Convergence and divergence in alternative successional pathways in Central Amazonia

Background: Plant succession and community assembly following different land-use histories in the Amazon Basin are poorly understood. Aims: Changes in woody vegetation were monitored across chronosequences of abandoned pastures and abandoned clearcuts in order to compare their successional patterns. Methods: In chronosequences, initially 5-19 years old in abandoned clearcuts and 2-11 years old in abandoned pastures, trees (≥ 3 cm dbh) were tagged and recruitment and mortality recorded annually for 12 years. Results: Stem densities exhibited no significant trend during the first 25 years of succession regardless of land-use history. Basal area in abandoned clearcuts increased rapidly in the first decade, outpacing accumulation in abandoned pastures, although basal area on the two pathways converged at 25 years post-abandonment. Transects in abandoned pastures were much more variable in stem density and basal area than those in abandoned clearcuts, reflecting cohort growth and thinning by the dominant genus Vismia in the pastures. Species density, initially similar in the young stands, increased at a much faster rate in abandoned clearcuts than in abandoned pastures, resulting in a large divergence after 25 years. Conclusions: Succession following deforestation in the Amazon exhibits alternative pathways that correspond to prior land use - abandoned clearcuts of primary forest or clearcuts converted to pastures through prescribed burns and later abandoned. The most important divergence in the two successions was the extremely slow accumulation of species over 25 years in abandoned pastures.