How deep is the sleep of tree buds in winter? A more erratic sleep for deciduous trees than previously thought is discovered. A new study by Romain Garrigues and co-authors showed that while absence of winter cold can keep trees asleep for longer, autumn warming can cause an early wake-up.

Romain explains: "Bud dormancy of deciduous trees is generally considered as a period when buds are closed and sleeping. We know that dormancy could be influenced by climate change and in particularly by warming trends. Elevated temperature could disrupt bud development by decreasing the cold temperature exposure (chilling accumulation) and subsequently prolonging the time required for bud opening (spring budburst)."

Romain's new study analyzed during two years the effect of fall warming on bud winter dormancy (endodormancy) of European beech (Fagus sylvatica L.). Throughout experiments, chilling was consistently diminished, yet the response of dormancy depth (indicating how profoundly buds are sleeping) and spring budburst exhibited variability between years. In fact, findings unveiled a potential dual effect of warming on bud development—both delaying and advancing bud opening in spring, related to the dormancy depth. 

Romain: "This discrepancy could potentially be attributed to variations in senescence onset and in the exposure to warmer temperatures. The research sheds light on the complex relationship between warming temperatures and bud development during autumn and winter, prompting a deeper understanding of the potential consequences for European beech trees."