Abstract

Plant species richness and diversity are widely used bioindicators of environmental condition, yet studies that trace a specific richness or diversity deficit to a specific, field-identified mechanism remain uncommon in the Niger Delta. This study assessed plant species diversity by quadrat sampling across six communities in three contrasting Local Government Areas (LGAs) of Rivers State namely; Ahoada West, Tai and Okirika. Sampling was carried out in both the wet and dry season, computing species richness, Shannon, Simpson and Margalef indices. Korokoro Tai in Tai LGA recorded the highest species richness in both seasons (14.00 ± 3.92 wet; 13.50 ± 3.70 dry), while Okirika Main Town recorded the lowest diversity of any site in both seasons (Shannon: 0.86 ± 1.03 wet; 0.45 ± 0.53 dry) despite recording the highest individual plant count of any site in the dry season (385 individuals, 25.9% of the 1,488 individuals counted across all nine sites that season), a combination indicating dominance by a small number of tolerant taxa rather than a genuinely unproductive site. Species-level analysis identified the specific mechanism: Nypa fruticans was recorded in every quadrat sampled at both Okirika-LGA communities in both seasons, and was the sole species present at two of four quadrats specifically, consistent with its documented profile as an aggressive, tidally distributed coloniser of disturbed mangrove and estuarine habitat. These findings demonstrate that a consolidated diversity deficit can, with appropriately fine-grained field data, be resolved into a specific, targetable ecological mechanism rather than treated as generalised habitat degradation with direct implications for how restoration resources should be allocated at Okirika Main Town, and for how diversity assessments are designed more broadly in disturbed tropical landscapes.