We studied experimentally how heterospecific attraction may affect habitat selection of migrant passerine birds in Finnish Lapland. We manipulated the densities of resident tit species (Parus spp.). In four study plots residents were removed before the arrival of the migrants in the first study year, and in four other plots their densities were increased by releasing caught individuals. In the second year the treatments of the areas were reversed, allowing paired comparisons within each plot. We also investigated the relative abundance of arthropods in the study plots by the sweep-net method. This allowed us to estimate the effect of food resources on the abundance of birds. The heterospecific attraction hypothesis predicts that densities of migrant species (especially habitat generalists) would be higher during increased resident density. Results supported this prediction. Densities and number of the most abundant migrant species were significantly higher when resident density was increased than when they were removed. On the species level the redwing (Turdus iliacus) showed the strongest positive response to the increased abundance of tits. Migrant bird abundances seemed not to vary in parallel with relative arthropod abundance, with the exception of the pied flycatcher (Ficedula hypoleuca) which showed a strongly positive correlation with many arthropod groups. The results of the experiment indicate that migrants can use resident tit species as a cue to a profitable breeding patch. The relationship between the abundance of the birds and arthropods suggests that annual changes in food resources during the breeding season probably do not have a very important effect on bird populations in these areas. The results stress the importance of positive interspecific interactions in structuring northern breeding bird communities.

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 km2 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 lo 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 showed 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 at the home range scale (100 m and 200 m radii) than in occupied areas Further more, 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 m 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

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We studied the occurrence and cover of epiphytic bryophytes and one lichen species (Lobaria pulmonaria (L.) Hoffm.) growing on Populus tremula L. trunks. Our aim was to explore the spatial scales where epiphyte species respond to their environment. At the landscape scale, fragmented Finnish old-growth forests close to the Russian border and farther west in a heavily fragmented landscape were compared with Russian sites with more continuous old-growth forest landscapes to assess the effect of landscape structure on epiphyte assemblages. We studied factors affecting populations at the level of individual sites and local habitat patches within the forests. Twelve sites were surveyed for epiphytes. We estimated epiphyte occurrence from 353 Populus tremula trunks. There seemed to be only minor differences in the structure of epiphyte assemblages between the three landscapes surveyed. Species richness varied also independently of the landscape structure but was positively related to regional Populus tremula abundance (alpha diversity) and the size of the substrate trunk (point diversity). At the regional scale, the most important factor affecting the occurrence of epiphytes was the abundance of Populus tremula. At the local scale, the size of the Populus tremula surveyed and tree density around the trunk surveyed correlated positively with the occurrence of some species. The size and abundance of Populus tremula as well as tree density are the most important factors for maintaining viable populations of the studied species.Key words: biodiversity, boreal forest, Bryophyte, forest management, landscape structure, Lobaria pulmonaria.

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