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Grey Squirrels

Grey squirrels (Sciurus carolinensis) were introduced to Britain from North America in the nineteenth century.

Damage and impact

Grey squirrel on a birch treeThey are now widely established and many people enjoy their presence, especially in urban parks and gardens.

However, grey squirrels pose a serious threat to our native red squirrels and cause significant damage to trees.

Threat to reds - the red squirrel population in England is confined to the islands in Poole Harbour, the Isle of Wight, and scattered sites in the north of England.

There are estimated to be only 15,000 red squirrels left but over 2 million greys. Greys have been largely responsible for this decline in red squirrels by spreading the deadly squirrel pox virus.


Native red squirrel - a protected species







Threat to trees - grey squirrels also strip bark from trees, causing between £6 and £10million of damage to broadleaved and coniferous woodlands per year in Britain.

This damage is a disincentive to tree planting and management and has a negative impact on biodiversity and on the overall economic value of woodlands. It also limits diversity of woodland planting so reducing potential resilience to pests, disease and climate change.


Bark stripping damage usually starts at the end of April and continues until the end of July (early September in high-risk years). Stripping might occur anywhere on the main stem and branches.

Grey squirrel damage on a birch treeVigorously growing and dominant trees are generally most affected. Damage levels vary between years and across sites within the same year. Trees younger than 10 years are not normally damaged because their stem and branches are too small (less than 50 mm diameter) to support a grey squirrel.

Bark on the main stem of trees older than 40 years is normally too thick to strip, but grey squirrels will strip the thinner bark on the larger branches in the crown.

Susceptible tree species

Planted or naturally regenerated trees aged between 10 and 40 years, especially sycamore, beech, oak, sweet chestnut, pine, larch and Norway spruce, are most vulnerable to damage.

However, other species (especially broadleaves) and age classes may be damaged, particularly in high-risk years.

Government policy and action

Efforts to control grey squirrels in England’s woodlands need to be effective, well coordinated and sustained to both protect and expand our vulnerable red squirrel population and to improve the environmental and economic value of our woodlands.

A review of government policy was carried out in 2013 and an updated national policy and action plan  was published in December 2014

Advice and guidance

Controlling Grey Squirrel Damage to Woodlands  provides full details of grey squirrel management strategy an methods.

Data gathered from surveys can be used to monitor how threatened populations of red squirrels are responding to conservation management or to environmental change, and they can also be used to assess the effectiveness of grey squirrel control measures.

Practical Techniques for Monitoring and Surveying Squirrels describes how to plan a survey and gives guidance on which method(s) to use.

Identifying squirrel damage: a concise guide

Further information

More information on the science, current research, and control techniques of grey squirrels is on the Forest Research website.

Last updated: 28th February 2017