The displacement of a river to a new position within its adjacent floodplain is called avulsion, and here we examine how a newly recognized style, called retrogradational avulsion, affects the surrounding floodplain in tropical rainforests using remote sensing. Retrogradational avulsions begin with a channel blockage that causes self‐propagating upstream dechannelization and flooding. While this flooding results in vegetation die‐off and floodplain sedimentation, few quantitative measurements of disturbance by retrogradational avulsions exist. Here, we first focus on land‐cover change following a single retrogradational avulsion in Papua New Guinea from 2012 to 2021. During the avulsion, the river dechannelized 892 m upstream, and the parent channel width doubled. Using maximum likelihood image classification, we observed healthy vegetation fluctuated around 4.3 km2, vegetation regrowth peaked in 2017 at 3.2 km2, dead vegetation peaked in 2013 at 2.1 km2, and visible extent of deposited sediment was greatest in 2015 at 0.44 km2. We also examined 19 other retrogradational avulsions in Papua New Guinea and South America using NDVI. The area of floodplain disturbance (i.e., vegetation die‐off and possible sedimentation) for each avulsion ranged from <1 to >13 km2 and scaled with the dechannelization area. Comparing our plan‐view disturbance results with FABDEM digital‐elevation data and ICESat‐2 surface elevation measurements, we hypothesize floodplain disturbance extent is a function of topographic relief. Our results also suggest that retrogradational avulsions, on average, perturb larger areas of forest compared to blowdowns, suggesting this might be an important disturbance regime that influences gap‐filling regeneration in tropical rainforests.

中文翻译：

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热带雨林上游迁移河流撕扯后的遥感土地覆盖变化和洪泛区扰动

河流向邻近漫滩内新位置的位移称为撕脱，在这里，我们利用遥感技术研究了一种新认识的类型（称为逆生撕脱）如何影响热带雨林中周围的漫滩。逆生撕脱始于河道堵塞，导致自我传播的上游脱河道和洪水。虽然洪水导致植被死亡和洪泛区沉积，但对退生撕脱造成的干扰的定量测量却很少。在这里，我们首先关注巴布亚新几内亚 2012 年至 2021 年单次退生撕脱后的土地覆盖变化。在撕撕期间，河流上游 892 m 失去河道，母河道宽度增加了一倍。使用最大似然图像分类，我们观察到健康植被波动约 4.3 公里2，植被再生量在 2017 年达到顶峰，达到 3.2 公里2，死亡植被在 2013 年达到顶峰，达到 2.1 公里2，2015年沉积物可见范围最大，为0.44公里2。我们还使用 NDVI 检查了巴布亚新几内亚和南美洲的其他 19 例逆行撕脱伤。每次撕脱的洪泛区扰动（即植被死亡和可能的沉积）范围为 <1 至 >13 公里2并与非通道化区域成比例。将我们的平面图扰动结果与 FABDEM 数字高程数据和 ICESat-2 表面高程测量结果进行比较，我们假设洪泛区扰动程度是地形起伏的函数。我们的结果还表明，与排污相比，平均而言，退行撕脱会扰乱更大面积的森林，这表明这可能是影响热带雨林间隙填充再生的重要扰动机制。