Question: How do species composition and abundance change in the medium term and can the detected fluctuations and trends be attributed to weather conditions or climate change? Location: Quartz fields of the Knersvlakte, Succulent Karoo, South Africa, a plant diversity hotspot. Methods: We monitored vascular plant composition and abundance of all taxa on 12 permanent plots (25 m2) over a period of 12 yr. With multiple regressions, we tested the effect of rainfall in different periods on species richness and abundance. Results: The plots showed significant inter-annual changes in population size, species richness and species composition. In general, plant populations showed a significant positive trend over the 12 yr analysed, while therophytes decreased significantly. Number of chamaephyte and geophyte individuals was positively influenced by rainfall of the preceding year, whereas therophytes were significantly positively influenced by rainfall of the same year. Conclusions: We conclude that the increase in inter-annual variability of rainfall has so far had no negative effects on the quartz field vegetation. However, observations of recent climatic trends and climate change projections suggest that there will be much stronger changes in rainfall and temperature patterns in the next decades. Continuous long-term monitoring of biodiversity is thus crucial to understand potential impacts of climate change in the Knersvlakte.