Linking response of aquatic biota to road restoration activities

Between 1973 and 1975 the U.S. Geological Survey collected aquatic biological data in streams in the Redwood Creek watershed.  At that time the basin had extensive areas of timber harvest, road construction, unstable hillslopes, and eroding stream channels.  Since then, about 300 km of abandoned logging roads have been removed and previously logged areas have revegetated.  In 2004 and 2005 previously studied streams were resampled to compare aquatic health in restored basins.  During the last 30 years, sediment transport rates in Redwood Creek have decreased.  Flood-deposited sediment is being removed from stream channels, resulting in more frequent and deeper pools.  Riparian canopy cover has increased, and periphyton growth rates have decreased, probably due to increased shade.  Currently summer water temperatures are adequate for salmonids.  An Index of Biological Integrity (IBI) was calculated for the streams, based on sampling of benthic macroinvertebrates.  Although IBI’s were highly variable, some general trends of improved stream health were noted.  Filtering-collectors, which are expected to increase in response to disturbance, were higher in 1974 than in 2004.  Insects exhibiting 2+ year life cycles, indicative of more stable channel conditions, were more abundant in 2004-2005 than in 1974, and diversity indices were also higher.  Density and biomass of tailed frogs in restored basins were still lower than in pristine streams.  Based on a small sample size of captured fish, steelhead condition improved in streams from 1974 to 2005.  Habitat improved both in basins with road restoration as well as in basins in which logging has ceased.