Introduced species are a most serious threat to biodiversity, second only to habitat degradation. The eastern gray squirrel (Sciurus carolinensis) is native to eastern North America, but has been introduced to several countries outside its natural range. In Europe, it has been introduced to Britain, Ireland, and Italy, and in all 3 countries it has spread and replaced the native European red squirrel (S. vulgaris). There are several possible explanations for the replacement of the European red squirrel by eastern gray squirrels, but the main hypotheses involve exploitation competition between the 2 species, although a disease that is fatal to red squirrels and possibly spread by the gray squirrel also may have contributed. Gray squirrels cause economic damage to forests by removing bark from trees, particularly broadleafed types such as oak and beech, and have the potential to suppress natural forest regeneration. In North America, eastern gray squirrels have been introduced into many areas in the Pacific Northwest, and throughout the southern part of Vancouver Island. They appear to be increasing their range and population densities. This paper outlines the history of eastern gray squirrel introductions to Britain and Italy, the effects on native species, and the management options currently in use and under evaluation. From this knowledge, we predict that gray squirrels on Vancouver Island may have detrimental impacts on the native North American red squirrel (Tamiasciurus hudsonicus) and the endangered Garry oak (Quercus garryana) ecosystem.
Bruemmer, Corrie, Lurz, Peter; Karl Larsen; John Gurnell. 1999. Impacts and Management of the Alien Eastern Gray Squirrel in Great Britain and Italy: Lessons for British Columbia (in Proc. Conference Biology & Management of Species and Habitats at Risk). Ministry of Environment, Lands and Parks. Conference Biology & ManagementProceedings. Vol. 1