STRUCTURE AND FUNCTION OF RIPARIAN ZONE AND IMPLICATIONS FOR JAPANESE RIVER MANAGEMENT

本文描述了随空间尺度变化的河岸带生态结构和功能。河岸带由谷底地貌和河岸植被组成。所讨论的功能包括：日光能量的衰减、树叶和针叶的输入、木质碎屑对溪流的贡献以及在运输过程中对流动物质的保留。这些主要功能直接或间接地影响河流、沙洲和洪泛平原的水和沉积物质量。树冠对河流提供的遮阳强烈影响着河流生态系统的水温和初级生产。落在溪流中的垃圾是溪流生物的重要食物来源，特别是在森林覆盖的源头溪流中。来自山坡和洪泛平原的粗木屑为有机和无机物提供了储存场所，并增强了水生生物的栖息地多样性。此外，河岸植被的茎和根将上游输送的无机和有机物质进行梳理，增加了河漫滩沉积物的土壤养分。谷底宽度的变化通过增加水力和地貌的复杂性，在保留水流中输送的物质方面起着重要作用。一般来说，这些功能随着流域面积的增加而减少，尽管在大河的洪泛平原上保留了一些功能。这种纵向变化的主要原因是由于河岸树木和河道的相对大小的变化。新的河流治理政策应强调河岸带的生态功能。最后，作者提出了基于保持物理和生态联系的概念，通过保护或创造景观元素来进行河流恢复规划。

This report describes the ecological structure and function of riparian zone which vary with spatial scale. The riparian zone consists of valley floor landform and riparian vegetation. The functions discussed are attenuation of sunlight energy, input of leaves and needles, contribution of woody debris to streams, and retention of flowing material out of transport. These primary functions directly or indirectly influence water and sediment qualities of streams, bars and floodplains. Shading provided by tree crowns over the stream strongly influences water temperature and primary production in lotic ecosystems. Litter falling into streams is a critical food resource for stream organisms, especially in forested headwater streams. Coarse woody debris supplied from hillslopes and floodplains create storage sites for organic and inorganic matters and enhance habitat diversity for aquatic biota. Moreover, stems and roots of riparian vegetation comb inorganic and organic matter transported from upstream, increasing the soil nutrients of floodplain deposits. Variation in valley floor width plays an important role in retaining materials transported in stream water by increaxing hydraulic and geomorphic complesity. Generally, these functions diminish with an increase in watershed area although some functions are kept in floodplains of large rivers. The main reason for this longitudinal variation is due to changes in the relative size of riparian trees and the stream channel. The new river management policy should emphasize the ecological functions of the riparian zone. Finally, the authors proposes river restoration planning by preserving or creating landscape elements based on the concepts of sustaining physical and ecological linkages.