Data from: Asymmetric winter warming advanced plant phenology to a greater extent than symmetric warming in an alpine meadow

The warming of terrestrial high-latitude ecosystems, while increasing,
will likely be asymmetric across seasons – where winter non-growing
seasons will warm more than summer growing seasons. Asymmetric winter
warming in temperature-sensitive ecosystems may delay spring phenological
events by reducing the opportunity that a plants’ chilling requirement is
met. Similarly, symmetric warming can advance spring phenology. To explore
the impact of asymmetric warming on plant phenology, we applied a
year-round warming and a winter warming treatment to our experimental
plots. Over a two-year period, we monitored leaf-out and flowering
phenology for 11 plant species. There was variation among species,
however, both winter and year-round warming, advanced the leaf-out day and
the first flowering day relative to the control treatment. Winter warming
advanced leaf-out and flowering phenology by 11.1 (± 2.4) and 12.6 (± 2.9)
days, respectively. However, year-round warming had less of an impact
advancing leaf-out and flowering phenology by 5.1 (± 2.1) and 10.0 (± 3.0)
days, respectively. Our study provides direct evidence that asymmetric
winter warming has a larger impact on plant phenology than symmetric
year-round warming. Increasing soil temperature in the winter from below
to above freezing temperatures advanced the spring phenology of alpine
plants. Winter warming increased soil temperature more than year-round
warming, which explains why phenology advanced under winter warming more
than under year-round warming. In addition, early or mid-season flowering
plant species displayed different phenology strategies in warmer winters.
Synthesis: Relative to other ecosystems, alpine ecosystems such as the
Tibetan Plateau will likely respond to asymmetric warming given the higher
amplitude of winter temperature increases due to climatic warming thus
seasonal variation in warming should be considered when predicting and
modelling the response of alpine ecosystems to climatic change.