The natural vegetation of well drained fields of Southern Santa Fe (Argentina) are a different kind of communities characterized by the abundance of several species of Stipa. When agricultural lands are abandoned, they are often recolonized by the original vegetation. The object of this paper is to analize the first ten years of secondary succession on a field under a long time of agriculture abandoned after a wheat crop. On the first year, wheat with annual weeds (Chenopodium album and Portulaca oleracea) appeared. After the first year, one plot was colonized by Baccharis salicifolia and the others by Carduus acanthoides, Cerastium glomeratum, Ammi majus, etc. The last years constitute another stage where diversity is reduced and a strong dominance of Baccharis salicifolia or Carduus acanthoides becomes visible. Johnson grass appeared at the begining of the succession and stayed for the whole period with high abundance values. So far no species of the natural communities have established on this field, possibly because not enough time has elapsed yet or because they are absent from the seed bank or in the neighbourhood.
Pampa; grasslands; Triticum aestivum; succession; diversity; vegetation dynamics
