Review Article |
Corresponding author: Tim Gardiner ( tim.gardiner@environment-agency.gov.uk ) Academic editor: Corinna S. Bazelet
© 2018 Jacqui Miller, Tim Gardiner.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Miller J, Gardiner T (2018) The effects of grazing and mowing on large marsh grasshopper, Stethophyma grossum (Orthoptera: Acrididae), populations in Western Europe: a review. Journal of Orthoptera Research 27(1): 91-96. https://doi.org/10.3897/jor.27.23835
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The large marsh grasshopper, Stethophyma grossum L. (Orthoptera: Acrididae), has undergone a significant range contraction in the UK and is now restricted to the bogs and mires of the New Forest and Dorset Heaths. In other parts of Western Europe, the species makes use of a wider range of wetland habitat types. Traditionally, many of these habitats would be managed through low intensity grazing, mowing, or both, and these measures are now often employed in the conservation management of wet grassland habitats. This paper reviews the effects of mowing and grazing on S. grossum populations, through looking at the potential impacts (both positive and negative) on different life stages of the grasshopper. Both techniques are valuable in the maintenance of an open and varied vegetation structure which is known to benefit S. grossum in all its life stages. However, grazing on very wet sites or at high intensity can result in trampling of vegetation and S. grossum eggs, and mowing which is too frequent may negatively affect populations through repeated losses of nymphs. Recommendations are given regarding the suitability of mowing and grazing for different habitats and intensity of management to generate the required vegetation structure. Measures are also outlined, such as the provision of unmown or ungrazed refuge areas, which can help reduce negative effects.
adults, biodiversity conservation, bog, eggs, grassland, management, mire, nymphs, vegetation structure, wetland
Grazing and mowing exert important influences on vegetation structure and are therefore key factors affecting grasshopper populations (
Stethophyma grossum (Figs 1, 2) is locally distributed across Europe and found from Ireland in the west, northern Spain and Italy in the south, east to Siberia and north as far as parts of Scandinavia (
S. grossum is herbivorous, feeding on the stems and seed heads of grasses, rushes and sedges (
In the UK, S. grossum is typically found on quaking acid bogs with purple moor-grass, Molinia caerulea (L.) Moench, bog myrtle, Myrica gale L., cross-leaved heath, Erica tetralix L., broad-leaved cotton grass, Eriophorum latifolium Hoppe, and white beak-sedge, Rhynchospora alba (L.) Vahl (
Its former distribution in the UK and current distribution in the rest of Western Europe shows a wider habitat usage, including areas of fenland, moorland, wet meadow and riverside (
Table
Country | Habitat types | References |
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Netherlands | Wet grasslands and meadows, floodplains, ditches and margins of waterbodies, fens, swamp, wet heath. |
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Belgium | Wet grasslands and meadows, swamp, bogs, ditches, wet heath. Land that is wet in winter. |
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France | Wetlands: marshes, reedbeds, flooded meadows, peat bogs, ditches. In the Alps, up to 2400-2700 m in altitude. |
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Luxembourg | Wet meadows, marshes, peat bogs, ditches. |
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Switzerland | Near open water or periodically flooded vegetation, wet meadows and pasture, peat bogs, ditches. Up to 2450-2700 m in altitude. |
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Austria | Peat bogs, fens, floodplains, ridges of raised bogs. |
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Germany | Marshes, edges of lakes, streams and ditches, wet meadows. Up to 1300 m in altitude. |
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Northern Italy | Lake margins, swamps, alpine fens, wet meadows. |
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Northern Spain | Wet peaty meadows, peat bog, wet mown meadows, margins of ponds and rivers. |
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England, UK | Bogs and mires in the Dorset and New Forest heaths. |
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Ireland | Mire, wet heath, blanket and raised bogs, Molinia-dominated grassland. By rivers and lakes. |
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Denmark | Raised bogs, wet meadows, nutrient-poor fen. |
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Fennoscandia | Bogs, meadows, by lakes and streams. |
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The traditional management of wet hay meadows and floodplain grasslands in Western and Central Europe centered on hay cutting and the grazing of livestock. Many wet areas were grazed by livestock at low intensities. This was sometimes combined with cutting for hay, with one early cut followed by grazing of the remnant sward. Alternatively, on some sites, hay cutting was carried out once or twice a year, typically in May-June and/or August-September (
The wet heath, mire and bog habitats of S. grossum in the UK and Ireland typically have a naturally open and patchy vegetation structure with areas of open water. The wettest parts of these habitats are not suitable for management by mowing or grazing, either in terms of the potential impacts on the habitat, or safety and accessibility for animals and machinery. Around the drier margins of these habitats, low intensity grazing by ponies or cattle during the summer may be used to help reduce the dominance of purple moor grass and reduce encroachment of scrub (
In wet grassland habitats, sensitive management by mowing and/or grazing is considered beneficial overall to S. grossum. The following section discusses considerations relating to mowing and grazing of wet grassland habitats and the requirements and characteristics of S. grossum eggs, nymphs and adults.
