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 decli ned virgin forest species. was accounted for by the structure of the l andscape 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 Informatio n System (GIS). Ten areas could be determined to be occupied by the fl ying squirrel. Results shelved that occupied areas did not deviate fro m unoccupied ones in total area. In unoccupied areas there were more m ature 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 mo re common than in occupied ones at distances between 200 m and 2 km ar ound 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 ha bitats (e.g. clear-cutting) at the local scale has a negative impact o n the flying squirrel. It is obvious that in the present situation whe re the population has severely declined and its optimal habitat is sti ll diminishing, every patch suitable for the species - whether occupie d or not - may be important for the population persistence.