Disturbance regimes of stream and riparian systems ? a disturbance-cascade perspective

Geomorphological processes that commonly transport soil down hillslopes and sediment and woody debris through stream systems in steep, mountainous, forest landscapes can operate in sequence down gravitational flowpaths, forming a cascade of disturbance processes that alters stream and riparian ecosystems. The affected stream and riparian landscape can be viewed through time as a network containing a shifting mosaic of disturbance patches — linear zones of disturbance created by the cascading geomorphological processes. Ecological disturbances range in severity from effects of debris flows, which completely remove alluvium, riparian soil and vegetation along steep, narrow, low-order channels, to localized patches of trees toppled by floating logs along the margins of larger channels. Land-use practices can affect the cascade of geomorphological processes that function as disturbance agents by changing the frequency and spatial pattern of events and the quantity and size distribution of material moved. A characterization of the disturbance regime in a stream network has important implications for ecological analysis. The network structure of stream and riparian systems, for example, may lend resilience in response to major disturbances by providing widely distributed refuges. An understanding of disturbance regime is a foundation for designing management systems. Copyright © 2000 John Wiley & Sons, Ltd.