Architecture of Mabea fistulifera Mart. (Euphorbiaceae), a Neotropical semideciduous tree: development and variations in crown allometry between environments

Tree crown growth reflects many aspects of the species' life history. It was postulated that the potential for a pioneer species to invade a deforested area, or maintain a viable population in a forest under intermediate disturbance regime, is related to the tree trunk growth rates, patterns of crown construction, as well as the ability to regenerate broken branches. We investigated if Mabea fistulifera Mart. (Euphorbiaceae) crown architecture and tree allometry varies in two contrasted environments in a secondary fragment of Atlantic rainforest: forest edge and interior. First, we described the development of crown architecture by following the growth of the crown in 15 young individuals, with special attention to growth and branching models and to the morphologic differentiation of axes. Secondly, allometric differences in crown construction patterns between environments were studied by quantifying 10 traits in 20 individuals from each environment. Nozeran architectural model was found, a process of parenchymatization of the terminal meristem and a tier of branches form distally followed by an orthotropic shoot forming the next relay axis. This results in modular sympodial branching and polyaxial morphology of branches, allowing this tree species to occupy different environments by quick expansion wherever light availability is higher, towards the upper canopy (forest interior) or towards one side (forest edge). Crown asymmetry occurred towards border sunlit spaces or in response to inner canopy openings caused by hilly topography. Crown structure and growth patterns here found are suitable for a pioneer species adapted to intermediate disturbance regime.