Wasp beetle by Nick Upton
Carefully managed grassland is capable of supporting a wide range of insects, which in turn support small mammals such as shrews and bats, and birds such as yellowhammers and song thrushes.
The grassland sites that tend to be more important for wildlife offer a variety of micro-habitats and enjoy a continuous system of manangement with no sudden changes.
Important features
The more an area of grassland has the following features, the more valuable it will be for invertebrates:
• Topographical variation – slopes, banks, ditches, hummocks, ant hills and even piles of rubble, with different aspects ensure structural diversity. These features will create wetter areas, over-wintering sites, warm and droughty areas – and different invertebrates will exploit the different micro-habitats within a varied site.
• Soil variation – the well-drained sandy and chalky soils tend to warm up more quickly and benefit a greater range of insects. These warm and crumbly soils are easy to burrow into, compared to the relatively cold and damp, heavier chalky boulder clay which is more likely to support insects that require damp ground for much of the year.
• Structural variation of the sward (and even better, an intimate mix in a relatively small area) – with a succession of different types from sun-baked bare ground to patchy scrub, including short open turf, tall grass and tussocks. Tussocks are especially important in creating a micro-habitat with a different micro-climate – providing nesting and over-wintering sites for some bumble bees, ground beetles and others, and food plants for caterpillars of moths and butterflies.
• Plant diversity and in all stages of development – ie plants flowering, setting seed and with last year’s dead seed heads and stems remaining provide a continuous season of feeding, breeding and overwintering sites. Many invertebrates will only lay their eggs on one particular food plant. The larvae of the white butterflies feed on a range of cruciferous plants, whilst the blues and copper require more specific, and often rarer, larval food plants. The larvae of the various browns and skippers feed on relatively common grasses in hedge bottoms, and then depend on flower and shrub nectar as adults. Plant seed heads and hollow stems of plants such as yarrow, knapweed, burdock and thistles provide vital dry winter shelter and food for many insects.
• Other habitats such as scrub and hedgerow immediately adjacent – these may provide the appropriate habitat for part of an insect’s life cycle that can’t be found in the grassland – to feed, rest, sun themselves, overwinter and use as a corridor, linking different areas of suitable habitat.
Pasture or hay meadow management?
Sensitive grazing management is usually better than hay meadow management for a greater range of invertebrates. Grazing at a low stocking density is a gradual process that avoids sudden, drastic changes to a site and can produce bare ground and a varied sward structure that suits a variety of species such as grounddwelling beetles, moths that like short turf, bees, wasps, ants, bugs, crickets and grasshoppers. Animal dung itself also supports a specialist dung fauna – in turn, feeding swallows and bats.
Hay meadow management primarily benefits the botanical interest of communities of plants and may well be the only practical option for small fragmented grassland sites. However, if timed carefully, cutting management can benefit many invertebrates that require tall grass and typical hay meadow flowering plants – such as crickets, grasshoppers, beetles, bugs, spiders, flies, bumblebees, butterflies and moths. Ideal management for hay meadows is to cut for hay and graze the aftermath (ie a combination of cutting and grazing).
Continuity of a site’s traditional management is usually more important for plants and invertebrates than suddenly converting from hay to grazing management.
Continuity of management
Avoid sudden management changes. Crucially, deciding how to manage an area of grassland should take account of the site’s management history. Grazing or cutting favours different plants and therefore insects and, over time with the same annual management, community of plants and insects will have adapted to suit this regime.
Suddenly changing this regime, even for just a year, may irreversibly harm a species – and still not actually encourage a greater diversity in its place. However, all grasslands require some management to prevent succession to scrub and woodland.
Cutting or hay meadow management
Cutting a hay meadow removes both nectar-rich adult food plants and plants on which eggs may have been laid and larvae are feeding. For insects, the hay cut can be catastrophic. However, in traditionally managed hay meadows, a variety of insect species, usually relatively common, have adapted to complete their sensitive developmental stages during the autumn, winter or spring so that the hay cut does not harm them. Finetuning cutting patterns in some of the ways suggested below can benefit even more species.
Although difficult, aim to create a grassland area that has variety in height – and the more intimate the mix of heights in a small area the better. Cutting management tends to produce a fairly uniform sward unless a careful management plan is produced to create variety across the site. Consider the following:
• Set cutting equipment at different heights on different parts of the site
• Always leave some areas of grass uncut completely for a year or longer – as scattered islands or, more practically, as strips mid-field or field edge, covering up to a third of the site in any one year and more on more infertile sites. Many insects spend part of their life cycles in dead stems, grass sheaths and seed heads so a cut at any time of the year could be disastrous.
• To prevent scrub encroachment, rotate these uncut areas. Leave them uncut for three years to create more tussocky structure and on infertile sites leave uncut for even longer.
• Lightly graze the aftermath – ideally with sheep and/ or cattle – to create variety in sward structure.
• Cuttings should always be removed – ideally as a once a year hay crop. Where cuttings are left they will damage the botanical and invertebrate interest by mulching the sward.
• Check the traditional date for cutting a hay meadow before changing it – doing so may completely change the plant community and thus the associated invertebrates. A late hay cut in mid-July is probably the least damaging for invertebrates. It may be better to cut part of the meadow earlier in June and cut the second part later in July to ensure some continuity of flowering plants (essential for nectar-dependent species) and retain some standing seed heads and stems over winter.
Pasture management
Choosing the appropriate grazing animal, stocking level and timing of grazing is dependent on many site factors. For example, intense rabbit grazing in some years may be sufficient grazing on its own, but in myxamatosis years additional livestock may be needed to graze an area. Be cautious – it is better to trial-graze small areas or under-graze a whole site, assess the impact and then adjust management, than to ‘blitz’ a site and possibly cause local extinctions. Ideally, aim to create a varied sward where a proportion of the tussocks, standing dead seed heads and some plant litter should still remain at the end of the grazing period – apparently under-grazed or untidy to some landowners. Check out the following table for grazing management options on different sites.
| Grazing animal | Suffolk grassland situation most suitable for | Timing options | Benefits/disadvantages to invertebrates |
|
Cattle |
Most grassland especially: • Wetter sites – where it is difficult to graze other animals • Fertile sites – (and especially prior to |
• Continuous grazing at low density • Winter grazing on drier sites • Light summer grazing on |
Selective grazing and heavier animals produces greater ground disturbance creating a sward with more structure – poaching, tussocks |
|
Horse |
• Relatively botanically species-poor sites – where they can do little harm • Small sites – where other grazers are • Large, complex sites – where patchy sward structure complements other habitat variety and site can be subdivided |
• Light to moderate spring, summer and autumn grazing may be acceptable on botanically poor or large sites |
Selective hard grazing |
|
Sheep |
• Infertile, dry sites – prone to drought • Large sites with varied topography • Small sites – where other animals are inappropriate • Botanically important sites (where botanical importance outweighs • Easily supervised sites – tethered, continuous but rotational grazing |
• Winter grazing (October to March) does least damage to dormant larval/pupal stages • Avoid heavy summer grazing • Any time if tethered and |
Tends to produce a short and uniform sward. Benefits uncompetitive low growing food plants such as thyme and birds’ foot trefoil so can be important for species dependent on these plants |
|
Goat |
• Neglected sites – especially good • Small sites – where other grazers are not available. • Easily supervised sites – tethered, continuous but rotational grazing |
• Winter grazing (October to March) as above • Avoid heavy summer grazing • Any time if tethered and |
Selective grazing habit |
|
Mixed |
• Large sites with varied topography |
• Avoid over-grazing or |
A combination of different |