Exploring Drivers of Invasiveness of the Plant Species \u3ci\u3eSenna obtusifolia\u3c/i\u3e in Rangelands to Secure Forage Production in West Africa

Rangelands in Sahelian countries are continuously over-grazed decreasing forage resources and causing rapid environmental changes. Senna obtusifolia is a less palatable plant species that becomes increasingly invasive. This research explored drivers of its invasiveness in the perspective to propose solutions to secure forage production in the pastoral reserves. Species composition and herbaceous aboveground biomass were assessed in rangelands with different levels of invasion of Senna obtusifolia along a climatic and land-use pressure gradient. A greenhouse experiment was conducted to test the competitiveness of this species. The development of Senna obtusifolia in rangelands affected significantly forage quantity. Indeed the biomass of the others herbaceous species decreased but not the species richness. The overgrazing of Sahelian rangelands combined to the floristic selection operated by livestock reduced the abundance of fodder species and fostered the expansion of S. obtusifolia. Moreover, S. obtusifolia had a good germination rate with a rapid growth that made it more competitive. Thus, in the interspecific competition experiment, the aboveground biomass of S. obtusifolia was not influenced when associated to legume, grass and perennial grass species respectively. After 3 years of full protection experiment, the abundance of S. obtusifolia decreased, hence its invasiveness in rangelands should be supported by the mixed effect of disturbance factors as grazing and drought that lead several plant species to be vulnerable and favor undesirable species expansion. The control of S. obtusifolia expansion is conditionned by the reformulation of the land management systems and the promotion of sustainable environmental policies