Ecosystem warming extends vegetation activity but heightens vulnerability to cold temperatures.

Area of Science:

• Ecology
• Climate Change Biology
• Plant Science

Background:

• Vegetation phenology shifts are key indicators of climate change impacts.
• Uncertainty exists regarding the future drivers of phenological trends, with potential shifts from temperature to photoperiod dominance.

Purpose of the Study:

• To investigate the effects of experimental whole-ecosystem warming on vegetation phenology in a boreal Picea-Sphagnum bog.
• To assess the role of photoperiod versus temperature in driving phenological responses under warming conditions.
• To project the extension of vegetation activity and associated risks under future climate scenarios.

Main Methods:

• Utilized digital repeat photography to derive phenological transition dates.
• Applied experimental whole-ecosystem warming treatments of up to +9°C.
• Confirmed findings through direct observation of vegetative and reproductive phenology and multi-year data collection.

Main Results:

• Experimental warming linearly correlated with delayed autumn green-down and advanced spring green-up in dominant woody species.
• Observed phenological responses showed little evidence of photoperiod constraint.
• Projected extension of vegetation activity by 1-2 weeks under moderate warming and 3-6 weeks under high emissions by the end of the century.
• Documented severe tissue mortality following a spring frost event due to failed photoperiodic cues and loss of frost hardiness.

Conclusions:

• Warming significantly alters boreal bog phenology, extending the period of vegetation activity.
• The risk of spring frost damage is likely to increase in a warmer world due to phenological mismatches.
• Current vegetation strategies may become suboptimal under future climate regimes, necessitating adaptation.