Plant community composition is the crucial factor for heath performance under precipitation extremes
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Question: Studying the effects of alterations in precipitation regime on plant communities, including drought and heavy rain spells, is gaining increased importance under climate change. Numerous studies focus on shifts in above-ground production, analysing, climate response of vegetative plant traits, but few consider plant fitness and reproduction. We investigated the response to climate manipulation of generative plant traits and the role of community composition for target species performance. Location: An experimental heathlands in Central Europe. Methods: We investigated the effects of extreme events such as drought and heavy rainfall, as well as homogeneous precipitation supply, i.e. continuous water availability, on experimental heath communities differing in species numbers (two, four) and functional groups (one, two). We investigated generative traits (number of flowers, number of seeds, seed rain, seed mass, germination rate and reproductive success) and vegetative traits (above-ground biomass, ratio of abundance in 2010 to abundance in 2005, cover) of the two common heath species Vaccinium myrtillus L. and Calluna vulgaris (L.) Hull. Results: First, the species composition of the community had a larger influence on target species traits than precipitation manipulations. Second, our four-species community had higher production of flowers, seeds and increased reproductive success of target individuals than the two-species C. vulgaris-V. myrtillus community. Third, homogeneous water supply (weekly irrigation) increased the reproductive success of C. vulgaris. Conclusions: Our results provide evidence that community composition and richness might be crucial for heath performance, with the facilitative effects of species interactions gaining increased importance under climatic instability.