Effects of Snow and Temperature on the Phenology of Alpine Snowbank Plants on Mt. Washington, New Hampshire

In northeastern North America, alpine snowbank (snowbed) communities are rare, highly diverse plant assemblages. They form in sheltered sites above treeline where late-lying snow provides insulation from late-season frosts and a longer-lasting source of water. We studied the effects of snowmelt timing and cumulative temperature on the vegetative and flowering phenology of seven common, alpine snowbank species on Mt. Washington, New Hampshire. We observed snowmelt date and plant phenology at 14 alpine snowbank sites over one growing season and collected temperature data using automated dataloggers. We used Pearson correlations to analyze the relationships between snowmelt timing and temperature (i.e., growing degree days) and plant phenology. Snowmelt date was positively correlated with the dates of peak phenophases, and lag time (time between snowmelt and peak phenophase) was negatively correlated with snowmelt date. Snowmelt timing consistently delayed the onset of phenological stages, but later snowmelt had a less-pronounced delay. Plants at later-melting sites experienced higher mean daily temperatures and accumulated growing degree days more quickly, leading to a shorter phenological cycle. Continued monitoring of snowmelt timing, temperature, and the phenology of alpine snowbank plants may provide clues to how climate change will affect alpine areas of northeastern North America, especially in terms of diversity, pollination, and abiotic interactions.