Discovering ecophysiological causes of different spring phenology responses of trees to climatic warming

Global warming has generally advanced the spring phenology of extratropical trees. In several cases, however, the advancing has levelled off, indicating a declining temperature sensitivity of phenological timing. The potential reasons for the decline have been actively debated, but no direct experimental evidence has been produced to support any of the theories put forward. With the aid of scenario simulations, we examined which ecophysiological tree traits restrict the advancing of the onset of spring phenology in four subtropical tree species under global warming. In the simulations, we applied process-based tree spring phenology models formulated on the basis of results of experiments specifically designed for examining the ecophysiological responses addressed. We identified three restricting ecophysiological traits: 1) the chilling effect operates at relatively low temperatures only, 2) the temperature sensitivity of spring phenology is low in the temperature range of +10 to +20 degrees C which is critical under climatic warming in subtropical conditions; and 3) the winter rest is deep. Unexpectedly, a high chilling requirement was not included amongst the restricting ecophysiological traits. Our experimentally based results show that the spring phenology of the trees under climatic warming is significantly affected by seemingly small and usually neglected details of the ecophysiological responses to chilling and forcing temperatures.

Automated summary

Global warming generally advances the spring phenology of extratropical trees, but in some cases, the advancing has leveled off, indicating a declining temperature sensitivity. The potential reasons for this decline have been debated, but no direct experimental evidence has been found. Through scenario simulations, this study examines the ecophysiological traits that restrict the advancing of spring phenology in four subtropical tree species under global warming. The results show that seemingly small and often neglected details of ecophysiological responses to temperature change significantly affect the spring phenology of trees under climatic warming.