Soil organic carbon stock assessment in forest ecosystems through pedogenic horizons and fixed depth layers sampling: What's the best one?

In soil organic carbon (SOC) survey, the role of sampling approach is crucial andshould not be underestimated. In this sense, the appropriateness of soil sampling bypedogenic horizons (PGH) and fixed depth layers (FDL) in forest is still a field ofdebate. The present work aimed to: (a) study the spatial variability of SOC concentra-tions and C stocks through PGH and FDL samplings in uneven-aged sweet chestnut,European beech and Norway spruce forests of the Apennine chain (Italy); (b) clarifythe major advantages and drawbacks of sampling by PGH and FDL. In a representa-tive area (1818 m) of each forest, a soil profile was investigated and eight addi-tional sampling points were selected. The sampling was performed both by PGH andFDL (0–15 and 15–30 cm). For each forest, no SOC content and C stock differencesin 0–30 cm soil depth were found between PGH (58.8 ± 5.3 g kg1and 103±7gha1, respectively) and FDL (52.7 ± 4.3 g kg1and 117 ± 9 Mg ha1, respec-tively) sampling. However, under Norway spruce, PGH sampling pointed-out that Cwas mainly stored in Oe and Oa horizons (51.1 vs. 146 Mg ha1in the 0–30 cmlayer). The higher coefficient of variation obtained when soil horizons were consid-ered (from 19.2% to 72.8% for PGH and from 16.5% to 25.7% for FDL) suggestedthat PGH sampling preserved the information about the spatial variability within anecosystem. The information loss about SOC vertical and spatial distribution wouldindicate the inability of FDL sampling to support decision-making plans addressed forsustainable use of soil resource