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.
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.