Abstract
One of the most important threats for open peat bog ecosystems is encroachment of woody species, which causes transformation of habitat conditions and leads to retreat of specialised species. Drainage increases the rate of succession. The aim of study is the assessment of human-accelerated succession in a transitional bog. The study was conducted in ‘Mszar Bogdaniec’ nature reserve (W Poland). The structure of vegetation and tree stands was described and compared using ordination methods. Near the peat bog border, tree stands of Betula pubescens developed. Towards the middle part of the peat bog, the number, cover and height of trees decreased. The central part of the peat bog was covered by Sphagno recurvi–Eriophoretum vaginati in dryer parts and Sphagno recurvi–Eriophoretum angustifolii in wetter parts. The study showed that the successional sequence in these conditions differs from the classical bog succession scheme. Despite high propagule pressure of Pinus sylvestris, the most important woody species was B. pubescens, which performed better than other species. Erechtites hieracifolia, an alien invasive herb species, which previously was rarely recorded in bogs, appeared when the bog was dried by drainage. In this study, it reached high frequency and abundance, which shows that it may be a next serious threat to disturbed wetland ecosystems.