Age and light effects on seedling growth in two alternative secondary successions in central Amazonia

Abstract

Abstract Background : In central Amazonia, previous low intensity land use engenders succession dominated by Cecropia spp. which proceeds at high rates; however, at higher intensity of use succession is arrested and dominated by Vismia spp. over the long-term. Factors driving these two successional pathways are unknown. Aims : We aim to elucidate seedling growth under the two alternative successional pathways. Methods : We experimentally determined the effects of successional age and photosynthetically active radiation (%PAR) on relative height growth (RHG) of nine species of shade-tolerant tree seedlings in secondary forests dominated by Cecropia and Vismia, varying in age from 1 to 20 years. Results : In Cecropia-dominated successions, seedling RHG decreased with increasing successional age and with associated decreasing %PAR. In Vismia-dominated successions, RHG was independent of successional age and %PAR, and %PAR did not change with successional age, being always higher than in Cecropia stands. The RHG of seedlings was lower in Vismia- than in Cecropia-dominated stands for similar %PAR levels. Conclusions : Successional age and light availability affect seedlings growth differently in the two successional pathways. Unlike in Cecropia-dominated successions, in Vismia-dominated secondary forests seedling growth is limited by factors other than light. In a scenario of increasing land use intensity constraints to seedling development in secondary forests can reduce species diversity in human altered landscapes.