Bright and Long: Day Length Modulates the Phenology of Two Myrtaceae Species in Upper Montane Mixed Ombrophilous Forest

The Upper Montane Mixed Ombrophilous Forest is a humid montane ecosystem characterised by cold winters and a rich Myrtaceae flora. We investigated the vegetative and reproductive phenology of Myrceugenia euosma (O. Berg) D. Legrand and Siphoneugena reitzii D. Legrand and its relationships with climatic variables over 35 months in southern Brazil. Using activity and intensity indices, circular statistics and generalised linear models, we assessed seasonality and climatic influences on phenophases. Both species exhibited continuous vegetative phenology. Reproductive phenophases were annual, seasonal and synchronous within species but temporally segregated between them. This phenological behaviour suggests niche partitioning that may reduce competition for pollinators and dispersers. Vegetative phenophases showed limited climatic dependence, with leaf flush in S. reitzii responding only to current day length. Reproductive phenophases were positively related to day length in both species, with distinct temporal lags. Comparisons of the mean onset and peak angles indicated interannual variation in most phenophases. Phenological advances were more frequent (13 events, 6–32 days) than delays (8 events, 6–59 days), suggesting climate‐related shifts. These results indicate that abiotic factors act as environmental filters shaping the phenological patterns of sympatric Myrtaceae in montane environments.