Study sheds new light on how Scottish beavers interact with the environment | About

A study from the University of Stirling has shed new light on how beavers reintroduced to Scotland indirectly interact with deer – and the impact on the forests they share.

Researchers found that nearly two-thirds of trees felled by beavers produced new shoots, which were more abundant and concentrated closer to the ground than other trees.

This could diversify the forest structure towards a mix of short and tall tree trunks, which should boost biodiversity, according to researchers from the Faculty of Natural Sciences.

The research, which also involved researchers from NatureScot and the James Hutton Institute, was carried out in eastern Scotland in established beaver habitats by studying almost 800 trees.

Scientists compared the number of shoots on beaver-felled trees to standing trees and collected 156 shoots with four different combinations of beaver and deer browsing to compare their nutritional levels and physical characteristics.

Re-sprouted beaver felled trees, River Teith, Callander

About four centuries ago, beavers in Scotland were threatened with extinction. A formal multi-agency reintroduction program involving experts from the University of Stirling and the study partners – the first of its kind for a mammal species anywhere in Britain – began in Argyll in 2009.

The Scottish Beaver Strategy 2022-2045 sets out the benefits and challenges of reintroduction, including environmental and economic opportunities and the need for management when necessary.

Dr. Kelsey Wilson, who led the new study as part of her PhD research at the University of Stirling, said: “Beavers have gradually returned, sometimes after long absences, to riverine or riparian forests that are often shared with large populations of browsing deer.

“Beavers use their sharp teeth to cut down trees of different sizes and species along the river. Their most favored trees, such as willows, usually respond by vigorously sprouting a crown of new shoots – similar to what happens with traditional coppicing.

“We found that almost two-thirds of the trees produced new shoots after being cut down by beavers. These shoots were more abundant, nutritious, and concentrated closer to the ground than other trees, making them an easily accessible food source for foraging deer.”

Biodiversity boost

As beaver populations increase, interactions with deer are expected to become more common in riparian forests, which are valued for their role in reducing pollution of rivers, protecting them from rising temperatures, buffering floods and as a food source for aquatic life.

A better understanding of beaver-deer interactions can help guide conservation efforts and habitat management strategies to meet national forest creation goals in the areas where these two species overlap.

Professor Nigel Willby from the University of Stirling, co-author of the study, said: “The way a forest is structured has a major impact on its biodiversity and value. Our research shows that tree felling by beavers can diversify forest structure into a mix of short and tall tree trunks, which should increase biodiversity overall.

“However, if more deer are attracted to riparian forests by the provision of a rich, accessible food source that beavers encourage through their logging behavior, this could suppress tree growth. This could simplify forest structure and hinder future forest restoration efforts.”

This research, which also involved Professor Alison Hester, senior scientist at the Hutton, was jointly funded by the University of Stirling, NatureScot and the Hutton as part of a four-year PhD project (2018 – 2023).

Complex role

Dr. Martin Gaywood, NatureScot’s Species Projects Manager, said: “We were pleased to help support this research, which explores the complex role of beavers in the Scottish environment.

“The Scottish Beaver Strategy has ambitions for wider recovery of beavers across Scotland, and therefore the potential interactions between beavers and deer will be an important consideration in planning, decision-making and management. Where beavers have been restored to new catchments, continued monitoring of the combined impact of herbivores in relevant forests is ongoing.

“Creating and managing riverside woodlands in the presence of beavers is a key focus of the work of the Scottish Beaver Advisory Group, and this research makes a further useful contribution to our knowledge base.”

The article Tree Felling by Beaver Promotes Regeneration in Riparian States While Increasing Resource Availability for Deer was published in the journal Forest Ecology & Management.