Floração e frutificação da comunidade arbórea na zona de preservação da vida silvestre base 4, Tucuruí, Pará: padrões gerais e variações entre espécies

Abstract

Knowledge of phenological pattems is of great importance for understanding the structure and functioning of natural ecosystems. Despite the great variety of pattems, knowledge of flowering and fruiting periodicity in tropical forests is limited. The objective of this study was to determine general pattems of flower and fruit production of a tree community in an open rainforest within the area of influence of the UHE Tucuruí Reservoir, and focus in particular on the Arecaceae family due to its importance as a resource for frugivorous fauna. The following questions were examined: 1) What flowering and fruiting pattems are presented by tree species in the local community? 2) Are these pattems repeated among years? 3) Are flowering and fruiting events related to variations in precipitation, insolation and temperature? 4) What pattems do palm species present? 5) Is there intra and interespecific phenological variation within the palm family? The region possesses two well defined seasons, a rainy and a dry one, August and September have the lowest precipitation. Average monthly temperatures are > 240C and the annual rainfall > 2,500 mm. In seven onhectare plots, ali individuais with a DBH > 10 cm were marked and monitored for the presence of flower buds, open flowers, unripe and ripe fruits each month from November/2004 to April/2007. The number of species and individuais in phenological activity was compared between years. Correlations with precipitation up to two months before, and insolation and temperature at the month of the event were undertaken. To characterize the phenology of the species in the community the first occurrence, synchrony (within Arecaceae), peak and duration of open flowers, immature (only Arecaceae) and mature fruits phenophases were calculated. During the study, 2,982 individuais distributed in 49 families, 152 genera and 295 species, including 331 palms belonging to five species were monitored. The dry season was the period with the largest percentage of species in flower, while for fruits it was the beginning of the rainy season. Phenophase start dates and peaks were not significantly different between years in the community as a whole. Flowering was positively correlated with insolation and temperature and negatively with precipitation while fruiting was negatively correlated with insolation and precipitation. The palm species differed in their degree of reproductive seasonality, but in general, they presented long fruiting periods. Extensive fruiting periods are commonly found in palms and can be related to a higher probability of seed dispersai and germination success. Among the palm species here, the majority of phenological variables analyzed did not occur at the same period and no evidence was found of philogenetic constraints among species. The phenological pattems found in the local community are similar to those found in other tropical forests. Due to the absence of studies before the implantation of the UHE dam it was not possible to verify if changes at the local landscape levei had affected phenological pattems. We suggest, however, that pattems have not been modified at the community levei, but some may be occurring at population leveis, possibly due to alterations in pollination and seed dispersai processes of some species.