Original paper

Oueme and Comoe: forest-savanna border relationships in two riparian ecosystems in West Africa

Natta, Armand K.; Porembski, Stefan

Abstract

The floristic composition, species richness and structure at river edges are compared between two gallery forests/savanna ecosystems along the Ouémé (central Benin) and Comoé (NE Côte d'Ivoire) rivers. Although the overall physiognomy of the two gallery forest sites seems similar and they share the most prominent families, there are marked differences in terms of canopy density and height, herb layer density, number of individuals, tree richness and diversity (H'), and species composition. Gallery forest width, top canopy density and height were more developed along the Comoé than along the Ouémé, but the herb layer is more luxuriant at the latter site. Concerning absolute density and basal area Cynometra megalophylla accounted for 9 to 16%, and 26 to 33%, respectively in the two sites. At the two sites this species was time and again the most frequent and dominant one at both riverside and in the middle of the gallery forest. A detailed comparison of the three gallery forest plot types (riverside, middle and savanna edge) revealed considerable differences and contrasting results concerning the dominant trees, species composition, the number of species and individuals, average height and diameter, and basal area. Species characteristic for the riverfront and the central portion of gallery forests were Cynometra megalophylla, Dialium guineense, Cassipourea congoensis, Syzygium guineense and Parinari congensis at both sites, with Pterocarpus santalinoides being particularly abundant along the Ouémé river. The savanna edge has the most distinct floristic composition with Pouteria alnifolia at both sites; Antidesma venosum, Fagara zanthoxyloides along at the Comoé site; and Ceiba pentandra, Albizia spp. and Antiaris toxicaria at the Ouémé site. The difference between the plot types concerning species diversity (H') was not statistically significant. The present study shows the variability and complexity of ecological processes between and within gallery forest sites.

Keywords

gallery forestforest edgesavannacore speciesbenincote d'ivoirewestafrica.