Nine years' soil seed bank and weed vegetation relationships in an arable field without weed control.
The soil seed bank and seedling recruitment of the weed vegetation were monitored over 9 years at two fixed plots (a shallowly ploughed plot and a deeply ploughed plot) within a regular three-course crop rotation without chemical weed control at Dijon (France). The composition of the soil seed bank and weed seedling floras were compared qualitatively (Jaccard's index), quantitatively (Steinhaus's index) and in dominance (Kendall correlation coefficient) using three indices of 'similarity'. Over time, the seed bank density increased five-fold on the shallowly ploughed plot and two-fold on the deeply ploughed plot. Meanwhile, the seedling density increased four-fold on the shallowly ploughed plot and three-fold on the deeply ploughed plot. However, seedlings accounted for only a small fraction of the seeds present, from 9.0 to 28.1% of the viable seeds, depending on the years. At the community level, a close correspondence was found between the annual species composition of the seed bank and the associated seedling vegetation (Jaccard's index: mean value 0.71, Steinhaus's index: mean value 0.68 and Kendall correlation coefficient: mean value 0.60). It was concluded that, in general, the similarity between seed bank and seedling assemblage increased over time, with more or less variability according to the year.