LB 31-259 - Plant phenological responses to climate in a semiarid Mediterranean biome

Climate change, particularly rising temperatures, has profoundly impacted species' phenology and the timing of life-cycle events in plants and animals. Maintaining phenology within a temporal window is vital for symbiotically interacting species, ensuring resource availability. However, climate change can disrupt this synchrony due to species' varying sensitivities to environmental cues. Although the influence of temperature is well-studied, the effect of other climatic variables, such as precipitation, still needs to be understood. Arid environments, expected to become drier with increased interannual rainfall variability, may experience significant changes in plant phenology, especially in ephemeral species that complete most of their life cycle during the rainy season. A common mechanism by ephemeral plants in arid ecosystems to cope with prolonged drought, high temperature, and radiation is to utilize the protective effect of shrubs. However, the impact of this nurse effect on plant phenology remains unexplored. We conducted a nine-year weekly monitoring of ephemeral plant communities in a semiarid environment in the LTER Bosque Fray Jorge National Park, Chile, recording the onset and duration of their phenophases (vegetative, flowering, and fruiting). We investigated the effects of temperature and precipitation patterns on the phenological changes of ephemeral species in areas with and without nurse shrubs. Additionally, we assessed the relative impact of these climatic variables and the nurse effect on native and exotic plant species. Our results demonstrate that plants growing in under-shrub microhabitats exhibited a later onset and shorter duration of phenophases. However, we found no significant differences in phenology between native and exotic annual plants or geophytes. Furthermore, we determined that 15 mm of cumulative rainfall is necessary to trigger ephemeral plant phenology, with delays in reaching this threshold associated with delayed onset of phenophases and reduced duration. Temperature played a secondary role, with distinct effects of autumn (pre-phenology) and winter (during phenology) temperatures. These findings provide empirical evidence that precipitation patterns in arid ecosystems critically determine the phenology of ephemeral plants, suggesting that climate change impacts on these patterns could significantly affect entire plant communities.Funded by DRCLASS UAI HARVARD, LTERB NSF 2025816, ANID/FONDECYT N° 3210814, ANID/FB210006