Dendrochronology and remote sensing reveal beaver occupancy and colonization dynamics in an expanding Arctic population

The North American beaver ( Castor canadensis ) is expanding its distribution in the Arctic tundra. Due to the species' capacity to engineer ecosystems, they can transform surface water dynamics and biogeochemistry, permafrost stability, vegetation composition, and impact Indigenous subsistence practices. Understanding past temporal occupancy dynamics of beavers is essential for assessing beaver colonization dynamics and impacts on ecosystems and people, but in the absence of historical data, new methods are required to address such knowledge gaps. By felling vegetation, beavers leave a clear historical signal of their occupancy and by damming rivers, they can also create a hydrological signal of their colonization. We combined dendrochronological techniques with satellite image time‐series analysis to infer beaver colonization and associated hydrological impacts at their northern range edge in the Inuvialuit Settlement Region in Arctic Canada. Over an ~130‐km transect, we recorded 60 detected beaver lodge and/or dam sites. At three focal sites across a latitudinal gradient, we collected 94 Salix and Alnus shrub stems with browsing scars. To reconstruct browsing histories and infer past beaver occupancy, we cross‐dated these against regional shrub‐ring chronologies spanning 1973–2023 ( Salix ) and 1968–2023 ( Alnus ), formed from 99 unbrowsed shrubs collected across the survey transect. The browsing histories provide evidence of beaver colonization in the region starting in 2008. The northern site record indicates occupancy between 2008 and 2022, the central site between 2015 and 2022, and the southern site between 2011 and 2023. We compared findings at one lodge–dam complex site with a remote sensing‐based time‐series decomposition method for the detection and characterization of surface water changes. Abrupt change in surface water extent was detected directly upstream of dams between 2015 and 2019, aligning with beaver browsing activity between 2015 and 2021. Convergent results across two independent novel methods give strength to the approach used and provide a link between browsing activity and hydrological impacts. Our findings indicate that combined dendrochronology and satellite image time‐series analysis may be applied elsewhere in the Arctic to gain insights into northward beaver range expansion and hydrological impacts in the understudied northern margins of their range.