Spring phenology in subtropical trees: Developing process-based models on an experimental basis

Process-based phenological models are currently used for assessing the effects of climatic warming on the timing of spring phenological events, such as leafout and flowering, in trees. However, the biological realism of the models may be undermined by the practices of often formulating the models solely on the basis of observational records of the phenological event rather than addressing the physiological processes actually modelled. Here we introduce a framework for developing process-based phenological models on the basis of experiments explicitly designed for this purpose and apply the framework to developing process-based models for leafout in four subtropical tree species. Our method is based on a hypothetico-deductive approach, where the air temperature responses of the simulated processes are inferred from their implications for the occurrence and timing of leafout in the experimental conditions. That approach has only rarely been taken with boreal or temperate trees, and to the best of our knowledge, never before with subtropical trees. Big differences were found between the four species in the air temperature responses modelled, and these differences implied major differences in the dormancy dynamics predicted for the four species. Together with the results of a recent modelling study based on observational data, our results highlight the importance of experimental studies for the development of biologically realistic process-based models of spring phenology in trees. The framework developed in the present study can be applied to developing such models for all tree species that show the phenomena of rest (endo-dormancy) and chilling requirement, no matter whether the trees are boreal, temperate, or subtropical.

Automated summary

Process-based phenological models are important for studying the timing of spring phenological events in trees. However, these models are often formulated solely based on observational records, neglecting the physiological processes. This study introduces a framework for developing process-based phenological models using experiments and applies it to four subtropical tree species.