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Purple moor grass and rush pastures (culm grassland - Devon and Cornwall)


This habitat type occurs on poorly drained sites in lowland areas with high rainfall in the western parts of Britain and in Northern Ireland. It is often found in conjunction with other habitat types such as wet heath, scrub and dry grassland, contributing to a patchwork of diverse habitats that will support a wide range of invertebrates. The soils are usually acidic, supporting a distinctive species-rich vegetation community with abundant Purple moor grass Molinia caerulea and Sharp-flowered rush Juncus acutiflorus.

BAP species found on this habitat include the Marsh fritillary butterfly (Eurodryas aurina), Brown hairstreak (Thecla betulae) (on blackthorn) and the Narrow-bordered bee hawkmoth (Hermaris tityus).


Wet grassland with rushes - The Flitts © Roger Key

Wet grassland with rushes - The Flitts © Roger Key

• Agricultural modification

This habitat is highly susceptible to agricultural modification and reclamation through drainage, cultivation and fertiliser applications

• Inappropriate management

Inappropriate management practices such as overgrazing and frequent burning

• Neglect

Lack of grazing can lead to rankness and scrub encroachment

• Afforestation

This has occured especially in Northern Ireland and Scotland

Habitat management

Maintain water levels

This habitat requires damp or waterlogged conditions, so any drainage operations will be damaging and should be prevented. The notable hoverfly Microdon myrmicae occurs in colonies of the ant Myrmica scabrinodis in tussocks about 10-30cm tall in otherwise waterlogged conditions. Any lowering of the water table could affect ant populations and consequently have a detrimental effect on the hoverfly. On drying sites, scrub invasion will be a greater problem.

Encourage diverse structure

Physical structure in grassland or rush pasture is as important for invertebrates as plant species composition, with medium to tall vegetation tending to hold more species and greater population densities than short vegetation. Tussocks of Molinia caerulea provide shelter and breeding habitats for many invertebrates and may be important for species such as the Nationally scarce acalyptrate fly Opomyza lineatopunctata; they should be retained and not cleared through over-grazing or cutting. Maintenance of rush pasture as part of a mosaic of habitat types on a site will ensure a wide range of microhabitats suitable for a greater variety of invertebrates.

Many insects require nectar and pollen as provided by a varied flora. Sallows and other flowering shrubs can be important in the spring. Various insect larvae live in flower heads or stems, so grazing or mowing will threaten to exterminate such fauna unless the management regimes are appropriate.

Maintain grazing

The best management technique for this type of habitat is grazing. This should be moderate to light so that the vegetation structure will maintain some diversity and not be reduced to a uniformly low sward. Species such as the Marsh fritillary butterfly (Euphydryas aurinia) cannot tolerate heavy grazing, especially if this occurs in the summer months. However, if grazing is abandoned, the Molinia/Potentilla mires that occur on culm grassland will deteriorate within a few years, leading to the spread of rank grasses or scrub and a resulting loss of invertebrate foodplants (e.g. Devil’s-bit scabious Succisa pratensis for Marsh fritillary). A rotational grazing or cutting regime may achieve good structural diversity, although an extensive grazing regime is best.

If putting grazing animals out on rush pasture for conservation management, it is important to remember that the use of avermectins to treat livestock will disrupt the development of invertebrate species associated with dung, such as the rove beetle Anotylus mutator. Alternative, less damaging worming treatments should be used.

Control scrub invasion

On rush pasture sites, scrub invasion should be prevented wherever possible. However, the complete removal of all scrub in the area will have the effect of reducing structural diversity and potential loss of habitat for some invertebrate groups, so some diversely structured scrub should be retained as a minor feature. The Brown hairstreak butterfly (Thecla betulae), for example, is found in Devon and South Wales in similar locations as culm grassland habitats. The butterfly lays its eggs on young blackthorn bushes and removal or over-cutting of these is highly detrimental to the species.

Maintain water bodies

If water-courses or waterbodies are present within this habitat, they should be carefully managed, if necessary, to avoid damaging habitats that may be used by aquatic invertebrates such as mayflies. Any work that is likely to damage marginal or riparian vegetation should be done in such a way as to leave a mixture of species and sward heights. Such work should be undertaken on one bank only and on short stretches such as 50m in each 200m in any one year, to ensure continuity of habitat. Shelving margins rather than sharp edges are far preferable.

BAP species associated with purple moor grass and rush pastures:

Narrow-bordered bee hawkmoth (Hermaris tityus)
Marsh fritillary butterfly (Eurodryas aurina)

For a more comprehensive list of species associated with this habitat, please see the download list.