Landscape characteristics associated with the occurrence of the flying squirrel Pteromys volans in old-growth forests of northern Finland

We investigated whether the occurrence of the flying squirrel, a declined virgin forest species. was accounted for by the structure of the landscape in northeastern Finland. We sampled 20 forest areas (1-77 km(2) in size) in 1995 for the occurrence of the species using a sampling plot method. landscape structure around occupied and unoccupied areas were compared using seven different radii ranging from 100 m to 10 km. Classified satellite images were analyzed with Geographic Information System (GIS). Ten areas could be determined to be occupied by the flying squirrel. Results shelved that occupied areas did not deviate from unoccupied ones in total area. In unoccupied areas there were more mature pine-spruce forests. and less matrix habitat, Lit the home range scale (100 m and 200 m radii) than in occupied areas. Furthermore, in unoccupied forest areas open habitats (clear-cuts, open fens) were more common than in occupied ones at distances between 200 m and 2 km around sampling plots. These differences resulted from both larger mean patch size of and smaller mean nearest neighbor distance between open habitat patches in unoccupied than in occupied forest areas, According to a logistic regression analysis, information on the amount of open habitat within 1 km radius alone correctly classified 75% of the areas into occupied and unoccupied ones. The probability of the presence of flying squirrel decreases with the increasing amount of open habitat within 1 km. The results suggest that increasing the amount of open habitats (e.g. clear-cutting) at the local scale has a negative impact on the flying squirrel. It is obvious that in the present situation where the population has severely declined and its optimal habitat is still diminishing, every patch suitable for the species - whether occupied or not - may be important for the population persistence.