|Shields Jr, Fletcher|
Submitted to: USDA Forest Service Research Notes
Publication Type: Research Notes
Publication Acceptance Date: 11/29/2004
Publication Date: 1/15/2005
Citation: Shields Jr, F.D., Knight, S.S. 2005. Large wood for stream habitat restoration: Harder than it looks. Stream Notes. Stream Systems Technology Center, Rocky Mountain Research Station, Fort, Collins, CO. p. 4-6. Interpretive Summary: Stream corridor ecosystems in agricultural watersheds are often severely degraded by erosion and sedimentation, and corrective measures involving stone are expensive, while those made from felled trees (large wood) are less costly and more closely resemble natural habitat features. In order to develop design criteria for large wood in deeply-eroded sand bed streams, we constructed 72 large wood structures along a stream in northern Mississippi. Initially large wood structures performed quite well, stabilizing the lower parts of steep, eroding banks. However, about two-thirds of the structures failed by the third year after constrution, probably due to wood decay, breakage, and inadequate anchoring. Fish communities in both the treated and untreated reaches improved after construction, becoming more similar to those found in less severely-damaged habitats. These findings will be useful to workers seeking low-cost, natural alternatives for stream stabilization and habitat restoration.
Technical Abstract: Structures made from large wood material have been used for controlling stream erosion for many decades and are increasingly being used to restore or rehabilitate stream habitats. Incising, sand-bed streams provide a particularly rigorous test of the large wood approach due to widely varying flows and rapid erosion and sedimentation common to such systems. We present results of a 5-year experiment featuring addition of large wood to a 2-km reach of a severely incised, sand bed stream. Large wood structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention. Habitat effects were initially positive, with increasing mean water depth. Fish populations responded in a fashion consistent with other stream habitat rehabilitations in this region: large-bodied, longer-lived centrarchids became more dominant. After three years, 36% of the large wood structures were destroyed, and 35% were damaged, partially due to inadequate anchoring. The effectiveness of large wood as a habitat restoration tool depends on its compatibility with the overall geomorphic context, biological factors, and design issues.