Spatial and temporal variation of large wood in a coastal river

Abstract

Large wood (LW) is a critical habitat-forming feature in rivers, but our understanding of its spatial and temporal dynamics remains incomplete due to its historical removal from waterways. Few studies have the necessary spatial and temporal extent and resolution to assess wood dynamics over long time periods or in response to flood disturbance. We used an exceptional dataset from 65 km of a free-flowing coastal river in Oregon, USA, to characterize LW dynamics over a 12-year period (1989–2000). Our objectives were to assess the spatial dynamics of LW over multiple spatial scales and characterize changes in these patterns in response to a major flood in November 1996. Higher LW densities were found in the tributaries, and higher temporal variation of density existed in the main stem. Within years and among reaches, LW density varied by 2 to 3 orders of magnitude across the river. Patterns of LW accumulation across the river were not comparably different when considered at spatial resolutions < 6 km. A large flood in 1996 homogenized the wood distribution across the system, particularly at fine spatial scales (that is, 1.5–0.1 km scales), but considerable heterogeneity was reestablished within 2–3 years post disturbance. At the habitat unit scale, LW tended to accumulate in locations with narrow channel widths, and to a lesser extent, in shallow reaches. These data highlight the dynamic nature of the natural wood regime in coastal rivers that is produced by continuous recruitment and transport through the system.