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Forest soil respiration (Rs) plays an important role in the carbon balance of terrestrial ecosystems. China's forest occupies a large part of the world's forest. However, due to the lack of integrated observation data and appropriate upscaling methodologies, substantial uncertainties exist in the Rs evaluation, which limits our understanding of the carbon balance. Here, we re‐evaluated the total soil carbon effluxes across China by combining field observations from 634 published annual Rs with a machine learning technique (i.e., Random Forest (RF)). Our results revealed that the combination of systematic measurements with the RF model allowed a definite estimate. The average annual Rs was 776.9 g C m−2 yr−1, ranging from 411.5 to 1,770.7 g C m−2 yr−1. Total forest soil carbon effluxes amounted to 1.17 Pg C yr−1 in China. Geographically, annual Rs showed a clear spatially increasing trend from northeast to southwest. Forest type is an important factor in determining the soil respiration rate. Bamboo and Evergreen broadleaf forests were higher than other types of forests. These results provide a unique insight into the magnitudes and mechanisms of soil CO2 emissions in China's forest ecosystems. Plain Language Summary: Soil respiration refers to the soil‐to‐atmosphere flux of CO2, primarily generated by root and microbial respiration. Accurate assessment of forest soil respiration in China is a significant part of global‐scale carbon cycles. However, due to the lack of integrated observation data and appropriate upscaling methodologies, substantial uncertainties exist in soil respiration evaluation. Here, we assembled a new database and used a random forest approach to re‐explore the total forest soil respiration and obtained reliable annual forest soil carbon efflux in China. These results contribute to a better understanding and quantification of the national and global carbon cycle. Key Points: The combination of systematic measurements with the random forest model allowed a definite estimateTotal forest soil carbon effluxes amounted to 1.17 Pg C yr−1 in ChinaForest type is an important factor in determining the soil respiration rate [ABSTRACT FROM AUTHOR]

Abstract The boreal larch forest of Eurasia is a widespread forest ecosystem and plays an important role in the carbon budget of boreal forests. However, few carbon budgets exist for these forests, and the effects of wildfire, the dominant natural disturbance in this region, on carbon budgets are poorly understood. The objective of this study was to quantify the effects of wildfire on carbon distribution and net primary production (NPP) for three major Dahurian larch (Larix gmelinii Rupr.) forest ecosystems in Tahe, Daxing'anling, north-eastern China: Larix gmelinii–Ledum palustre, Larix gmelinii–grass and Larix gmelinii–Rhododendron dahurica forests. The experimental design included mature forests (unburned), and lightly and heavily burned forests from the 1.3-million-ha 1987 wildfire. We measured carbon distribution and above-ground NPP, and estimated fine root production from literature values. Total ecosystem carbon content for the mature forests was greatest for Larix–Ledum forests (251.4 t C ha-1) and smallest for Larix–grass forests (123.8 t C ha-1). Larix–Ledum forests contained the smallest vegetation carbon (13.5%), while Larix–Rhododendron contained the largest vegetation carbon (63.1%). Fires tended to transfer carbon from vegetation to detritus and soil. Total NPP did not differ significantly between the lightly burned and unburned stands, and averaged 1.58, 1.29 and 1.01 t C ha-1 year-1 for Larix–grass, Larix–Rhododendron and Larix–Ledum lightly burned stands, respectively. Above-ground net primary production (ANPP) of heavily burned stands was 92–95% less than unburned and lightly burned stands. The estimated carbon loss during the 1987 fire showed substantial variability among forest types and fire severity levels. Depending upon the assumptions made about the fraction of the landscape occupied by the three larch forest types,... [ABSTRACT FROM AUTHOR]