Boreal plant decline in southern Sweden during the twentieth century

Abstract During the 1900s, land use changes and pollution were the main drivers of species abundance changes. A warmer climate is predicted to become increasingly influential during the present century and its effect is already well documented in arctic and alpine ecosystems, while there is less evidence in the boreal region. In this study, repeated surveys were used from three south-Swedish provinces (Skåne, Bohuslän, and Uppland), situated in the boreo-nemoral or northern nemoral vegetation zones, to explore changes in 81 boreal vascular plant taxa during mainly the latter half of the twentieth century. The changes were evaluated at grid cell resolutions of 5 or 2·5 km. To detect underlying patterns and mechanisms, frequency changes were tested against e.g. plant height and Ellenberg’s indicator values in linear regressions and ANOVAs. Boreal taxa showed a general decrease, with 70 significant decreases and 11 increases of 145 taxon × province combinations. Median annual decrease rates across species ranged from 0·2 to 1·8% among provinces. Two main patterns emerged: (1) low growing plants decreased more than taller plants; and (2) boreal taxa tended to decrease more towards their rear (southern) edge of distribution. Small boreal plants seem especially vulnerable, probably because they are sensitive to land use changes, including increased fertility, ceased management of semi-natural grasslands, and ceased water logging stress, which favour tall, competitive species. Obvious climate change effects appear subordinate hitherto, but small boreal plants still need special care to persist in their southern realms during the twenty-first century.