Using a new database of plant macrofossils of the Czech and Slovak Republics to compare past and present distribution of hypothetically relict fen mosses

Modern databases containing large amounts of botanical data are a promising source of new results based on large data analyses. We used a new database of plant macrofossils of the Czech and Slovak Republics to compare the recent distributions of putative relict species of fen bryophytes with their past distributions since the late glacial. All the species studied occur in late-glacial sediments, but mostly in regions where they are recently recorded (19–21st centuries). There are specific regions rich in putative relict species of fen bryophytes both in late glacial / early Holocene times and recently. In some cases the target species were, however, found outside the recent distribution range where environmental conditions are no longer suitable for their occurrence. We further found that the total number of the glacial and early-Holocene records greatly exceeds the total number of records for the middle Holocene, when succession to woodlands or bogs resulted in a reduction in species of bryophytes that are specific to open rich fens. The observed patterns may imply a relict status of the target species. We especially documented a substantial decline in the abundance of species requiring a high and stable water level (Drepanocladus trifarius, Meesia triquetra and Scorpidium scorpioides), both throughout the Holocene and during the most recent transformations of the landscape. In contrast, those species that tolerate transient decreases in water level persisted into recent times at more localities (Calliergon giganteum, Hamatocaulis vernicosus, Paludella squarrosa). Macrofossil data cannot, however, provide a quantitative analysis of the distribution of a species, because the number of recent data usually greatly exceeds the number of fossil records. The reason is that the area sampled in palaeoecological research is very small as it is time-consuming and expensive; cores or excavations usually are of only a few square centimetres. Despite this shortcoming, macrofossil data are an important, but not the only, source of evidence for the identification of the relict status of a species.