A study has provided new evidence of beavers' expansion into the Canadian Arctic by dating the changes they have made to the tundra landscape as they spread northwards.
Published in the journal Ecosphere, the research combines tree‑ring analysis, or dendrochronology, with satellite imagery of surface water to pinpoint the spread of the North American beaver (Castor canadensis) in a remote part of Canada's Northwest Territories.
Beavers are ecosystem engineers, capable of changing landscapes through the construction of dams, which can alter the stability of permafrost and impact the flow of water, fish populations and local livelihoods.
Led by researchers from Anglia Ruskin University (ARU) in Cambridge, England, this new study shows that beavers leave behind a datable environmental record. Their browsing creates scars within the growth rings of shrubs, and their dams generate hydrological changes detectable from space.
Their northward expansion is thought to be driven by climate change, with the Arctic tundra experiencing increased shrubification. Species such as Salix (willow) and Alnus (alder), which provide food and construction material for beavers, have become more abundant as temperatures rise.
Working alongside the Indigenous environmental guardian and monitoring group, the Imaryuk Monitors, researchers surveyed locations in the Inuvialuit Settlement Region from Inuvik north to Tuktoyaktuk, on the coast of the Arctic Ocean, recording 60 beaver lodges or dam sites and collecting Salix and Alnus stems containing scars from beaver browsing.
To reconstruct browsing histories and confirm past beaver occupancy, these samples were cross-dated against regional shrub-ring chronologies spanning 1973–2023 (Salix) and 1968–2023 (Alnus), providing evidence of beaver colonisation in the region starting in 2008.
Satellite analysis revealed that at one large lodge-dam complex, beaver activity caused a significant and abrupt expansion of surface water between 2015 and 2019. This flooding, detected through satellite data, matched a period of intense browsing recorded in shrub‑ring samples at the site, providing strong agreement between two independent methods.
Senior author Dr Helen Wheeler , Associate Professor of Ecology at Anglia Ruskin University (ARU), said: "The engineering activities of beavers leave a clear trail of evidence, and our findings confirm important aspects of beaver occupancy at locations extending northwards as far as the shores of the Arctic Ocean.
"Arctic Indigenous communities are already observing rapid environmental change, and beaver range expansion is part of that shift. Their impacts on lakes, rivers, fish populations and traditional practices make understanding these dynamics a priority for the Inuvialuit community.
"As the Arctic continues to warm, the presence of beavers could increase further. The approach we've used in this research can help track these changes and support local communities and decision-makers."
The scientists say that this form of research could prove particularly useful for reconstructing wildlife activity in locations where long-term field observations are absent or incomplete.
Lead author Dr Georgia Hole, who carried out the work while at Anglia Ruskin University (ARU) and is now based at Durham University, said: "In the Arctic, we often lack the historical baselines needed to understand ecological change. This study shows how we've developed an approach to reconstruct that missing history.
"Beavers effectively write their history into the landscape with each shrub they cut and every pond they create by damming streams. By dating browsing scars in willow and alder using dendrochronological techniques, and linking these to hydrological changes detected in satellite imagery, we're able to pinpoint when and where beavers were present.
"Our findings demonstrate a powerful new way to track past beaver colonisation in Arctic regions that are rapidly transforming under climate change."
The study was carried out as part of the BARIN project funded by CINUK, the Canada-Inuit Nunangat-United Kingdom Arctic Research Programme. The researchers work in close collaboration with Inuvialuit research partners and communities, whose knowledge and engagement are central to the research.
