Tree damage

Tree crown loss through squirrel damage by Kay Haw


Grey squirrels negatively impact the health of the UK’s trees and woods through bark stripping. Damage creates open wounds, weakens, stresses and kills trees. This is a serious problem at a time when the UK is working to increase its tree and woodland cover for the many essential benefits trees provide.


High densities of juveniles can strip bark from the main stem and branches of trees between April and September. Grey squirrels target young broadleaved trees, mostly 10-40 years of age, and repeat the damage year after year if the population remains high and unmanaged.


The 1985 Broadleaves Policy saw a change towards planting more tree species that support native biodiversity and have the potential to provide an important hardwood timber resource. However, there is a reluctance to plant broadleaves for timber purposes due to the impact of bark stripping by high densities of grey squirrels.


Species particularly susceptible to damage include biodiverse and high value trees such as oak, beech, hornbeam and sweet chestnut. Whereas species such as lime, horse chestnut and wild cherry are far less or unaffected.



Grey squirrel bark stripping damage on beech at Trelowarren by Kay Haw



Tree health

Bark stripping weakens trees and creates open wounds that can result in irreversible damage and infection by pathogens. This destructive activity can also lead to girdling, cutting off the tree’s nutrient supply from its roots, which causes tree fatalities.



Biodiversity

As trees mature they provide niches and habitat for a huge range of different species. A mature oak can support over 2,000 different species, but is one of the trees most targeted by grey squirrels. To ensure the woods planted today develop into the biodiverse ancient woods of the future, many landowners and managers actively reduce grey squirrel numbers to protect the trees.



Squirrel damage on beech by John Morris



Timber production

As grey squirrels cause the loss of leaders, lesions, callus growth and dysfunctional shape, trees are prevented from achieving good timber form. In 2019, the European Squirrel Initiative released new figures estimating the cost of grey squirrel damage to the forestry industry to be in excess of £40 million a year. Although the total economic costs increase due to the need to import timber, which also increases the risks of importing further tree pests and diseases.



Ecosystem services

Mature, healthy trees provide a wealth of ecosystem services, such as cleaning our air and water, improving soil quality and function, mitigating heavy rainfall and flooding events, and reducing and sequestering atmospheric carbon. The UK aims to increase its tree planting rates to provide more of these benefits, but many young trees and woods are struggling due to grey squirrel damage.



Bark stripping damage in the National Forest by Daniel Small


Donate to our research into an oral contraceptive to reduce grey squirrel numbers and protect the UK’s trees. Progress in the third of the five-year project is good and hopes are high that this innovative work will provide an effective, less labour intensive, non-lethal method for managing grey squirrels.


We still needs to raise £250,000 to complete the project. Anyone wishing to support the research can donate online.