Mediterranean silvopastoral systems provide a wide range of ecosystem services, among which soil C sequestration is one of the most relevant. Although the role of trees in enhancing soil C content of silvopastoral systems is widely recognized, the impacts of the tree cover on the overall soil C balance and hence the soil C sequestration rates are not clear enough to identify feasible options and effective management pathways. This study aimed to assess the effect of trees on soil C balance in a Mediterranean cork-oak silvopastoral system under contrasting cover classes. A three-year study was conducted in a Long-Term Observatory in Sardinia (Italy). A hierarchical design was used to test the tree effect (below and outside the tree crown projection) and the tree cover (high tree cover – from 39% to 42%; low tree cover – from 15% to 36%) on the soil C balance. The C balance was calculated as the difference between the C input from the herbaceous and tree components of the ecosystem and the C output from soil heterotrophic respiration. The position with respect to the tree stem influenced the C input, the C output, and the overall C balance. The tree class influenced only the C output and C balance. The annual C balance was higher (more gains) in low-covered areas below the tree crown projection (8.30 ± 0.72 Mg ha⁻¹ of C) than in open pasture and high-covered areas. At the field level, the overall weighted C balance was significantly influenced by tree cover; according to this last evidence, the maximum C balance was reached at about 24% tree cover. The results highlight the importance of management practices oriented to increase herbage production, tree cover, and regulating tree distribution, which in turn can provide ecosystem services such as SOC sequestration.

地中海林牧系统提供了广泛的生态系统服务，其中土壤碳封存是最相关的一种。虽然树木在提高林牧系统土壤碳含量方面的作用已得到广泛认可，但树木覆盖对整体土壤碳平衡的影响以及土壤碳固存率还不够明确，无法确定可行的选择和有效的管理途径。本研究旨在评估树木对地中海软木-橡树林牧系统在不同覆盖等级下土壤碳平衡的影响。在撒丁岛（意大利）的一个长期天文台进行了一项为期三年的研究。分层设计用于测试树木效应（树冠投影下方和外部）和树木覆盖率（高树覆盖率 - 从 39% 到 42%；低树木覆盖率——从 15% 到 36%）土壤碳平衡。碳平衡计算为生态系统草本和树木成分的碳输入与土壤异养呼吸的碳输出之间的差异。相对于树干的位置影响了 C 输入、C 输出和整体 C 平衡。树类仅影响 C 输出和 C 平衡。低于树冠预测 (8.30 ± 0.72 Mg ha 树类仅影响 C 输出和 C 平衡。低于树冠预测 (8.30 ± 0.72 Mg ha 树类仅影响 C 输出和 C 平衡。低于树冠预测 (8.30 ± 0.72 Mg ha^-1 of C) 比开放牧场和高覆盖区域。在田间水平上，整体加权碳平衡受树木覆盖率的显着影响；根据这最后的证据，在大约 24% 的树木覆盖率时达到了最大的碳平衡。结果强调了以增加牧草产量、树木覆盖和调节树木分布为导向的管理实践的重要性，这反过来又可以提供生态系统服务，如 SOC 封存。