Environmental Gradient: An Ecological Surrogate to Phytosociological Diversity of a Tropical Mangal-Rainforest-Ecotone in a Hydromesic Tripartite Plant Community

Aim: To assess influence of edaphic environmental gradients as surrogate to phytosociological diversity in a hyromesic habitat. Study Design:  A systematic sampling approach of line-transect method was used. Place and Duration of Study: Field sampling: tropical mangal-rainforest ecotone in parts of Asarama, Andoni, Niger-Delta, Labortory analysis: Jack Petroanalytical Laboratory, and University of Port Harcourt Ecology Laboratory, Port Harcourt, Nigeria, between September 2020 and August 2021. Methodology: Soil sampling and analyses was based on ASTM, Stewarte and conventional methods and the data obtained was subjected to statistical analysis. Results: Recorded 90 plant species across the sampled sites with a prevalence of 6 (65.9%) species in mangrove, 64 (70.33%) in ecotone and 55(60.44%) in rainforest sites respectively. Floristic density and life form in mangrove had 121ha-1, 3 megaphanerophytes and mesophanerophytes respectively, in ecotone 1660ha-1, 9 megaphanerophytes, 24 mesophanerophytes and 39 microphanerophytes and in rainforest 574ha-1, 13 megaphanerophytes, 18 mesophanerophytes and 24 microphanerophytes. Highest frequency of occurrence: 1 species (80%), 4 species (100%) and 1 species (80%) in mangrove, ecotone and rainforest sites, respectively. Highest abundance: mangrove (1 species), ecotone (9 species) and rainforest (3 species). Highest density: mangrove (1 species), ecotone (8 species) and rainforest (3 species). Distribution: greater in ecotone with contiguous pattern in the order: ecotone>rainforest>mangrove, among which had dissimilarity in response to significant species diversity difference in relation to significant difference in edaphic physico-chemical factors of the study sites. The mangrove site had the most acidic pH, highest salinity, moisture and electrical conductivity while rainforest and ecotone had highest organic carbon and matter. A significant negative correlation between EC & pH, and salinity & pH and positive correlation between salinity & EC as well as positive correlation between pH & OC, pH & OM, OC & OM and negative correlation between EC & OC, EC & OM were recorded. Conclusion: This variation determined the presence, growth and abundance of the species reported in the respective study sites especially in the ecotone.