Snow as a parameter of bryophyte niche partitioning in snow-beds of the Tatra Mountains (Western Carpathians)

Understanding relationships between microclimate and bryophyte species diversity in alpine conditions creates a background for investigation into the response of vegetation to potential climate changes and anthropogenic pressure. This study presents the reaction of spore-bearing plants (liverworts and mosses) to the main thermal gradients in the snow-beds of the Tatra Mountains (Western Carpathians) and the mechanisms behind these response patterns. The results were based on direct, year-long temperature measurements in 47 permanent plots located at sites where the plant cover is formed largely by bryophytes. Data were gathered in 2010-2013 using Onset Hobo Pro v.2 temperature data loggers. Habitat variables i.e. seasonal snow cover duration (SCD), zero curtain period (ZC) and July mean ground surface temperature (MGST_VII) were determined using the ground surface temperature (GST) method. Additionally, the sum of potential incoming solar radiation in July (PISR_VII) was analysed on the basis of the localisation of permanent plots. Using detrended correspondence analysis (DCA) and redundancy analysis (RDA), we analysed the relationships between the species composition and the microclimatic variables. The generalised additive model (GAM) was employed to investigate the response curves of bryophyte species to snow parameters (SCD and ZC). Humidity (expressed as ZC temperature parameter) proved to have the highest impact on the distribution of bryophytes in snow-beds. Moreover, ground temperature in the vegetative season (in July, MGST_VII) and altitude had statistically significant effects. The responses of liverworts to microclimate gradients were more varied in comparison with those of the mosses. Humidity significantly affects the occurrence of the species of both groups in snow-beds. However, mosses respond to ground temperature (MGST_VII), whereas liverworts respond to SCD, and this distinguishes the niches of these groups. The ZC is a significant parameter affecting plant functional group composition, demonstrating a high relationship between cryptogamic plants and alpine climate. Pohlia ludwigii, Nardia breidleri and Moerckia blyttii prefer the high humidity of the snow-beds, while Marsupella condensata, M. apiculata and Pohlia drummondii are associated with dry habitats.