Experimental evidence of future drier and warmer conditions affecting flowering of two co-occurring Mediterranean shrubs

We aimed to assess the impact of drier and warmer conditions on flowering traits of two common species of the coastal Mediterranean shrublands, Erica multiflora and Globularia alypum, which flower in autumn and winter. To achieve this goal, we performed a field experiment over two years, using a novel nonintrusive technique to prolong the drought period or to create passive nighttime warming. Drier conditions (17%-29% reduction in annual mean soil moisture) delayed most of the studied flowering phenophases, altered the length of the flowering period, decreased the functional flower production, and extended the flower life span in both species. Warmer conditions delayed and advanced, respectively, the onset of autumn and winter flowering of G. alypum in the first year. Higher temperatures also decreased the number of G. alypum plants with functional autumn flowers by 20%, whereas they increased the number of G. alypum plants with functional winter flowers by 28%. Therefore, our results indicate that drier and warmer conditions might alter the flowering phenology and production of these Mediterranean species. This, in turn, might lead to a change in the species composition and structure of these Mediterranean shrublands in the long term.