Changes in alpine vegetation over 50 years in the Western Tatras (Slovakia)

This paper examines changes in alpine vegetation over 50 years in the Western Tatras part of the Western Carpathians Mountains in Slovakia. We focus on the following most widespread vegetation types: subalpine to subnival grasslands (alliance Juncion trifidi Krajina 1933), snowbed vegetation (alliance Festucion picturatae Krajina 1933) and dwarf-shrub vegetation (alliances Loiseleurio-Vaccinion Br.-Bl. in Br.-Bl. et Jenny 1926 and Vaccinion myrtilli Krajina 1933). The historical 1971–1977 sampling dataset was re-sampled in 2016–2017 and our research is based on a comparison of 40 pairs of these relevés. Herein, we studied (i) changes in species frequencies; (ii) changes in phytodiversity and site conditions using estimates of Ellenberg’s eco-indices and (iii) comparison of historical and current relevés over time using the nonmetric multidimensional scaling gradient analysis (NMDS) ordination method. The frequency curves reveal differences; especially in the most frequent species at 37.5−80%, which reach higher values in the current data. The higher 7.5−25% value of medium-frequent species in the historical relevés indicates progressive homogenisation of the examined vegetation. In addition, the Shannon-Wiener index of individual vegetation types revealed no significant differences in diversity or average number of species. The historical relevés included 75 species while 74 were confirmed in the current data. Statistically significant differences were determined in light factor for all three vegetation groups. This was due to the retreat of some light-demanding species. While NMDS indicated changes in Festucion and Vaccinion relevés over time, the Juncion group relevés did not follow this trend, thus confirming their high stability. The observed changes between current and historical data are attributed to changes in climate and altered land use with the cessation of grazing.