Demographic variation of dwarf birch (Betula nana) in communities dominated by Ledum palustre and Vaccinium uliginosum

Abstract

The structure and demographic processes were compared in shrub communities to test the effects of vegetation succession on population growth, fecundity and abundance of the dwarf birch (Betula nana L.), which is a rare and endangered plant species in Poland and a glacial relict in Central Europe. The effects of Ledum palustre L. and Vaccinium uliginosum L. were studied in the Linje nature reserve in Chelminskie Lake District (northern Poland), in three permanent plots on a peat bog. Vegetative growth and reproduction of B. nana were lower in plant communities dominated by L. palustre and V. uliginosum, than in a reference site. Fecundity was also lower, despite the fact that the percentage share of potentially fertile age groups was similar in all study sites. Mortality of ramets was independent of vegetation, both for juvenile and mature stages. The results confirm that B. nana is intolerant of shade, and it is more abundant in vegetation without competitors. Light limitation can lead to its decline, primarily by a decrease in vegetative growth. Sexual reproduction may be negatively affected by shade, but it plays only small role in population growth. Butterfly larvae can destroy inflorescences, and thus contribute to low effectiveness of sexual reproduction. Increasing density of shrubs and trees in peat bogs can reduce the abundance of dwarf birch, and can lead to the extinction of its local populations.