Impacts of beaver dams on riverscape burn severity during megafires in the Rocky Mountain region, western United States

Megafires, defined as fires with burn areas greater than 100,000 acres (404.7 km²), result partly from increasingly short wet seasons coupled with consistently hotter, drier summers, and partly from past forest management decisions. Historically rare, megafires have become increasingly common in recent years. In this study, we examined the impact of megafires on riverscapes with beaver dams to explore the resilience of these habitats. We investigated whether beaver-modified riverscapes are more resistant to the impacts of megafires than geomorphically similar riverscapes lacking beaver dams. Our analysis utilized remotely sensed and field-collected data from three Rocky Mountain region megafires that burned in 2020. Our results showed that riparian areas with beaver dams (1537 beaver dams, which occurred in 658 out of 13,933 valley bottom segments evaluated) had significantly reduced burn severity compared to riverscapes without beaver dams or to areas outside the river corridor. Additionally, when riverscapes were classified according to their modeled beaver dam capacities (a metric closely linked to riparian habitat quality), areas with beaver dams had consistently lower burn intensities than those without beaver dams, even within the same theoretical dam capacity class. Our results indicate that riverscapes with a high degree of manipulation by beavers have significant resistance to burning during megafires. This resistance may also provide valuable secondary benefits in postfire ecosystem health, water quality, and biodiversity.