Structure and function of large wood in Ozark headwater streams and its relationship to fish community structure

Abstract

Fish community structure in headwater streams is often influenced by a suite of abiotic variables, such as water depth and flood frequency, channel substrate composition, and in-stream large wood (LW). Wood retained in streams and rivers performs a variety functions; for example, it alters flow, stores sediments, and provides habitat for aquatic biota. The objectives of this study were to (1) quantify and characterize LW, (2) quantify the geomorphic functions of LW, and (3) identify the relationship between LW and fish community structure in Ozark headwater streams. Ten stream reaches with a gradient of LW were sampled in the Ozark-St. Francis National Forest, AR, USA. Single LW pieces, organic accumulations, and root wads were quantified and the geomorphic function of all LW recorded. Fish were identified, enumerated, and massed. LW density in our 10-study streams ranged from <1 to 12 per 100 m2 and >50% functioned to store sediments, stabilize banks, or retain organic matter. Larger diameter wood was associated with altered flow (r = 0.64, p = 0.04) and LW storing sediments tended to also stabilize banks (r = 0.73, p = 0.02). There was no relationship between LW metrics and total fish abundance or biomass; however, stream reaches with higher volumes of organic accumulations supported higher creek chub (r 2 = 0.75, p = 0.005) and southern redbelly dace biomass (r 2 = 0.62, p < 0.02). Although LW densities were among the lowest recorded for US streams, LW still played an integral role in structuring stream geomorphology and providing habitat to some dominant headwater fish species.