Research on Structures of Riparian Forest and its Function for Disaster Prevention

1.淤地坝后的木本植物群落结构及其受河水的影响为了弄清河岸林的结构，对淤地坝后河床上的两个木本植物群落进行了调查。多药泽兰和柳的高径生长，作为先锋树种和优势树种的优势度与沉积区宽度有关，有向下游发展的趋势。优势树种的年龄与实测洪水年相吻合。树高和树种分析结果表明，上下游林分结构存在明显差异。也就是说，上游河流对木本植物群落的影响更强，泥石流破坏的频率也更高.洪水频率对河岸林树种组成的影响通过对河岸林树种分布与河床断面形态的比较，阐明了洪水频率对河岸林树种结构的影响。根据洪水位的测量和计算结果，认为该场地是裸露的或仅被杨柳灌木覆盖，每年有洪水发生。在洪水年复一年的场地内，以杨柳为优势树种，多蕊泽兰和锦带花为次要树种。在几十年一遇洪水的地方，杨柳种类缺乏，阔叶树发展为河岸林。这是指河岸林的横向结构按距河流的距离和特定的高度分为若干树种类型。

1. Structure of woody communities behind check dams and the influence of stream water on itTwo woody communities on riverbed behind check dams were surveyed to clarify the structure of riparian woods. The growth in height and diameter of Euptelea polyandra and Salix spp., which are pioneer and dominant trees, was related to the width of sedimentary area and had a tendency to show the better condition with higher dencity in lower reach. The ages of dominant trees have agreed with the observed flood years. The analysis results of tree height and species indicated a obvious difference of woods structure between upper and lower reach. Namely, the influence of stream water on woody communities is stronger in upper reach, and frequency of destroying by debris flow is also higher.2. Constitution of woods species in reparian forest related to the flood frequencyThe distribution of riparian woods was compared with the cross section forms of riverbed in order to clarify the influence of flood frequency on woods structure. As the result of surveying and calculation of flood stages, it has been considered that the site, where floods occur sometimes per year, is bare or covered only by willow shrub. In the site, where floods arise once in few years, willow grows as dominant tree, and subordinate trees are consisted of Euptelea polyandra and Weigela hortensis. Where floods appear once for several decades, willow species lack and broadleafed trees develops as riparian woods. It means that traverse structure of riparian woods is devided to several types of tree species, according to the distance from stream and to the specific height.