Floristic Composition, Tree Canopy Structure and Regeneration in a Degraded Tropical Humid Rainforest in Southwest Nigeria

Abstract

Floristic composition, plant species diversity, tree canopy structure and regeneration were assessed in a degraded tropical humid rainforest in Nigeria using a systematic line transect sampling technique for plot demarcation. All plants in a plot were identified and classified into families while the diameters and heights of trees with diameter at breast height (Dbh) >10cm were measured. Tree basal area, total volume, density, dominance, frequency, Importance Value Index (IVI), Shannon-Weiner diversity (H1) and Equitability Indices (EH) were then computed. A species-area curve was used to determine the relationship between forest area and number of species encountered while tree height was used to assess canopy structure. Eighty-three plant species belonging to 78 genera in 39 families were identified. Trees were the predominant plant form with 46 species (172 trees ha-1) while 7 shrubs, 15 lianas, 13 herbs, 1 grass and 1 fern species were recorded. Tree basal area and total volume were 10.29±0.88 m2 ha-1 and 22.43±1.85 m3 ha-1 respectively. The tallest tree height (35m) was recorded for Terminalia superba while the shortest (9.3m) was Ficus mucuso. The three most abundant families were Fabaceae (15.9%), Sterculiaceae (9.8%) and Moraceae (7.3%) while the most dominant species were Trema orientalis (4%), Terminalia superba (4%) and Mansonia altissima (6.29%) with IVI of 14.92%, 14.79% and 13.73%, respectively. A high level of tree species diversity was observed with H1 and EH of 3.65 and 0.97 respectively. There were 29 tree species found to be naturally regenerating (seedlings and saplings) and no species was found in the emergent layer. Despite the high level of anthropogenic interference in the ecological processes, Akure–Ofosu forest reserve remains highly diverse in plant species composition and it has great potential for restoration if properly managed with silvicultural interventions such as seed supplementation and/or enrichment planting which would encourage the rapid return of the complex forest conditions.