Which conditions determine the presence of rare weeds in arable fields?

We detected 46 of the 65 rare weeds that are known to inhabit the study area, but their frequency was very low. Cereal crops, either alone or in mixtures with legumes, enhanced the probability of finding rare weed species, while fertilization had a detrimental effect. Other management practices that were considered had no effect on the presence of rare arable weeds. However, selected rare species tended to fare better under particular local conditions and to be favored by specific management practices. In contrast, a significant amount of the variance of the rare weed presence was explained by farm-related and field-related random factors. Thus, the occurrence of rare arable species is apparently determined by stochastic factors that may be related to the local species pool that likely depends on the history of fields and farms. Therefore, conservation efforts should be focused on areas currently inhabited by rare arable species.