Étude comparée de la végétation de 1964 et 2011 en milieu pâturé: Cas du CRZ de Dahra

Abstract

Objective: A comparative study of the vegetation of the CRZ-Dahra during years 1964 and 2011, aims to appreciate the evolution of herbaceous phytomass, as well as some structural parameters of herbaceous and woody cover. Methodology and results: Using Geographic Information System (GIS), 55 vegetation surveys were carried out in 2011 on the same points used by Raynal (1964). The species richness, the frequency and the specific contribution of herbaceous and woody plants were assessed for each year, as well as the Shannon index, the regularity, the Jaccard index and the herbaceous biomass production. The latter characteristic was subjected to an analysis of variance followed by a separation of means using the Turkey's multiple comparison procedure (with a level significance fixed at the 5% level). The results indicate a decrease in herbaceous phytomass production (P<0, 05) and of plant diversity. The decline in plant diversity is reflected by a decrease of species richness of both herbaceous and woody plants. In the herbaceous layer, it is noted an increase of the specific contribution (CSi) of grasses (Poaceae) while that of legumes (Fabaceae) and other herbaceous plants (Phorbs) experienced a decline. The tree cover is characterized by an increase in species of the family of Mimosaceae and a decrease of those belonging to the Combretaceae. However, Mimosaceae, Balanitacea and Combretaceae presented the most significant relative frequencies and contributions for the two years of study. Conclusion and application of the results: This study revealed a vegetation change at the CRZ Dahra. This shift is structurally marked by a decline of its floristic richness and diversity, as well as of its herbaceous phytomass production. These results may contribute to a better understanding of the evolution of the vegetation in Sahelian pastoral ecosystem. They may also be valorized for the planning of agrosylvopastoral areas in order to improve the preservation and the management of plant resources.