Abstract

Carbon credits in Prosopis africana, Parkia biglobosa, Morinda lucida and Daniellia oliveri were investigated in Makurdi, Benue State, Nigeria over twelve months (November 2015 to October 2016) as losses through litter production. Litterfall rate and composition were measured using litter traps and quadrats on the floor, while carbon was determined as 50% of litter (dry weight). There were significant differences (p<0.01) in rates of litter production and composition (in trap and on the floor) across months and species. Mean total litterfall (g m^-2) was 36.98, with leaf litter contributing 17.20 (46.51%), wood litter 12.44 (33.64%) and miscellaneous litter 7.33 (19.82%), with bimodal peaks in January (94.89 ± 13.01) and July (43.28 ± 23.92) between P. africana (18.81 ± 20.49) and M. lucida (57.16). Plant height correlates negatively with litterfall (r = -0.699, R²= 0.489, p=0.001) and crown diameter (r =-0.611; R²=0.0373, p=0.004). P. biglobosa, and M. lucida have the highest litter turnover rates (2.01, 2.71), while residence times were generally ≤ 1 day in both seasons. Carbon stocks in plant litter (tones/ m^-2 y^-1) ranged between M. lucida (0.105, 0.062) and P. africana (0.035, 0.035). Species with higher litter production loose more carbon, while the fast loss of litter from the floor that less litter is available for biogeochemical sequestration of carbon and reduces productivity in the system.

Keywords: Carbon credits; Litter fall; Litter biomass; Turnover rate; Residence time; Prosopis africana; Parkia biglobosa; Morinda lucida; Daniellia oliveri; Makurdi