Changes in the moss layer in Czech fens indicate earlysuccession triggered by nutrient enrichment

Temperate fens are rapidly losing their specialized species. This applies even to seemingly untouched fens, in which the moss layer in particular is undergoing rapid succession.We analysed historical and recent vegetation-plot data from fens in the agricultural landscape on the Bohemian Massif (Czech Republic) to test the hypotheses that (i) more acidicolous and/or competitively stronger species that benefit from increased nutrient availability regionally increase in frequency and in percentage cover, and (ii) these competitively stronger bryophytes have become more tolerant of high pH because of the increased nutrient supply.We worked with two datasets: a precise dataset (themost similar pairs of samples from the same fens) and a large dataset (all of the historical and recent samples from the area studied). We found that calcicolous brown mosses specialized for growing in fens have recently been retreating to places with the highest pH, being replaced by more nutrient-demanding species such as Calliergonella cuspidata, Sphagnum palustre, S. teres and Straminergon stramineum in most of rich fens. Sphagnum fallax and S. flexuosum spread only in poor fens. At the level of individual species, the intensity of change in species abundance (cover-weighted frequency change) correlated significantly with the median potassium concentration in the biomass of species based on a large set of recent data.We conclude that nature conservancy authorities should monitor changes in the species composition of the moss layer as thismay signal the initial phase of nutrient enrichment of seemingly intact fens in agricultural landscapes.