Extreme winter warm event causes exceptionally early bud break for many woody species

In many ecosystems, climate is changing faster during winter compared to other seasons. However, we lack basic information about the responses of many species to winter climate change, including extreme warm events. Extreme warm events may have particularly strong influences at the end of winter, when some species begin to break dormancy while the risk of freezing remains high. Here, we monitored bud burst of 101 temperate woody species following an extreme warm event during winter to investigate species responses to this anomalous event and determine whether functional traits predicted species responses. Following six consecutive days of extreme warm temperatures in winter, nearly half the surveyed tree and shrub species had an advanced stage of bud phenology. Responding species were most likely to be shade-intolerant, phylogenetically related, and have weaker dormancy requirements. Based on established species response thresholds to spring temperatures in the region, species were expected to be unresponsive to warm temperatures this early in the year, yet many species broke dormancy. Species responses to this extreme winter warm event highlighted how climate change can alter well-established species-climate associations. In an era of increasing climate change creating novel winter conditions, continued monitoring both long-term and following extreme events is needed to understand new speciesclimate dynamics.