Comparison of new and existing agri-environment scheme options for biodiversity enhancement on arable land

1. A multi-site experiment was conducted on six arable farms in eastern England for 5 years to investigate the effectiveness of new agri-environment scheme options for conserving and enhancing a broad range of taxa and ecosystem functions; 2. The six treatments varied in the degree of management intervention from growing a cereal crop with restricted use of pesticide to complete removal of land from production and either allowing natural regeneration of vegetation or sowing seed mixtures which included: seed-bearing crops, tussocky grasses, pollen-and nectar-rich forbs, and fine-leaved-grasses and forbs. All treatments were compared with a conventional cereal crop control; 3. Residual soil fertility in the non-cropped field margins remained as high as the cropped land despite 5 years of cutting and removal of vegetation in the absence of fertiliser input. However, it was possible to establish and maintain a diverse mixture of wildflowers on this fertile soil and this resulted in a significant (25%) increase in soil carbon as measured by loss on ignition compared with the cropped treatments; 4. Diversity of plant species was highest in the sown wildflower margins and this was maintained throughout the study. However, annual cultivation of the field margin was the only treatment to promote the diversity of declining arable plants; 5. Bumblebee abundance was significantly higher (×14) in margins sown with pollen- and nectar-rich species compared with all other treatments for the first 3 years only. Diversity of rare bees was also higher in this treatment. After year 3 there was a marked decline in the abundance bee forage plants and a corresponding increase in grass cover. Bee abundance and species richness was significantly higher in the wildflower margins compared with the other treatments throughout the experiment; 6. Butterfly abundance and diversity was highest in the wildflower, and pollen and nectar margins compared with the other treatments throughout the experiment; 7. Abundance and diversity of soil macro invertebrates was significantly higher in the non-cropped margin treatments sown with perennial seed mixtures compared with the cultivated treatments. Abundance of earthworms was 50% higher in these undisturbed, perennial margins; 8. Abundance of soil surface active detritivores was significantly higher in the non-crop margins compared with the cropped treatments in both autumn and spring. Seed predators were more abundant in the natural regeneration margins in the autumn. Richness and abundance of all invertebrates was significantly lower in the tussocky grass margins compared with all other treatments in the spring, probably reflecting lower activity; 9. Diversity of canopy-active invertebrates caught by both suction and sweep net sampling was significantly higher in the wildflower margins compared with all other treatments. Diversity was SID 5 (Rev. 3/06) Page 3 of 66 also higher in the other non-crop margins compared with the crop. Total abundance of invertebrates was higher in non-cropped margins compared with the crop treatments. This reflected a greater abundance and diversity of detritivores, herbivores and pollinating insects. In contrast, abundance of predatory (beneficial) invertebrates was significantly higher in the tussocky grass and wildflower margins; 10. Abundance of farmland bird indicator species in winter was significantly higher in the field centre patches sown with seed bearing crops compared with the adjacent crop. However, the magnitude of these differences declined considerably after the December visit each year as seed resources diminished. There was also evidence of a marked decline in the quality of this habitat after year 3; 11. Small mammal activity was significantly higher in the patches sown with wild bird seed mixture compared with the crop and field margin during the winter months. However, this pattern of utilisation was reversed in the summer; 12. Synthesis and applications: removal of land from arable production was a more practical and effective means of enhancing biodiversity and ecosystem functions than extensification of management practices. Creation of species-rich field margin vegetation resulted in significant beneficial effects for the widest range of taxa and functions both above- and below-ground. Management prescriptions specifically targeted to the requirements of declining taxa were generally more effective than those designed to deliver a broader range of environmental benefits. However, the benefits delivered by two of these ‘targeted’ prescriptions (pollen and nectar and wild bird seed mixtures) were short-lived and did not persist in after year 3. Such habitats will require frequent re-establishment in new locations.