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Objectif : L’etude comparative de la vegetation du CRZ de Dahra en 1964 et 2011, a pour but de voir l’evolution de la phytomasse herbacee et de certains parametres structuraux du couvert herbace et ligneux. Methodologie et resultats : Avec l’aide du SIG, 55 releves de vegetation ont pu etre effectues en 2011 sur les memes points que ceux realises par Raynal (1964). La richesse, la frequence et la contribution specifique de la flore herbacee et ligneuse sont evaluees pour ces deux annees de meme que l’indice de Shannon, la regularite, l’indice de Jaccard et la phytomasse herbacee. Cette derniere est soumise au test de Tukey au seuil de 5%. Les resultats indiquent une baisse de la phytomasse herbacee  (significative au seuil de 5%) et de la diversite floristique. Cette derniere est marquee par une diminution de la richesse specifique de la flore herbacee comme ligneuse. Au niveau du couvert herbace, il est note une augmentation de la contribution specifique (CSi) des graminees (Poacees) tandis que celle des legumineuses (Fabacees) et des autres herbacees (phorbes) a connu une regression. Le couvert ligneux est caracterise par une augmentation des especes de la famille des Mimosacees et une diminution de celles des Combretacees. Toutefois, les Mimosacees, Balanitacees et Combretacees presentent les frequences relatives et les contributions les plus importantes pour ces deux annees. Conclusion et application des resultats : cette etude a permis de constater une modification de la vegetation du CRZ de Dahra marquee sur le plan structural par une baisse de sa richesse et de sa diversite floristique ; de meme que sa phytomasse herbacee. Ces resultats peuvent, contribuer a la comprehension de l’evolution de la vegetation des ecosystemes saheliens pastoraux et, etre valorises en amenagement pastoral et  agrosylvopastoral en vue d’une meilleure preservation et gestion des ressources vegetales. Mots cles : richesse, diversite, phytomasse, vegetation Comparative study of the vegetation in a grazed area between 1964 and 2011. The case of the CRZ Dahra 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. Keywords : richness, diversity, phytomass, vegetation

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