Do seasonal changes in light availability influence the inverse leafing phenology of the neotropical dry forest understory shrub Bonellia nervosa (Theophrastaceae)?

Oscar M Chaves,Gerardo Ávalos

doi:10.15517/rbt.v56i1.5522

Abstract

In tropical dry forests most plants are deciduous during the dry season and flush leaves with the onset of the rains. In Costa Rica, the only species displaying the opposite pattern is Bonellia nervosa. To determine if seasonal changes in light availability are associated with the leaf and reproductive phenology of this species, we monitored leaf production, survival, and life span, as well as flower and fruit production from April 2000 to October 2001 in Santa Rosa National Park. Leaf flushing and flower bud production took place shortly after the autumnal equinox when day length starts to decrease. Leaves began expansion at the end of the wet season, and plants reached 70 % of their maximum leaf area at the beginning of the dry season, maintaining their foliage throughout the entire dry period. Leaf shedding occurred gradually during the first three months of the wet season. Leaf flushing and shedding showed high synchrony, with leaf numbers being related to light availability. Maximum leaf production coincided with peaks in radiation during the middle of the dry season. Decreasing day length induces highly synchronous flower bud emergence in dry forest species, but this is the first study indicating induction of leaf flushing by declining day length.

Highlights

B. nervosa is an understory shrub abundant in deciduous and semi-deciduous forests throughout the pacific coast of Mesoamerica, from southern Jalisco, Mexico, to northwestern Costa Rica (Ståhl 1989, Ståhl and Källersjö 2004)
We explored the extent to which seasonal changes in light availability are associated with the leafing and reproductive phenology of B. nervosa
In weakly seasonal tropical forests the vegetative and reproductive phenology of canopy trees is concentrated during periods of high irradiation

Summary

Introduction

B. nervosa is an understory shrub abundant in deciduous and semi-deciduous forests throughout the pacific coast of Mesoamerica, from southern Jalisco, Mexico, to northwestern Costa Rica (Ståhl 1989, Ståhl and Källersjö 2004). A crop of new leaves, flushed in synchrony, is likely to be more efficient controlling gas exchange during the dry season peak in understory light availability than a crown composed of overlapping leaf cohorts of different ages. This is afforded by a considerably deep root system (down to 8 m, Janzen 1970, 1983, Oberbauer 1985), which facilitates access to subsoil water when the majority of the plant community is deciduous. This is becoming critically important within the context of rapid changes in weather conditions related to global warming, which are influencing the phenological behavior and carbon budget of tropical forests (Wright et al 1999, Clark et al 2003)

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