Canopy phenology of a dry forest in western Brazil

J Ragusa-Netto,Rr Silva

doi:10.1590/s1519-69842007000300024

Abstract

Dry forests are common, although highly threatened in the Neotropics. Their ecological processes are mostly influenced by rainfall pattern, hence their cycles exhibit contrasting phases. We studied the phenology of canopy trees in a primary dry forest in Western Brazil in the foothills of the Urucum mountain chain, in order to improve our knowledge on the functioning of these poorly-known forests. Leaf shedding started in the early dry season and was massive in the latter part of this period. Most leaf loss occurred in dry hills, while wet valleys remained evergreen. Anemochorich and autochorich species predominated in dry hills, presumably due to their tolerance to dry conditions and enhanced exposition to winds, which favour diaspores removal and dispersal. Conversely, zoochorich species dominated the wet valleys. Flowering was intense in the late dry season, the driest period of the year, while fruiting was massive just after the onset of rains, as well as flushing. Therefore, most flowering was unrelated to wet conditions, although such an abiotic factor, potentially, triggered the major fruiting episode, widely comprised by zoochorich species. Anemochorich and autochorich species flowered and fruited in the course of the long dry season. The contrasting environmental conditions present in the hills and valleys determine the arrangement of a mosaic in which patches of zoochorich and evergreen trees alternate with patches of non zoochorich and highly deciduous species. Consequently, species with such syndromes exhibited marked flowering and fruiting patterns, accordingly to the pronounced seasonality.

Highlights

Dry forests are widespread in the neotropics, and as major features exhibit low trees, scarce understory, and pronounced leaf shedding in the course of the dry season (Bullock and Solís-Magallanes, 1990)
As dry forests occur in highly seasonal areas, flowering and fruiting pattern are mostly influenced by rainfall pattern
As phenology studies are a useful tool to improve our knowledge on the functioning of the dry forests, in this study we examined the leaf, flower, and fruit phenology of canopy trees in the foothills of the Urucum mountain chain (Serra Santa Cuz)

Summary

Introduction

Dry forests are widespread in the neotropics, and as major features exhibit low trees, scarce understory, and pronounced leaf shedding in the course of the dry season (Bullock and Solís-Magallanes, 1990). In such forests, most plant families include one or exceptionally few species (Gentry, 1995), which usually are patchily distributed (Hubbell, 1979). Taking into account the temporal pattern of water availability as the most important factor determining leaf, flower, and fruit production in the dry forests (Bullock, 1995), their effect on canopy trees is expected as more severe, since this vegetation layer is under harsher environmental conditions in relation to the more wet and dark understory (Lowman and Wittman, 1996). A major consequence on canopy phenology is a contrasting dynamics, which includes wide modifications of forest microclimate, as well as the relationships with primary consumers, whose activities are markedly seasonal (van Schaik et al, 1993)

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Conclusion