Wissmar, Robert C.; Swanson, Frederick J. 1990. Landscape disturbances and lotic ecotones. In: Naiman, Robert J.; Decamps, Henri, eds. The ecology and management of aquatic-terrestrial ecotones. 4. Paris, France: United Nations Educational, Scientific and Cultural Organization: 65-89.
oflandscape disturbances in controlling ecotone function and stability. Loticecotones are described as zones of transition between adjacent ecologicalsystems having characteristics uniquely defined by space and time scales andby the strength of interactions between systems. They are considered to besensitive to gradients of limiting factors and landscape changes caused byphysical and biological disturbances. In uplands or headwaters of mountainstream systems, physical disturbances, and interactions with landform con-ditions and hydrologic regimes, are of major importance in determining thestructure and dynamics of ecotones. Lotic ecotones of high relief landscapesare viewed as being less stable than those of lowlands because they are subjectto more frequent and diverse disturbances and complex topographic effects.Landfornt slopes, topographic aspects, edaphic gradients, and other geomorphicfactors influence gravity-driven flow paths of materials and the availability ofwater and energy to transport materials. Disturbances such as landslides andfloods, in narrow upland valleys, combine to exert lateral control on uplandlotic ecotones. These controls on ecotone .lanction and stability can be mostevident in ecotones near lotic systems having steep channel slopes wherefluvial and geomorphic processes strongly influence the development of riparianvegetation.
Field and modelling studies suggest several approaches for evaluatingtemporal and spatial effects of disturbance regimes and topographic factorson ecotonal riparian communities and their stability. Field studies includedisturbance histories and changes in ages of riparian forest patches for twodifferent types of mountain valleys (fluvial and glacially formed) in the CascadeMountains of Oregon and Washington, USA. The determination of the relativephysical stability of lotic ecotones is approached using geomorphic concepts of phases of landform change and recovery following disturbance, and timeintervals for disturbance recurrence. Recommendations are provided foradditional descriptive and quantitative approaches that could be used inmanaging lotic ecotones.