Changes in the impact and control of an invasive alien: the grey squirrel (Sciurus carolinensis) in Great Britain, as determined from regional surveys

Abstract

The grey squirrel, Sciurus carolinensis Gmelin, was introduced into sites in England, Wales, Scotland and Ireland from the United States and Canada between 1876 and 1929. Soon after its introduction there were reports of damage to trees by seasonal bark stripping activity. Surveys in state and private forests since 1954 have monitored their distribution and impacts. Two surveys also gathered information on control efforts used to minimise damage. Grey squirrel population range has expanded significantly in Britain over the last 50 years and continues to do so. Survey results show high variability between years in damage recorded, consistent with the understanding that damage is triggered by high numbers of juveniles entering the population following a good breeding season. Results also show high variability between tree species in levels of damage recorded, but that thin-barked tree species are most at risk of damage from grey squirrels. Further, results show that the economic cost of damage can be high and that control measures will be ineffective if not appropriately targeted. The findings support suggestions that grey squirrels in mainland Europe should be eradicated to prevent future population expansion and any accompanying impacts on commercial timber crops.