Tipos funcionais fenológicos em espécies lenhosas da caatinga, Nordeste do Brasil

Abstract

In tropical dry forests, functional types have been remarkably useful to describe plant responses to environmental factors, based on morphological, physiological and phenological characteristics. For caatinga this issue has not been addressed by any study. Our hypothesis is that in deciduous plants with low wood density (LWD), that store large amounts of water,flushing and flowering will be triggered by increasing photoperiod, which coincides with absence of rain, while in plants with high wood density, both deciduous (HWD) and evergreen (EV) these phenological events will be related to soil water availability. To this end, we determined the phenological functional types of 27 woody species from a caatinga area in the municipality of Serra Talhada, Pernambuco.Flushing, leaf fall, flowering and fruiting were determined from April 2007 to October 2009 and related to their wood density,water retention capacity and water potential before dawn. We also compared these phonological events in plants receiving 500 mm of irrigation at the beginning of the dry season (August-October 2008) to those of a non-irrigated control area. In the control area,LWD species maintained a high water potential throughout the seasons and started shedding their leaves at the end of the rainy season and flushed and / or flowered in the dry season, when the photoperiod was increasing. On the other hand, the water potential of HWD species varied greatly along the seasons and flushing and flowering were positively correlated to rainfall. The water potential of EV species varied less than that of HWD ones and they flushed during the dry season and flowered at the end this season. Along irrigation, LWD species remained leafless and did not flush or flower, while HWD species maintained their leaves, flushed and flowered. The results confirm the hypothesis and demonstrate that the three functional groups (evergreens and deciduous high and low wood density species) have distinct physiological and phenological patterns, induced by either water availability or photoperiod.