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

摘要

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.Plain Language Summary Downed wood in rivers creates habitat and nutrients for organisms in streams and on floodplains. Humans have negatively impacted valley bottoms through the removal of downed wood. We measured the amount of downed wood in valley bottoms in four mountain river basins to understand what factors, both local and regional, determine how much wood is stored in river corridors. We found that at the regional scale, logging, precipitation, and forest characteristics control the supply of wood to valley bottoms. At a more local scale, the shape of the valley bottom and the way in which wood is stored (either as accumulations known as jams or as individual logs) determine how much wood can be trapped in the valley bottom. We present a conceptual model that ties these factors together and can guide our understanding and management of how much wood is in rivers.