Trends and Variability in Temperature Sensitivity of Lilac Flowering Phenology

Abstract The responses of plant phenology to temperature variability have many consequences for ecological processes, agriculture, forestry, and human health. Temperature sensitivity ( S T ) of phenology could measure how and to what degree plant could phenologically track climate change. The long‐term trends and spatial patterns in S T have been well studied for vegetative phenology such as leaf unfolding, but trends to be expected for reproductive phenology in the future remain unknown. Here we investigate trends and factors driving the temporal variation of S T of first bloom date (FBD). Using the long‐term FBD records during 1963–2013 for common lilac ( Syringa vulgaris ) from 613 stations in Europe, we compared changes in S T from the beginning to the end of the study period. The Spearman partial correlations were used to assess the importance of four influencing factors. The results showed that the temporal changes in S T of FBD varied considerably among time scales. Mean S T decreased significantly by 0.92 days °C −1 from 1963–1972 to 2004–2013 ( P  < 0.01), but remained stable from 1963–1987 to 1989–2013. The strength of FBD and temperature relationship, the spring temperature variance, and winter chill all impact S T in an expected way at most stations. No consistent responses of S T on photoperiod were found. Our results imply that the trends and variability in S T of flowering phenology are driving by multiple factors and impacted by time scales. Continued efforts are still needed to further examine the flowering‐temperature relationship for other plant species in other climates and environments using similar methods to our study. Key Points Temporal changes in temperature sensitivity of lilac flowering date from 1963 to 2013 were quantified Temperature sensitivity decreased from 1963–1977 to 1999–2013 but remained stable from 1963–1987 to 1989–2013 Changes in temperature sensitivity can be attributed to combined effects of three driving factors