John Libbey Eurotext

Science et changements planétaires / Sécheresse

Tree/grass interactions in Sahelian zones Volume 17, issue 1, Janvier-Juin 2006

Authors
BP 897, Antananarivo 101 Madagascar, Laboratoire d’écologie végétale, Faculté des sciences, Université Cheikh Anta Diop (Ucad), BP 5005, Dakar Sénégal
  • Key words: agroforestry, semiarid zone, sylvopastoralism, Sahel
  • Page(s) : 318-25
  • Published in: 2006

The study of the interactions between tree and grass is of prime necessity for a better understanding of the functioning of those complex ecological systems which are widely spread in semiarid regions. In order to describe the tree/grass interactions in sahelian zones, two well-studied models were selected: the first one is the Acacia raddiana sylvopastoralism system and the second one is the Faidherbia albida agroforestry system. In sahelian zones and more generally in semiarid countries, it was shown that trees modify the specific composition of the spontaneous herbaceous vegetation. They also have a favourable impact on the phenology, the productivity, and the quality of the spontaneous or cultivated herbaceous vegetation. Increased understory herbaceous productivity was interpreted as a result of better microclimatic and greater fertility within the canopy zone. In sahelian regions, characterized mainly by aridity and depletion of nutrients, trees have therefore a positive impact on the herbaceous stratum. In wetter regions, with higher tree density, irradiance by limiting carbone uptake in shade seems to be the major determinant of tree/grass interactions. The boundaries of the knocking over stage were evaluated at 700-800mm of annual rainfall and a 60% canopy cover.