Cecropia growth pattern periodicity - could a neotropical genus be a good biological clock to estimate the age of disturbed areas?

Abstract

In the tropics, the surfaces covered with secondary forests are rapidly increasing due to the high deforestation rates. Forest succession is a slow process and continuous data on vegetation change are scare. To study this change, the chronosequence approach has been used but in order to implement it, the knowledge of the secondary forest ages is necessary; however, this information is difficult and/or expensive to gather. Yet, a posteriori reconstruction of individual development in emblematic tropical pioneer trees could be helpful to determine the age of a tree and the moment of individual establishment after a perturbation. In this study, I propose a straightforward and fast method to estimate the age of secondary forests based on the individuals? age estimation of Cecropia, one of the most important pioneer genera of the Neotropics. The objectives of this dissertation were: i) to characterize the developmental pattern of C. sciadophylla, in order to establish a simple protocol to determine the age of C. sciadophylla individuals, ii) to determine how the growth pattern of C. sciadophylla, varies the year and to characterize the stability of this pattern across the species distribution range, iii) to determine the flowering frequencies of Cecropia species and to identify the relationship between flowering events and climate secondary forests in the Neotropics. I found a high annual periodicity in flowering and branching processes, and an alternation of long and short nodes in C. sciadophylla populations. Also, I found that Cecropia inferred ages were highly correlated with real perturbation ages in all cases (i. e. slash and burn agricultural sites, a forestry road, and mining sites. In addition, I propose 21 Cecropia species that show annual flowering patterns and that are distributed over the geographical range of the genus, as potential chronometer species. For the first time it is shown that Cecropia genus is a promising and very precise tool for dating disturbances and studying secondary forest dynamics in the Neotropics