Carbon and Nitrogen Turnover Times of South Korean Forests Estimated via Data-Model Fusion

Biogeochemical models use estimates of carbon (C) and nitrogen (N) turnover times for the future projection of global forest C and N stocks, but unexplained variation in the C and N turnover times is causing considerable uncertainty. This study aimed to estimate C and N turnover times of South Korean forests and explain their variation with forest type, temperature, precipitation, stand age, and ecosystem C:N ratio. We used the balance method and data-model fusion to estimate the C and N turnover times. Data-model fusion was used to integrate the National Forest Inventory data (2011–2020) with a biogeochemical model, Forest Biomass and Dead organic matter Carbon and Nitrogen (FBD-CAN). The N turnover time (376–499 years) was ∼45 times longer than the C turnover time (9–10 years). Forest type had no substantial effects on the C and N turnover times. However, the C and N turnover times were positively correlated with stand age and ecosystem C:N ratio, and negatively correlated with temperature. Overall, ecosystem C:N ratio, stand age, temperature, and precipitation explained 45%, 15%, 12%, and 3%, respectively, of the total variation of the C and N turnover times. These results contribute to the understanding and prediction of forest C and N changes in a changing world and highlight the importance of considering C:N ratio for reliable estimation of the C and N turnover times.