Typology of the woody synusium of the Karthala forest, Comoro Archipelago.
Aim - We realised a phytoecological study in the Karthala forest. The objective was to define and characterise the main plants groups that could be used to adjust the biodiversity management and preservation programmes in the Comoro archipelago. Methods - The phytoecological study was based on 78 vegetation relevés set up along fourteen transects arranged in an East-West direction following the altitudinal gradient. The data were subjected to multivariate analysis (FCA, FDA) to define the various groups. To characterise each group, we used Shannon diversity index, regularity index of Pielou and similarity index of Jacquard, as well as distribution of the woody species settlement. Results - Natural forest area was disciminated from fields and cultural area. In the natural forest area, three groups were distinguished, according to the altitudinal gradient and the nature of the substrate: (a) forest of low and average altitude invaded by Psidium cattleyanum var. coriaceum, (b) humid evergreen forest of high altitude with Tambourissa comorensis et Weinmannia comorensis, (c) forest of high altitude with volcanic lava flow characterised by Rapanea comorensis above which there is an ericoid moor with Philippia comoriensis. The study of the woody vegetation structural parameters showed a gradient of density that increases with the altitude, whereas the land area decreases. The same way, at higher altitudes the species richness and the regeneration potential of plants decrease. Conclusion - The traditional methods of multivariate analysis allowed us to distinguish three different groups which differ from each other by their diversity and their structure, which are depending on presence and/or absence of human settlement, as well as on men's activities.