Weather fluctuations drive short-term dynamics and long-term stability in plant communities: A 25-year study in a Central European dry grassland

Question Infrequent events of extreme drought or extreme temperatures may considerably affect the structure and functioning of vegetation. Here we investigate how fluctuations in precipitation and temperature shape year-to-year dynamics and plant species composition in a dry grassland community, and how this variation affects plants with different life histories. Location Dry grassland (Festucion valesiacae) in the Pavlov Hills, SE Czech Republic. Methods Long-term trends in vegetation change in the grassland studied were assessed by the ordination of plot records from vegetation surveys performed between 1930 and 2019. In addition, year-to-year changes in vegetation were studied in seven permanent plots of 16 m(2)surveyed annually from 1993 to 2018. Variation in species composition and abundances was related to temperature and precipitation in the preceeding two springs, summers, autumns and winters using ordinations and mixed-effect linear models. Results There were no remarkable directional changes in the grassland community over the period 1930-2019. However, during the last 25 years, the community exhibited pronounced year-to-year fluctuations, which depended on weather conditions in the previous two years. Species with different life histories (e.g. perennials vs. annuals) and different ecology (e.g. ruderal vs. dry-grassland species) responded differently to specific weather patterns. Perennials were sustained by wet summers, annuals benefitted from wet springs and autumns and moderately warm and wet winters, and covers of ruderals of mixed life histories increased after dry summers. Conclusions Plant species composition in a Central European dry grassland shows remarkable year-to-year dynamics in response to weather patterns over the previous two years. These community changes are non-directional and contribute to the stability of this grassland, which has not changed considerably over the past 90 years. However, increasing frequency of drought events because of ongoing climate change can result in a directional change with an expansion of ruderal species.