Biomass estimations and carbon stock calculations in the oil palm plantations of African derived savannas using IKONOS data

This study developed biomass models to calculate carbon stock levels of the West African oil palms (Elaeis guineensis) using multi-date wet and dry season IKONOS images. Two benchmark areas of the derived savanna eco-regions of Africa were selected for analysis. Allometric equations related above-ground palm biomass to their stem heights. Empirical regression models based on field plot data were established to determine wet and dry biomass (kg m−2) of oil palm plantations in IKONOS images. The best models were exponential, involving bands 3, 3 and 1, or 3 and 4, and explaining between 63 and 72% of the variability in the data. Model evaluations with independent datasets showed there is 28-36% uncertainty in dry biomass predictions. At the landscape level, multi-date IKONOS data mapped oil palm plantations with an overall accuracy of 88-92%. However, the ability of IKONOS data to differentiate various age groups of oil palms was limited with a high degree of intermixing of classes. The best results were obtained when delineating agro-palm (palms mixed with agriculture and fallows), palm of 1-3 years, and palm of 4-5 years at an overall accuracy of 74.5% using all four IKONOS bands. The results indicate the need for additional spectral bands in the IKONOS sensor. The total carbon per unit area of oil palms was calculated across age groups for the two benchmark areas of West Africa and were 14.75 and 14.94 tonnes ha−1 (or Mg ha−1), respectively. The corresponding dry biomass (kg m−2) were 29.5 and 29.88 tonnes ha−1 (or Mg ha−1). The age of the oil palms were between 1 and 5 years across benchmark areas. The mean rate of accumulation of carbon was 2.95 t C ha−1 year−1 in benchmark area 1 and 2.99 t C ha−1 year−1 in benchmark area 2.