Structure and function of riparian zone and implications for Japanese river management

This paper describes the ecological structure and function of riparaian zonewhich vary with spatial scale. The riparian zone consists of valley floor landformand riparian vegetation. The functions discussed.are attenuation of sunlight energy,input of leaves and needles, contribution of woody debris to streams, and retentionof flowing material out of transport. These primary functions directly or indirectlyinfluence water and sediment qualities of streams, bars and floodplains. Shadingprovided by tree crowns over the stream strongly influences water temperature andprimary production in ecosystems. Litter falling into streams is a criticalfood resource for stream organisms, especially in forested headwater streams.Coarse woody debris supplied from hillslopes and floodplains create storage sites fororganic and inorganic matters and enhance habitat diversity for aquatic biota.Moreover, stems and roots of riparian vegetation comb inorganic and organic mattertransported from upstream, increasing the soil nutrients of floodplain deposits.Variation in valley floor width plays an important role in retaining materials trans-ported in stream water by increasing hydraulic and geomorphic complexity. Gen-erally, these functions diminish with an increase in watershed area although somefunctions are kept in floodplains of large rivers. The main reason for this longitu-dinal variation is due to changes in the relative size of riparian trees and thestream channel. The new river management policy should emphasize the ecologicalfunctions of the riparian zone. Finally, the author proposes river restoration plan-ning by preserving or creating landscape elements based on the concepts of sustain-ing physical and ecological linkages.
Key Words: Riparian zone, Riparian structure, Ecological function, Floodcontrol, River environment.