Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå SE-901 83, Sweden.
International Institute for Applied Systems Analysis, Laxenburg A-2361, Austria.
Proc Natl Acad Sci U S A. 2024 Oct 15;121(42):e2401035121. doi: 10.1073/pnas.2401035121. Epub 2024 Oct 10.
Most measurements and models of forest carbon cycling neglect the carbon flux associated with the turnover of branch biomass, a physiological process quantified for other organs (fine roots, leaves, and stems). Synthesizing data from boreal, temperate, and tropical forests (184,815 trees), we found that including branch turnover increased empirical estimates of aboveground wood production by 16% (equivalent to 1.9 Pg Cy globally), of similar magnitude to the observed global forest carbon sinks. In addition, reallocating carbon to branch turnover in model simulations reduced stem wood biomass, a long-lasting carbon storage, by 7 to 17%. This prevailing neglect of branch turnover suggests widespread biases in carbon flux estimates across global datasets and model simulations. Branch litterfall, sometimes used as a proxy for branch turnover, ignores carbon lost from attached dead branches, underestimating branch C turnover by 38% in a pine forest. Modifications to field measurement protocols and existing models are needed to allow a more realistic partitioning of wood production and forest carbon storage.
大多数森林碳循环的测量和模型都忽略了与树枝生物量周转相关的碳通量，而其他器官（细根、叶子和茎）的碳通量已经被量化。通过综合分析来自北方森林、温带森林和热带森林的数据（184815 棵树），我们发现，包括树枝周转在内，可使地上木生产量的经验估计增加 16%（相当于全球 1.9PgC），与观察到的全球森林碳汇相当。此外，在模型模拟中将碳重新分配到树枝周转中，会使持久的碳储存——树干木材生物量减少 7%至 17%。这种普遍忽视树枝周转的现象表明，在全球数据集和模型模拟中，碳通量估计存在广泛的偏差。树枝凋落物，有时被用作树枝周转的替代物，但它忽略了附着在死树枝上的碳损失，在松树林中，这种方法会导致对树枝 C 周转的低估，幅度达到 38%。需要对现场测量方案和现有模型进行修改，以便更真实地划分木材生产和森林碳储存。
