North American beavers began colonizing parts of the Arctic in 2008. (Getty)
Beavers, usually found in forests and woodlands, are steadily moving north into the Canadian Arctic. A new study has discovered when they arrived in different parts of the Arctic by studying scars on shrubs and comparing them to satellite images showing changes in bodies of water.Science The researchers combined two methods including tree ring analysis, known as dendrochronology, and satellite observations to build a timeline of their activity.The findings suggest that North American beavers (Castor canadensis) began colonizing parts of the region in 2008. The researchers say this approach could help scientists understand how wildlife spread in areas where there are few long-term records and could also help monitor environmental change.
Beavers are changing the Arctic
Beavers are often described as ecosystem engineers because they are able to reshape the places where they live. They build dams on water courses and rivers, and create ponds.The changes could have wide-ranging impacts. Beaver dams can also affect the stability of permafrost, permanently frozen ground found throughout much of the Arctic. It can also affect fish habitat and water flow.Scientists believe that the northward expansion of beavers is linked to climate change.
As temperatures rise, the Arctic is seeing more shrubs growing across the tundra.Shrubs such as willow (Salix) and alder (Alnus) provide food and building materials for beavers. As these plants spread, the landscape becomes more hospitable to the animal.
The bushes were recorded when the beavers arrived
A team from Anglia Ruskin University in Cambridge, England, worked with the Imaryuk Monitors, an indigenous ranger and environmental monitoring group in the Inuvialuit settlement area in Canada’s Northwest Territories.The researchers surveyed the area extending from Inuvik to Tuktoyaktuk on the coast of the Arctic Ocean. During their fieldwork, they recorded 60 beaver sites or dam sites.They also collected stems from willow and alder bushes that had been chewed by beavers. Beavers leave scars on plants they chew that become preserved within the annual growth rings of shrubs. By analyzing the rings, scientists were able to determine the year in which each scar was formed.The researchers also compared the shrub samples to regional growth ring records covering the period from 1973 to 2023 for willow and from 1968 to 2023 for alder. This helped them determine when beavers first occupied different sites. Their analysis showed evidence of beaver colonization beginning in 2008.
Beavers leave scars on the plants they chew. (Representative image of arctic willow)
Satellites confirmed that major changes had occurred
The team also used satellite images to study how bodies of water change over time. At one large dam and beaver lodge complex, satellite data showed a sudden increase in surface water between 2015 and 2019.
The timing matched a period when shrub samples showed heavy beaver browsing at the same location.Because both methods indicate the same period of activity, the researchers say this provides strong evidence that beavers were responsible for the changes seen in the landscape.Combining ground-based observations and satellite data has given scientists greater confidence in reconstructing the animal history of the region.
Beavers write history
Lead author Dr Georgia Hall, who conducted the research while at Anglia Ruskin University and is now based at Durham University, said one of the biggest challenges in Arctic research is the lack of long-term records.“In the Arctic, we often lack the historical baselines needed to understand environmental change. This study shows how we have developed an approach to reconstruct this lost history,” she said.Dr. Hall explained that beavers leave behind a record of their activity every time they cut down bushes or build dams.“Beavers effectively write their history in the landscape with every shrub they cut and every pond they create by damming streams,” she said. “By dating browsing scars in willow and alder using arboriculture techniques, and linking them to hydrological changes detected in satellite images, we are able to determine when and where beavers were present.”“Our findings demonstrate a powerful new way to track past beaver colonization in Arctic regions that are rapidly transforming under climate change.”The researchers say this method could be particularly useful in remote areas where scientists have not been able to conduct regular field observations over many years.