Changes in Stream Food Webs Following Forest Harvest? Quantifying Bottom up Responses

In the Pacific Northwest, multiple large scale studies are evaluating whether current forest harvest methods lead to impacts for streams and stream food webs. Although regulatory agencies tend to focus on responses of single metrics, i.e. temperature or sediment, as proxies for system responses, the study of ecosystem processes and multiple components of food webs are vital to increase current understanding of trophic linkages and potential consequences of forest harvest for aquatic biota. 

In the Trask River Watershed Study, western Oregon, we are conducting an integrated study of effects of forest harvest on stream food webs, instream habitat, chemistry, and hydrology in small streams.  We hypothesized that we would see ‘bottom up’ effects from increased light and instream nutrients following the harvest of whole small watersheds and large portions of the riparian forests in 2011. We are finding surprisingly limited responses at lower resource levels, including standing stocks of epilithon, chl a, fine benthic organic matter and primary production. We are evaluating whether these findings might be influenced by increased number of consumers at sites. Understanding of the processes and interactions between factors influencing stream ecosystem responses will increase our ability to extrapolate findings from these sites to other landscapes.