School of Geography, Earth and Environmental Sciences, University of Birmingham, B15 2TT Birmingham, United Kingdom;
Birmingham Institute of Forest Research, University of Birmingham, B15 2TT Birmingham, United Kingdom.
Proc Natl Acad Sci U S A. 2019 Mar 5;116(10):4382-4387. doi: 10.1073/pnas.1810512116. Epub 2019 Feb 19.
Although the existence of a large carbon sink in terrestrial ecosystems is well-established, the drivers of this sink remain uncertain. It has been suggested that perturbations to forest demography caused by past land-use change, management, and natural disturbances may be causing a large component of current carbon uptake. Here we use a global compilation of forest age observations, combined with a terrestrial biosphere model with explicit modeling of forest regrowth, to partition the global forest carbon sink between old-growth and regrowth stands over the period 1981-2010. For 2001-2010 we find a carbon sink of 0.85 (0.66-0.96) Pg year located in intact old-growth forest, primarily in the moist tropics and boreal Siberia, and 1.30 (1.03-1.96) Pg year located in stands regrowing after past disturbance. Approaching half of the sink in regrowth stands would have occurred from demographic changes alone, in the absence of other environmental changes. These age-constrained results show consistency with those simulated using an ensemble of demographically-enabled terrestrial biosphere models following an independent reconstruction of historical land use and management. We estimate that forests will accumulate an additional 69 (44-131) Pg C in live biomass from changes in demography alone if natural disturbances, wood harvest, and reforestation continue at rates comparable to those during 1981-2010. Our results confirm that it is not possible to understand the current global terrestrial carbon sink without accounting for the sizeable sink due to forest demography. They also imply that a large portion of the current terrestrial carbon sink is strictly transient in nature.
尽管陆地生态系统中存在大型碳汇这一事实已得到充分证实，但碳汇的驱动因素仍不确定。有人认为，过去土地利用变化、管理和自然干扰对森林动态的影响可能导致了当前碳吸收的很大一部分。在这里，我们利用全球森林年龄观测资料的汇编，结合具有明确森林再生建模功能的陆地生物圈模型，将 1981-2010 年期间全球森林碳汇分为成熟林和再生林两个部分。对于 2001-2010 年，我们发现，在完整的成熟林中存在一个 0.85（0.66-0.96）Pg 年的碳汇，主要位于湿润热带地区和西伯利亚北部地区，以及 1.30（1.03-1.96）Pg 年的碳汇位于过去干扰后再生的林分中。再生林中近一半的碳汇仅由于人口变化而产生，如果没有其他环境变化，这种情况就会发生。这些受年龄限制的结果与使用受人口统计数据驱动的陆地生物圈模型集合模拟的结果一致，这些模型是根据历史土地利用和管理的独立重建进行的。我们估计，如果自然干扰、木材采伐和重新造林的速度与 1981-2010 年期间的速度相当，那么仅通过人口统计数据的变化，森林将在活生物质中额外积累 69（44-131）Pg C。我们的研究结果证实，如果不考虑森林动态引起的大量碳汇，就不可能理解当前的全球陆地碳汇。这也意味着当前陆地碳汇的很大一部分在本质上是严格暂时的。
