Diversidade, composição e biomassa de plantas vasculares em plantios de Acacia Mangium Will. numa área de contato savana/floresta no Norte da Amazônia

Abstract

Forest plantations of non-native species accounted for about 7% of the forest cover of the land surface in 2005 and it is expected that in the future such forest systems will reach 20%. Therefore, this study aimed to evaluate the effect of pure plantations of Acacia mangium Willd. established in areas originally occupied by savanna (locally termed ‘lavrado’) on the establishment success of vascular plants, by analyzing three attributes of the community structure - diversity, composition, and biomass. All plants with a base diameter ≥ 1 cm were measured in 28 0.05-ha plots, with 11 plots allocated in natural areas of lavrado and 17 plots in A. mangium plantations. A total of 1,180 individuals belonging to 68 species of plants were sampled in these plots. Species diversity was higher in A. mangium plantation than in the natural areas of lavrado, even although the number of individuals sampled in A. mangium plantation plots was smaller for both 1- 4.9cm size class and all dataset. There was floristic differentiation between A. mangium plantation and lavrado, with high density of forest species and low density of lavrado species in A. mangium plantation. Moreover, while lavrado plots presented high floristic similarity among them, but plots under A. mangium plantation were far less similar, indicating a more heterogeneous vegetation in this habitat. The biomass of vascular plants in A. mangium plantation was, on average, about one fifth of that found in natural lavrado sites, but in lavrado 92.6% of the total biomass was allocated in only two species – Curatella americana and Byrsonima crassifolia, whereas in A. mangium plantation the two species that represented the highest proportion of biomass, Posoqueria latifolia and Byrsonima crassifolia, comprised 43% of the total biomass. In A. mangium plantation, species classified as forest species and typical lavrado species accounted for 72.8% and 27.2% of total biomass, respectively. Biomass partition between non-pioneer and pioneer forest species was fairly similar, with an estimate of 0.72 Mg/ha and 0.86 Mg/ha, respectively. The results of this study show that A. mangium plantation implicated in environmental changes, resulting in high local and regional diversity of plants and favoring the colonization of some alien forest species.