The fabric of wood: patterns and processes of river and floodplain large wood on the Merced River, Yosemite National Park, California
Date
2020
Authors
Iskin, Emily, author
Wohl, Ellen, advisor
Rathburn, Sara, committee member
Morrison, Ryan, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
This research on the Merced River above Nevada Falls in Yosemite National Park quantifies large wood loads (m3 wood/ha) and the spatial distribution of wood in the bankfull channel, the floodplain, and the adjacent valley bottom, and tests hypotheses that give physical evidence of the dynamics that recruit, transport, and deposit large wood in the river corridor. The upstream portion of the study area includes a recently burned section of the Merced River corridor and the downstream portion of the study area includes a section of floodplain with undisturbed forest. Field work was conducted in June and July of 2019. The results indicate that different processes drive the dynamics of LW on the floodplain versus in the river. Large wood transport capacity is greater in the channel than on the floodplain, as reflected in larger diameter wood in channel jams than in floodplain jams (assuming trees next to the river are not significantly larger than those on the floodplain) and distribution of burned wood throughout the whole study area in the river but only in burned portions of the floodplain. Jams can occur across the entire width of the floodplain but tend to be concentrated near the channel and a greater proportion of large wood may be within jams in burned portions of the floodplain. Mean floodplain wood loads on the Merced floodplain are 250 m3/ha overall, with non-significant differences between burned (median = 230 m3/ha) and unburned (median = 300 m3/ha) portions of the floodplain. Mean valley bottom wood load is 150 m3/ha (area beyond the active floodplain that was not inundated in 2019 (mean water year discharge recurrence interval of 8 years) and is of similar elevation to the active floodplain (e.g. not terraces or hillslopes)). A multivariate analysis of potential predictors of wood load on the floodplain indicates that the proportion of large wood in logjams is significant for the floodplain overall, and for both burned and unburned areas. This research is important because it expands the data on LW to include a medium-sized, undisturbed, and partially-burned river in California. Increased knowledge of LW in river corridors aids in the protection and restoration of our nation's rivers.