On the Increasing Occurrence of a Green Christmas: A Perspective from Long-Term Eddy Covariance Observations on Winter Dormancy Interruptions in a Subalpine Forest

Seasonal dormancy in temperate and boreal forests is an adaptive trait that guarantees tree survival during the winter season. This phenomenon is mainly affected by temperature and photoperiod. However, increasing evidence suggests that winter dormancy is not a static state but rather a dynamic period influenced by intermittent warm spells that can temporarily reactivate ecosystem processes. These dormancy interruptions, particularly during "Green Christmas" events — characterized by reduced snow cover and anomalous winter temperatures — have the potential to alter seasonal carbon fluxes, shift forest phenology, and alter physiological cycles. As climate change intensifies, understanding the frequency and implications of these interruptions becomes crucial for predicting long-term shifts in ecosystem carbon dynamics and energy fluxes.