Floristic composition, structure and diversity of riparian forests in southwestern Nigeria: conservation is inevitable

Abstract

The Nigerian riparian forest ecosystems had declined in extent and distribution and this had been attributed mainly to land use change. This study intended to provide understanding links between plant diversity, composition, structures and disturbances both anthropogenic and natural processes inducing the vegetation dynamics. Nine study sites were used for this study, within each site, five (5) plots (0.25 ha in size) were marked out, placed systematically at an interval of 10 m along transect. Complete enumeration of plants species was carried out and identified to species level. Diversity indices and structural parameters were determined and anthropogenic activities were ranked. A total number of 233 plant species were identified, belonging to 80 families; out of which, Euphorbiaceae and Apocynaceae were dominant families. The density and basal area ranged from 2200 to 6000 ha −1 and 2.59 to 17.58 m 2 ha −1 respectively across the study sites. Pterocarpus santalinoides, Alchornea cordiflora, Chassalia kolly, Tetracera spp., Fimbristylis, Bambusa vulgaris and Cyrtosperma senegalense were the dominant species. The Shannon diversity index ranged from (1.38-3.49), Simpson (0.66-0.97) and Evenness diversity was (0.43-0.84). Fisher alpha (10.03-30.21) and Whittaker beta diversity (0.36-0.89) values were highest in Ipetumodu (site VIII) and lowest in Ilesha (site II). Seventy-three (73%) of the species in this study had low important value index (IVI). The dominance of some lianas and herbaceous species in the riparian forest sites showed disturbances, stages of ecological succession and regeneration of the vegetation. Conservation is inevitable towards maintaining and protection of species diversity, ecosystem roles and services of these forests in Nigeria.