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

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 aimed 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 1–20 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.

Keywords:

• Amazon
• ecosystem degradation
• growth rate
• photosynthetically active radiation
• tropical forest diversity
• Vismia

Acknowledgements

We thank the landowners from ZF4 and ZF7 for allowing us to use their secondary forests to carry out this experiment and for all the support during field work. We also thank all BDFFP staff for logistical support, especially Luiz Raimundo de Queiroz, José F. Tenaçol Andes Júnior, Antonio Martins and Cicero Lopez da Silva for assistance in seedlings transplant. Emilia Albuquerque and Flávia Amend helped during field work. We thank Jay Geaghan and Suping Zhang for statistical guidance. Natalia Norden, Robin Chazdon, Marielos Peña-Claros and Frans Bongers provided very helpful comments on earlier versions of the manuscript. This project was supported by (1) the Biological Dynamics of Forest Fragments Project (BDFFP) a bi-national collaboration of the Instituto Nacional de Pesquisas da Amazônia (INPA) and the Smithsonian Tropical Research Institute (STRI), (2) the US National Science Foundation (DEB-0639114 and DEB-1147434) and (3) the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). This is publication 595 in the Technical Series of the Biological Dynamics of Forest Fragments Project, BDFFP/INPA/STRI.