Impacts of Restoration Projects on a Sahelian Woody Vegetation after 21 Years: The Simiri Plateaus (Niger) Case Study

Abstract

To face the soil and vegetation degradation in Niger, anti-erosion structures, such as scarification of the surface of the ground, half-moons, benches, trenches, stony cordons, were built in 1989 on three Simiri plateaus. Native and introduced woody species were planted and grasses were sown within the structures. This study aims at evaluating what has become the restoration of the woody vegetation cover compared to an un-restored woody cover located on a nearby similar site. Dendrometric parameters and alpha and beta diversities of the four woody stands in 36 sampled plots were analyzed and compared. The following dendrometric values were found significantly lower in the control than in the restored stands: 3.9% against 12.4-16.8% for the recovery rate, 4.3 against 6.3-10.2 cm for the largest stem diameter, 0.2 against 0.8-1.2 m²/ha for the basal area, and 1.6 against 2.0-2.5 m for the tree height. However, the number of stems per trees was found significantly greater in the un-restored stand (6.6) than in the restored ones (1.8-2.7). The values of dendrometric parameters remained low, as well as the alpha and beta diversities whatever the stand. Nevertheless, population perceptions on the restoration impacts that were collected through focus groups indicated positive impacts on downstream crop yields.