Influences of riparian forest structure and stand development on vertebrate biomass in headwater streams

Printer-friendly version

Riparian forests are dynamic, changing as a result of stand development processes, disturbance, and anthropogenic activities, which in-turn influence large wood recruitment, light availability, and organic matter inputs to adjacent streams. In this study, we evaluated how the age and stage of riparian stand development influenced adjacent stream habitat, light availability and biota in western Oregon headwaters. We first assessed changes in stream habitat and fish biomass over time as we revisited five sites where surveys conducted in the late 1970’s had demonstrated increased fish biomass in response to greater light associated with riparian harvest. Surveys in 2014 indicate that trout biomass in these reaches has decreased – likely in response to riparian stand development, canopy closure, and reduced primary production.  We also used a space-for-time approach to explore relationships between the age/stage of the riparian forest, stream habitat, stream light availability, periphyton stocks, invertebrate abundance, and vertebrate (fish and salamander) biomass in 9 streams with paired old-growth and second-growth reaches. Canopy openness was positively correlated with periphyton stocks, invertebrate abundance, and total vertebrate biomass, suggesting strong bottom-up controls on stream biota. These results highlight the importance of stream light regimes and the potential for riparian forest age controls on light to influence invertebrate and vertebrate populations.