Some Evidence for an Adaptive Linkage Between Leaf Phenology and Shoot Architecture in Sapling Trees

Abstract

1. We test an expectation regarding the phenology of leafing in sapling trees: that the inclination of the terminal shoot from the vertical in species with a flushing type leaf emergence will be greater than that of species with successive leafing. 2. A large inclination of the terminal shoot will minimize self-shading among leaves that emerge simultaneously; this may be an advantage in maximizing carbon gain. A small inclination leads to more self-shading but allows a sapling to attain a greater height within a shorter period; this may be an advantage in situations where shading by adjacent plants is a greater potential problem than self-shading. 3. We observed that the shoot inclination in Tilia japonica and Quercus crispula, which have a flushing type leaf emergence, was more than 30 ° in open, sunlit habitat. In contrast, the shoot inclinations of Betula platyphilla var japonica and Alnus hirsuta, which have successive type leaf emergence, were less than 10°. These observations suggest a functional linkage between leaf-emergence pattern and shoot inclination that can be considered adaptive if selection is maximizing carbon gain by the whole shoot over the growing season.