Above- and Belowground Carbon Stocks in a Miombo Woodland Landscape of Mozambique

Quantifying ecosystem carbon stocks is vital for understanding the relationship between changes in land use and carbon dioxide emissions. Here, we estimate carbon stocks in an area of miombo woodland in Mozambique, by identifying the major carbon stocks and their variability. Data on the biomass of tree stems and roots, saplings, and soil carbon stocks are reported and compared with other savannas systems around the globe. A new allometric relationship between stem diameter and tree stem and root biomass is presented, based on the destructive harvest of 29 trees. These allometrics are combined with an inventory of 12,733 trees on 58 plots over an area of 27 ha. Ecosystem carbon stocks totaled 110 tC/ha, with 76 tC/ha in the soil carbon pool (to 50 cm depth), 21.2 tC/ha in tree stem biomass, 8.5 tC/ha in tree coarse root biomass, and 3.6 tC/ha in total sapling biomass. Plot-level tree root:stem (R:S) ratio varied from 0.27 to 0.58, with a mean of 0.42, slightly higher than the mean reported for 18 other savanna sites with comparable aboveground biomass (R:S = 0.35). Tree biomass (stem + root) ranged from 3.1 to 86.5 tC/ha, but the mean (32.1 tC/ha) was well constrained (95% CI 28-36.6). In contrast, soil carbon stocks were almost uniformly distributed and varied from 32 to 133 tC/ha. Soil carbon stocks are thus the major uncertainty in the carbon storage of these woodlands. Soil texture explained 53 percent of the variation in soil carbon content, but only 13 percent of the variation in woody carbon stocks. The history of disturbance (fire, elephants, logging/charcoal production, and shifting cultivation) is likely to decouple changes in woody carbon stocks from soil carbon stocks, mediated by tree grass interactions.