Estimating Carbon Sequestration Rates on a Regional Scale

Abstract

Two regional case studies on carbon (C) sequestration rate for the forested land of Sweden are compared; one is based on direct measurements of the humus layer and the other a theoretical study based on calculable stable residue (limit-value approach). For both studies, the country was subdivided into grid cells and Kriging interpolation was used. In the first case study, Kriging was used to interpolate humus-layer thickness over 41 years, giving an increase all over the region which was positively related to temperature sum. Thickness of the humus layer was converted to amount of C using bulk density and in a next step to increase in humus-layer C. Over 41 years, the average rate for the country was 251 kg C ha⁻¹ year⁻¹. With just two dominant tree species, a comparison was made. In humus layers, Scots pine stands sequestered C at a higher rate than Norway spruce, whereas Norway spruce appears to sequester more in the mineral soil, which suggests different mechanisms for the two systems. The second case study was a theoretical one based on measured data. Actual evapotranspiration (AET) was used to estimate foliar litter fall for pine, spruce, and deciduous trees in 1 × 1 km grid cells. Estimated stable fractions were used to calculate the annual contribution of stable fraction (based on limit values), which corresponds to stable humus and a multiplication by 0.5 gave the sequestered amount of C.