Typical soil organic carbon (SOC) measurements do not account for the higher SOC concentration adjacent to, inside and under the trunks of large trees, or for the root volume which displaces soil and thereby reduces spatial density of SOC. Any net difference between these two omissions could have a significant impact on carbon accounts for the conversion of a primary forest with large trees to a type of land cover with much smaller trees, or no trees, such as to a secondary forest on short harvest cycles, or to deforested land, respectively. To improve knowledge of carbon stocks in primary forests, for better carbon management and climate change modelling, we sampled SOC and soil bulk density directly under large tree trunks, inside tree trunks, in the humus mounds in the buttress region, and under the humus mounds. The measurements were in primary Eucalyptus regnans mixed-forest. SOC was formulated as a function of depth. Adjacent to the trees, 90% of the total cumulative SOC was estimated to be within ~2.6 m of the mineral soil surface. That SOC was compared with an earlier measurement in the same locality of SOC in-between trees, away from the trunk and buttress. The SOC under large tree trunks was about four times more concentrated than in-between trees. Formulae that link SOC, root volume, and buttress shape, to tree diameter and ground slope were applied to forest stands within 54.4 ha of primary forest. When the under-trunk SOC was tallied with the organic soils associated with the buttress region and in nearly decomposed logs, SOC at the unit-area-level increased by ~7% [95% CI: 3–12%] relative to the in-between-tree SOC alone, and the absolute increase was 21 Mg ha-1 [95% CI: 10–37 Mg ha-1] of SOC. Our results suggest that, at least for land use change that fells mature trees >1 m in diameter, there may have been higher greenhouse gas emissions from past forest attrition than have been inferred. Globally, we identified 50 example tree species, other than E. regnans, that may also have extra SOC at the stand-level in the absence of fire. Additional SOC per hectare was positively correlated with basal area of trees, which increases with the number of large trees in a stand. The maintenance of large trees will help ensure higher levels of forest carbon. The protection of medium-sized trees will be necessary to ensure existence of large trees in the future.

中文翻译：

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大树下被忽视的土壤碳

典型的土壤有机碳 (SOC) 测量未考虑大树树干附近、内部和下方的较高 SOC 浓度，或取代土壤从而降低 SOC 空间密度的根体积。这两个遗漏之间的任何净差异都可能对碳账户产生重大影响，因为将拥有大树的原始林转变为拥有小得多的树木或没有树木的土地覆盖类型，例如在较短的收获周期中转变为次生林，或分别到森林砍伐的土地。为了提高对原始森林碳储量的了解，为了更好的碳管理和气候变化建模，我们直接在大树干下、树干内部、扶壁区的腐殖土丘和腐殖土丘下对 SOC 和土壤容重进行了采样. 测量是在原始的 Eucalyptus regnans 混交林中进行的。SOC 被公式化为深度的函数。在树木附近，总累积 SOC 的 90% 估计在矿质土壤表面约 2.6 m 内。将该 SOC 与树之间同一位置的 SOC 较早测量值进行比较，远离树干和扶壁。大树干下的 SOC 浓度大约是中间树木的四倍。将 SOC、根体积和支柱形状与树木直径和地面坡度联系起来的公式适用于原始林 54.4 公顷内的林分。当树干下的 SOC 与与扶壁区域相关的有机土壤和几乎分解的原木相一致时，单位面积水平的 SOC 相对于中增加了约 7% [95% CI: 3–12%] -仅在树之间的 SOC，SOC 的绝对增加为 21 Mg ha-1 [95% CI：10-37 Mg ha-1]。我们的结果表明，至少对于砍伐直径大于 1 m 的成熟树木的土地利用变化，过去森林损耗造成的温室气体排放可能比推断的要高。在全球范围内，我们确定了 50 种示例树种，除 E. regnans 外，在没有火灾的情况下，这些树种在林分水平上也可能具有额外的 SOC。每公顷额外的 SOC 与树木的基面积呈正相关，随着大树数量的增加而增加。维护大树将有助于确保更高水平的森林碳。中型树木的保护将是确保未来大树存在的必要条件。至少对于砍伐直径大于 1 m 的成熟树木的土地利用变化而言，过去森林损耗造成的温室气体排放量可能比推断的要高。在全球范围内，我们确定了 50 种示例树种，除 E. regnans 外，在没有火灾的情况下，这些树种在林分水平上也可能具有额外的 SOC。每公顷额外的 SOC 与树木的基面积呈正相关，随着大树数量的增加而增加。维护大树将有助于确保更高水平的森林碳。中型树木的保护将是确保未来大树存在的必要条件。至少对于砍伐直径大于 1 m 的成熟树木的土地利用变化而言，过去森林损耗造成的温室气体排放量可能比推断的要高。在全球范围内，我们确定了 50 种示例树种，除 E. regnans 外，在没有火灾的情况下，这些树种在林分水平上也可能具有额外的 SOC。每公顷额外的 SOC 与树木的基面积呈正相关，随着大树数量的增加而增加。维护大树将有助于确保更高水平的森林碳。中型树木的保护将是确保未来大树存在的必要条件。在没有火灾的情况下，也可能有额外的 SOC。每公顷额外的 SOC 与树木的基面积呈正相关，随着大树数量的增加而增加。维护大树将有助于确保更高水平的森林碳。中型树木的保护将是确保未来大树存在的必要条件。在没有火灾的情况下，也可能有额外的 SOC。每公顷额外的 SOC 与树木的基面积呈正相关，随着大树数量的增加而增加。维护大树将有助于确保更高水平的森林碳。中型树木的保护将是确保未来大树存在的必要条件。