Impoverishment of resident old-growth forest bird assemblages along an isolation gradient of protected areas in eastern Finland

Abstract

Fennoscandian conifer forests have experienced a major landscape transformation during the 1900s. Currently, only scattered patches of old semi-natural forests exist in eastern Finland. However, on the Russian side old and mature forests still cover large tracts. We aim to show how the proximity of protected areas to the Russian border affects their species assemblages. We also ask how well the multi-scoring procedure applied by governmental ministries to design reserve networks performs in terms of bird protection . Censuses were conducted in fifteen old-growth forest areas located at varying distances (0-120 km) from the Finnish-Russian border in 1997. Data were gathered on ten non-migratory species that are mostly associated with old-growth or mature forests, many of which show decreasing population trends in Finland during the 1900s. Both the total density and number of species decreased as distance from the Russian border increased. Ofthe individual species, the Black Woodpecker (Dryocopus martius) showed the highest decrease in its relative population density. The Siberian Jay (Perisoreus infaustus) and the Treecreeper (Certhia familiaris) occurred only in the areas closest to the Russian border . The number of species peaked close to the border: the average number of species in the standardized 50 ha area decreased from 5.0 to 2.0 as distance increased from 0-10 km to 80-120 km. The results support views of the negative impact of isolation on old-growth specialist bird species. However, the habitat quality within the remaining patches -such as the amount of coarse woody debris -may also affect local bird assemblages . The ranking procedure applied in the old-growth areas in Finland turned out to be non-informative for birds. The ranks were not related to the population densities or number of resident species.