Long-Term Impacts of Severe Wildfire and Salvage Logging on Macroinvertebrate Assemblages and Food Web Structure in Rocky Mountain Headwater Streams

Abstract

Wildfire is an important natural disturbance on forested landscapes influencing both physical and biological processes. The Lost Creek wildfire in 2003 was one of the more severe on Alberta’s eastern slopes and provided a unique opportunity to assess the long-term impacts of wildfire on northern Rocky Mountain watersheds. The objectives of this research were to determine if persistent wildfire effects on streamflow and water quality produced effects on macroinvertebrate assemblage structure in burned and burned & salvage-logged watersheds and to evaluate potential effects on aquatic food web structure. Benthic macroinvertebrates and Cutthroat Trout (Oncorhynchus clarkii) were sampled eight years after the wildfire. Multivariate analysis of macroinvertebrate assemblage structure and stable isotope analysis were used to assess the long-term impacts of the wildfire on aquatic fauna. Reference, burned and burned & salvage-logged watersheds each supported a unique macroinvertebrate assemblage, suggesting that different mechanisms (resource availability and habitat limitation) were driving the ecological response in wildfire affected watersheds. Stable isotope analysis (carbon and nitrogen) showed a shift in macroinvertebrate food web structure in burned watersheds to a greater reliance on instream primary productivity. Trout showed no difference in growth metrics or resource utilization between reference and burned watersheds. Post-wildfire salvage-logging produced additional impacts to macroinvertebrate assemblages in affected watersheds highlighting the importance of addressing cumulative impacts to aquatic ecosystems.