The Importance of Biogeography to Biodiversity of Bird Communities of Coniferous Forests

Abstract

Bird communities of coniferous forests attain their largest species numbers in central Siberia; these numbers are gradually declining towards the periphery of the boreal zone. A secondary maximum of species numbers is found in the Alps. Boreal belts of southern (Mediterranean) mountains are impoverished in numbers of species, although "xenoecious" species inhabit coniferous forests. The uneven geographical dispersion of species is caused by isolation and migration paths during Pleistocene changes of vegetation belts. Considering the subspecies level, Siberian elements reach the Alps and the Rhodope Mountains, Palaearctic elements even extend to the Canaries. Mountain regions along the Mediterranean sea are characterised by many endemic subspecies. Boreal ecosystems include the most specialised species. Similarity of bird fauna assemblages is highest between boreal regions and lowest in Mediterranean areas. Biodiversity diminishes in the boreal forests from central Siberia onwards, in southern extrazonal regions from the Alps to periphery regions. Small isolated populations on southern mountain tops are most endangered.