CARBON STORAGE POTENTIAL AND FOREST STRUCTURAL ATTRIBUTES OF A PROTECTED SECONDARY TROPICAL FOREST IN SOUTHWESTERN NIGERIA

Abstract

Protected forests play a vital role in the global carbon cycle by acting as major carbon sinks and mitigating atmospheric carbon dioxide (CO2) concentration. This forms the basis for undertaken this study with a view to assess the tree species composition, aboveground biomass, and carbon stock of T. A. Afolayan Wildlife Sanctuary located within the Federal University of Technology, Akure, Ondo State, Nigeria. The sanctuary covers an area of 270 × 350 m and is divided into eight transects, separated at 50 m apart. The first two of the eight transects have been degraded and are used for recreational purposes. In this study, all the eight transects were considered for the assessment using a systematic sampling design. Eight sample plots of 25 × 25 m were systematically established at 50 m intervals across the eight transects. All trees with Diameter at Breast Height (DBH) greater than 10 cm were identified and measured for relevant growth variables. Basal area, volume, biomass, and carbon stock were calculated using standard forestry equations and species-specific wood densities from the Global Wood Density Database. A total of 163 individual trees belonging to 34 species were recorded, with Hildegardia barteri being the most abundant species. A reverse J-shaped diameter distribution is an indication of a continuous regeneration and structural stability. Biomass and carbon stock varied considerably among species, with Milicia excelsa having the highest biomass (1,244,083.95 kg ha-1) and carbon stock (622,041.97 kg ha-1), followed by Pterocarpus mildbraedii with biomass and carbon values of 867,388.38 kg ha-1 and 433,694.19 kg ha-1, respectively. The estimated average aboveground carbon stock in the sanctuary was approximately 245.55 tons ha-1, which falls in the range of well-stocked tropical forests in southwestern Nigeria. The study provides baseline information necessary for sustainable forest management, biodiversity conservation, and future carbon accounting initiatives.