It has been predicted that Northern Europe will experience a rise in temperature of 2.3–5.3°C from now until 2100. This increase in temperature may lead to vegetation change along altitudinal gradients. To test this prediction, we recorded plant-species composition in 1995 and 2005/06 in Swiss pre-alpine fen meadows (800–1400 m a.s.l.). Despite no obvious changes in the management of these fens, overall, plant-species richness (cumulative number of plant species at five plots per site) significantly increased over this period. This was mainly due to an increase in the number of thermophilous, rich-soil indicator and shade indicator species which corresponded to increased community productivity and shading within the vegetation layer. In contrast, fen specialists significantly declined in species numbers. The strongest shift in vegetation composition occurred at the lowest sites, which overall had a higher colonization rate by new species than did sites at higher altitudes. Vegetation change along the altitudinal gradient was also affected by different types of land management: early- flowering species and species with low habitat-specificity had high colonization rates in grazed fens, especially at low altitudes.