The Effect of Dams on Riparian Vegetation Dispersal

9725384 WohlRiver筑坝导致流态和地貌过程的改变，从而导致下游河岸植被的变化。 现有植被的变化可能是由于自然生境和水文条件的改变，水坝也可能干扰河岸物种繁殖和早期生命阶段的关键机制。 传播的繁殖体，和沉积的种子在适合长期生存的网站是重要的决定因素，许多河岸物种的持久性和影响河岸植物群落的组成和结构。本研究的目的是：（1）。确定各种传播和存储机制（风，水，土壤种子库）在殖民新的网站和构建河岸植物群落沿着山溪的相对重要性; 2.）测量水坝中断这些过程的程度; 3.）记录各种河岸物种的种子在水柱中的位置以及种子与沉积地貌和水文状况的沉积模式。 对三条受管制的高坡度山区溪流的实地研究将：1。记录气生和水分散种子对沿着边缘和沙洲表面定殖的相对贡献，2.）在蓄水池上游和下游的几个横截面处对空气和水分散的种子进行采样，以及3.）测量的运输力学，浮力和活力的持续时间，和模式的种子沉积的三个重要的河岸植物物种（复叶槭，赤杨，和桦fontinalis）的关系，在现场和水槽实验的通道形式和水文过程。 了解种子输送机制沿着自然和调节流和种子释放的时间之间的相互作用，并在适当的时候暴露的苗床的可用性，将提供一个坚实的科学基础，修改流量制度在一年中的某些时候，以促进关键河岸物种的繁殖成功。

9725384WohlRiver damming results in modifications of flow regimes and geomorphic processes, which lead to changes in riparian vegetation downstream. Changes in existing vegetation may result from modifications in the physical habitat and hydrology, and dams may also interfere with critical mechanisms of reproduction and early life stages of riparian species. Dispersal of propagules, and the deposition of seeds in sites appropriate for long-term survival are important determinants of the persistence of many riparian species and influence the composition and structure of riparian plant communities. The objective of this study is: 1.) to determine the relative importance of various dispersal and storage mechanisms (wind, water, and soil seed banks) in colonizing new sites and in structuring riparian plant communities along mountain streams; 2.) to measure the degree to which dams interrupt these processes; 3.) to document where seeds of various riparian species are transported in the water column and the depositional patterns of seeds in relation to depositional landforms and hydrologic regimes. Field studies on three regulated, high gradient mountain streams will: 1.) document the relative contributions of aerial and water dispersed seeds to the colonization of surfaces along river margins and bars, 2.) sample aerially and water dispersed seeds at several cross sections both upstream and downstream from impoundments and 3.) measure the transport mechanics, duration of buoyancy and viability, and patterns of seed deposition of three important riparian plant species (Acer negundo, Alnus incana, and Betula fontinalis) in relation to channel form and hydrologic processes both in field and flume experiments. Understanding the mechanisms of seed delivery along natural and regulated streams and the interactions between the timing of seed release, and the availability of exposed seedbeds at appropriate times, will provide a solid scientific basis for modifying flow regimes at certain times of the year to facilitate the reproductive success of key riparian species.