Weed communities of arable fields in the Sudanian and the Sahelian zone of West Africa
Wittig, Rüdiger; Becker, Ute; Ataholo, Mandingo
Up t o now, only a few authors have published relevès or synoptic tables of the segetal vegetation of rainfed fields of the West African Sahelian and Sudanian zone. Only one of them ( Ataholo 2001) has presented a rich relevé material, but no higher syntaxa were validly described. In this paper, we have compiled all relevés available in order to present a syntaxonomic overview on the segetal vegetation mentioned above. The segetal vegetation of rain-fed arable fields in West Africa floristically is clearly differentiated into the Ipomoeo eriocarpae-Commelinetalia benghalensis and the Mitracarpo hirti-Alysicarpetalia ovalifolii. The first order represents the weed vegetation of house fields and gardens which are highly fertilized with organic waste. The second order comprises the segetal vegetation of fields that are only weakly fertilized or do not even receive any fertilizer. While the first order unifi es only one alliance, within the second order three alliances can be identifi ed. The Tridaco procumbentis-Schwenckion americanae contains mainly South Sudanian communities, the Spermacocion chaetocephalae is a North Sudanian alliance and the Jaquemontion tamnifoliae has a Sahelian character. The species composition of these units not only mirrors the geographic position or the extra zonal situation, but also the length of the fallow period and the soil conditions. Many species that are abund ant in the South Sudanian zone only grow on the most humid fields of the Sahelian zone. The same is true for Guinean species occurring in the Sudanian zone. Floristically, the Sudanian segetal vegetation strongly differs from that of the weed communities described so far from other tropical regions. But there are obvious affi liations to the annual ruderal vegetation of Sudanian West Africa.