A great deal of our woodland management at Trelissick revolves around the removal of trees that have been severely damaged by grey squirrels. Often these trees are mal-formed, stunted and feeble, leaving them unstable and unsafe, particularly when in close proximity to one of our footpaths. The consequences of the grey squirrel introduction to our native woodlands is still yet to be fully understood but it is already evident that a huge number of broadleaved trees will never reach maturity as a result. This blog post examines where the squirrels have come from and why they present such a severe threat to the British countryside.
The introduction of grey squirrels
Over the last century, the grey squirrel (Sciurus carolinensis) has been on an unstoppable advance across the British Isles. As a species, it has come to exemplify the threats faced by our native wildlife from invasive, non-native species’.
Recent research suggests that the success and extent of the grey’s occupation can be almost entirely attributed to the actions of a select few landowners during the late 1800’s. Grey squirrels, the fleet-footed, furry mammals, that have become such a ubiquitous sight around our gardens and woodland actually originate from North America. They were captured, imported and released into Britain as a fashionable estate accessory in a time before anyone knew any better.
The Imperial College, in London, has recently published findings that lay the blame (more or less) at the feet of one man – the 11th Duke of Bedford, Herbrand Russell, who attained ten grey squirrels and released them into the gardens of his home at Woburn Abbey in 1890. He also sent the squirrels to his friends as gifts so that they might also release them on their own estates and was at the heart of the grey squirrel discharge into Regent’s Park, London.
The report goes on to state, “Grey squirrels are not as crazy invaders as we think – their spread is far more our own fault.” It was previously thought that grey squirrels, through various dominant characteristics, have spread across the UK in a virtual invasion but this is now believed to be incorrect. Further genetic studies carried out by the college have found that local populations of grey squirrel are not closely related in parentage and have actually originated from vastly different locations – the only way this could have occurred is through significant human intervention.
The displacement of red squirrels
The grey squirrel has become infamous for displacing our native red squirrels (Sciurus vulgaris) in British woodlands. The two species cannot co-exist for several reasons, chief of which is the squirrelpox virus carried by the greys. The greys are immune to this disease but it can be passed onto the reds when the two species come into contact. It has been approximated that the loss of red squirrels in Britain has happened twenty times faster than it would have done had the greys not carried this virus.
Another reason for the virtual disappearance of the red squirrel is the competitiveness of the grey. The grey is the larger of the two, at twice the weight, and has the behavioural advantages of foraging the woodland floor and the ability to digest acorns, both of which are adaptations that elude the red.
Resultantly, the UK now has a population of grey squirrels estimated at 5 million compared to around 120, 000 red squirrels, 75% of which are in Scotland. The last red squirrel was seen in Cornwall in 1984.
Grey squirrels – a threat to biodiversity
Some among you might ask, ” what does it matter if we have red squirrels or grey squirrels? – one is clearly better adapted than the other!” This may indeed be true on one level but grey squirrels actually pose a grave threat to our trees, woodlands and the overall biodiversity of Britain, whereas the native reds do not.
Grey squirrels cause an enormous amount of damage to our native trees by stripping away bark in order to access the sweet tasting sap beneath and, in some cases, even cause the death of the tree. The removal of this sap results in severe retardation of growth, weakening, deformity and increased proneness to fungal infection. Our trees are most vulnerable to attack when they are between 10 and 40 years old, after which their bark becomes too thick to strip.
A survey carried out by the Royal Forestry Society puts grey squirrels as a greater threat to broadleaved woodland than damage caused by grazing deer or even diseases such as ash dieback.
The cost to our economy through losses sustained in commercial forestry alone is estimated at over £50 million per year although the real price is many times that value with damage to gardens, parks and woodlands not included in that figure. On the Trelissick Estate, we lose trees to high winds every year because squirrel damage has rendered them too weak to withstand the weather.
Grey squirrels further damage our biodiversity by predating on the eggs and chicks of our native woodland birds. Several studies have shown that number of birds are significantly smaller in areas that house sizeable grey squirrel populations.
Re-introduction of red squirrels to Cornwall
The Cornwall Red Squirrel Project is an initiative that has been set up to re-introduce red squirrels into Cornwall. The group website states:
‘Cornwall is ideally suited to this project because of its relative isolation from the mainland, and the presence of wooded valleys and mixed woodland which offer suitable red squirrel habitat. The project will start with reintroductions on The Lizard and in West Penwith. These sites have been identified in a habitat survey as being suitable for re-introduction. As the two areas are surrounded by sea on three sides they are also more easily defended against re-population by grey squirrels’.
Their website is also a fantastic resource for all information on this subject and was immensely useful when compiling this particular blog post. It can be found at:
Further action at Trelissick:
On the property we avoid putting down poison in the countryside at all costs. Trapping grey squirrels can be very labour intensive for a small ranger team and doesn’t exclusively target the desired species. We have found the best way to keep on top of the squirrel population is through controlled shooting which we attempt to undertake whenever time and resources permit. We intend there to be a squirrel cull on the property soon and so thought is timely to offer the reasons why we take such action to reduce numbers of these animals at Trelissick.
– The National Trust ranger team, Trelissick and North Helford