Nature http://doi.org/gdxvxs (2018)

A lengthening growing season in response to recent warming is well documented in temperate and high-latitude vegetation, but the extent to which this trend can be expected to continue under future warming depends on whether other environmental factors become more limiting in these unprecedented conditions.

To explore climate change-related phenological shifts, Andrew Richardson from Northern Arizona University and co-authors use digital repeat photography of a whole-ecosystem warming experiment (up to +9 °C) set in a boreal Picea–Sphagnum bog ecosystem. They find that temperature linearly correlates with delayed autumn green-down and advanced spring green-up. This suggests an extension of the period of vegetation activity of 1–2 weeks under a ‘CO2 stabilization’ scenario (RCP 4.5; +2.6 ± 0.7 °C) — and 3–6 weeks under a ‘high emission’ scenario (RCP 8.5; +5.9 ± 1.1 °C) — by the end of the century.

There was little to indicate that responses were constrained by photoperiod; this allowed green-up and loss of frost hardiness to occur when spring frost risk was still high, suggesting that vulnerability to spring frost damage will increase in the future.