Assessment and Mapping of Soil Organic Carbon Stocks in Boreal Montane Forest Permafrost Region: A Case Study of Northeastern China

Permafrost carbon pool stability is threatened by climate warming. Challenges in evaluating the carbon storage potential of boreal montane forest permafrost regions include the lack of understanding of the control mechanisms of soil organic carbon (SOC) stocks change and of timely, spatially explicit estimates. The SOC stocks in typical montane forests within the permafrost regions of Northeast China were investigated in 2023. Partial least squares structural equation modeling (PLS-SEM) was employed to quantify the effects of topography, climate, vegetation physiological phenology, C input, permafrost conditions, and soil environment on SOC stocks, and a spatial distribution map of SOC stocks in the 0–30 cm soil layer was generated. The results indicate that topography regulates C input through three distinct pathways by shaping the climate: directly, and indirectly via the permafrost environment and plant physiology and phenology, thereby driving the spatial pattern of SOC stocks. C input exerted the strongest influence on SOC stocks across all soil layers, with its effect gradually weakening with increasing depth. It is concluded that depth-specific environmental factors must be considered in SOC dynamics assessment. The mean SOC stocks in the 0–30 cm soil layer was estimated to be approximately 9.37 kg/m². High SOC stocks values were consistently concentrated along river margins across all soil layers. In this work, we also demonstrated that spatially explicit estimates of SOC stocks based on timely investigations are important for assessing C storage against the background of considerable environmental changes across the boreal montane forest permafrost regions.