Long-term vegetation stability in northern Europe as assessed by changes in species co-occurrences

Background: The effect of the anticipated climate change on the stability of vegetation and the factors underlying this stability are not well understood. Aims: Our objective was to quantify long-term vegetation changes in a range of habitats in northern Europe by exploring species co-occurrences and their links to diversity and productivity gradients. Methods: We re-sampled vegetation in 16 arctic, mountain and mire sites 20 to 90 years after the original inventories. A site-specific change in species assemblages (stability) was quantified using species co-occurrences. Using a randomisation test we tested whether the changes observed were significantly greater than those expected by chance. Relationships between patterns in vegetation stability and time between surveys, numbers of plots, or species diversity and proxies for productivity, were tested using regression analysis. Results: At most sites the changes in species co-occurrences of vascular plants and bryophytes were greater than those expected by chance. The changes observed were found to be unrelated to gradients in productivity or diversity. Conclusions: Changes in species co-occurrences are not strongly linked to diversity or productivity gradients in vegetation, suggesting that other gradients or site-specific factors (e.g. land use or species interactions) may be more important in controlling recent compositional shifts in vegetation in northern Europe.