Identifying and characterizing the ontogenetic component in tree development

Observed growth, as given, for instance, by the length of successive annual shoots along the main axis of a plant, is mainly the result of two components: an ontogenetic component and an environmental component. We made the assumption of a decomposition model where the ontogenetic growth component and the environmental component (mainly of climatic origin) were combined in an additive manner. This relies on the fact that ontogeny generally has a longer term effect than time-varying environmental factors; see Barthélémy and Caraglio (2007). A key question is whether the ontogenetic growth component along an axis (i.e. successive entities built by the same meristem) at the growth unit or annual shoot scale takes the form of a trend (i.e. a “long-term change in the mean level”) or of a succession of roughly stationary phases. The main variable of interest is the length of the entity but additional variables may be useful such as the number of growth units for polycyclic annual shoots or the number of branches when the branches can be considered as morphologically similar.