Do field boundaries act as refugia for grassland plant species diversity in intensively managed agricultural landscapes in Britain

Initiatives to restore characteristic plant species diversity to degraded habitats require target plant species populations to be established and maintained. In landscapes managed intensively for agriculture, species that are foci for restoration efforts may be scarce, being confined to core reserves of less-modified habitat or persisting as fragmented populations on linear landscape features. Botanical data from small and large-scale surveys across Britain was used to investigate whether grassland plants favoured by less intensive management persisted on field boundaries despite increasing productivity in the adjacent field. At low field productivity, field species richness was, on average, higher than in field boundaries. As productivity increased, boundary plots reduced in richness at a slower rate than adjacent fields thus boundaries became relatively richer in grassland species than adjacent fields. Species compositional similarity between fields and their boundaries also declined with increasing field productivity. Grassland field boundaries can function as refugia. However, the lower relative species richness of boundaries next to the least productive fields indicated that some plant species will, on average, be increasingly uncommon or absent in boundaries as field productivity increases. High residual variation in these relationships was linked to local variation in conditions between fields and their boundaries. Field boundaries next to highly productive grasslands appear to function as partial refugia for grassland plants. While highly species rich boundaries can locally occur next to species poor fields, the species richness of most boundaries falls well short of values typical of the least productive fields.