Natural and Anthropogenic Controls on Wood Loads in River Corridors of the Rocky, Cascade, and Olympic Mountains, USA

Abstract

Wood in rivers creates habitat, shapes the morphology of valley bottoms, and acts as a pool of organic carbon (OC). Effective riverine wood management depends on a robust understanding of the spatial distribution of wood throughout river networks. This motivates the analysis of wood load in relation to both reach‐ and basin‐scale processes. We present wood load data coupled with precipitation, forest stand characteristic, land use, and geomorphic data across four basins in the Rocky, Cascade, and Olympic Mountains of the western U.S. We compare basins with differing land use within the same climatic region and basins in differing climates and statistically model intrabasin wood load variability. Wood load is a function of metrics that generally describe river corridor spatial heterogeneity, metrics that describe wood storage patterns, and, at a broader scale, metrics that relate to wood supply. From this, we generate a conceptual model to describe controls on wood load across spatial scales. We use this model to propose that spatial heterogeneity and wood storage pattern together determine reach‐scale wood trapping efficiency. Trapping efficiency in turn regulates how wood supply to valley bottoms determines wood load. We also find that wood in an undisturbed basin stores significant amounts of OC and that wood load restoration has the potential to restore significant amounts of OC to valley bottoms. This conceptual model of wood load controls may serve as a framework to guide wood load modeling and restoration at multiple scales.

Drivers of Low Instream Large Wood Retention and Imprints of Wood Mobility in Mountain Nonperennial Streams of a Mediterranean Semiarid Environment

“…Despite the presence of a high number of mobilized LW pieces, we observed a limited number of LW pieces clustered into jams at the expense of individual, dispersed pieces. A low frequency of jams was previously reported from glaciogenic semiarid basins of the Rocky Mountains, which also had overall low LW storage in the channels (Scott & Wohl, 2018). These two observations from semiarid environments with limited LW recruitment suggest that low LW abundance in the channels can be solely responsible for the decreased clustering ability of wood pieces despite their high potential for mobility.…”

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

“…Similarly, restoring wood jams, which can trap and store wood for significant periods of time, can have a significant impact on increasing wood loads in river corridors. These inferences are supported by correlations among channel spatial heterogeneity, wood load, and wood jams in both smaller mountain streams (e.g., Livers & Wohl, ; Livers et al, ; Scott & Wohl, ) and larger rivers (e.g., Gurnell et al, ) relative to those in our study.…”

The Transience of Channel‐Spanning Logjams in Mountain Streams

“…Multithread-channel reaches also contain a higher average distribution density than single-thread reaches. Similar spatial trends have been demonstrated in other studies (Braudrick & Grant, 2001;Gurnell et al, 2000;Livers & Wohl, 2016;Scott & Wohl, 2018;Wyzga & Zawiejska, 2005). For the Southern Rockies data set, wide, low-gradient valley reaches with greater logjam distribution density exhibit greater interannual variation in distribution density but are also resilient to high peak flows in that logjam distribution density values return to preflood levels within a few years.…”

“…Site configurations that trap wood in the study area include ramp and bridge wood pieces (Beckman & Wohl, 2014), the presence of secondary channels, and wider and lower gradient valley reaches (Wohl & Cadol, 2011). Maintaining or restoring a natural wood regime (Wohl et al, 2019) and the riverine spatial heterogeneity that enhances wood trapping and retention (Ruiz-Villanueva et al, 2016;Scott & Wohl, 2018), and that wood storage in turn creates (Collins et al, 2012), are integral to sustaining the geomorphic and ecological effects of channel-spanning logjams.…”