Authors: Kröel-Dulay, György; Orbán, Ildikó;Kertész, Miklós;Mojzes, Andrea;Szitár, Katalin;Ónodi, Gábor;

Since climate is a major determinant of both the distribution of major vegetation types and the delicate pattern of coexistence in plant communities, changing climate will inevitably lead to shifts in plant species composition. Despite substantial increase in temperature (>1°C) and changes in precipitation in many regions, well-documented changes in vegetation composition associated with changing climate are rare, and future changes have high uncertainties. By combining a long-term monitoring study and precipitation manipulation experiments, we investigated the effects of extreme weather events (drought) and chronic precipitation change on species dominance in an endemic sand grasslands in Central Hungary. Extreme drought events in the last 20 years led to gradual shift in species dominance from one perennial grass (Festuca vaginata) to another one (Stipa borysthenica), while the prolonged lack of drought allowed recovery. Drought and watering experiments reproduced these patterns, but went beyond and highlighted that recurring summer droughts lead to a decline of both perennial grasses and induce a shift to annual species. Our results indicate that these grasslands are prone to a major dominance shift in response to repeated summer droughts predicted for the future, with major consequences on ecosystems functioning and conservation of its endemic species.