Floodplain Large Wood and Organic Matter Jam Formation After a Large Flood: Investigating the Influence of Floodplain Forest Stand Characteristics and River Corridor Morphology

Abstract

AbstractThe controls on large wood (LW; wood >1 m in length and >0.1 m in diameter) and coarse particulate organic matter (CPOM; organic material >1 mm in diameter) deposition on floodplains have rarely been assessed, and there are few studies that explore the bidirectional interactions between wood, standing trees, and geomorphic processes. We use field data from West Creek, Colorado, USA, to assess the influence of river corridor morphology and forest stand density on the depositional patterns of floodplain LW and CPOM accumulations (jams) resulting from an extreme flood. Relatively high LW loads per area (mean ± SE = 678.6 ± 192.3 m3 ha−1) point to the importance of extreme floods for LW deposition on floodplains. We find that LW jams decreased in size with distance from and elevation above the channel, but that CPOM jams did not, demonstrating that the relatively smaller CPOM can be more easily transported within a forested floodplain. Steeper reaches contained smaller LW and CPOM loads per area, which may indicate that reaches with higher stream power during the flood were less depositional. As forest stand density increased, the number of CPOM jams per area increased, and a majority of jams were pinned by standing trees. Trees were trapping locations for LW and CPOM, highlighting the importance of preserving riparian forests. Floodplain LW and CPOM provide habitat and nutrients to floodplain ecosystems and influence geomorphic processes, creating an opportunity to use LW in restoration while reducing potential hazards caused by in‐channel LW.