaf shedding behaviour on growth-ring distinctness and anatomy. We observed a high variability of tree-ring boundaries anatomy and distinctness within and among individuals and species. Although, for some semi-deciduous species, higher incidence of distinct growth rings appears to be related with a more pronounced seasonal climate, no general trends are observed for the assembly of studied species. Growth rings are variable within individuals depending on the considered organ: trunks tend to show more distinct rings than branches. Growth-ring distinctness is difficult to implement as a trait to measure tree performance when only based on abrupt changes in fibre size and cell wall thickness. From the potential growth-ring markers identified in the IAWA list of hardwood features, those applying to vessel and parenchyma density and distended rays appear to be more useful in tropical trees than abruptly flattened latewood fibres or abrupt changes in vessel diameter.

Despite increasing recognition of the relevance of biological cycling for Si cycling in ecosystems and for Si export from soils to fluvial systems, effects of human cultivation on the Si cycle are still relatively understudied. Here we examined stable Si isotope (δ30Si) signatures in soil water samples across a temperate land use gradient. We show that – independent of geological and climatological variation – there is a depletion in light isotopes in soil water of intensive croplands and managed grasslands relative to native forests. Furthermore, our data suggest a divergence in δ30Si signatures along the land use change gradient, highlighting the imprint of vegetation cover, human cultivation and intensity of disturbance on δ30Si patterns, on top of more conventionally acknowledged drivers (i.e. mineralogy and climate).

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