Résumé
Spatio-temporal seed dispersal is a major process in structuring annual plant communites. However, few emipirical studies have quantified the relative contribution of seed dormancy and seed dispersal on annual plant diversity. In agroecosystems, weeds which are mostly annual species producing dormant seeds can be found both in annual row crops and in semi-natural habitats such as grasslands (fig. 1). Spatial mass effect from grasslands to annual crops have been reported to support weed diversity in annual crops. Similarly, the presence of grasslands in crop successions increases weed diversity in the following annual crops. Both temporal and spatial dispersal from grasslands may thus support weed diversity in arable crops. However, agroecosystems are characterized by highly spatio-temporal dynamics of land use change which questionned the contribution of spatial and temporal presence of grasslands to maintain weed diversity.