Alterações na dinâmica e demografia de árvores tropicais após fragmentação florestal na Amazônia Central

Abstract

Deforestation in the Brazilian Amazon is still increasing, transforming areas covered once by continuous forest in agricultural fields, pastures and patched forests. Few years after clearance, a large part of these areas will be abandoned and a natural revegetation will take place. In forest remnants, changes in the demography and dynamics of these isolated tree communities will start immediately, known by a series of studies on a large range of subjects, however less is known about changes on the species-specific level of the trees. This study, in a general approach, was focused on the demography and dynamics of the 20 most abundant tree species occurring in continuous forests and three 10 ha forest fragments North of Manaus, Brazil, 16 years after isolation. In both environments, a negative population growth was verified for most of the selected species. In fragmented forests, a hyper-dynamism was registered characterized by an increase in mortality and recruitment and consequently an increase in turnover. A population modeling applied for the next seven thousand years did not indicate any local extinction for these abundant specie in both environments, however did preview a substantial change in the structure of the forest fragments with a reduction in the canopy height. In a more specific approach, this study looked at the effect of forest fragmentation on seed and seedling ecology of the selected species Minquartia guianensis Aubl. (Olacaceae black manwood). Seed dispersal by birds seemed to be crucial for germination success and seed predation was higher in fragmented forests. Seedling growth in height was extremely slow and in the second year after germination mean increment was higher in fragmented forests, probably due to lighter environment. The growth simulation for a Minquartia guianensis seedling revealed that would be necessary 30 to 150 years for one individual to reach 10 cm DBH. Results provided by this study may be useful for conservation of biodiversity, management of forest fragments and achievement of forest exploitation sustainability.