Effect of initial pools on carbon balance calculations – a case of larch plantations in northeastern China

<jats:p>Abstract. Carbon dioxide (CO2) released during the decomposition of harvest residues reduces the net carbon sequestration of stands planted on clear-felled sites. All other dead organic materials (DOM) present in the stand, such as litter and dead trees, also decompose and release CO2 into the atmosphere. Carbon is also released when discarded wood products made from previously harvested wood decay. Carbon sequestration is overestimated, especially in young stands, if the CO2 released from DOM and discarded wood products is ignored in calculations. This study developed models to predict the biomass of DOM pools in the stand and the remaining biomass of products made from previously harvested wood. Initializing these biomass pools with the models and simulating DOM decomposition and product disposal helps eliminate overestimates in the carbon sink calculations for young plantations. When these models were integrated into simulation software, it showed that a young larch stand planted on a clear-felled site acts as a carbon source for about 10 years. Thinning treatments convert the stand into a carbon source for 3–7 years. Optimization with carbon subsidies and taxes indicated that higher CO2 prices extend the optimal rotation length and increase the average carbon stock of the rotation. However, carbon pricing never turned the stand into a permanent carbon sink. Carbon sequestration in Chinese plantation forests can be improved by reducing thinning and increasing rotation lengths. The positive effects last as long as it takes to adopt the revised management practices across all forests.</jats:p>