biostudies-literatureMulder CPHNational Science Foundatione70160https://www.ebi.ac.uk/biostudies/studies/S-EPMC12918847biostudies-literatureUnknown113(2)<h4>Premise</h4>High-latitude plants initiate flower primordia at least 1 year before flowering. While impacts of rising temperatures on phenology in the flowering year are well studied, the effects of warmer temperatures in the initiation year (IY; the year before flowering) are virtually unknown.<h4>Methods</h4>At 19 sites in interior Alaska, we experimentally warmed flower primordia of seven boreal species in the initiation year, flowering year, or both and tracked flowering phenology in the flowering year for two cohorts. For two species (Vaccinium uliginosum and Vaccinium vitis-idaea), we also tracked developmental stages of flower primordia.<h4>Results</h4>Warming in the flowering year resulted in earlier flowering for four species (V. vitis-idaea, Rhododendron groenlandicum, ViburnuAmerican journal of botanyContrasting effects of experimental warming in the initiation year and the flowering year on flower phenology of boreal understory species.PMC12918847DEB-1655951 to C.P.H.M. and DEB-1655831 to P.K.D.DEB‐1655951 to C.P.H.M. and DEB‐1655831 to P.K.D.Mulder CPHDiggle PKSchaub EPfalseContrasting effects of experimental warming in the initiation year and the flowering year on flower phenology of boreal understory species.<h4>Premise</h4>High-latitude plants initiate flower primordia at least 1 year before flowering. While impacts of rising temperatures on phenology in the flowering year are well studied, the effects of warmer temperatures in the initiation year (IY; the year before flowering) are virtually unknown.<h4>Methods</h4>At 19 sites in interior Alaska, we experimentally warmed flower primordia of seven boreal species in the initiation year, flowering year, or both and tracked flowering phenology in the flowering year for two cohorts. For two species (Vaccinium uliginosum and Vaccinium vitis-idaea), we also tracked developmental stages of flower primordia.<h4>Results</h4>Warming in the flowering year resulted in earlier flowering for four species (V. vitis-idaea, Rhododendron groenlandicum, Viburnu2026-01-01T00:00:00Z2026 Feb2026-07-16T07:53:20.229Z2026-07-09T10:46:26.053ZS-EPMC129188474167023810.1002/ajb2.70160