SummaryOver recent decades, biomass gains in remaining old-growth Amazonia forests have declined due to environmental change. Amazonia’s huge size and complexity makes understanding these changes, drivers, and consequences very challenging. Here, using a network of permanent monitoring plots at the Amazon–Cerrado transition, we quantify recent biomass carbon changes and explore their environmental drivers. Our study area covers 30 plots of upland and riparian forests sampled at least twice between 1996 and 2016 and subject to various levels of fire and drought. Using these plots, we aimed to: (1) estimate the long-term biomass change rate; (2) determine the extent to which forest changes are influenced by forest type; and (3) assess the threat to forests from ongoing environmental change. Overall, there was no net change in biomass, but there was clear variation among different forest types. Burning occurred at least once in 8 of the 12 riparian forests, while only 1 of the 18 upland forests burned, resulting in losses of carbon in burned riparian forests. Net biomass gains prevailed among other riparian and upland forests throughout Amazonia. Our results reveal an unanticipated vulnerability of riparian forests to fire, likely aggravated by drought, and threatening ecosystem conservation at the Amazon southern margins.

中文翻译：

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火灾对亚马逊南部边缘森林生物量动态的影响

摘要近几十年来，由于环境变化，剩余的古老亚马逊森林中的生物量增加已经下降。亚马逊地区的巨大规模和复杂性使得理解这些变化、驱动因素和后果非常具有挑战性。在这里，我们使用亚马逊-塞拉多过渡的永久监测地块网络，量化最近的生物质碳变化并探索其环境驱动因素。我们的研究区域覆盖了 30 块高地和河岸森林，在 1996 年至 2016 年间至少采样了两次，并受到不同程度的火灾和干旱的影响。使用这些图，我们的目标是：（1）估计长期生物量变化率；(2) 确定森林变化受森林类型影响的程度；(3) 评估持续的环境变化对森林的威胁。总体而言，生物量没有净变化，但不同森林类型之间存在明显差异。12 座河岸森林中有 8 座至少发生一次燃烧，而 18 座高地森林中只有 1 座发生燃烧，导致被烧毁的河岸森林碳损失。在亚马逊流域的其他河岸和高地森林中，净生物量增加占主导地位。我们的研究结果揭示了河岸森林对火灾的意外脆弱性，可能因干旱而加剧，并威胁到亚马逊南部边缘的生态系统保护。