Analyzing growth components in trees Yann Guédon (1) , Yves Caraglio (2) , Patrick Heuret (2) , Emilie Lebarbier (3) and Céline Meredieu (4) (1) CIRAD, UMR DAP and INRIA, Virtual Plants TA A-96/02, 34398 Montpellier Cedex 5, France E-mail: guedon@cirad.fr (2) UMR CIRAD/CNRS/INRA/IRD/Université Montpellier 2 Botanique et Bioinformatique de l’Architecture des Plantes TA A-51/PS2, 34398 Montpellier Cedex 5, France E-mail: caraglio@cirad.fr, heuret@cirad.fr (3) UMR INA P-G/ENGREF/INRA MIA, 16 rue Claude Bernard 75231 Paris Cedex 05, France E-mail: lebarbie@inapg.fr (4) INRA, Unité EPHYSE - “Ecologie Fonctionnelle et Physique de l’Environnement” Site forêt-bois, 69 route d’Arcachon, 33 612 Cestas Cedex, France E-mail: Celine.Meredieu@pierroton.inra.fr Running title : tree growth components Abstract 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. An open question is whether the ontogenetic component along an axis at the growth unit or annual shoot scale takes the form of a trend or of a succession of phases. Various methods of analysis ranging from exploratory analysis (symmetric smoothing filters, sample autocorrelation functions) to statistical modeling (multiple change-point models, hidden semi-Markov chains and hidden hybrid model combining Markovian and semi-Markovian states) are applied to extract and characterize both the ontogenetic and environmental components using contrasted examples. This led us in particular to favor the hypothesis of an ontogenetic component structured as a succession of stationary phases and to highlight phase changes of high magnitude in unexpected situations (for instance when growth globally decreases). These results shed light in a new way on botanical concepts such as “phase change” and “morphogenetic gradient”. Key words : autocorrelation function; hidden semi-Markov chain; linear filtering; morphogenetic gradient; multiple change-point detection; ontogeny; phase change; plant architecture. 1