Phenology and radial stem growth periodicity in evergreen subtropical rainforest trees

Abstract

A close relationship between leafing, flowering, fruiting and radial growth has been conjectured to occur in tropical and subtropical rainforest trees. Radial stem growth, in particular, has been associated with the activity of the two secondary meristems, the vascular cambium and, to a lesser degree, the phellogen. In tropical trees vascular cambium activity may occur either virtually year-round, or it may be restricted to a short season. Phellogen and vascular cambium activities may or may not correspond to each other. In subtropical environments, even evergreens may demonstrate seasonal phenology in leaf initiation, flowering and seed set. In the present study, phenological events were analyzed in the evergreen species Aphananthe monoica, Pleuranthodendron lindenii and Psychotria costivenia. A correlation analysis showed that more than half of the variation is shared by phenological event variables (leafing, flowering and fruiting) and radial growth variables (vascular cambium and phellogen activity, and vascular tissue differentiation). Leaf initiation, flowering and vascular cambium activation were the most closely-related simultaneous events during the summer; whereas fruiting, phellogen activity and vascular tissue differentiation were the most closely-related simultaneous events during the summer and fall. This could explain why the leaf initiation and expansion stages, which produce growth regulators, are directly involved in radial growth.