ATBC 2012 49th Annual Meeting Bonito-MS, Brasil
S11.OC.03 Successional age and light effects on seedling growth in alternative successional sequences in the Central Amazon Jakovac ACC1,2, Bentos TV1, Mesquita RCG1, Williamson GB3,1 - 1Instituto Nacional de Pesquisas da Amaz么nia - Projeto Din芒mica Biologica de Fragmentos Florestais, 2 Wageningen University - Forest Ecology and Forest Management Group, 3Louisiana State University - Dept. of Biological Sciences In central Amazonia, land use intensity leads to different rates of succession along alternative successional pathways characterized by initial dominance of Cecropia spp or Vismia spp. Cecropia stands follow the classical succession with fast rates of species turnover while Vismia stands exhibit much slower rates of change. Aiming to deeply understand the constraints leading to this alternative successional pathways, we studied seedlings performance under Vismia and Cecropia chronosequences. Through a controlled experiment we determined the effects of successional age and photosynthetic active radiation (%PAR) on relative growth rates (RGR) of nine species of shadetolerant tree seedlings in Cecropia and Vismia dominated successions, varying in age from 1 to 20 years. In every stand we applied two paired treatments to evaluate the role of light in limiting seedlings growth: the original canopy intact and the canopy thinned to 65% of the original basal area. Our results showed that in Cecropia stands, RGR and %PAR decreased with increasing successional age, and RGR was limited by light. In contrast, in Vismia stands light levels and seedling RGR were independent of successional age, and RGR did not vary with %PAR and was lower than in Cecropia stands even under similar light levels. Our study demonstrates that seedlings under Cecropia and Vismia successions perform differently in response to successional age and light availability. Based on seedlings responses, Cecropia successions experience environmental changes through time that facilitate species transitions whereas Vismia successions show few changes and maintain a limiting environment to seedling growth. Even 15 years after abandonment, Vismia-dominated stands are still extremely nonfunctional in restoring environmental features essential to further successional development. These results emphasize that secondary forests regenerating after sequential burning events in Central Amazon may require restoration efforts to disrupt the positive feedbacks precluding natural succession.
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