ASSESSMENT OF TREE PHYTOSOCIOLOGICAL CHARACTERISTICS AND CONSERVATION STATUS IN NATURAL FOREST ECOSYSTEM AND ENRICHMENT PLANTING SITES IN SOUTHWEST, NIGERIA

ABSTRACT This study compared tree phytosociological characteristics, structural attributes, and conservation status across three forest types in southwestern Nigeria: Akure Enrichment Planting (AEP), Omo Biosphere Reserve (OBR) and the Strict Nature Reserve (SNR). Using a systematic plot design (24 plots: 2 × 100 m transects per forest, with four 20 × 20 m plots per transect) all living trees with DBH ≥ 10 cm were measured and identified. Stand and species metrics computed included relative density, relative dominance, Importance Value Index (IVI), basal area, stem volume, Shannon-Wiener diversity (H′), Margalef richness, Simpson concentration and other standard phytosociological indices. Results show clear structural and compositional gradients. The SNR was the most mature and species-rich site (57 species; H′ = 3.34; mean DBH ≈ 23.3 cm; BA ≈ 9.88 m²; volume ≈ 583.0 m³), OBR intermediate (52 species; H′ = 3.29; mean DBH ≈ 20.6 cm; BA ≈ 6.85 m²; volume ≈ 153.9 m³) and AEP the least mature though numerically dense (47 species; H′ = 3.11; mean DBH ≈ 18.1 cm; BA ≈ 5.45 m²; volume ≈ 86.4 m³). Dominant taxa differed by forest: AEP, Ceiba pentandra, Cordia millenii, Brachystegia eurycoma; OBR, Terminalia superba, Cordia platythyrsa, Cola gigantea; SNR, Khaya grandifoliola, Terminalia superba, Brachystegia nigerica (high IVI values). Several IUCN-listed species (Cordia platythyrsa, Pterygota macrocarpa, Sterculia oblonga, Khaya species) occur at low densities across sites, underlining conservation concern. The study concludes that enrichment planting has increased stem abundance but lags behind natural reserves in structural maturity, biomass and conservation value; it recommends targeted enrichment with native climax species, protection of indicator taxa, and long-term phytosociological monitoring to steer restoration toward natural-forest benchmarks.