School of Geography, University of Leeds, Leeds, UK.
Service of Wood Biology, Royal Museum for Central Africa, Tervuren, Belgium.
Nature. 2020 Mar;579(7797):80-87. doi: 10.1038/s41586-020-2035-0. Epub 2020 Mar 4.
Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions. Climate-driven vegetation models typically predict that this tropical forest 'carbon sink' will continue for decades. Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53-0.79), in contrast to the long-term decline in Amazonian forests. Therefore the carbon sink responses of Earth's two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature. Despite the past stability of the African carbon sink, our most intensively monitored plots suggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth's intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth's climate.
结构完整的热带森林在 1990 年代和 21 世纪初吸收了全球陆地碳吸收量的一半左右，去除了约 15%的人为二氧化碳排放。受气候驱动的植被模型通常预测，这种热带森林“碳汇”将持续数十年。在这里，我们使用跨越 11 个国家的 244 个结构完整的非洲热带森林来评估碳汇的趋势，将其与来自亚马逊地区的 321 个已发表的样地进行比较，并研究趋势的潜在驱动因素。在 1990 年代至 2015 年的三十年中，完整的非洲热带森林中活地上生物量的碳汇一直保持稳定，为每年每公顷 0.66 吨碳（95%置信区间为 0.53-0.79），与亚马逊森林的长期下降形成对比。因此，地球两个最大的热带森林的碳汇反应已经出现分歧。这种差异主要是由于树木死亡导致的碳损失造成的，在非洲没有检测到多十年的趋势，而在亚马逊地区则长期增加。两个大陆都显示出树木生长的增加，这与大气二氧化碳和空气温度升高的预期净效应一致。尽管非洲碳汇过去一直保持稳定，但我们监测最密集的样地表明，自 2010 年以来，碳损失有所增加，与亚马逊相比有所延迟，表明两个大陆的碳汇饱和存在异步。一个包括二氧化碳、温度、干旱和森林动态的统计模型解释了观察到的趋势，并表明非洲汇的长期未来下降，而亚马逊汇继续迅速减弱。总体而言，地球完整热带森林对碳的吸收在 1990 年代达到峰值。考虑到全球陆地碳汇的规模正在增加，独立的观测结果表明，北半球陆地上最近的碳吸收量有所增加，这进一步证实了我们的结论，即完整的热带森林碳汇已经达到峰值。热带森林碳汇的这种饱和和持续下降对旨在稳定地球气候的政策产生了影响。
