The Amazon forest is increasingly vulnerable to dieback and encroachment of grasslands and agricultural fields. Threats to these forested ecosystems include drying, deforestation, and fire, but feedbacks among these make it difficult to determine their relative importance. Here, we reconstruct the central and western Amazon tree cover response to aridity and fire in the mid-Holocene—a time of less intensive human land use and markedly drier conditions than today—to assess the resilience of tree cover to drying and the strength of vegetation-climate feedbacks. We use pollen, charcoal, and speleothem oxygen isotope proxy data to show that Amazon tree cover in the mid-Holocene was resilient to drying in excess of the driest bias-corrected future precipitation projections. Experiments with a dynamic global vegetation model (LPJ-GUESS) suggest tree cover resilience may be owed to weak feedbacks that act to amplify tree cover loss with drying. We also compare these results to observational data and find that, under limited human interference, modern tree cover is likely similarly resilient to mid-Holocene levels of aridification. Our results suggest human-driven fire and deforestation likely pose a greater threat to the future of Amazon ecosystems than drying alone.

亚马逊森林越来越容易遭受草场和农田和农田的侵占。对这些森林生态系统的威胁包括干旱，森林砍伐和火灾，但其中的反馈使其难以确定其相对重要性。在这里，我们重建了全新世时期中部和西部亚马逊树种对干旱和火灾的反应（当时人类土地使用的强度较低，并且条件比今天明显干燥），以评估树种对干燥的抵抗力和强度。植被-气候反馈。我们使用花粉，木炭和蛇麻草的氧同位素替代数据显示，全新世中期的亚马逊树木覆盖物对干燥的适应能力超过了最干燥的，经过偏差校正的未来降水预测。使用动态全球植被模型（LPJ-GUESS）进行的实验表明，树木覆盖物的复原力可能归因于微弱的反馈，这些反馈会放大干燥造成的树木覆盖物损失。我们还将这些结果与观测数据进行比较，发现在人为限制的情况下，现代树木的覆盖物可能同样具有适应新茂中部干旱水平的能力。我们的结果表明，人为引发的火灾和森林砍伐可能比单独干燥会给亚马逊生态系统的未来带来更大的威胁。