Tree species diversity, volume yield, biomass and carbon sequestration in urban forests in two Nigerian cities

Urban forests contribute greatly to the conservation of biodiversity and are able to store carbon in the same way as other forest ecosystems. This research investigated the diversity, volume yield, biomass and carbon sequestration of tree species in urban forests in two Nigerian cities (Port Harcourt and Ilorin) selected using simple random sampling. In Nigeria there is no record of quantitative assessment of carbon sequestration in urban forests. Biodiversity and growth data were obtained from about 20% of the built-up areas of the two cities. Non-destructive approach was used for above ground biomass estimation. Biomass data was used to quantify carbon stock to estimate the amount of carbon sequestrated by the urban forests in the two cities. The results revealed a total of 746 individual trees distributed among 37 species and 19 families in Port Harcourt, while 556 individual trees distributed among 46 species and 18 families in Ilorin urban forest. Shannon-Wiener diversity index for Port Harcourt was 3.39 while that of Ilorin was 3.61. The total carbon stored by the urban forest of Port Harcourt was estimated at 67,979.08 tons and Ilorin urban forest carbon stored was estimated at 91,512.49 tons. The average carbon density of the urban forest of Port Harcourt was estimated at 136.15 tons/ha and 7.82 tons/ha was estimated for Ilorin urban forest. Tree species diversity has greater impact on biomass accumulation which determines carbon sequestration and mitigation of harsh climatic conditions. Selection and planting the right species as avenue trees, building parks and gardens, urban landscaping can improve urban forest carbon sequestration and producing other urban forest ecosystem functions.