Positive effects of an extremely hot summer on propagule rain in upper alpine to subnival habitats of the Central Eastern Alps

Abstract

Background: Propagule production and dispersal largely determine the distribution and potential migration ability of alpine plant species. Variation in reproductive success caused by year-to-year variation in climate may critically influence these processes. Aims: To obtain estimates for the propagule rain in high-alpine plant communities and detect potential dispersal events from lower elevations. Methods: The magnitude and composition of the propagule rain was studied in different plant communities along an elevation gradient from the upper alpine to subnival zone. Propagules were trapped at eight elevations from 2760 to 3070 m a.s.l. for three years from July to September 2003–2005. Vascular plant species and their cover were recorded in an area with a radius of 10 m surrounding the traps. Results: A five- to 10-fold higher propagule rain was observed in 2003, a year with an exceptionally hot summer, compared to 2004 and 2005. Propagule and species numbers varied highly among years and community types. Few propagules of non-local origin were recorded in any year. Conclusions: Extremely hot summers are likely to greatly magnify the propagule rain size of species in alpine habitats. Such ‘mast years’ may contribute to enhanced and accelerated vegetation changes in alpine habitats in the absence of limiting factors.