Periodicity and growth pattern variability for six Cecropia sciadophylla populations in the Amazon basin and Guiana shield

International audienceThe genus Cecropia Loefl. includes pioneer trees that colonize canopy gaps and cleared areas. It is widely distributed from Mexico to Northern Argentina and the West Indies. The simple architecture of Cecropia conforms to the model of Rauh; that is, it has orthotropic axes with lateral flowering and rhythmic branching. In a recent study it was found that C. obtusa in French Guiana, have a strong annual periodicity for growth, branching and flowering processes, with annual emission of 35 nodes. To determine the ages of Cecropia trees would help to pinpoint the date of the area’s disturbance, and for this, one possibly is to understand their developmental and architectural changes over time. Axes are made of a succession of nodes and internodes whose length and associated lateral productions remain visible and measurable over years. Thus, by describing the tree trunk node by node it is possible to depict the sequence of events involved in tree development. In this work we have focused on /Cecropia sciadophylla/, a species found throughout the Amazon basin, the Guiana region, and the Llanos region in Colombia. For 89 trees of C. sciadophylla, from two populations in French Guiana and four populations in Colombia, we recorded internode length and any presence of branches and flowers for each node. Using autocorrelation coefficients, we found a high periodicity in elongation, flowering and branching processes. An alternation of long and short nodes with a period that varies between 23 and 25 nodes, flowering processes with a period that varies between 22 and 25 nodes, and stages of branches produced each 23 and 25 nodes, or its multiples, were founded. We found differences in the average height and average number of nodes at which first branches and inflorescences were produced in all populations but the maximum annual elongation was similar among the populations. Considering that flowering is annual for many species of this genus, the main conclusion of this work is that strong annual growth, branching, and flowering rhythms exist for this tropical species. Although our results show a strongly rhythmic and clear topological periodicity, several elements, like the height and number of nodes at which the first branch and first inflorescence are produced, differentiate the six studied populations. This suggest that in spite of a strong ontogenetic restriction for the annual average number of nodes emitted, different environmental factors, like rainfall and soil fertility, could be the cause of the variation seen in the growth pattern