Using forest residues reduces soil carbon stock

These changes in soil carbon stocks are remarkable compared to the other greenhouse gas emissions caused by the use of forest residues for energy. On a national scale, soil carbon stocks play an important role in forest carbon balances.

Changes in soil carbon stock need to be assessed reliably and transparently because we need more information on the effects of climate change and forest management on soil carbon. This is also stressed by climate conventions which have set practical reporting requirements for changes in soil carbon stock. The large spatial variability of soil carbon goes together with relatively slow changes in stocks, which, in turn, hinders the assessment of soil carbon stocks and their changes by direct measurements. Models therefore widely serve to estimate carbon stocks and stock changes in soils.

A recent doctoral thesis developed and tested the soil carbon model YASSO for upland forest soils. The model was aimed to take into account the most important processes controlling the decomposition in soils, yet remain simple enough to ensure its practical applicability in different applications. The model was applied to study the effects of intensified biomass extraction on the forest carbon balance, to estimate the effects of soil carbon deficit on net greenhouse gas emissions of energy use of forest residues and to assess the national scale forest carbon balance for Finland’s forests.

YASSO managed to describe sufficiently the effects of both the variable litter and climatic conditions on decomposition. When combined with the stand models or other systems providing litter information, the dynamic approach of the model proved to be powerful for estimating changes in soil carbon stocks on different scales.