The Effects of Small Scale Riparian Disturbance on Fish Habitat and Food Sources in Forested Streams

Forested headwater streams rely on their riparian areas for temperature regulation, woody debris inputs, sediment retention, and terrestrial invertebrate inputs.  The products and services of riparian areas may be altered by disturbances such as timber harvest, windthrow, development, fire, or disease.  This study investigated the effects of riparian forest disturbance by removing trees using 50% and 90% basal area harvests (BAHs) and by directly felling some trees into streams.  Riparian manipulations occurred along eight streams in eastern West Virginia. 

Water temperatures in the 90% BAH treatments were potentially disruptive to stream biota.  The new roads and log landings associated with the treatments had no detectable effect on sedimentation and turbidity.  Large woody debris (LWD) additions increased habitat complexity but no net increase in pool area was observed.  There was, however, greater morphological instability within the LWD addition sections as pools were both created and destroyed at significantly higher rates.  The treatments had no detectable effects on aquatic invertebrate communities.  Within the 90% BAH treatments, significant changes in the terrestrial invertebrate inputs were observed.  The abundances of larger-bodied taxa increased, which in turn increased the biomass of terrestrial invertebrates that entered the stream.  

Understanding the effects of riparian disturbance on streams is critical in preserving their functionality.  Experimentally manipulating small (250 m x 30 m) riparian patches may be a good analog for small-scale natural and anthropogenic disturbances.  These common events are assumed to alter streams, but there are few experimental studies quantifying their effects.