Key message: 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.Context: 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.Aims: 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.Results: 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.Conclusion: 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.

Forest productivity declines with tree age. This decline may be due to changes in metabolic functions, resource availability and/or changes in resource allocation (between growth, reproduction and storage) with tree age. Carbon and nitrogen remobilization/storage processes are key to tree growth and survival. However, studies of the effects of tree age on these processes are scarce and have not yet considered seasonal carbon and nitrogen variations in situ. This study was carried out in a chronosequence of sessile oak (Quercus petraea Liebl.) for 1 year to survey the effects of tree age on the seasonal changes of carbon and nitrogen compounds in several tree compartments, focusing on key phenological stages. Our results highlight a general pattern of carbon and nitrogen function at all tree ages, with carbon reserve remobilization at budburst for growth, followed by carbon reserve formation during the leafy season and carbon reserve use during winter for maintenance. The variation in concentrations of nitrogen compounds shows less amplitude than that of carbon compounds. Storage as proteins occurs later, and mainly depends on leaf nitrogen remobilization and root uptake in autumn. We highlight several differences between tree age groups, in particular the loss of carbon storage function of fine and medium-sized roots with tree ageing. Moreover, the pattern of carbon compound accumulation in branches supports the hypothesis of a preferential allocation of carbon towards growth until the end of wood formation in juvenile trees, at the expense of the replenishment of carbon stores, while mature trees start allocating carbon to storage right after budburst. Our results demonstrate that at key phenological stages, physiological and developmental functions differ with tree age, and together with environmental conditions, influence the carbon and nitrogen concentration variations in sessile oaks.

It was time to take stock. We modified the humipedon classification key published in 2018 to make it easier and more practical. This morpho-functional taxonomy of the topsoil (humipedon) was only available in English; we also translated it into French and Italian. A standardized morpho-functional classification of humipedons (roughly the top 30–40 cm of soil: organic and organomineral surface horizons) would allow for a better understanding of the functioning of the soil ecosystem. This paper provides the founding principles of the classification of humipedon into humus systems and forms. With the recognition of a few diagnostic horizons, all humus systems can be determined. The humus forms that make up these humus systems are revealed by measuring the thicknesses of the diagnostic horizons. In the final part of the article, several figures represent the screenshots of a mobile phone or tablet application that allows for a fast recall of the diagnostic elements of the classification in the field. The article attempts to promote a standardized classification of humipedons for a global and shared management of soil at planet level.