Construction of dams in the mid-20th century reduced channel dynamism, sediment transport, and regeneration of riparian trees on the Missouri River. Opportunities for forest regeneration, however, may occur where the Missouri River or tributaries deposit sediments in reservoir headwaters, forming deltaic and associated upstream backwater areas. One such delta-backwater occurs at the confluence of the Niobrara and Missouri rivers upstream from Lewis and Clark Lake in southeastern South Dakota and northeastern Nebraska. We investigated spatiotemporal patterns of tree recruitment through vegetation sampling in 2017–2018, dendrochronology, and analysis of aerial photography from 2006 to 2016. We sampled woody vegetation in 47 plots and took tree-ring samples from one to two trees within each plot to determine establishment dates. Woody vegetation was dominated by Populus deltoides (cottonwood) and Salix amygdaloides (peachleaf willow) in the tree layer and Salix interior (sandbar willow) in the shrub layer. Tree establishment occurred primarily in 2010–2012 and was distributed throughout the study area, including at the delta-reservoir interface. LiDAR data showed that most of the delta-backwater experienced a 0.5-m increase in elevation in 2005–2011, a period that included high flows in 2010 on the Niobrara River and 2011 on the Missouri River. Woody vegetation decreased 8% from 2006 to 2012, but doubled from 2012 to 2016, colonizing areas of previous sandbar and herbaceous vegetation. These woodlands represent early successional habitat that is in decline elsewhere along the river. Understanding vegetation dynamics within reservoir delta-backwaters may be vital for forecasting changes in regulated riverine landscapes, assessing biodiversity values of these ecosystems, and informing sustainable reservoir management.

中文翻译：

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密苏里河水库三角洲回水中木本植被的扩张

20 世纪中叶的水坝建设减少了密苏里河河道的活力、泥沙输送和河岸树木的再生。然而，当密苏里河或支流在水库源头沉积沉积物，形成三角洲和相关的上游回水区时，可能会出现森林再生的机会。南达科他州东南部和内布拉斯加州东北部的刘易斯和克拉克湖上游的尼奥布拉拉河和密苏里河汇合处就是这样一种三角洲回水。我们通过 2017-2018 年的植被采样、树木年代学和 2006 年至 2016 年的航空摄影分析研究了树木招募的时空模式。我们在 47 个地块中采样了木本植被，并从每个地块内的一到两棵树上采集树轮样本以确定成立日期。树层和柳内部的三角杨（棉花）和柳杏仁（桃叶柳）（沙洲柳树）在灌木层。树木的建立主要发生在 2010-2012 年，分布在整个研究区域，包括三角洲-储层界面。激光雷达数据显示，大部分三角洲回水在 2005 年至 2011 年期间经历了 0.5 米的海拔升高，这一时期包括 2010 年 Niobrara 河和 2011 年密苏里河的高流量。从 2006 年到 2012 年，木本植被减少了 8%，但从 2012 年到 2016 年翻了一番，占据了以前的沙洲和草本植被区域。这些林地代表了沿河其他地方正在衰退的早期演替栖息地。了解水库三角洲回水中的植被动态对于预测受管制河流景观的变化、评估这些生态系统的生物多样性价值、