Habitat associations of old forest bird species in managed boreal forests characterized by forest inventory data

Conservation areas are important for many species associated with old forests, but most individuals still occur in commercially-used forest landscapes. We conducted three-visit breeding bird surveys in a total of 37 study squares of 1 km(2), and used National Forest Inventory data to evaluate habitat associations of birds linked with old forests in three geographical regions: southern, eastern and northern Finland. All study squares were located within managed forests. Out of the total of 23 pre-selected old-forest species, 12 were recorded in the study squares of all three study regions; the number of species varied between 16 and 21 among the regions. The total abundance did not significantly vary among the regions, but the abundances of many single species varied significantly among the regions. Forest-patch size was the single most important factor, positively affecting the abundance of most of the species considered. Development class affected most species in the south and east, and species associated with mature and old forest stands in general. Tree height and stand age were included into the models more often than tree species and diameter. In general, forest patch size, developmental class, age and tree height were among the most important factors in explaining the abundance of old-forest bird species in commercially-used forests. These stand characteristics appeared particularly important for resident species and cavity nesters. Our results indicate that the responses of old-forest bird species to environmental variation in managed, forested landscapes are individualistic, and different factors may affect them in different regions. Variables included in the patch-level forest-inventory data well explained abundance variation of species associated with old forests. Our results underscore the importance of integrating national forest-inventory and bird-survey data to obtain information about species habitat requirements and forest-sector related information about the effects of forestry on birds.