The Decadal Effects of Wildfire on Macroinvertebrate Communities in Southwest Montana

In the western United States, wildfires are increasing in frequency, intensity, and size due to climate change and historical land management practices. These environmental events have reshaped forested landscapes, affecting stream ecosystems and riparian zones. High-intensity wildfires can increase sediment and nutrient loading, reduce riparian canopy cover, and alter in-stream habitat, leading to changes in macroinvertebrate community composition. While the immediate (1-10 years) wildfire effects on macroinvertebrates are fairly well documented, decadal (10+ years) responses remain understudied. This research gap limits our understanding of post-fire trajectory and stream ecosystem resilience. To address this knowledge gap, we can identify how wildfires alter macroinvertebrate (aquatic insects) community trajectories. I investigated the effects of high-intensity wildfires on macroinvertebrate communities in southwest Montana using a Before-After-Control-Impact (BACI) design and a time-since-fire approach. Using long-term macroinvertebrate data from the Montana Department of Environmental Quality, I examined how functional feeding groups and life history traits may impact community composition 1–20 years post-fire. As fire increases sunlight and nutrients in streams, I expect increased algal production and a shift in functional feeding groups favoring those groups that primarily consume algae, like collectors and grazers. In addition, I predict that the post-wildfire macroinvertebrate community will favor individuals with more than one generation per year because they tend to have faster population growth rates and could spread more rapidly. Overall, there was a lot of variation in macroinvertebrate community composition changes across streams within both burned and unburned sites.