Talk Influence of roadfield boundary structure and management practices on the functional composition of roadfield plant communities

Management practices made on road verges are currently implemented to preserve biodiversity in agricultural landscapes. These boundaries are generally constituted of four elements – i.e. the safety zone, the berm, the ditch and the embankment – which differ in terms of taxonomic composition, primarily due to differences in the nature and intensity of anthropogenic disturbances. The influence of mowing practices on taxonomic composition of plant communities has been extensively studied; however a better understanding of plant response to various disturbances using trait-based approaches could be a relevant supplement to taxonomic approaches to guide management practices. Management programs usually involve differences in the frequency and timing of mowing, nevertheless it has been shown that the proximity of road verges to field margins can also lead to additional disturbances from arable fields. Although most studies have investigated the relationships between management practices carried out on road verges elements and changes in plant communities within these managed elements, only a few have also focused on the potential influence of road verge management practices in adjacent field margins. We addressed two questions: (1) How road-field elements shape the functional composition of plant communities? (2) How road-field management practices influence the functional composition of plant communities within each element?

We sampled the berm, the embankment and the field margin of 40 road-field boundaries of cereals fields located in Central-Western France, where local authority experienced a delayed mowing of some berms from early to late summer. We characterised management practices made on each element, i.e. mowing frequency and/or timing, inputs of herbicide and nitrogen fertilizers. We extracted from databases nine functional traits known to be influenced by management practices studied. To determine the relationships between species traits and environmental variables, we performed partial RLQ analyses to remove confounding effect of the environmental context. Then, we used the fourth-corner statistic to quantify the link between traits, environmental factors and partial RLQ axes.

Community functional response differed both between road-field elements and due to management practices made. Competitive and hemicryptophyte species were associated to berms, while ruderal and therophyte species were associated to field margins. In berms, ruderal species flowering earlier were associated to one early mowing, while competitive and nitrophilous species presenting a later flowering in June were associated to one late mowing. Moreover, in field margins, zoochorous species were associated to late mowing of the berm. Finally, both in field margins and embankments, dicotyledonous species were associated with an increase in herbicide treatment in arable field.

We emphasised that mowing practices made on road verges for biodiversity issue influence the functional composition of plant communities within these green infrastructures, and can also shape the functional composition of plant communities in adjacent arable field margins. Our results should also be useful for the establishment of effective management programs on right-of-way of other linear transportation infrastructures such as electric rights-of-way.

Road verge; Berm; Embankment; Field margin; Mowing; Plant functional traits; partial RLQ