LARGE WOOD IN A MOUNTAINOUS STREAM NETWORK: ECO-GEOMORPHIC ASSOCIATIONS, LAND USE EFFECTS, AND IMPLICATIONS FOR INSTREAM HABITAT AND CARBON STORAGE POTENTIAL

Large wood, derived from riparian and upland forests, strongly interacts with fluvial geomorphic processes in river corridors. These complex, reciprocal linkages between forest, wood, flow, and sediment dynamics may play an important role in forming and maintaining stream habitat and controlling organic carbon storage. As a result, these eco-geomorphic relationships and their response to land use are of great interest to river science and management. In this study, we use a combination of remote sensing and field survey data to examine instream large wood distribution in a mountainous stream network in northern Washington with a history of forest harvest. Specifically, we examine spatial associations between large wood, forest canopy, and geomorphic characteristics at the valley and channel scale. Among channel features, we focus on those relevant for habitat and carbon storage, such as morphological complexity and pool characteristics. Preliminary analysis suggests that instream large wood and large wood jam densities are associated with valley geometry and confinement as well as local characteristics of the forest canopy. We also find correlations between large wood and channel complexity as well as pool characteristics. Overall, these preliminary findings suggest that, despite the legacy of past logging, valley-scale geomorphic processes in our study site exert detectable influence on large wood distribution. Land use effects on wood appear to be mediated by forest canopy characteristics. Our findings are also consistent with an important role of the reciprocal interactions of wood and channel dynamics in creating instream habitat features typically associated with high-quality habitat and retention of organic carbon.