The site comprises the whole of the natural (unregulated) course of the Biebrza river (164 km long) and its valley, along the border of the buffer zone of Biebrza National Park. The valley can be divided into three parts (the upper, middle and lower basin), which differ in physiography, hydrography and ecological character. In the upper basin the river is small and cuts through peat deposits. This area has been partly drained and presently consists of bogs, pastures and meadows, with fragments of marshy pine Pinus forest and mixed forest of oak Quercus and Pinus. The middle basin is dominated by fens, being a mosaic of open and scrub-covered sedge-beds and meadows on alluvial soils. Here there are two extensive areas of natural birch Betula forest and some areas are covered with swampy alder Alnus forest (admixed with spruce Picea) and fragmented Pinus forest. The lower basin floods in spring, so is used for haymaking and non-intensive cattle- and horse-grazing. The lower basin is 30 km long and 5-12 km wide. Valley mires here (mainly fens) are natural and have not been modified by man. Along the river are extensive wet meadows (covering c.10% of the lower basin) and many oxbow lakes covered with reeds Phragmites. Areas which are regularly and extensively flooded each spring are dominated by sedge-beds. Unflooded areas are covered by variably dense forest of willow Salix and Betula, as well as sedge-beds. Scrub succession here is proceeding rapidly. Farther away from the river there are extensive young riverside forests Alnus in marshy areas and fragments of mixed forest Quercus/Pinus.
This is the most important breeding place in central and western Europe for some threatened or localized species such as Gallinago media, Crex crex, Porzana porzana, Aquila clanga and Chlidonias leucopterus, and is also an important site for migrating waders, ducks, geese and Grus grus. Breeding species of global conservation concern that do not meet IBA criteria: Aythya nyroca (1-3 pairs), Haliaeetus albicilla (four pairs), Crex crex (common).
Pressure/threats to key biodiversity
Unsustainable exploitation of birds is high. In the upper basin, local people propose further drainage of bogs, and illegal fires are set by land-owners every year. The middle basin was partly drained in the nineteenth century. Fishermen and tourists cause some disturbance to birds. The part of the IBA outside the National Park comprises the buffer zone to the park. The site is an amalgamation of three sites (the former `PL100'-`PL102') identified in the previous pan-European IBA inventory (Grimmett and Jones 1989).
National Partial International Partial59,223 ha of IBA covered by National Park (Biebrzañski, 59,223 ha). 59,223 ha of IBA covered by Ramsar Site (Biebrzañski, 59,223 ha).
BirdLife International (2020) Important Bird Areas factsheet: Biebrza river valley. Downloaded from
http://www.birdlife.org on 06/04/2020.