Abstract

Beavers are widely recognized ecosystem engineers that create persistent habitat structures such as lodges; yet, the conditions under which these structures fail to support occupancy remain poorly understood. We show that high-severity spring wildfire can precipitate abrupt functional collapse of these habitats. Following a May 2025 wildfire along Besnard Lake (Saskatchewan, Canada), we inventoried all 51 beaver lodges along the 154-km burned shoreline. Lodge occupancy declined markedly relative to pre-fire conditions; occupancy along the same shoreline segments decreased from 48.1% (26 of 54 lodges) in 2019 to 5.9% (3 of 51 lodges) after the fire. Among 32 lodges that could be matched between surveys, occupancy declined from 13 lodges in 2019 to 2 lodges in 2025. While 32 lodges experienced burning (of which 28 were partially or fully collapsed), structural damage alone did not predict occupancy. Occupied lodges occurred in areas of lower burn severity and where living deciduous vegetation remained available. These findings suggest a disturbance-driven decoupling between the physical persistence of engineered structures (i.e. lodges) and the ecological resources (i.e. food) required to sustain beavers. Under early-season, high-severity fire conditions, shoreline habitats that normally exhibit multi-year stability may rapidly fail due to loss of forage connectivity rather than lodge destruction alone.