Laboratoire Évolution et Diversité Biologique, UMR 5174 (CNRS/IRD/UPS), 31062 Toulouse Cedex 9, France.
Institute of Ecology, College of Urban and Environmental Sciences, and Key Laboratory for Earth Surface Processes of the Ministry of Education, Peking University, Beijing 100871, China.
Proc Natl Acad Sci U S A. 2022 Sep 13;119(37):e2116626119. doi: 10.1073/pnas.2116626119. Epub 2022 Sep 6.
Intact tropical rainforests have been exposed to severe droughts in recent decades, which may threaten their integrity, their ability to sequester carbon, and their capacity to provide shelter for biodiversity. However, their response to droughts remains uncertain due to limited high-quality, long-term observations covering extensive areas. Here, we examined how the upper canopy of intact tropical rainforests has responded to drought events globally and during the past 3 decades. By developing a long pantropical time series (1992 to 2018) of monthly radar satellite observations, we show that repeated droughts caused a sustained decline in radar signal in 93%, 84%, and 88% of intact tropical rainforests in the Americas, Africa, and Asia, respectively. Sudden decreases in radar signal were detected around the 1997-1998, 2005, 2010, and 2015 droughts in tropical Americas; 1999-2000, 2004-2005, 2010-2011, and 2015 droughts in tropical Africa; and 1997-1998, 2006, and 2015 droughts in tropical Asia. Rainforests showed similar low resistance (the ability to maintain predrought condition when drought occurs) to severe droughts across continents, but American rainforests consistently showed the lowest resilience (the ability to return to predrought condition after the drought event). Moreover, while the resistance of intact tropical rainforests to drought is decreasing, albeit weakly in tropical Africa and Asia, forest resilience has not increased significantly. Our results therefore suggest the capacity of intact rainforests to withstand future droughts is limited. This has negative implications for climate change mitigation through forest-based climate solutions and the associated pledges made by countries under the Paris Agreement.
完整的热带雨林在最近几十年里已经经历了严重的干旱，这可能会威胁到它们的完整性、固碳能力和为生物多样性提供庇护的能力。然而，由于缺乏覆盖广泛地区的高质量、长期观测数据，它们对干旱的反应仍然不确定。在这里，我们研究了完整的热带雨林如何在全球范围内以及过去 30 年里对干旱事件做出反应。通过开发一个长期的泛热带时间序列（1992 年至 2018 年）的每月雷达卫星观测，我们表明，反复发生的干旱导致在美洲、非洲和亚洲的 93%、84%和 88%的完整热带雨林中，雷达信号持续下降。在 1997-1998 年、2005 年、2010 年和 2015 年的热带美洲干旱期间，以及在 1999-2000 年、2004-2005 年、2010-2011 年和 2015 年的热带非洲干旱期间，以及在 1997-1998 年、2006 年和 2015 年的热带亚洲干旱期间，都检测到雷达信号的突然下降。热带雨林对各大陆严重干旱的抵抗力（即在干旱发生时维持干旱前状态的能力）相似，但美洲的热带雨林始终表现出最低的恢复力（即在干旱事件后恢复到干旱前状态的能力）。此外，尽管在热带非洲和亚洲，完整的热带雨林对干旱的抵抗力在减弱，但恢复力并没有显著增加。因此，我们的研究结果表明，完整雨林抵御未来干旱的能力是有限的。这对通过基于森林的气候解决方案来缓解气候变化以及各国根据《巴黎协定》做出的相关承诺产生了负面影响。
