Baeothryon alpinum (L.) T.V. Egorova (Cypercaeae) in the Polish Lowlands: distribution, population decrease and implications for conservation

A total of 47 localities of Baeothryon alpinum, hosting population of more than 100 000 shoots, were recorded in the lowland part of Poland during field surveys in the years 2003-2009. Among them were 25 populations discovered for the first time. Out of 57 sites of the species known from literature and unpublished (including herbarium) sources, 35 were not confirmed during the survey, 27 of them being definitely extinct. B. alpinum shows a clear pattern of distribution in Poland, with three main areas of occurrence: 1) the north-easternmost Poland (Lithuanian Lake District with the adjacent parts of the Masurian Lake District and the upper Biebrza river valley in North Podlasie Lowlands), which is part of the species boreal main range; 2) scattered localities in north-western Poland; 3) mountain mires at higher altitudes in the Sudetes and Tatra mountains and the adjacent part of southern Poland. The main aggregation of localities is found in Augustów Forest (including the Sejny Lakeland and Wigry National Park), and in the Góry Sudawskie region with adjacent areas. The biggest Polish population in the "Kobyla Biel" fen near Augustów consisted of several dozens of thousands of shoots. The Lithuanian Lake District is an area of general importance for the conservation of B. alpinum in Poland. The species is threatened, first of all, due to secondary succession (mires overgrowing with shrubs, trees and reed) and requires conservation measures as well as establishing nature reserves in places where it occurs. The degree that B. alpinum decreases in number is strikingly different in particular regions of Poland - it has lost most of its localities in north-western Poland and in Masurian Lake District, while in the Lithuanian Lake District and the upper Biebrza valley there are minor losses only. Depending on the region (from the west to the east and from the south-west to the north-east), the species should be given extinct or critically endangered (regions of north-western and southern Poland), endangered (Masurian Lake District), vulnerable (North Podlasie Lowlands) and near threatened (Lithuanian lake District) status. Although the disappearance of the populations beyond the species main range is a common phenomenon, the presented pattern is man-related and connected with differences in land management