Dissertation Research: Persistence mechanisms of pioneer riparian forests in meandering rivers

半干旱地区河流走廊两旁的杨树和柳树在养分循环和土壤发育中发挥着关键作用，提供可以降低水温的遮荫，是陆地和水生生物的重要食物来源。这些物种通常生长在洪水事件后新暴露的底物上，由于土地转换和水坝对河流流量的调节，这些物种在北美经历了显著的下降。这些物种的栖息地已经被最好地了解，河流弯道中的尖沙洲受到河流治理的严重限制，因此有必要更好地了解其他地点的建立过程。废弃的河道，或称牛弓湖，是许多蜿蜒河流的共同特征。它们作为鱼类等可移动水生生物的避难所的重要性早已得到承认。废弃的河道也可能为杨柳和杨树的建立和持续提供适宜的生境。一个将废弃河道内的沉积和植被动态联系起来的概念模型表明，条件随着时间的推移而变化，从物理因素主导森林动态的时期到更多地由生物相互作用驱动的条件，特别是对光和水的竞争。这一模型将通过一项社区竞争研究进行测试，该研究将沿着现实的环境梯度进行。这项研究集中在加利福尼亚州的中央山谷，涉及跨学科的合作者以及政府机构和自然保护协会的资源经理。在研究发展的早期就征求了管理人员的意见，研究人员继续积极地与这个社区接触，以便能够及早和经常地交换信息。培养博士生和让本科生参与研究将产生额外的更广泛的影响。

The cottonwood (Populus) and willow (Salix) trees that line river corridors in semi-arid regions play key roles in nutrient cycling and soil development, provide shade that can reduce water temperatures, and are an important food source for terrestrial and aquatic organisms. These species, which typically establish on newly exposed substrate left after flood events, have experienced significant declines in North America due to land conversion and the regulation of river flows by dams. The habitat for establishment of these species that has been best understood, point bars in river bends, has been severely limited by river regulation, creating a need to better understand establishment processes in other locations. Abandoned channels, or oxbow lakes, are a common feature associated with many meandering rivers. Their importance as refugia for mobile aquatic organisms, such as fish, has long been recognized. Abandoned channels also may provide habitat suitable for the establishment and persistence of cottonwood and willow. A conceptual model that links sedimentation and vegetation dynamics within abandoned channels suggests that conditions change through time from a period during which physical factors dominate forest dynamics to conditions driven more by biotic interactions, particularly competition for light and water. This model will be tested with a community competition study along a realistic environmental gradient. This research, focused in the Central Valley of California, involves collaborators across disciplines and resource managers at government agencies and The Nature Conservancy. Input from managers was solicited early in study development, and researchers continue to actively engage with this community so that information can be exchanged early and often. Additional broader impacts will result from training a doctoral student and involving undergraduate students in the research.