The calculation of changes in forest carbon stock, or the forest carbon sink, is based on annual growth (increment) and removals due to harvesting (drain). The calculation follows IPCC guidelines and relies on data provided by UPM, including annual stem volumes, growth data, land area datasets, and harvesting volumes.
Volume is converted into biomass using species-specific densities and biomass expansion factors (BEF) (Hirigoyen et al., 2021). The carbon content of biomass is assumed to be 50%, and carbon is converted to carbon dioxide using the factor 44/12.
In the Increment-Drain method, tree growth (increment) is calculated using annual volume growth and BEF factors, including the bark portion of the tree. Forest removal (drain) is determined based on harvesting data. The net carbon sink, representing the annual change in forest carbon stock, is obtained as the difference between growth and removals. The calculation includes cultivated eucalyptus species Eucalyptus dunnii and Eucalyptus grandis.
Changes in soil carbon stock are calculated using the dynamic Yasso07 soil model (Tuomi et al. 2011, Finnish Meteorological Institute), which simulates carbon decomposition and changes up to a depth of 1 meter. The modeling is based on the amount and quality of litter input, as well as local weather conditions. The methodology is continuously developed in collaboration with the Natural Resources Institute Finland (LUKE).
Litter input is estimated plot-specifically for the entire rotation period of the forest stand. The tree volume of previous rotations is calculated based on UPM's growth models, and the plantation's rotation period is assumed to be 11 years. Litter input is estimated for different tree parts (trunk, leaves, branches, roots) using species-specific and general conversion factors.
Daily temperature and precipitation data are obtained from meteorological stations across Uruguay, maintained by INIA (National Agricultural Research Institute of Uruguay).
Both tree and soil calculations are carried out separately for eucalyptus plantations owned and leased by UPM. The annual carbon sink is reported as the sum of plot-specific carbon sink values, considering both growth and the impact of harvesting on forest carbon stock.
Literature references:
Hirigoyen, A., Resquin, F., Navarro-Cerrillo, R., Franco, J., & Rachid-Casnati, C. (2021). Stand biomass estimation methods for Eucalyptus grandis and Eucalyptus dunnii in Uruguay. BOSQUE, 42(1), 53–66. https://doi.org/10.4067/S0717-92002021000100053
IPCC guidelines Volume 4: https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol4.html
Tuomi, M., Laiho, R., Repo, A., & Liski. J. 2011. Wood decomposition model for boreal forests. Ecological Modelling 222 (3): 709-718. doi:10.1016/j.ecolmodel.2010.10.025
