Alternative successional pathways in the Amazon Basin

1 Successional pathways were evaluated in two Amazonian secondary forest communities with different land-use histories. Sites which had been clearcut without subsequent use were dominated after 6-10 years by the pioneer genus Cecropia (Moraceae), whereas those used for pasture before abandonment were dominated by the pioneer genus Vismia (Clusiaceae). 2 There were 58 plant families and 300 species identified in Cecropia stands but only 43 families and 147 species were identified in Vismia stands. There were 77 species in common (Sorensen similarity = 0.34). 3 Differences in species number and composition of recruiting individuals between stand types were significant and were a function of the dominant pioneer genus, stem density, distance from primary forest, and land-use history. Regeneration under Vismia canopy was dominated by small Vismia individuals (25% of plants < 2 cm basal diameter), whereas regeneration under Cecropia canopy was more diverse and did not include a single young Cecropia. 4 The number of regenerating plants in both secondary stand types dropped off sharply with distance (5, 25, 50, and 100 m) from primary forest, suggesting that seed dispersal was limiting plant recruitment. Species richness also declined with distance and could be explained by the decline in plant density. Species richness in Cecropia stands increased linearly with plant density, but in Vismia stands the richness increase with density was a decelerating function. 5 For the central Amazon, secondary succession involves a more rapid return of primary forest species if deforestation is not followed by use as pasture before abandonment.