S. grossum eggs require high humidity levels for successful development and are very sensitive to dehydration (
Grazing while S. grossum is at the egg stage may result in the direct destruction of eggs by trampling, particularly on the wettest sites (
The distribution of early instar nymphs is thought to be a product of the female choice of habitat for oviposition, as young nymphs have limited mobility and therefore do not tend to disperse from their hatching location (
Mowing can have a significant effect on the density of nymphs. If mowing takes place during the early summer, the density of early instar nymphs is likely to drop significantly afterwards (
Adult S. grossum also tend to be found in locations with relatively high soil moisture levels, perhaps due to their need to oviposit in wetter areas.
The following recommendations are derived from the studies of S. grossum populations in Western Europe and are relevant to the management of wet grasslands including wet meadows and pasture, floodplain grassland and fens. As discussed above, S. grossum is currently only found in valley mires and bogs in the UK (and predominantly so in Ireland), therefore many of these recommendations will not be directly applicable to UK and most Irish populations. In mire and bog habitats, management should focus on protecting sites from activities likely to cause drying, although removal of encroaching scrub and/or management of dominant grasses or bog myrtle may occasionally be required on the drier margins of such sites.
A sensitive mowing regime can be beneficial for the management of wet meadows for S. grossum (
It would therefore appear that wet grasslands managed for S. grossum should be cut at least once (though no more than twice) a year, depending on site-specific habitat needs, and with the aim of avoiding the vulnerable early nymph stage. If an early cut is required, ideally this should be before S. grossum has hatched, but the needs of other species present should also be considered. If a late summer cut is required, this should be after mid-September when most of the egg-laying is complete. In order to minimize mortality of grasshoppers (and other invertebrates), the use of a bar mower (rather than a rotary or flail mower) set to a minimum height of 10 cm is recommended (
Low intensity grazing is a useful method for managing vegetation height and density and tends to create a more varied vegetation structure than mowing alone (
A summary of the advantages and disadvantages of mowing and grazing are presented in Table
Mowing | Grazing | |
Advantages | Creates an open sward structure. Restricts scrub encroachment. | Creates a varied sward structure. Reduces cover of dominant grasses. Restricts scrub encroachment. |
Disadvantages | Mortality of nymphs. Displacement of adults. Potential effects on other species (e.g. ground-nesting birds). | Poaching of wet habitats.Displacement of adults. Trampling of eggs. Overgrazing possible. Potential effects on other species (e.g. ground-nesting birds). |
The following recommendations for mowing and grazing as part of the management of wet grassland habitats occupied by S. grossum can be derived from this review:
– Grazing and/or mowing (dependent on habitat type) are valuable management techniques for the maintenance of the open and varied vegetation structure required by S. grossum.
– Grazing should be at a low stocking density (and, where necessary, for a limited time-period), and nearby ungrazed refuge areas should be maintained.
– Grazing of very wet areas should be avoided.
– Wet grasslands should be cut once a year, or twice at the most, depending on the vegetation type.
– If early mowing is used, this should be before the main hatching period from mid-June onwards where possible (depending on the needs of other species) and late mowing should be after the main oviposition period from mid-September onwards.
– Use a bar mower set to a minimum height of 10 cm to minimize mortality.
– Grasshoppers should be allowed to escape mowing by carrying out operations only on warm, sunny days when grasshoppers are active, retaining unmown refuge areas nearby and leaving the hay crop on the surface for a few days before removal.
The following recommendations relate to the management of wet heath, mire and bog habitats, such as those used by S. grossum in the UK and Ireland:
– Protect sites from activities likely to cause drying of habitats.
– Grazing (and mowing) should be avoided in the wettest areas, particularly in mires and bogs.
– If necessary, low intensity grazing could be used on the drier margins of such sites during the summer months to reduce dominance by grasses or encroachment of scrub.
Recommended management measures for habitat types used by S. grossum in the UK and Western Europe are summarized in Table
Habitat | Management | Frequency | Additional measures |
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Alpine pasture | Light grazing1 | 2-3 months/year | Livestock moved to valleys in winter. |
Ditch banks | Mowing | 1-2 cuts/year | Unmown refuges (exclosures). |
Fen | Sedge cutting | 1 cut/year | Uncut refuges (exclosures). |
Mire/bog* | Avoid grazing | n/a | Protect from drying.May need to manage scrub encroachment. |
Reedbed | Reed cutting | 1 cut/year | Uncut refuges (exclosures). |
Wet heath* | Light grazing | Summer/all year | Ungrazed refuges (exclosures).Avoid grazing of very wet areas. |
Wet grassland | Mowing | 1-2 cuts/year | Unmown refuges (exclosures). |
Many thanks to Paul Brock for the use of his photographs, and to the following people who provided literature sources: Bjorn Beckmann, Paul Brock, Bryan Edwards and Martin Harvey.