BIOMASS AND CARBON STOCK ASSESSMENT IN OKOMU NATIONAL PARK, EDO STATE, NIGERIA.

Abstract

Natural forests store large quantity of carbon, and at present there is great interest in assessing that quantity correctly. The natural forests in National Parks and Game Reserves are particularly important, not only because they provide habitat and food to wildlife but also because of their long term roles in carbon sequestration. In this study, biomass and carbon stock assessment was carried out for Okomu National Park. Using systematic line transects, 14 nested plots were laid. Each main plot was 50 m x 50 m in size. Within each main plot, subplots of 20 m x 20 m and 10 m x 10 m in size were established. All trees with diameter at breast height (dbh) of 20 cm and above were enumerated. A sub plot of 20 m x 20 m was laid where trees with dbh of 10 cm to 20 cm were enumerated. Within the subplot a sub-sub plot of 10 m x 10 m was also laid where the lower vegetation were counted and identified. Moreso 1 m x 1 m sub-sub-sub plot was laid at the relatively undisturbed corner of the plot for the collection of litter samples in Okomu National Park. Enumeration includes tree identification and measurement of tree growth data. In addition, tree core samples were collected from diametrically opposed positions at breast height. Both fresh weight and dry weight of the core samples were taken while volumes of the core samples were estimated using analytical method. Volume, wood density, biomass and carbon stock were estimated for all the tree species per hectare and for the entire National Park. The data was analysed using descriptive statistics and regression analysis. The results indicate that the most prominent timber species in the 50 m x 50 m plots are Terminalia ivorensis and Celtis biondii with Nine tree species per hectare, in the sub-plots of 20 m x 20 m the most prominent species is Trichilia monadelpha with 27 tree species per hectare, likewise within the 10 m x 10 m sub-sub plots the most prominent timber species is Rinorea dentata with 2,714 tree species per hectare. Diameter distribution of the trees typifies natural forest stand structure with more trees at the lower diameter classes. A total number of 33 dead standing trees were encountered in all the enumerated plots while a total number of 62 trees were fallen dead trees encountered in all the plots. The mean biomass and carbon stock for the standing dead trees is (421.81 kg and 210.90 kg) while the mean biomass and carbon stock for the fallen dead trees is (450.42 kg and 225.21 kg). The total biomass per hectare estimate in the National Park is 756.11 t/ha while the total carbon stock per hectare is 378.05 t/ha. The mean biomass per hectare is 54.01 t/ha with the confidence limit of 18.53 (lower limit) and 89.48 (upper limit) while the mean carbon stock per hectare is 27.00 with a confidence limit of 9.27 (lower limit) and 44.74 (upper limit). The results suggest that the National Park is a huge reservoir of carbon with great potential to contribute to climate change mitigation.