Stream temperature as a metric of effective forest practices: Responsiveness of small streams

S.L. Johnson. USFS PNW Research Station, Corvallis, OR 97331 USA

Stream temperature is an easily measured and commonly used water quality parameter for monitoring responses of stream ecosystems to forest practices. However, policy guidelines for riparian zone management vary widely among states and provinces. Although much has been learned about stream temperature responses to clearcutting, many questions about effects of current forest practices on temperatures in small streams and stream networks remain unanswered. For example, what density of riparian cover is necessary to maintain cold temperatures in headwater streams? Can small streams be warmed without influencing downstream temperatures? Most guidelines focus on potential impacts to fish bearing streams; effects of increased temperatures on ecosystem processes and macroinvertebrates in headwater streams has not been a priority. Better understanding of factors which influence not only maximum but minimum temperatures will highlight riparian zone management practices that minimize impacts to stream temperature regimes. Studies show that the type of stream geomorphology can influence stream temperatures, with bedrock streams being much more responsive to incoming radiation. Little is known how changes in type or density of riparian vegetation potentially influence microclimatic factors. Heat energy budgets, if calculated using onsite microclimatic measurements, can provide checks of our current understanding of dominant mechanisms of heat exchange.