ATBC 2012 49th Annual Meeting Bonito-MS, Brasil
S11.OC.05 Convergence and divergence in alternative successional pathways in Central Amazonia Williamson GB1,2, Mesquita RCG2,3, Longworth JB1, Bentos TV2, - 1Louisiana State University - Department of Biological Sciences, 2Biological Dynamics of Forest Fragments Project - Instituto Nacional de Pesquisas da Amazônia (INPA) and Smithsonian Tropical Research Institute , 3Instituto Nacional de Pesquisas da Amazônia-INPA - Department of Ecology The impact of different land use histories on plant succession in the Amazon Basin is poorly known. Two different land use types, abandonment after clearcuts of mature forest and conversion to pastures following clearcuts, lead to domination by different pioneer species, Cecropia species and Vismia species, respectively. We measured changes in vegetation structure and composition over 25 years of succession by monitoring woody plants on sites 2-19 years after abandonment annually for 12 years. We found that stem densities exhibited no significant trend during the first 25 years. Basal area in Cecropia transects increased quickly in the first decade, outpacing accumulation in Vismia transects, but the two had converged in basal area after 25 years. Vismia transects were much more variable than Cecropia transects in stem density and basal area, reflecting cohort growth and thinning in the Vismia succession. Species density increased linearly at a much faster rate in Cecropia than Vismia transects, creating a large divergence after 25 years. Dominance by Cecropia decreases more quickly than dominance by Vismia. Whereas Cecropia sites decreased dramatically in Sorenson similarity during the first decade of succession, Vismia sites remained more similar to each other. This study confirms that succession following primary forest clearings in the Amazon exhibits alternative pathways that correspond to prior land use—clearcuts without further disturbance versus clearcuts converted to pastures. The main divergence in the two successions is the extremely slow accumulation of species and persistence of the dominant species over 25 years in abandoned pastures.
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