Short-term successional change does not predict long-term conservation value of managed arable field margins

Field margins have been widely advocated as a means of integrating agronomic and biodiversity objectives and are included in agri-environment schemes across Europe. However, information on the long-term development of field margin plant communities remains limited. We describe a long-term experiment on the effects of field margin management on biodiversity and weed species. Swards were established by natural regeneration or sowing a grass and wildflower seed mixture, and treatments manipulated the frequency and timing of mowing, application of herbicide and leaving of hay. Vegetation was monitored to evaluate the extent to which early conclusions remained valid after 13 years. Although early successional trends suggested that naturally regenerated swards would rapidly become dominated by pernicious perennial weeds, and that sown swards would exclude such species, neither was true in the longer term. Sown swards were eventually invaded by unsown perennials, but they remained distinct from naturally regenerated swards. Plant species richness declined throughout the experiment. Annuals were lost most rapidly from sown swards but, under natural regeneration, loss could be modified by mowing. Perennial species initially increased during natural regeneration before stabilising. In sown swards they declined under all treatments. Species richness in naturally regenerating swards was promoted initially by mowing twice annually. After 13 years, timing and frequency of mowing had no significant effect on species richness although it still influenced sward composition. Leaving cut hay lying produced species-poor swards. We conclude that the choice of establishment and management methods for arable field margins significantly affects the long-term conservation value of the swards.