Small-scale dynamics of plant communities in an experimentally polluted and fungicide-treated subarctic birch-pine forest

Pollution from the Cu-Ni smelter at Monchegorsk, Kola peninsula, has result ed in major changes in the plant communities surrounding the smelter. Howev er, very little pollution reaches northern Finland, which makes it possible to use this area for field experiments to study the mechanism of community change under pollution load. A field experiment was established to study t he possible effect of pollution on the subarctic forest community, with Cu- Ni pollution and acid rain (AR) used as treatments. A fungicide (F)-treatme nt was also added to estimate the significance of plant-fungus interactions in community response. Floristic similarity decreased during the experimen t, both within and between treatments. Cu-Ni- and AR-treatments did not hav e any effect on species richness. The Cu-Ni treatment reduced significantly the number of new species arrivals in plots, whereas the number of local e xtinctions remained constant. The heavy metal treatment resulted in a decre ase in the bryophyte cover. The cover of Linnea borealis increased slightly due to the Cu-Ni-treatment, but decreased due to the AR-treatment. The F-t reatment also resulted in a lower richness than in the untreated variant. A gain, this effect was due to the reduced number of arrivals, whereas the nu mber of local extinctions remained unchanged. The F-treatment also resulted in a higher cover of bryophytes and dwarf shrubs. Changes in species richn ess of subarctic understorey plant communities were mainly caused by the di fferential arrival of species under different environmental conditions. As the number of arrivals was negatively correlated to the F-treatment, the pr esence of (presumably positive) interactions between vascular plants and fu ngi may have an influence on the response of a community to pollution. (C) Elsevier, Paris.