Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

<jats:title>Abstract</jats:title><jats:sec><jats:title><jats:bold><jats:italic>Key message</jats:italic></jats:bold></jats:title><jats:p><jats:bold>We demonstrate that, beyond leaf phenology, the phenological cycles of wood and fine roots present clear responses to environmental drivers in temperate and boreal trees. These drivers should be included in terrestrial ecosystem models.</jats:bold></jats:p></jats:sec><jats:sec><jats:title><jats:bold><jats:italic>Context</jats:italic></jats:bold></jats:title><jats:p>In temperate and boreal trees, a dormancy period prevents organ development during adverse climatic conditions. Whereas the phenology of leaves and flowers has received considerable attention, to date, little is known regarding the phenology of other tree organs such as wood, fine roots, fruits, and reserve compounds.</jats:p></jats:sec><jats:sec><jats:title><jats:bold><jats:italic>Aims</jats:italic></jats:bold></jats:title><jats:p>Here, we review both the role of environmental drivers in determining the phenology of tree organs and the models used to predict the phenology of tree organs in temperate and boreal forest trees.</jats:p></jats:sec><jats:sec><jats:title><jats:bold><jats:italic>Results</jats:italic></jats:bold></jats:title><jats:p>Temperature is a key driver of the resumption of tree activity in spring, although its specific effects vary among organs. There is no such clear dominant environmental cue involved in the cessation of tree activity in autumn and in the onset of dormancy, but temperature, photoperiod, and water stress appear as prominent factors. The phenology of a given organ is, to a certain extent, influenced by processes in distant organs.</jats:p></jats:sec><jats:sec><jats:title><jats:bold><jats:italic>Conclusion</jats:italic></jats:bold></jats:title><jats:p>Inferring past trends and predicting future trends of tree phenology in a changing climate requires specific phenological models developed for each organ to consider the phenological cycle as an ensemble in which the environmental cues that trigger each phase are also indirectly involved in the subsequent phases. Incorporating such models into terrestrial ecosystem models (TEMs) would likely improve the accuracy of their predictions. The extent to which the coordination of the phenologies of tree organs will be affected in a changing climate deserves further research.</jats:p></jats:sec>