The role of the permanent soil seed bank in early stages of a post-agricultural succession in the Inland Pampa,Argentina

We studied the soil seed bank composition in four old fields of different ages, after abandonment from agriculture. Complete seed bank composition was assessed by direct seed separation from soil samples and identification to species. Most species found in the seed bank were not important in the present seral communities. Seed of the species that dominated the early succession were generally not found. Additionally, there were very few propagules rather than on the germination of in situ propagules. We suggest that pampean grasses evolved under that the course of post-agricultural succession will depend strongly on the pattern of arrival of exogenous propagules rather than the germination of in situ propagules. We suggest that pampean grasses evolved under disturbances of low intensity and/or a disturbance regime dominated by small gaps, in which open areas could be rapidly colonized from the edges and/or by remnant vegetative propagules. The changes produced by the introduction of agriculture triggered the invasion by exotic species adapted to the new disturbance regime.