Medicinal Vitex species (Lamiaceae) occupy different niches in Haut-Katanga tropical dry woodlands

Background and aims - Sustainable management of the medicinal plant resources provided by tropical forests is of utmost importance to human populations in developing countries. Trees and shrubs of the genus Vitex (Lamiaceae) are of great medicinal importance in Haut-Katanga (SE D.R. Congo), frequently used to treat tropical diseases. However, the security of supply is threatened, particularly by urban sprawl and mining. A conservation strategy for medicinal plants is urgently needed. In this context, we try to better understand the ecological factors (mostly soil) explaining the distribution of three medicinal species of Vitex (Lamiaceae) (V. fischeri, V. madiensis, and V. mombassae) that co-occur in the tropical dry woodlands in the region of Lubumbashi. Material and methods - In 114 plots (10 m radius), comprising at least one species of Vitex, all woody species with a DBH = 10 cm were inventoried and soil samples were collected. Multivariate Regression Trees (MRT) combined with indicator species index IndVal and Redundancy analysis (RDA) were used to characterise habitats and woody plant communities associated to each Vitex species and to explain the variability of plant community composition. Key results - Four habitats were identified, and the three Vitex species differ significantly in ecological range. Vitex fischeri is a specialist of a most distinctive community on high Mg and low Al soil (termite mounds). Vitex mombassae is indicative of one habitat, corresponding to low altitude (< 1230 m) plots. Vitex madiensis has a broader range, being a generalist of all habitats except termite mounds. Conclusion - These results emphasise the importance of a detailed knowledge of species ecology to design speciesspecific conservation strategies, even for congeneric species occurring in sympatry in the same landscape.