Climate warming impact on the carbon balance in forest soils in Russia

The carbon balance in forest soils (CBFS) was studied on the basis of the geostatistical process model “BIGIN” (Biosphere Greenhousegas Inventory). Warming in boreal forests in the baseline period (1990 ± 5 yr.) initiates a shift in the CBFS towards its decrease, i. e. CO2 source. In the horizon “O”, the decrease in the CBFS is minus 101.4 MtC. The warming of the climate by 1.5 °C and 3 °C will cause a further decrease in the CBFS by 345.7 MtC and 691.4 MtC, respectively. In moderately warm forests, climate warming initiates the formation of a positive CBFS, i. e. CO2 sink. In the horizon “O” of the soils of moderately warm forests, climate warming in the baseline period and in the future leads to the development of positive CBFS, i. e. CO2 sink of 62.4 MtC, 212.8 MtC and 425.4 MtC, respectively. Positive changes in the CBFS in boreal and moderately warm forests in the studied range of climatic temperatures were noted in the horizon “A1” (7.3 MtC, 24.9 MtC and 49.8 MtC) and the horizon “Bh” (14.1 MtC, 48.0 MtC, 96.2 MtC). Climate warming initiates a total negative CBFS (minus 17.6 MtC). Further warming of the climate by 1.5 °C and 3.0 °C will lead to a decrease in the CBFS by minus 60.0 MtC and minus 120.0 MtC. In terms of CO2-equivalent, this will amount to 4%, 13% and 27% of the total country annual emission in 2020. Negative CBFS is not an indicator of emission strengthening. The final conclusion about CO2 source/sink can be made only when analyzing the forest ecosystem when conducting a coupled soil-stand analysis. The error in the estimation of the CBFS in the soil organic profile in the baseline period is ± 23.0 MtC at a confidence level of P = 0.67 and ± 47 MtC at a confidence level of P = 0.95. With an increase in temperature by 1.5 °C, the error will be ± 80.0 MtC and ± 160.0 MtC at confidence levels of P = 0.67 and P = 0.95 respectively. The magnitude of the error will be ± 160.0 MtC and ± 320.0 MtC at confidence levels P = 0.67 and P = 0.95 respectively with an increase in temperature by 3.0 °C.