Approaches for Carbon Budget Analyses of the Siberian Forests

This report carried out by Timo Karjalainen and Jari Liski is a contribution to the analyses of carbon balances of the Siberian forests. The report contains two inter-linked sections. The aim of the first section was to develop a method to assess carbon budget for tree biomass at ecoregional level in Siberia. Tree biomass carbon budgets contain estimates on the initial amounts of carbon in the whole tree biomass, as well as its dynamics. The calculation method developed based on the structure of the Russian forest database at IIASA and available models describing tree growth and biomass allocation in Siberia. Calculated litter production is used as input for separate calculations on the soil organic matter carbon budget (Liski, 1997). Stand level analyses showed that the developed method describes vegetation carbon budget in a plausible manner. The stand level analyses are the platform for regional assessments. There are, however, several matters that should be taken into account in the regional assessments. These relate to stand structure, description of stand replacing disturbances, and availability of data. In the second section, different models describing the dynamics of organic C in forest soils were developed and then compared. The model judged to describe the dynamics of soil C in the most realistic way contains five compartments for different litter and three for soil organic matter (the so called soil C model). Temperature was considered the most important climatic factor that regulates the decomposition in boreal forests. The effective temperature sum with a +5 degree C threshold was chosen to describe the temperature impact on the decomposition. The application of the developed models was tested on the issues of impacts of species, harvesting intervals and harvesting residues left on the site. For a full-scale application of the developed soil carbon models for Siberia and Russia, the special features of permafrost soils and peatlands need to be added to the models.