Swanson, F. J.; Pearce, A. J. 1988. An approach to estimating the effects of Waldsterben on sediment production. In: Proceedings of a workshop on consequences of forest damages on high elevation streams in Switzerland; 1987; Zurich, Switzerland. Zurich, Switzerland: Eidg. Technische Hochschule: 35-46.
Overall catchment response to Woldsterben or other forest disturbances iscontrolled by the effects of forest vegetation on rate, amount, and spatialpatterns of runoff and sediment production. This paper reviews an approach toestimating the effects of Waldsterben or other disturbances of vegetation onsediment production from hillslopes and channels. The companion paper byPearce presents the actual estimates of changes in total sediment delivered tothe Gangbach stream based on field studies in the Gangbach catchment. Thesestudies were conducted during a workshop on effects of waldsterben on sedimentand debris flow production. The reason for undertaking this analysis is thatthe rate and timing of sediment production from hillslopes can stronglyinfluence the magnitude of property damage, the productivity of soils onhillslopes, and the generation of debris flows and excessive bedload that candamage downstream areas.
Since the Gangbach catchment examined in this workshop is a single study siteand one with limited extent of forest cover due to climatic, soil, and land usefactors, we feel that it is worthwhile discussing our analytical approach ingeneral terms. This general approach could be developed further and appliedelsewhere. Prediction of changes in hydrology and sedimentation in theGangbach and most other basins its size is greatly limited by:
the diversity of geomorphic processes and geologic, geomorphic,hydrologic, and vegetative conditions.
the lack of a well-studied, analogous forest disturbance to guidepredictions
3. a lack of quantitative description of preset rates of sedimentproduction processes in the catcl-iment.
With these limitations in mind, our contribution in laying out a general schemefor analysis may be of greater value for assessing the effects of Waldsterbenon other catchment areas than the actual estimates for the Gangbach catchment.The Gangbach estimates were based on only a few days of field observations withlittle opportunity to assess how typical the Gangbach area is of regions underthreat from Waldsterben.