Amazonia contains the most extensive tropical forests on Earth, but Amazon carbon sinks of atmospheric CO₂ are declining, as deforestation and climate-change-associated droughts^1,2,3,4 threaten to push these forests past a tipping point towards collapse^5,6,7,8. Forests exhibit complex drought responses, indicating both resilience (photosynthetic greening) and vulnerability (browning and tree mortality), that are difficult to explain by climate variation alone^{9,10,11,12,13,14,15,16,17}. Here we combine remotely sensed photosynthetic indices with ground-measured tree demography to identify mechanisms underlying drought resilience/vulnerability in different intact forest ecotopes^18,19 (defined by water-table depth, soil fertility and texture, and vegetation characteristics). In higher-fertility southern Amazonia, drought response was structured by water-table depth, with resilient greening in shallow-water-table forests (where greater water availability heightened response to excess sunlight), contrasting with vulnerability (browning and excess tree mortality) over deeper water tables. Notably, the resilience of shallow-water-table forest weakened as drought lengthened. By contrast, lower-fertility northern Amazonia, with slower-growing but hardier trees (or, alternatively, tall forests, with deep-rooted water access), supported more-drought-resilient forests independent of water-table depth. This functional biogeography of drought response provides a framework for conservation decisions and improved predictions of heterogeneous forest responses to future climate changes, warning that Amazonia’s most productive forests are also at greatest risk, and that longer/more frequent droughts are undermining multiple ecohydrological strategies and capacities for Amazon forest resilience.

亚马逊流域拥有地球上最广阔的热带森林，但亚马逊大气中 CO ₂的碳汇正在减少，因为森林砍伐和与气候变化相关的干旱^1,2,3,4有可能将这些森林推向崩溃的临界点^{5, 6,7,8} 。森林表现出复杂的干旱反应，表明恢复力（光合绿化）和脆弱性（褐变和树木死亡），这很难仅用气候变化来解释^{9,10,11,12,13,14,15,16,17} 。在这里，我们将遥感光合指数与地面测量的树木人口统计相结合，以确定不同完整森林生态环境中干旱恢复力/脆弱性的机制^18,19 （由地下水位深度、土壤肥力和质地以及植被特征定义）。在肥力较高的亚马逊流域南部，干旱反应是由地下水位深度决定的，浅水位森林具有弹性绿化（其中更大的可用水量增强了对过量阳光的反应），与脆弱性（褐变和树木死亡率过高）形成鲜明对比。更深的地下水位。值得注意的是，随着干旱时间的延长，浅水位森林的恢复能力减弱。相比之下，肥力较低的亚马逊流域北部地区，树木生长缓慢但生命力更强（或者是高大的森林，有深根的水源），支持着更耐旱的森林，不受地下水位深度的影响。 这种干旱响应的功能生物地理学为保护决策和改进对未来气候变化的异质森林响应的预测提供了框架，警告亚马逊流域生产力最高的森林也面临着最大的风险，并且更长时间/更频繁的干旱正在破坏多种生态水文战略和能力亚马逊森林恢复力。