Interactions between tree and understory herbaceous vegetation in semiarid sahelian and soudanian zones: The influence of grazing

The aim of this study is to assess, in two protected plots, the impact of grazing on the modifications in the structure of the herbaceous stratum due to tree action. The ecological preferences of herbaceous species in the open and under cover are defined following observations based on two vegetation cycles (1995 and 1998) using floristic inventory and vegetation sampling methods. Herbaceous phytomass production is estimated through the standing crop method, when each of the two vegetation cycles is at its highest. The influence of the tree on the herbaceous stratum is the same in both the protected and control zones, where two juxtaposed units, i.e. the herbaceous cover on the one hand and the grass-tree complex on the other hand, can be clearly distinguished. The distinction is clearer in the protected zone as grazing, a disruptive factor, is completely eliminated. Under cover, both the specific diversity and phytomass production of the herbaceous stratum are increased, with a rise in the order of 30 top 40% for phytomass production.