Vistula River Valley as the ecological corridor for mammals

River Vistula, one of the large (1047 km in length) European rivers preserved in semi-natural, dynamic condition, is recognized as important corridor that enables birds and fishes to migrate for long distances. To test whether the Vistula valley provides corridor function also for mammals, field surveys and habitat modelling for six target species: Bank vole Myodes glareolus, Yellow-necked mouse Apodemus flavicollis, Pine marten Martes martes, Beaver Castor fiber, Wild boar Sus scrofa, and Elk Alces alces, were under-taken in the 135 km long fragment of the valley from 529 (Warsaw) to 685 km (Włocławek). The data collected documented the occurrence of at least 51 mammals (5 Insectivora, 14 Chiroptera, 1 Lagomorpha, 16 Rodentia, 11 Carnivora, 4 Artiodactyla), and the higest species richness was noted in the fragment of river valley covered with mixed forests which makes up the protected area called Kampinos National Park. This protected area (385 km[^2]) contains coniferous and mixed forests, inland dunes, wetlands, and mosaic of extensively used meadows, pastures, alder forests and fields. The LARCH (Landscape Ecological Analysis and Rules for the Configuration of Habitat) (Van der Sluis and Romanowski 2005) model outputs indicated the potential for large viable populations of species analysed in the river valley. The LARCH SCAN analysis showed that habitats of modelled species were well connected and their local populations formed highly sustainable network. The spatial cohesion of habitats was generally highest in Kampinos NP and along the fragment of River Vistula from 580 to 618 km. It is concluded that high cohesion of habitats facilitates dispersion of animals and provides potential for gene flow among the populations in the valley. Riparian forests and islands are important for connecting the local populations of mammals of two river banks and are the key elements to provide functional continuity of the corridor along the river in places, where it is discontinued on one bank. The scenario analysis demonstrates potentially negative effects of river regulation and construction of two dams on viability of mammalian populations and spatial cohesion of their habitats. The future corridor function of the River Vistula valley depends mostly on preservation of it.s dynamic, semi-natural condition.