9 YEARS SOIL SEED BANK AND WEED VEGETATION RELATIONSHIPS IN AN ARABLEFIELD WITHOUT WEED-CONTROL

1. The soil seed bank and the seedling recruitment of the weed vegetat ion were monitored over 9 years at two fixed plots (a shallowly plough ed plot and a deeply ploughed plot) within a regular three-course crop rotation without chemical weed control at Dijon (France). 2. The comp osition of the soil seed bank and weed seedling floras were compared q ualitatively (Jaccard's index), quantitatively (Steinhaus's index) and in dominance (Kendall correlation coefficient) using three indices of 'similarity'. 3. Over time, the seed bank density increased fivefold on the shallowly ploughed plot and twofold on the deeply ploughed plot . Meanwhile the seedling density increased fourfold on the shallowly p loughed plot and threefold on the deeply ploughed plot. However, seedl ings accounted for only a small fraction of the seeds present: from 9. 0 to 28.1% of the viable seeds, depending on the years.4. At the commu nity level, a close correspondence was found between the annual specie s 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). 5. Generally, t he similarity between seed bank and seedling assemblage increased over time, with more or less variability according to the year.