Composição florística e fenologia de quatro áreas de floresta de terra firme com diferentes históricos de alteração antrópica no município de Manaus

Abstract

Urbanization, as well as environmental changes related to it, creates both new restrictions and opportunities for plants that remain in forest patches segregated by the urban matrix. In order to shed some light on the resulting effects of this process, this study explored the impact of antropogenic disturbance on the floristic and phenology of tree communities in the fragmented landscape of Manaus city, Amazonas state, Brazilian Amazonia. Four areas were selected for floristic survey and phenological monitoring: Adolpho Ducke forest reserve (RFAD), Acariquara and Coroado forests, both located in the campus of the Federal University of Amazonas, and the forest fragmented owned by the Brazilian Industry Social Service (SESI). These areas reflect a gradient of rising antropic disturbance: RFAD  Acariquara  Coroado  SESI. Floristic surveys were carried out on 10 x 250m plots, totalizing one hectare for each study area, and all plants with DBH >= 5cm were marked. Phenological observations were made or seven years, and the occurrence of phenophases (i.e. flowering, fruiting, leaf flushing and leaf fall) in each marked plant were recorded throughout that time. Climate data from Manaus (i.e. cumulative rainfall, air relative humidity and average temperature) were obtained monthly, their relations to community-level phonological patterns were investigated by means of generalized linear models (GLM). Direct gradient analysis revealed that floristic composition strongly varies between areas. RFAD, Acariquara and Coroado have family assemblages progressively less inclusive, in this order; SESI has a predominantly dissimilar flora in relation to the others. Pair-wise comparisons between areas with Jaccard’s dissimilarity indices confirmed this result at the level of species. Besides, species number declined as a function of greater antropization. In all study areas, the greatest number of flowering individuals occurred between the end of the dry season and the beginning of the wet season; the greatest number of fruiting individuals coincided with the wet season. Peaks of leaf flushing and leaf fall occurred during the dry season in all areas. Environmental variables explained relatively little of the observed variation in each of the phenophases. In general, phenological correspondence between areas was greater for vegetative phenophases; association between reproductive phenophases in different areas was highly variable. Both positive and negative relations were found between cumulative rainfall and the number of trees in each phenophase, whereas only positive relations were observed with the number of fruiting trees. In general, average temperature had positive effects on the expression of all phenophases, but air relative humidity has both positive and negative effects on the number of trees with new leaves, flowers and fruits; only positive effects were found on leaf fall. Besides, fruiting was mainly determined by flowering in earlier months. These discrepant results are accord with previous suggestions that adaptive mechanisms of tropical trees should render them weakly responsive to climate. Factors such as genetic constitution, physiological state, demography and ecological interactions may take part in the remaining, unexplained phonological variation. It is suggested that future studies should integrate the contributions of both abiotic and biotic factors to the regulation of tree community phenology. The understanding of plant phenology in tropical environments under rising antropization in fundamental for the adequate conservation and management of ecological functions in urban forest remnants.