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RESEARCH PRODUCT

Consequences of sown grass margin strip on weed flora

subject

description

The intensification of the management of weed populations, led by a potential decrease in the yield and quality of crop harvest, has largely induced their decline in arable zones across the last decades. This floristic decline in arable landscape, has induced a loss of a larger biodiversity because the presence of others organisms (birds, insects, mammals) are strongly linked with the abundance of trophic resources as weed are. To counter with this loss of biodiversity and to limit the negative impacts of farming practices on environment, numerous agri environmental schemes were launched through Europe. In France, sown grass strips were established by farmers along streams and rivers to limit the pesticide drifts and the hydric soil erosion. The field margin strips are mainly sown with grass mixtures and do not receive neither pesticides nor fertilizers. Consequently, their establishment in the arable landscape for many years, without compensation payments for farmers, spark many fears concerning the weed risk that they could represent for adjacent field. At the opposite, these non-cropped areas adjacent to cultivated fields could be an opportunity to maintain weed populations providing ecosystem services for agriculture which were more and more highlighted. This PhD work shows that sown grass strips harbour large flora diversity. The weed communities are mainly structured by the type of adjacent boundary (hedge, river, ditch, etc.). The succession of disturbance and competition phase caused by mowing and competition of sown species respectively, do not allow annual species to maintain their populations in this habitat where they rarely reach fructification stages. The frequently observed species are perennials but rarely dominated over the sown cover. Even if the sown grass strips show high level of species richness, mainly composed by arable species, these strips do not enhance the spread of species from the boundary to the field core. Indeed, at least at short term, the sown grass strips decrease the edge effect because they were established where the flora transition between the boundary and the field previously occurred. Moreover, the establishment and management practices cost for farmers, reasonably at the farm scale. Although some fears on the decline of annual species, the sown grass strips represent an opportunity for the weed management at the field scale as well as at the landscape scale. Joint study linking the flora with other organisms (soil microflora, grasshoppers) have been initiated and could allow to put the environmental sown grass strips to good use for biodiversity.