Earlier flowering, later fading: Plant diversity loss restructures alpine phenology via competitive release

Abstract Understanding how plant phenology responds to rapid global change is critical for predicting vegetation dynamics and ecosystem functioning. While climate warming accelerates phenological shifts, particularly advancing flowering in alpine species, the role of biodiversity loss remains less clear. Drawing on theory suggesting that competition for resources among coexisting species can delay reproduction, we predicted that plant diversity loss would accelerate reproductive phenology via competitive release. Through a 12‐year plant species removal experiment in a Tibetan alpine meadow, we demonstrate that plant diversity loss restructured alpine phenology by driving earlier flowering (strongest in forbs) and later fading (i.e. delayed flowering senescence, strongest in grasses). These shifts extended flowering durations in most species, with stronger effects following the removal of dominant sedges or diverse forbs than after the loss of abundant grasses or proportional thinning of species across functional groups. Population‐level trends mirrored individual responses. Remaining species consistently faded later and extended their flowering durations across all removal treatments, although earlier flowering occurred specifically in grasses following forb loss. Phenological shifts correlated more strongly with declining species richness than with changes in soil temperature or nutrients. Across functional groups, earlier flowering was correlated with the number of species lost, whereas delayed senescence and extended flowering durations were observed in species‐poor communities. Synthesis. Our study provides robust experimental evidence that biodiversity loss restructures flowering phenology across scales—from the individual to the population and community levels—primarily through competitive release, regardless of whether a few dominant species, many common species, or a proportional thinning of species across functional groups are lost. These findings highlight a biotically driven mechanism of phenological change, with cascading implications for plant community assembly, species coexistence and ecosystem resilience under global change.