Abundance, Restoration, and Transport of Unanchored Large Wood in a Small River in Central Idaho

Removal of large wood along and within streams has disrupted processes that are essential for the establishment of important habitat for fish in many areas. Therefore, habitat improvement activities often include addition of large wood to streams. Historical timber harvests in portions of the Yankee Fork drainage reduced the abundance of large wood in these areas compared to areas that have not experienced harvest. In this study, large wood was added to the Yankee Fork to simulate wood recruitment to the stream by natural processes, including streamside trees falling into the stream, avalanches, and debris flows. The added wood was not buried, anchored, or purposefully wedged to prevent movement. Therefore, natural stream dynamics could reposition the wood, resulting in natural fish habitat. The abundance of large wood in the treatment reaches, although not static, was maintained over multiple years despite the occurrence of a near 25-year high-flow event. Tracking of 20 radio-tagged pieces of added large wood over 5 years revealed a maximum transport distance of 940 m, with most pieces moving <28 m in any given year. The results of the present study demonstrate that large-wood abundance in a small river, increased by simulating natural processes, can be maintained at levels observed in similar reference areas despite high flows and some wood transport. The restoration approach proposed in this study is appropriate for small rivers on public or undeveloped private land; however, caution should be exercised in rivers where man-made infrastructure could be damaged by unanchored large wood.

Automated summary

The removal of large wood in streams disrupts the establishment of fish habitat, so habitat improvement activities often involve adding large wood to rivers. This study demonstrates that adding large wood to the Yankee Fork, simulating natural wood recruitment processes, can maintain the abundance of large wood and create natural fish habitat. Tracking research shows that even in the face of high flow and wood transport, the abundance of added large wood can be maintained at levels observed in reference areas.