Ecophysiological modelling of cessation of wood formation phenology in temperate and boreal forest trees

Wood phenology is an important indicator of ecosystem response to climate change. However, compared to leaf phenology, the understanding of wood phenology is still in its infancy. In this study, we developed the first ecophysiological model to simulate the cessation of wood formation for two major Northern Hemisphere conifer species (Pinus sylvestris and Picea abies). The model developed postulates cessation of wood formation to be driven by both photoperiod and temperature. We calibrated and validated the model based on the GLOBOXYLO database documenting the occurrence of phenological stages in wood formation. We focused on two European species here, namely Pinus sylvestris and Picea abies, totaling 96 site-years. The model received support for both species with a root mean square error of 12.6 days and 8.6 for the prediction of validation data, respectively. The model accuracy was significantly related to the within-population variability in the observed data of cessation of wood formation, with higher prediction errors in years when trees of the same population were not in sync. Moreover, we found the number of radial cell and tree diameter to also affect the cessation of wood formation based on a path analysis model. This study improves the knowledge of the role of environmental and ontogenetic factors controlling the cessation of wood formation in the temperate and boreal zones.