Field margins for grassland biodiversity

Field margins and beetle banks have featured for quite some time as a conservation action for farmland wildlife in arable systems. They have well-documented benefits for plant diversity, invertebrate diversity and as habitat and feeding area for a variety of mammals and birds. Our research group is also interested in field margins - but in grazed grassland systems.

Just over a decade ago, we established an experiment to investigate the wildlife benefits of field margins in a grassland dairy system. Helen Sheridan's doctoral research (funded by Teagasc's Walsh Fellowship Scheme) established experimental field margins in the intensively managed dairy grasslands on our research farm at Teagasc, Johnstown Castle, and published the first results in 2008.
There were three different types of establishment methods for field margins:
1. the existing vegetation was fenced to exclude cattle
2. the existing vegetation was sprayed off and rotovated, the existing seed bank allowed to develop, and fenced to exclude cattle
3. the existing vegetation was sprayed off and rotovated, the field margin sown with a grass and wildflower mixture, and fenced to exclude cattle.
We also established margins of different widths (1.5m, 2.5m and 3.5m).

Helen Sheridan (left) established these field margins at Teagasc, Johnstown Castle, Wexford in 2003, and they will be resampled again in 2013 by Blathnaid Keogh. 

The margins were established in three different ways, at three different widths, and have since been subjected to a grazing/non-grazing treatment. We measured plant and invertebrate diversity on them. 

Overall, we found that:

• reseeding had a positive effect on botanical diversity when compared to the other two treatments
• exclusion of fertiliser alone (as in treatment 1) could not be recommended, and resulted in very slow change of botanical diversity
• the reseeded margins had greater abundance of invertebrates than that in the other two treatment, which in turn had greater invertebrate abundance than a control sample in the grazed field adjacent to the margins.

Ideally, we would recommend the maintenance and protection of existing field margins in grasslands, especially those with botanical diversity and species of conservation interest. However, where the existing vegetation has no existing plants or seed bank with plants of conservation interest (as on intensively managed dairy farms), then the use of seed mixtures is a relevant strategy to improve the wildlife on the farm. These need not necessarily be used on all margins of the farm (and seed mixtures are not cheap), but could be targeted at areas that connect other habitats and landscape features.

Sheridan et al. 2008. Plant and invertebrate diversity in grassland field margins. Agriculture, Ecosystems & Environment 123: 225-232.