Structure démographique et répartition spatiale des populations de Sclerocarya birrea (A. Rich.) Hochst. du secteur sahélien du Niger

Abstract

The main purpose of this study was to analyse the population structure and spatial distribution of Sclerocarya birrea stands in the protected forests of Dan Kada Dodo and Dan Gado and their peri- pheral areas. These parameters have to be known to ensure that the stands are managed sustainably. Sample inventory plots measuring 50 x 20 m were iden- tified by random stratified sampling in the three land use units identified (tree steppe, agroforestry sector, adjacent agricultural zones). Tree diameter at 1.30 m above the ground, total height and the two diameters perpendicular to the crown of S. birrea were measured. To define spatial distribution, S. birrea individuals were mapped in two 1.96 ha plots (140 x 140 m) in the “tree steppe” and “agroforestry sector” units. The results show that S. birrea individuals are distributed in random aggregates of varying sizes (about 7 m and 25 m), which is consistent with their zoochorous and barochorous fruit dispersal pattern and the capacity of the species for vege- tative propagation. The highest densi- ties (25.2 individuals/ha), basal areas (1.6 m2/ha) and average heights (6.9 m) were in the protected forest sectors. The bell-shaped distribution curve for stand height and diameter classes reflects the better representation of intermediate classes than extremes. However, the erra- tic structure observed in the “adjacent agricultural zones” indicates a highly irregular distribution of diameter classes. We conclude that S. birrea populations require more effective conservation, with more appropriate restoration strategies to be developed.