Hydropeaking impacts on riverine plants downstream from the world's largest hydropower dam, the Three Gorges Dam.

Hydropeaking has become a global issue because of extensive hydropower dam construction worldwide. Yet, its ecological impacts on riverine ecosystems are not well studied. We explored the effects of hydropeaking on riverine plants, based on data from a ~300 km reach downstream of the world's largest hydropower dam, the Three Gorges Dam. We tested three hypotheses relating to hydropeaking impacts on species elevational distributions, assemblage structure and species-specific biomass patterns by generalized linear mixed modelling and joint species distribution modelling. We found that, first, hydropeaking greatly shaped species elevational ranges, leading to expansions of herbs to high elevations and shifting species dominance at low elevations. Secondly, we detected contrasting effects of hydropeaking on assemblage-level characteristics of herbs. The inundation induced by hydropeaking had strong effects on assemblage composition and biomass allocation, where more biomass was allocated to belowground part. Hydropeaking blurred the species richness-biomass relationship, although it had little effect on species richness or plot-level biomass. Thirdly, hydropeaking induced inundation was the most important covariate driving species biomass patterns of riverine plants, although complex species-specific effects were identified, and random effects were often large in fitted models. We concluded that hydropeaking likely acted as a major driver of plant community assembly in rivers with a hydropower dam. Conservation and restoration of riverine plants can benefit from the inclusion of water level management in operational schemes of hydropower dams, especially during the early life history stages.