We characterize the decay and piece shape categories of downed large wood in channels and floodplains of 7 river corridors in Colorado, Montana, North Carolina, and Utah to evaluate how proportions of wood in these categories varied with respect to location (channel, floodplain), disturbance history, wood recruitment (fluvial transport, tree fall), and biome. We hypothesized that decay state and piece shape would differ more between floodplain and channel locations in river corridors with no recent inundation-related large wood transport on the floodplain than in river corridors with recent floodplain inundation. Results support our hypothesis with respect to decay but not piece shape. Decay state differs more between floodplain and channel locations in river corridors with no recent disturbance. These results suggest the benefits of retaining and reintroducing decayed wood in floodplains.

At each site, we characterized at least 100 pieces of downed, dead wood within the river corridor. We characterized each piece with respect to location (active channel, floodplain), mode of recruitment to the river corridor (fluvial transport, treefall), decay state (5 categories, after Robison and Beschta, 1990 and Waddell, 2002), piece shape (4 categories in a classification developed for this study), and length and diameter. The individuals who assigned decay and shape categories agreed on characteristics during an initial field visit and used photographs of example pieces in each category from the first field site for calibration at field sites visited subsequently. Although conifer forests of Colorado and Montana are unlikely to have major branches on most wood pieces, we included major branches as a category to facilitate use of this ranking in forests with substantial numbers of deciduous trees, such as the Utah and North Carolina sites. We delineated floodplain boundaries based on changes in vegetation between the floodplain and adjacent uplands; breaks in slope and elevation above the active channel; highwater marks, if present; and fluvial erosional and depositional features. We inferred mode of recruitment based on presence of a partially anchored root mass or proximity to a shattered tree trunk or a decayed stump for treefall, as well as orientation with respect to flow direction (multiple parallel pieces in close proximity indicated fluvial transport). Fluvially transported pieces do not include pieces recruited through debris flows or landslides, which are not present at the study sites. Tree fall pieces resulted from tree mortality, blowdowns, and bank erosion. We used a handheld GPS (Garmin eTrex, + 3 m horizonal accuracy) to locate each piece of wood and to map the edges of the active channel.

Robison EG, Beschta RL. 1990. Characteristics of coarse woody debris for several coastal streams of southeast Alaska, USA. Canadian Journal of Fisheries and Aquatic Sciences 47, 1684-1693. https://doi.org/10.1139/f90-193

Waddell KL. 2002. Sampling coarse woody debris for multiple attributes in extensive resource inventories. Ecological Indicators 1, 129-153. https://doi.org/10.1016/S1470-160X(01)00012-7