Summary The soil seedbank of a wheat crop grown with four tillage systems (mouldboard plough, disk, chisel and no‐tillage) for 3 years was analysed. Density and composition of seedbanks varied according to tillage system and depth. The mouidboard plough crop had seedbanks with the lowest seed density and there was no difference in density or composition at 0‐5 cm and 5‐10 cm depth whereas no—tillage had a more dense seed bank, especially in the upper part of the soil profile. Diversity of seedbanks also increased from mouidboard plough, to disk, to chisel, to no‐titlage, which had the most diverse bank. Therefore, the data strongly support the hypothesis that the systems causing less disturbance allow the build‐up of a larger and more diverse soil seed bank.

We examined the spatial distribution of two bromeliad species with contrasting functional traits in the understory of a xerophytic South American Chaco forest. Aechmea distichantha is a facultative terrestrial species with well-developed phytotelma and short rhizomes, whereas Bromelia serra is a strictly terrestrial species with soil-exploring roots and long rhizomes. Both bromeliads develop colonies on relatively elevated patches in Schinopsis balansae forests. We evaluated the roles of environmental controls, limited dispersal, and interspecific competition as drivers of the different distribution of these bromeliads. We mapped the overstory, understory and topography of 16 forest plots with bromeliads (400 m 2 each, subdivided in 100 4-m 2 subplots). We sampled soil characteristics on sectors dominated by each bromeliad species. We used structural equation modeling to assess direct and indirect associations of each bromeliad species cover with environmental conditions, abundance of conspecifics in the vicinity, and local abundance of the other species. A. distichantha cover increased on elevated subplots with high tree/shrub basal area, whereas B. serra cover showed the opposite pattern. In addition, A. distichantha cover was negatively associated with B. serra cover, but not vice versa, and cover of both species increased with the abundance of nearby conspecifics, suggesting that limited vegetative dispersal partly accounted for their distribution. Sectors dominated by A. distichantha had lower soil bulk density and higher organic matter content than those dominated by B. serra. According to our model, influences of competition and limited vegetative dispersal reinforce the association between distribution of these bromeliads and environmental heterogeneity of the forest understory.

The River Paraná is the second largest river of South America and its flood plain is covered by different kinds of forests and herbaceous vegetation. It is subject to an annual pulse of flooding; floods larger than the normal annual ones at irregular periods of few year and catastrophic extraordinary floods few times in a century. The last catastrophic flood was in 1983, followed by a short lived high flood in 1992. The catastrophic flood destroyed almost completely the herbaceous vegetation. Our hypotheses are, on the one hand, that the plant communities of this area will be restored rapidly, and on the other, that there will be a succession process which will produce a shift of communities so that, those on the higher part of the elevation gradient will encroach the ones at its lower part.We analyse, by means of the floristic composition, the effect of disturbance induced by catastrophic floods on the vegetation stability and dynamic processes, in an internal depression and pond of the riparian plant communities in an island of the River Paraná valley.The results strongly support the first hypothesis.