Fig. 2: The apparent spring phenological sensitivity to temperature demonstrated in situ in one of the longest time series of phenological observations.

a The growing degree days (GDD) required for cherry trees growing in Liestal to flower depend on the year. The regression line represents the long-term average GDD ±1σ, and the dots represent the underlying raw data of in situ phenological observations¹⁴. While we cannot rule out decreasing chilling as a driver of declining spring phenological temperature sensitivities, lower chilling should increase the required thermal time to budburst [see refs. ^5,10], whereas here no systematic trend in GDD over time was observed. b Representation of the time to Liestal cherry tree blooming as a function of temperature under the assumption of constant GDD across years. The regression line represents simulated mean values ±1σ, and the dots represent the underlying raw data. c The log–log transformed time to blooming-temperature relationship of the data shown in (b) to linearize the relationship.