The historical process of deforestation was analyzed to evaluate the regeneration potential of forests from soil seed bank of Porto Rico island (53° 15'W and 22° 45'S) in the upper Paraná river floodplain. Remnant forest fragments were identified and measured and the structure of arboreous vegetation and the composition of the seed bank of the forests and grassland of the island were evaluated. Results showed a fast process of deforestation with critical levels of forest: the remaining twice fragments represented only 5.98% of the total surface of the island. Disturbance by cattle raised on the island continuously degraded the fragments (backward succession), while expansion of areas with pasture favored severe impoverishment of the seed banks flora. The latter factor, soil compaction, and characteristics of seeds of existing arboreous species in the bank suggested that the immediate reestablishment of vegetation was more conditioned to introduction processes of seeds (by rain and ''flood seed'') than by stock of seeds in the bank.
Deforestation; alluvial forest; floodplain; Paraná river; Brazil
