Indirect Effects of Climate Change on Stream-Riparian Ecosystems: a View on Forest, Fire, and Flow Dynamics from Idaho's Salmon River Basin

Responses of stream-riparian ecosystems to global climate change (GCC) are driven by direct shifts in temperature and precipitation.   However, GCC is predicted to alter the composition and global distribution of terrestrial ecosystems as plant species distributions shift with climate regime.  Western North America, in particular, is predicted to experience GCC-induced alteration of forest ecosystems through changing dynamics of wildfire and beetle outbreaks.  Because stream-riparian ecosystems are coupled to uplands via material and energy flows, such shifts in terrestrial disturbance regimes and spatial distributions may affect aquatic ecosystems. We hypothesize that in regions like Idaho’s Salmon Basin indirect effects of GCC (e.g., on forest, fire, and flow dynamics) mediate structural and functional responses of stream-riparian ecosystems.  We predict that these effects may yield greater change than would be expected based solely on temperature and precipitation shifts. We assess these direct and indirect effects in the context of large river networks in western North America such as the Salmon River, which are projected to experience shifts from snow to rain-driven hydrology and increased frequency and extent of wildfire and beetle outbreaks. Through a combination of synthesis and qualitative modeling we show how changes in terrestrial disturbance regimes may mediate GCC effects on ecosystem inputs (water, sediment, light, nutrients, organic matter) with interactive consequences for production of stream organisms like fish, whole ecosystem metabolism and ecosystem exports of water, sediment, nutrients and carbon.  The results of this synthesis and modeling suggest that predictions of GCC effects on stream-riparian ecosystems, including populations of stream fishes, will need to incorporate potential indirect interactions associated with changing terrestrial disturbance regimes.