Linking Fish, Forests, Fire, and Stream Function

Field technicians electrofishing in McRae Creek in the H.J. Andrews Experimental Forest for the Scale Consumer and Lotic Ecosystem Rates (SCALER) field experiment. Photo by Lina DiGregorio, Oregon State University.

Three lines of research are underway related to this topic. We are collecting and analyzing data from various streams originating in the Coast and Cascade Ranges of Oregon. The first study, with Alba Argerich, employs a field experiment at the H.J. Andrews Experimental Forest to evaluate the role of stream consumers in stream functional processes by manipulating densities of aquatic vertebrates for about 40 days. It aims to understand observed responses of macroinvertebrates and stream functional processes of nutrient uptake, stream respiration, primary production, and metabolism.

The second and third studies, with Ashley Coble, used a stratified random sampling design to select one set of streams across a gradient of watershed stand-age in coastal Oregon and another set of streams across a gradient of watershed stand-age and fire severity in streams in the Cascade Range to understand aquatic responses, including periphyton (stream algae and diatoms), macroinvertebrates, amphibians, fish, and riparian vegetation, as well as temperature, large wood, canopy cover, and water chemistry. 

Factors influencing stream function, showing links above and below the surface among biological (plants, invertebrates, amphibians, fish) and physical (substrate, channel properties, flow) components of streams. Drawing by Kathryn Ronnenberg, USDA Forest Service.

We found that forested streams, fire, and large wood are linked (Coble et al. 2023). Fire severity explained more of the variation in large wood volume than pre-fire watershed stand age. Higher-severity fires burned more overstory riparian vegetation, leading to increased light, dissolved organic matter (DOM) concentrations, and macroinvertebrate densities, along with reduced canopy cover, large wood diameter, macroinvertebrate diversity, and fish densities. We did not observe increases in coarse wood or large wood volume or associated increases in fine sediment as expected, likely because of a lack of high-intensity rain events in the first year following fire.

Although we understand that consumers that feed on periphyton and other organisms in the stream play important roles in food webs, it is less clear how consumers connect to the level of stream functional processes, and how those relationships change across watershed stand-age and fire severity. This research will collectively contribute to an ecosystem-based understanding of aquatic-riparian ecosystems.

Continued comprehensive aquatic and riparian ecosystem monitoring of these watersheds will aid in understanding long-term effects of post-fire management activities on aquatic ecosystems, including salvage logging, which is expected to affect large wood recruitment to streams for decades. 

Burned area along Big Creek, Clackamas River basin, Mount Hood National Forest 1 year after the 2020 Riverside Fire. Photo by Brooke Penaluna, USDA Forest Service. Photo by Brooke Penaluna, USDA Forest Service.

Collaborators

• Alba Argerich, University of Missouri, School of Natural Resources

• Ashley Coble, National Council for Air and Stream Improvement, Inc.

• Bureau of Land Management

• Campbell Global

• LLC; Giustina Resources

• Oregon Department of Forestry

• Port Blakely

• Rayonier

• U.S. Department of Agriculture Forest Service

• Weyerhaeuser Company