A Comprehensive Budget for Woody Debris Recruitment, Storage, and Removal in Large Coastal Rivers

Joshua Latterell, Master's Project

The proposed research is intended to be a capstone study of large woody debris (LWD) dynamics; we will use a budgeting approach to craft a new ecosystem-level understanding of natural LWD dynamics in the Pacific Coastal Ecoregion (PCE). We will assess magnitude and variability in LWD recruitment, storage, and removal for two protected river systems exemplary of large rivers in the PCE; the Queets and Hoh rivers in Olympic National Park (ONP). Three years of detailed field surveys, in combination with analysis of a 62-year aerial photo record will be used to estimate the relative importance of six processes regulating LWD storage in each river system: 1) riparian stand mortality, 2) vegetative disturbances, including fire and windthrow, 3) bank erosion, 4) landslides and debris flows, 5) fluvial LWD transport, and 6) decay and fragmentation. These parameters will be estimated using a geographic information system (GIS), overlay analysis, tagging, dendrochronology, forest growth models, and forest mensuration techniques. Since these processes likely vary in importance with channel size and confinement, we will investigate each process in six of the primary reach types found in river systems of the PCE: a) unconfined pool-riffle, b) unconfined plane-bed, c) confined plane-bed, d) unconfined step-pool, e) confined step-pool, and f) confined cascades. This approach will enable the construction of a spatial model able to predict annual and long-term volumetric change in LWD at the reach or system level, based on channel characteristics, position in the channel network, and riparian forest structure. By characterizing these process rates for a comprehensive set of major channel types, this project will cultivate an ecosystem-level perspective on LWD dynamics applicable region-wide.