Roadsides: an opportunity for biodiversity conservation

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Questions: How do roadsides interact with patches of natural vegetation in shaping perennial plant communities in fragmented agricultural areas? Are the observed differences due to the type of roadside (i.e. roadcuts, embankments or road verges) or are there other factors driving community structure and composition? Location: Stretch of motorway A3 and its surrounding area, central Spain. Methods: We analysed the variation in perennial plant species composition and diversity among 92 plots (400 m2 ). The plots were located in five different environmental scenarios, three of them in a fragmented landscape (patches of natural vegetation, embankments and roadcuts) and two in an unfragmented landscape (natural vegetation and road verges). In each plot, the cover of each perennial plant species and eight soil variables were assessed. We used phi coefficient of correlation to determine the scenario preferences of each species, Kruskal–Wallis tests to compare the soil variables between landscape scenarios and eight descriptive variables of the community, and RDA and partial RDA to evaluate the relative importance of the type of environmental scenario on the floristic community. Results: We identified 130 species, with only 16 species never appearing on roadsides. Perennial total cover, species richness, inverse Simpson’s index and number of protected species showed no significant differences between the five scenarios considered. In contrast, the number of nutrient-demanding species and restricted-range diversity had lower values in natural vegetation plots. Soil variables and the type of scenario together explained 28.5% of the species composition variation. Of this percentage, 6.8% was explained by soil variables, 12.1% by the type of scenario and 10.0% of the variation was shared between the two data sets. Conclusions: Our results show that almost all perennial species occurring in natural vegetation patches were also able to reach and settle in roadsides. However, soil conditions and other specific roadside variables generate different plant communities. In spite of the differences found between the perennial plant community of roadsides and their surrounding area, roadsides are excellent reservoirs of biodiversity.