Investigating Carbon Storage and Sequestration Potential of Urban Forest Patches in Nigerian State Capitals

This study investigates the carbon storage capacity and sequestration potential of urban forest patches in five Nigerian state capitals representing different geopolitical zones: Abuja (North Central), Kano (North West), Enugu (South East), Ibadan (South West), and Port Harcourt (South South). Urban forests in Nigerian cities constitute an undervalued carbon sink, and their quantification contributes to national greenhouse gas inventory accuracy and supports the case for urban greening in climate change mitigation policy. Vegetation surveys were conducted at thirty urban forest patches across the five cities, using standard forest plot methods to measure tree density, diameter at breast height, height, and species composition. Above-ground biomass was estimated using allometric equations validated for tropical African species. Below-ground biomass was estimated using the root-to-shoot ratio. Soil organic carbon was measured from core samples to 30 centimetres depth at a subset of sites. Carbon sequestration rates were estimated from repeat measurement plots combined with growth rate data from species-specific literature. Results show wide variation in carbon stocks across urban forest types, with denser forest patches in Enugu and Port Harcourt containing up to three times the carbon stock per hectare of more fragmented patches in Kano and Abuja. Estimated carbon sequestration rates average 2.1 tonnes of carbon dioxide per hectare per year across sampled patches. Aggregate urban forest carbon stocks across the five cities are estimated at 126,000 tonnes of carbon dioxide equivalent. The study recommends incorporating urban forest carbon stocks into Nigeria's greenhouse gas national inventory calculations. Keywords: urban forest, carbon sequestration, greenhouse gas, Nigerian cities, biomass.