An elevational shift of cryophilous bryophytes in the last century - an effect of climate warming?

Aim To investigate altitudinal range shifts of bryophytes in Switzerland by comparing recent altitudinal distributions with historical distributions derived from herbarium specimens. Location Switzerland, covering 41,285 km(2) in Central Europe. Methods We used a dataset of 8520 herbarium specimens of 61 bryophyte species and compared altitudinal data between the two periods 1880-1920 and 1980-2005. The records we used were not specifically sampled for climatological analyses, but originate from non-systematic fieldwork by various collectors. Historical and recent records were distributed all over Switzerland with occurrences in all major biogeographical areas. To account for different sampling efforts in the two time periods, different subsampling procedures were applied. Results Overall, we found a significant mean increase in altitude of 89 +/- 29 m which was mainly driven by the cryophilous species (+222 +/- 50 m). The mean increase in altitude of cryophilous species corresponds to a decadal upward shift of 24 m. The upper range limit of cryophilous species also increased by 189 +/- 55 m, but there was no effect on the lower range limit. For intermediate and thermophilous species neither mean, nor upper or lower range limits changed. However, the proportion of records of thermophilous to cryophilous species increased considerably at lower altitudes, but levelled off above approximately 1800 m. Main conclusions We conclude that cryophilous bryophytes are expanding their range to higher elevations in Switzerland and that at lower elevations, a slow extinction process is going on, probably as a result of climate warming trends. The observed decadal upward shifts of cryophilous species closely match those reported from vascular plants in Europe and those expected, given recent estimates of climate warming trends. We emphasize that herbaria provide valuable data that can be used to detect ongoing changes in the distribution of species.