Phenology and Ecophysiology of Tropical Trees: Erythrina Poeppigiana O. F. Cook

Abstract

Under the climatic conditions of San Jose, Costa Rica, leaf fall, flowering, and shoot emergence of Erythrina poeppigiana O. F. Cook were markedly asynchronous among trees of the same population, suggesting strong endogenous control of the tree's development. During 1 yr, trees passed through two cycles of leaf shedding and shoot emergence. The endogenous periodicity of leaf shedding appeared to be primarily the result of leaf senescence. During the dry season, leaf senescence and hence leaf shedding were enhanced by tree water deficits. As a consequence of leaf shedding, water stress was alleviated and shoot emergence occurred, even under continued drought. The degree of water stress, reflected in stem shrinkage, was affected by tree size, soil moisture availability, and seasonal changes in evapotranspiration. Large trees at dry sites water deficits and hence passed through leaf change early in the dry season, while smaller trees and trees at humid sites did so up to 3 mo later. The phenology of Erythrina along an altitudinal gradient of increasing atmospheric water stress showed a transition from an evergreen to a deciduous habit. At permanently humid sites, all phenological phases occurred simultaneously on the same tree. With increasing drought, consecutive developmental stages tended to be more separate in time and more synchronized. In humid tropical climates, characterized by the absence of significant environmental stress, the periodic development of Erythrina is thus primarily determined by variables such as leaf age and tree size, which affect the tree's internal functional balance. Increasing environmental stress, in tropical environments most likely drought, may secondly synchronize certain phases of the basic endogenous rhythmicity with seasonal climatic changes.