Plant regeneration directs changes in grassland composition after extreme drought: a 13-year study in southern Switzerland

1 The cover of plant species was recorded annually from 1988 to 2000 in nine spatially replicated plots in a species-rich, semi-natural meadow at Negrentino (southern Alps). This period showed large climatic variation and included the centennial maximum and minimum frequency of days with greater than or equal to 10 mm of rain. 2 Changes in species composition were compared between three 4-year intervals characterized by increasingly dry weather (1988-91), a preceding extreme drought (1992-95), and increasingly wet weather (1997-2000). Redundancy analysis and ANOVA with repeated spatial replicates were used to find trends in vegetation data across time. 3 Recruitment capacity, the potential for fast clonal growth and seasonal expansion rate were determined for abundant taxa and tested in general linear models (GLM) as predictors for rates of change in relative cover of species across the climatically defined 4-year intervals. 4 Relative cover of the major growth forms present, graminoids and forbs, changed more in the period following extreme drought than at other times. Recruitment capacity was the only predictor of species' rates of change. 5 Following perturbation, re-colonization was the primary driver of vegetation dynamics. The dominant grasses, which lacked high recruitment from seed, therefore decreased in relative abundance. This effect persisted until the end of the study and may represent a lasting response to an extreme climatic event.