Field margin grass strips: opportunity or threat for the weed management in arable landscapes?

Sown grass strips could be an opportunity (refuge) or a threat (source of crop infestation) for weed management in arable landscapes. Firstly, our field surveys recorded 187 weed species, among which 90% were arable species, mostly perennial and wind dispersing species, here mostly represented by the Asteraceae family. Even if sown grass strips harboured a high richness of unsown species (26 weed species/grass strip), the richness did not vary according to the time since establishment. Weed community composition drastically changed over time, with a quick shift (within the 2 first years) from annual to perennial species, and from common agricultural weeds to non-arable species. Secondly, flora surveys performed with continuous transects from the field margin to the field centre showed clear plant spatial patterns. The sown grass strips acted as an ecotone with a sharp vegetation transition. Weeds occurring within the centre of the sown grass strips radically differed from species occurring within the first 0.5m of the cultivated area (only 15% of similarity between communities occuring in both habitats). Moreover, classical field margins influenced the weed composition up to 4.5m in the field whereas sown grass strips influenced the weed composition only up to 2m. We concluded that sown grass strips could be an opportunity to maintain plant diversity at the landscape scale and to decrease weed dispersion from the field margin to the field core in the short term. However, we discussed the long term impacts, especially to maintaining high level of annual species and segetal species in these perennial semi-natural habitats