Geomorphic Effects and Habitat Impacts of Large Wood at Restoration Sites in New England

ABSTRACT Large wood (used interchangeably with the term “instream wood”), which refers to trees, logs and other wood within a channel, is beneficial to river ecosystems and is being used more frequently as a component of river restoration projects. We identified metrics to evaluate the effectiveness of large wood to promote ecological and geomorphic complexity within channels, which are frequent restoration goals, and employed them at several sites in New England with naturally recruited or placed large wood. Results from our signed‐rank tests for the hypotheses we quantitatively evaluated revealed no significant differences in depth variability, velocity variability, velocity magnitude, or depth magnitude between reaches with and without large wood across all sites. Large wood structures did not cause the geomorphic and hydraulic changes we expected to see at either our restoration or natural recruitment sites. Wood additions were not effective at creating pools or other habitat features in erosion‐resistant channels with cobble and gravel beds, but did create pools in channels with sufficient quantities of sand bedload to mobilize. We suggest that in watersheds previously occupied by continental glaciers, river restoration projects that use large wood may have limited success at generating desired hydraulic or geomorphic responses due to the relative insensitivity of the landscape to disturbance over management timescales.