Spatial Distribution of Channel and Floodplain Large Wood in Forested River Corridors of the Northern Rockies

摘要

Planform geometry, spatial heterogeneity, and large wood abundance and distribution were characterized using combined remote imagery and field surveys along lengths of 20-28 km in four river corridors (channels and floodplains) in northwestern Montana. Study sites included four planform geometries: meandering, straight, braided, and multichannel. Planform spatial heterogeneity of channels and floodplains, such as proportion of the active channel in bars, sinuosity, braiding index, and the number of active channels, differs in relation to channel planform type. Braided and multichannel rivers have significantly greater spatial heterogeneity of channels and floodplains and store significantly greater volumes of wood in the channel. Wood is preferentially stored in jams, and jams are preferentially stored in shallow areas of the active channel (midchannel bars, inner bends, and secondary channels) and in abandoned channels on the floodplain. We interpret these results using a conceptual model in which boundary conditions create sufficient valley-bottom width for the development of planform spatial heterogeneity, which then promotes storage of large wood. The results of this study can inform management that protects or restores spatial heterogeneity.