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? r <br />7 <br />Aquatic and Riparian Resources - <br />EFFECTS OF TIMBER AARVEST ON AQUATIC AND RIPARIAN RESOURCES ? <br />Timber harvest can affect aquatic resources by increasing water yield and by potentially ? <br />increasing erosion and sedimentation. Harvest in riparian zones reduces streamside vegetation, <br />which can increase annual and daily stream temperature fluctuations, reduce overhead cover, and ? <br />decrease the supply of large woody material available for recruitment to streams. Conversely, <br />logging slash and debris can choke streams and reduce dissolved oxygen levels as debris decays, <br />creating anoxic conditions toxic to fish and other aquatic organisms. Major increases in erosion ? <br />from harvested azeas themselves aze unusual, but the road and skid trail network associated with <br />timber sales can increase the risk of erosion and sedimentation. <br />Changes in vegetative structure from timber harvest also lower the quality of riparian corridors ? <br />used by terrestrial wildlife species by reducing cover and changing available food and forage <br />sources. ? <br />Increases in flows, changes in riparian vegetation, and impacts to streambanks from logging <br />operations all have the potential to alter fish habitat in streams on the Forest in watersheds where ? <br />timber harvest occurs. Direct effects of vegetation removal are most likely to result in reductions <br />in overhead cover that provides hiding and resting areas for fish. Indirect effects of timber <br />harvest would include changes to thermal buffering that could increase summer or decrease M <br />winter temperatures to sub-optimal ranges, increasing stress on fish during these periods or <br />changing reproductive potential due to delayed spawning or emergence. Other indirect effects I <br />would be reductions in spawning and hiding cover as a result of increased substrate <br />embeddedness and pool filling from sedimentation. However, provided that timber harvest does <br />not exceed the hydrologic threshold, and that watershed conservation practices to protect riparian <br />? <br />areas are implemented, changes in fish habitat occurring as a result of vegetation management <br />should be minimal. Care during project planning and implementation is needed to ensure that <br />vegetation management does not impair attainment of desired conditions for aquatic and riparian <br />? <br />habitats or affect viability of aquatic indicator species.. <br />All alternatives aze achievable, but risk of adverse consequences to watersheds and fisheries ? <br />increases with increasing harvest levels. The potential for impacts to water resources is <br />proponional to scheduled harvest acres, and is shown below. Average drainage densities for <br />crenulated drainages, intermittent streams, and perennial (potentially fish-bearing) streams were <br />calculated from GIS (geographic information system) stream data for all NFS lands on the <br />AR'vF, excludin? the Williams Fork draina2e and Pawnee National Grassland. <br />? <br />I <br />IF <br />? <br />Chaprer Three • 128 <br />?