The Effect of Dams on Riparian Vegetation Dispersal

9725384WohlRiver筑坝导致河水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栖息地和水文的改变，大坝也可能干扰河岸物种繁殖和早期生命阶段的关键机制。繁殖体的扩散和种子在适合长期生存的地点的沉积是许多河岸物种持续存在的重要决定因素，并影响河岸植物群落的组成和结构。本研究的目的是：1.)确定各种扩散和储存机制(风、水和土壤种子库)在殖民新地点和沿山溪构建河岸植物群落方面的相对重要性；以衡量大坝对这些过程的干扰程度；3)记录各种河岸物种的种子在水柱中运往何处，以及种子的沉积模式与沉积地貌和水文状况的关系。对三条受调节的高坡度山溪的实地研究将：1.记录空中和水中散布的种子对沿河边缘和沙洲表面的殖民的相对贡献，2。在蓄水池上游和下游的几个横截面上，用空气和水采样散布的种子。在野外和水槽实验中，测量三种重要的河岸植物(枫树、赤杨和桦木)的输运机制、浮力持续时间和生存能力以及种子沉积模式与河道形态和水文过程的关系。了解自然和调节溪流的种子输送机制，以及种子释放时间和适当时间裸露苗床的可用性之间的相互作用，将为改变一年中某些时间的水流状况，促进关键河岸物种的繁殖成功提供坚实的科学基础。

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.