By Rita Winkler, Dan Moore, Todd Redding, David Spittlehouse, Brian Smerdon and Darryl Carlyle-Moses
Abstract: The effects of forest disturbance on hydrologic pro- cesses and the generation of streamflow are highly variable and are influenced not only by the disturb- ance, but also by the weather and the biophysical characteristics, of the watershed. This chapter has described how forest harvesting and natural disturb- ance-related changes in fundamental hydrologic processes, including precipitation, interception, evaporation, and soil moisture, can influence hill- slope flow, groundwater, and streamflow. The details
the forest canopy account for some of the variability in hydrologic processes, such as snow accumulation and melt, among stands, but year-to-year differences in snowfall patterns account for the largest propor- tion of the variability (Winkler et al. 2005; Winkler and Moore 2006). Therefore, estimates of recovery derived from measurements made over a relatively small number of seasons may not adequately repre- sent the range of weather conditions expected within a given watershed, and at best, represent average conditions. The greatest uncertainty lies in the ap- plication of stand-scale recovery estimates and ECA indices to the evaluation of hydrologic change at the watershed scale. Linkages between stands, hillslopes, and entire watersheds are complex and vary with
the weather and the watershed; consequently, these linkages have not been quantified. A 50% recovery in snow accumulation or melt may not represent a 50% recovery in peak flow magnitudes. The ECA index provides only an indication of potential hydrologic change based on the extent of disturbance. It should not be used as a substitute for professional analyses and field assessments.
of past and ongoing research in British Columbia and elsewhere can be found in the references cited. New initiatives are building on this foundation by linking stand-scale processes to watershed response; by conducting modelling over greater temporal and spatial scales, with scenarios of extensive harvesting and changing climates; and by conducting field re- search to quantify the effects of natural disturbance on hydrology and hydrologic recovery.