Diversity and structure of woody stands in the contracted vegetation of western Niger following a rainfall and anthropisation gradient

The aim of this study was to characterise the diversity and structural parameters of the woody stand in the contracted vegetation of western Niger at three sites located along a rainfall and human settlement gradient. An inventory of the woody flora and a measurement of the dendrometric characteristics of the trees were carried out on 120 plots of 2500 m2 subdivided into plots 12.5 m apart. The species richness was 17 species in 9 genera and 12 families on all the sites investigated, with 11 species on the Kouré plateau, 13 on the Guittodo plateau and 17 in the Gorou Bassounga classified forest. Density was 234.79, 555.09 and 683.79 ind/ha, basal area 4.21, 7.2 and 8.62m2/ha and tree cover 19.8, 45.34 and 60.75¨%, respectively on these three sites. In terms of structure, the stand has a high proportion of relatively young individuals. Shannon's diversity (2.37 to 2.81 bits) indicates that the environments are of low diversity and Pilou's equitability (0.56 to 0.63) highlights a phenomenon of dominance in the three stands. The lowest similarity index (0.44) is obtained between the Kouré plateau and the Gorou Bassounga classified forest, and the highest (0.46) between the Kouré plateau and the Guittodo plateau. These results testify to the low diversity and young structure of this dying vegetation.