Modelling leaf coloration dates over temperate China by considering effects of leafy season climate

Abstract

Current process-based models of autumn phenophases are generally based on autumn temperature and/or photoperiod cues. The dependence of autumn phenology on environmental conditions occurring throughout the leafy season has been overlooked. In this study, we incorporated the effect of leafy season temperature and precipitation in process-based models with the aim to improve the modelling of autumn phenology. We tested the ability of three existing and three new autumn phenology models in predicting the occurrence of leaf coloration of four deciduous tree species during 1981–2012 across temperate China. The results show that the models taking the effects of both the leafy season temperature and low precipitation into account performed best over both calibration and validation data. Compared with existing autumn phenological models, the best models predict that the potential delay of autumn phenology in a warmer world is modulated by the impact of leafy season climate on leaf senescence in a complex way: increased leafy season temperature tends to hasten the occurrence of leaf coloration while low leafy season precipitation tends to delay it. Additionally, we tested the hypothesis of a local adaptation of tree phenology through the evaluation of site-specific model parameterizations. Local fittings of the critical temperature sums in all models did not improve the model ability to simulate the occurrence of leaf coloration, which suggests either that local adaptation of leaf senescence process is virtually non-existent across the populations considered or that the genetic variation of leaf coloration traits among populations cannot be detected by our models. Our findings highlighted the importance of leafy season climate in autumn phenology modelling and its possible offset effect in the response of autumn senescence to future warming.