Droughts cause extreme anomalies in tropical forest growth, but the direction and magnitude of tropical forests in response to droughts are still widely debated. Here, we used four satellite-based canopy growth proxies (CGPs), including three optical and one passive microwave, and in situ fluxes observations from eddy covariance (EC) measurements for a retrospective investigation of the impacts of historical droughts on tropical forest growth from a statistical point of view. Results indicate two opposite directions in drought-related canopy dynamics across pantropical forests. The canopy of tropical forests with higher CGPs is more vulnerable to drought stress and recovers faster in the post-drought recovery period. In contrast, the canopy of tropical forests with lower CGPs increases during the drought period and declines in the subsequent recovery period, which is beyond general expectation. In situ measurements from eddy-covariance flux towers showed that forests with higher gross primary production and latent heat flux decreased photosynthesis and evapotranspiration during the drought period but increased photosynthesis and evapotranspiration faster during the post-drought recovery period, supporting the findings from satellite observations. Our statistical analysis against climatic factors predicts that higher-CGPs tress with probably taller and bigger canopies are more responsive to shortage of water availability caused by drought; while lower-CGPs tress with shorter and smaller canopies are more responsive to sunlight availability and tend to increase their canopy leaves and enhance photosynthesis in sunnier days during the drought period. Our results highlight the differences in tropical forests in responding to drought stress, which are worth incorporated in Earth system models for time-series evaluations.

中文翻译：

---

跨热带森林的双向干旱相关冠层动态：基于卫星的统计分析

干旱导致热带森林生长出现极端异常，但热带森林应对干旱的方向和幅度仍然存在广泛争议。在这里，我们使用了四个基于卫星的冠层生长代理 (CGP)，包括三个光学和一个无源微波，以及来自涡度协方差 (EC) 测量的原位通量观测，用于回顾性调查历史干旱对热带森林生长的影响一个统计的观点。结果表明整个热带森林与干旱相关的冠层动态存在两个相反的方向。CGPs较高的热带森林冠层更容易受到干旱胁迫的影响，在干旱后的恢复期恢复得更快。相比之下，原位涡协方差通量塔的测量结果表明，初级生产总值和潜热通量较高的森林在干旱期间减少了光合作用和蒸散，但在干旱后恢复期间增加了光合作用和蒸散更快，这支持了卫星观测的结果。我们针对气候因素的统计分析预测，具有更高和更大冠层的 CGP 较高的树木对干旱导致的可用水短缺反应更敏感；而具有较短和较小冠层的较低CGP的树木对阳光的可用性更敏感，并且在干旱期间倾向于增加它们的冠层叶子并在阳光充足的日子里增强光合作用。我们的研究结果突出了热带森林在应对干旱压力方面的差异，