| Summary: | Thesis (M.S.) University of Alaska Fairbanks, 2023 Wildfire is a dominant natural disturbance process throughout boreal North America and fires are increasing in size, frequency, and severity. However, little is known about how wildfire affects boreal fish populations and aquatic habitat despite the substantial impacts of fire on ecosystem processes, and even less is known about how fire effects are mediated by species interactions. For example, North American Beavers (Castor canadensis) are affected by and can influence wildfire dynamics, and their engineering has complex effects on aquatic habitats. North American Beavers therefore have the potential to mediate wildfire effects on aquatic ecosystems and fish populations. Here I investigated relationships between wildfire and the distribution of beavers and a common fish species across a fire-dominated riverscape in Interior Alaska. First, I used satellite imagery to locate and enumerate beaver ponds throughout five large watersheds (total area: 20,711 km²) and modeled the relationship of beaver pond density (ponds per km²) as a function of wildfire history, stream geomorphology, hydrology, and vegetation composition. I then used a simulation to conceptualize the impacts of wildfire and beaver dams on Arctic Grayling (Thymallus arcticus) habitat availability under variable hydrologic conditions. Next, I sampled 62 streams for Arctic Grayling environmental DNA (eDNA) and sampled 10 of those streams for Arctic Grayling abundance. I used a generalized linear model (GLM) and N-mixture model to understand the relationship between eDNA concentration and Arctic Grayling abundance and distribution throughout the study area. I found that wildfire metrics explained most variation in beaver pond density (pseudo R² = 0.75) across the landscape and were positively associated with beaver pond density, although geomorphological and hydrological parameters were also important. My simulations indicated that beaver dams can create substantial barriers to fish dispersal during ...
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