Underestimation of boreal forest soil carbon stocks related to soil classification and drainage

Soil organic carbon (C), accumulated over millennia, comprise more than half the C stored in boreal and temperate forest landscapes. We used the Norwegian forest inventory- and soil survey network (n=719, no deep organic soils) to explore the validity of a deterministic model representation of this pool (Yasso07). We statistically compared simulated and measured soil C stocks and related differences (measured â simulated) to site factors (drainage, topography, climate, vegetation, C:N ratio and soil classification). Median C stocks (kg C m-2) were 5.0 (model) and 14.5 (measurements). Soil C differences related to site factors (r2: 0.16 â 0.37). For Brunisols, Gleysols and wet Organic soils, differences related primarily to topographic wetness. For Regosols, Podzols and Dystric Eluviated Brunisols, they related to climate, profile depth, and, in some cases, drainage class and site index. We argue that soil moisture regimes in our study area overrule tree productivity effects in the determination of soil C stocks and present conditions for soil formation that the model cannot (and does not explicitly) account for. These are processes such as humification and podsolization that involve eluviation and illuviation of DOC with sesquioxides to form spodic B-horizons and carbon enrichment due to hampered decomposition in frequently anoxic conditions.

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