Assessment of Carbon Sequestration in Borgu Sector of Kainji Lake National Park, North-Central Nigeria

Abstract

Trees species-based carbon-stock estimates are rare in Nigeria. Therefore, we investigated individual trees’ abilities using non-destructive approach with systematic sampling technique. One hundred circular plots were laid, using pre-classified Landsat-OLI/TC image of Borgu Sector. Plot centres were located and marked with global positioning system receiver. The main plots with 12.61 m radius (500 m2 ) were subdivided into subplots of 5.64 m radius (100 m2 ). Trees with diameter at breast height (Dbh) ≥10 cm were measured in the main plots, while trees with ≥5 but <10 cm Dbh were considered in the subplots. Species identification and measurements were executed. Core samples were collected at breast height using 5 mm increment borer. Core samples were oven-dried at 70°C to constant weights. Wood densities were then calculated as oven-dried weights/fresh volumes. Above-ground carbon were determined as 50%-biomass. Soil samples were diagonally collected at three points within sample plots at two depths, using core sampler and soil auger for 600 samples. Samples were air-dried, ground and sieved through a 2 mm sieve. Core sampler and rings were used for measuring bulk density. Samples were oven-dried for 24 hours at 105°C. Soil organic matter was determined by Fe2SO4 titration of an acid-dichromate digestion, and organic carbon concentration was calculated. Tree carbon data were analyzed using allometric equations involving wood density, Dbh and tree-height and ANOVA. Thirty-five tree species in 16 families were encountered. Detarium microcarpum was the most frequently occurring (18.8%). Tree species richness, diversity and importance value indices were 2.852, 4.779, and 41.76 ± 35.41, respectively. Vitellaria paradoxa and Afzelia africana were the only vulnerable species identified. Trees with larger-Dbh sequestered more carbon. Consequently, Adansonia digitata with a mean Dbh of 111.4 ± 0.00 cm sequestered the highest amount (2.8 tons/ha), which were significantly different from others (p < .05). Securidaca longipendiculata had the least carbon stock (0.001 ton/ha). Meanwhile, soil carbon were higher in plots dominated by Acacia kosiensis, V. paradoxa, and Grewia mollis at 0.006758 ton/ha, averagely 0.073 ± 0.0021 ton/ha of carbon-stock and CO2 of 0.271 ± 0.010 ton/ha sequestered, respectively.