Field margin at RSPB's Hope farm, Knapwell, Cambridgeshire

Field margins on grasslands

Grassland systems allowed to go to seed can be of real value to nesting birds and insects.

Field margins on grasslands

Grass and broad-leaved plants which are allowed to go to seed and develop a structure can be particularly valuable as they can be used by nesting birds and large, long-lived insects.

Leaving uncut margins around mown grass fields can provide this. Alternatively, fenced-off strips along the edge of grazed fields can offer similar benefits.

Key points

  • Uncut margins or corners of mown fields offer an easy way of providing seed food for birds and habitat for insects.
  • Creating buffer strips on intensive grassland and taking field corners out of management are options under the Defra Entry Level Stewardship.
Grass

Benefits to wildlife

Grass margins maintained through the winter will harbour over-wintering insects

A grass strip which is only cut or grazed once every three years will harbour large, long-lived insects whose life cycle would be disrupted by the mowing or grazing which takes place on the rest of the field. These insects will be an important food source for birds, especially when collecting food for chicks.

Grass margins that are not grazed or cut provide food for seed-eating birds

For birds, the availability of seed food is often the most limiting factor on modern livestock farms. The decline of arable fodder crops and the large-scale switch from hay to silage has reduced seed availability. 

Around mown fields, uncut strips of at least two metres in width can provide a temporary seed source, although much of this will be lost during aftermath grazing. Wider fenced-off strips, which are cut or grazed once every three years, can, however, provide seed food for birds for longer periods.

Tussocky grass margins can provide nest sites for ground-nesting birds

A tussocky grass strip which is only cut or grazed once every three years provides nesting habitat for birds. 

Strips situated against a short, thick hedge provide an ideal nesting habitat for birds such as whitethroats and yellowhammers.

How to create uncut margins

To create uncut margins around mown fields, you should:

  • Leave at least a two-metre uncut margin around the edge of mown fields. 
  • Avoid applying fertiliser to the uncut strip to reduce wastage and encourage a greater diversity of plants. Retain the margin if the grass ley is reseeded.
  • The margin can be grazed, along with the aftermath, following the final cut. It is, however, beneficial to maintain a tussocky sward at the end of the grazing period to preserve habitat for over-wintering insects.
Survey of plant rich field margin, RSPB's Hope farm, Cambridgeshire

Managing fenced-off strips

There are many ways to manage fenced-off strips (or field corners) around the edge of mown fields or grazed pasture.

  • Strips which can be left ungrazed and uncut have the added benefits of providing the tussocky grass margins required by nesting birds such as yellowhammers, preserving habitat for long-lived insects, voles for barn owls and nest sites for harvest mice.
  • The best location for these strips is next to thick hedgerows or semi-natural habitats. Strips next to woodland are of little benefit to nesting birds due to the risk of predation, but may be used by hunting barn owls, or to protect ancient woodland from the impacts of intensive grassland management.
  • Strips can vary in size, but it is worth creating a few wider strips (averaging six metres wide) rather than margins around the whole field, as the area will need to be managed by cutting or grazing at least once every three years.
  • The strips can also be used to straighten any awkward edges of grass fields and act as wildlife corridors to link natural habitats such as woodlands.
  • You might wish to install a permanent gated fence, or use temporary fencing whenever stock are grazing the field. The latter option is more practical for a mown field, where grazing only needs to be excluded for short periods. 
  • It is important to avoid applying fertiliser to the strip to encourage a greater variety of plants. 
  • If a pernicious weed problem develops, then it should be treated by use of a weed wiper or spot treatment with herbicide.
  • Control the vegetation once every three years by cutting and removing, or grazing, from September onwards. If you have more than one strip then avoid managing all of the strips in this way in the same year. This provides a greater diversity of sward types which increases the benefits for birds and insects.
  • If pernicious weeds are present such as ragwort or thistles then topping to a height of no less than 12cm may be required after 1 July.
Buffer strips on grassland screenshot

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How to create and manage arable field margins. PDF, 130Kb.

Buffer strips on grassland advisory sheet (England)

How to create and manage buffer strips on grassland margins. PDF, 301Kb.

Buffer strips on grassland advisory sheet (Scotland)