Impact of flooding frequency on the diversity and structures of riparian forests in Southwestern, Nigeria

Riparian zones have been found to be a complex ecosystem subjected to flooding events of varying intensity and frequency. It is well established that flooding influences the vegetation dynamics of riparian forests but there is paucity of information on the impact of flooding frequency on the diversity, structure and composition in riparian forests in Nigeria. The Height Above Nearest Drainage (HAND) model was adopted in this study to generate flooding frequency across the host watershed/sub-basins where the study sites are located. The HAND algorithm was implemented in ArcGIS environment using SPOT DEM as input layer. Multiple regression and Canonical Correspondence analysis were employed to assess the impact of flooding frequency on structure and diversity of the study sites. The mean flooding frequency (years) across the study sites, ranged from 0.18-7.80, with Ifetedo site being the highest and Ilesha site the lowest. Flooding frequency impacted on the species richness and soil annual volume loss/gained across study sites. The study established that flooding frequency are the natural driver influencing species density, alluvial deposition and regeneration dynamics. The annual and total volume of soil gained/loss impacted on the diversity indices, species dominance and evenness of riparian forests in Southwestern Nigeria. • The lack of influence between the flooding frequency and the amounts of litters retained in the forest floors across study sites as shown by weak positive correlation may indicate that the intensity of flooding was not sufficient to influence decomposition, litter accumulation or removal from the forest floor across the study sites • The annual and total volume of soil loss/gained influenced species diversity, dominance and evenness across study sites. This might be a function of the intrinsic ability of these natural drivers trigged by flooding frequency to dictating the vegetation dynamics of the riparian forests. • This study has successfully proposed a quantitative evaluation of the relationship between flooding frequency and biodiversity attributes of riparian forests in Southwestern Nigeria, where ecosystem services are diminishing and forest resources are threatened • The study established that flooding frequency are the natural driver influencing alluvial deposition with significant negative/inverse impact on the annual/total volume of soil gained or loss in riparian forests, regeneration as seedling densities of woody species is more pronounced in sites with high flooding frequencies and a very direct positive impact on the species richness of riparian forests in Southwestern, Nigeria