Amy Nicoll, MSc
Amy Nicoll, MSc
Downstream characteristics of in-stream wood in Wigwam Creek, Alberta
In this study I examined downstream patterns of wood characteristics and stand dynamics in a small basin in the Upper Foothills of Alberta. Fourteen study reaches were surveyed for wood size, orientation, position, origin and function, channel parameters including bankfull width, depth, slope and bed surface texture, and tree diameter, density and species composition of the adjacent riparian forest using the point centred quarter method. Based on geomorphic process domains, total stream power estimations and critical thresholds of change among wood attributes, I determined that wood movement began between 7-10km² drainage area. Upstream of this point wood had relatively little geomorphic function and decay was the main output process. Wood characteristics responded strongly to the downstream increase in transport capacity. Wood loads ceased to resemble adjacent forests near the colluvial-fluvial boundary as wood began to be affected by transport. Total wood load decreased, and wood orientation changed from perpendicular to parallel as transport capacity increased downstream. Decay classes 1, 2 and 5 were more abundant in transport-limited reaches while decay class 3 was more abundant downstream. Log positions within the channel varied with transport capacity, with fewer bridges and more loose and braced wood found downstream of the valley step. Partial bridges and anchored wood occurred in the same amounts throughout the stream network. Wood distribution changed from segregated in transport-limited reaches to aggregated in transporting reaches. Most logs had been dead for less than 40 years, but some had persisted for over 125 years in transport-limited reaches. The mean age of woody debris did not change downstream since riparian stands were similar along the stream network. These findings have implications for forest management and aquatic systems in the Upper Foothills region.