Résumé
Ecological succession theory predicts that soon after disturbance, community diversity results from species colonization while competitive interaction plays an increasing influential with time since disturbance. While weeds species in arable fields face frequent disturbances, they also face intense competition for light as they are over-dominated by the crop species. Thus, both colonization and competition may shape weeds community diversity in arable fields. Using a semi-experimental approach, we analysis the evolution of weed diversity throughout time in 56 winter cereal cropping seasons. We use the crop sowing date as proxy of the last disturbance. We predict that in the absence of the crop species, weed diversity increases with time since crop sowing date until arable field’s carrying capacity is reached. Conversely, in the presence of the crop, we expect competition for light to prevent the establishment of late germinating species and select for shade tolerant species so that weed diversity showed a hump-shaped relationship with time since crop sowing date. We found a hump-shaped relationship between weed diversity and time since crop sowing date both in presence of absence of the crop species. A functional diversity analysis revealed that the hump-shaped curve results from the succession of autumn and spring germinating weed species. However, weed richness was always higher in the absence of the crop, revealing that crop competition structure weed diversity since crop sowing date. This analysis suggests that competition may occur in early successional stage plant community as long as species colonization is not limiting.