Structural description of two Isoberlinia dominated vegetation types in the Wari-Maro Forest Reserve (Benin)

An tree-inventory of Isoberlinia natural mixed stands was carried out in the tree-savannas and woodlands of the Wari-Maro Forest Reserve (Republic of Benin) to serve as basis to improve existing management strategies. Measurements were done in 96 rectangular plots of 30 × 50 m with a cumulative area of 14.4 ha. The two vegetation types were mainly distinguished by the overall tree-density (225.2 stems/ha in tree-savannah against 202.8 stems/ha in woodland), the overall mean height of the stands (13.1 and 14.6 m, respectively) and the mean height of Isoberlinia trees (14.1 and 16.8 m respectively). The other parameters (mean diameter, basal area, basal area contribution of Isoberlinia trees, bark thickness, tree-density of Isoberlinia trees as well as the Shannon diversity index and Pielou evenness index) had essentially the same values for the two vegetation types. The stem diameter structure of Isoberlinia stands in the two vegetation types had an “inverse-J” shape for the whole stand and the “I” shape for Isoberlinia trees. The stem diameter of Isoberlinia decreased on average 1.9 cm/m tree-height. Isoberlinia seedlings were more abundant below the canopy of mature trees than further away. The main dispersal mode of the species consisted of dropping the seeds from pods under the mother tree, and suckering which resulted in the observed aggregated distribution of the trees. These results were used to propose management strategies for the two vegetation types.