Data from: Ecosystem carbon density and allocation across a chronosequence of longleaf pine forests

Forests can partially offset greenhouse gas emissions and contribute to climate change mitigation, mainly through increases in live biomass. We quantified carbon (C) density in 20 managed longleaf pine (Pinus palustris Mill.) forests ranging in age from five to 118 years located across the southeastern USA and estimated above and belowground C trajectories. Ecosystem C stock (all pools including soil C) and aboveground live tree C increased nonlinearly with stand age and the modeled asymptotic maxima were 168 Mg C/ha and 80 Mg C/ha, respectively. Accumulation of ecosystem C with stand age was driven mainly by increases in aboveground live tree C, which ranged from <1 Mg C/ha to 74 Mg C/ha and comprised <1% to 39% of ecosystem C. Live root C (sum of below-stump C, ground penetrating radar measurement of lateral root C, and live fine root C) increased with stand age and represented 4% to 22% of ecosystem C. Soil C was related to site index, but not to stand age, and comprised 39% to 92% of ecosystem C. Live understory C, forest floor C, down dead wood C and standing dead wood C were small fractions of ecosystem C in these frequently burned stands. Stand age and site index accounted for 76% of the variation in ecosystem C among stands. The mean root to shoot ratio calculated as the average across all stands (excluding the grass stage stand) was 0.54 (standard deviation of 0.19) and higher than reports for other conifers. Long-term accumulation of live tree C, combined with the larger role of belowground accumulation of lateral root C than in other forest types, indicates a role of longleaf pine forests in providing disturbance-resistant C storage that can balance the more rapid C accumulation and C removal associated with more intensively managed forests. Although other managed southern pine systems sequester more C over the short-term, we suggest that longleaf pine forests can play a meaningful role in regional forest C management.

森林可通过提升活生物量的方式，部分抵消温室气体排放并助力气候变化减缓（climate change mitigation）。本研究对分布于美国东南部的20个经营型长叶松（longleaf pine，*Pinus palustris* Mill.）林分进行了碳密度量化分析，这些林分的林龄介于5至118年之间；同时估算了地上与地下碳动态轨迹。生态系统碳储量（涵盖包括土壤碳在内的所有碳库）与地上活立木碳储量均随林分年龄呈非线性增长，模型拟合得到的渐近最大值分别为168 Mg C/ha与80 Mg C/ha。生态系统碳储量随林分年龄的积累主要由地上活立木碳储量的增长驱动：地上活立木碳储量介于<1 Mg C/ha至74 Mg C/ha之间，占生态系统碳储量的比例为<1%至39%。活根碳（为伐桩下碳、探地雷达（ground penetrating radar）测定的侧根碳与活细根碳的总和）随林分年龄增长而增加，占生态系统碳储量的4%至22%。土壤碳与立地指数（site index）相关，但与林分年龄无关，其占生态系统碳储量的比例为39%至92%。在这些高频火烧经营林分中，活林下植被碳、枯落物层碳、倒木碳与立枯木碳仅占生态系统碳储量的极小份额。林分年龄与立地指数可解释样地间生态系统碳储量76%的变异量。所有样地（排除草本幼龄阶段林分）的平均根冠比（root to shoot ratio）为0.54，标准差（standard deviation）为0.19，高于其他针叶树的相关研究报道值。活立木碳的长期积累，加上侧根碳地下积累相较于其他林型更为显著的特征，表明长叶松林可提供抗干扰碳储存（disturbance-resistant C storage），该储存方式能够平衡高强度经营森林伴随的更快碳积累与碳移除过程。尽管其他经营型南方松林系统在短期内可固存更多碳，但本研究认为长叶松林在区域森林碳管理中可发挥重要作用。