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BIODIVERSITY REFERENCE
 
British habitats
 
   Chalk Grassland and Downs   
 
(page 2)


VEGETATION

There is excellent, detailed discussion of the constitution of chalk grasslands in Rodwell et al. (1992). A major grassland community is their NVC community CG2, 'Festuca ovina-Avenula pratensis grassland'.

A summary of the principal NVC plant communities of the chalklands may be added here at a later date, but at present just a few general comments are made. Rather obviously, some of the major plant species of the grazed grasslands are grasses. Red Fescue (Festuca rubra) and a species of Sheep's Fescue (F. ophioliticola, commonly treated as a subspecies of F. ovina) are well able to cope with periods of dry conditions, as can Crested Hair-grass (Koeleria macrantha). Other characteristic grasses include Meadow Oat-grass (Helictotrichon pratense, = Avenula pratensis), Downy Oat-grass (H. pubescens) and Quaking Grass (Briza media).

While chalk slopes might be expected to be too dry for sedges, Glaucous Sedge (Carex flacca) is also often a significant component of chalk turf.

The herbaceous plants of chalk turf are too numerous for any attempt at listing and ancient, 'unimproved' pastures are notable both for their diversity of species and also, often, the presence of rare species. Members of the pea family (legumes) are important as they possess nitrogen-fixing root nodules (with the symbiotic bacterium Rhizobium or its relatives) and they are able to compete well in these low-nitrogen grasslands. Bird's-foot Trefoil (Lotus corniculatus) is a generally common legume in short, dry turf on many kinds of soil and it flourishes in chalk turf as elsewhere. Looking superficially rather similar is the Horseshoe Vetch (Hippocrepis comosa), a specialist chalk and limestone species that can sometimes turn areas of downland into a blaze of yellow. It is important as a butterfly food-plant.

Orchids (family Orchidaceae) are a particular feature of some grasslands, often where there has been some past disturbance, and some of our rarest species are confined to the chalk. Among the more frequent species are the Bee Orchid (Ophrys apifera) and Pyramidal Orchid (Anacamptis pyramidalis). Nationally rare species include the Monkey Orchid (Orchis simia), once relatively widespread on the North Downs but now confined through habitat loss to single native localities in Kent and Oxfordshire, and the Late Spider Orchid (Ophrys fuciflora), known only in East Kent (authors in Wigginton, 1999).

 
Horseshoe Vetch (Hippocrepis comosa) is a characteristic plant of chalk pastures, often locally abundant and no doubt important as a nitrogen-fixing legume. It is of vital conservation importance as the sole food plant of the Adonis Blue and Chalkhill Blue butterflies.
Photograph: near Royston, Hertfordshire, 2003.
 
 
Hoary Plantain (Plantago media), another characteristic plant of chalk pastures. The leaves are arranged in a basal rosette, where they are less at risk from grazing, and then the pale lavender flowering spikes arise to colour extensive areas of turf in the early summer.
Photograph: Isle of Wight, 2004.
 
 
The Dwarf Thistle (Cirsium acaule) is frequent in very short turf in chalk pastures in the south of England. Like many other pasture plants its leaves are in a basal rosette, where they are at less risk from grazing animals, their protection reinforced by their abundant, sharp spines. Even the flowering stem is usually very short. It is also called the "Picnic Thistle", from the fact that it often grows on the warm turf slopes commonly selected for picnics, and, since it is inconspicuous when not in flower, it can add unexpectedly to the picnicking experience.
Photographs: Blows Downs, Bedfordshire, 2004.
 
 
Eyebright (Euphrasia nemorosa). Eyebrights (in Britain and Europe) are annuals of short grasslands. They are hemiparasites, in that they have poor root systems of their own and they attach to the roots of other herbaceous plants, primarily for water and minerals as they are, themselves, photosynthetic. Being annuals, they must have available germination sites in the turf and they need protection from early drought during germination and host-establishment.
 
E. nemorosa is the principal Eyebright species of calcareous grassland in Britain, though it is also frequent on non-calcareous soils in the south.
(Environmentally dwarfed plants on upland limestone are often misidentified as E. confusa but prove to be E. nemorosa when protected from excessive grazing.)
In rough, lowland grassland on chalk, as illustrated here, E. nemorosa is usually well grown and displays characteristically rather dark, glossy and sharply-toothed leaves.
Photograph: Blows Downs, Bedfordshire, 2004.
 
In very short, long-established chalk turf in scattered localities on the chalk downs there also occurs a later-flowering species, E. pseudokerneri. This latter species, rated 'nationally scarce', is disadvantaged compared with E. nemorosa when grazing is reduced and it is also threatened by hybridisation between the two species (Silverside, in Stewart et al., 1994).

When grazing is lower or reduced, coarser grasses can become important, often forming dense stands that eliminate most of the herbs of the grazed turf. Two principal grasses that can become dominant are Upright Brome (Bromopsis erecta) and Tor-grass (Brachypodium pinnatum).

Reduction or cessation of grazing can also lead to invasion by scrub, often an alarmingly rapid process. Hawthorn (Crataegus monogyna) is often the major invasive species, but typically it is accompanied by wild rose species (e.g. the Sweet Briar, Rosa rubiginosa) and a variety of other shrubs such as the Wild Privet (Ligustrum vulgare) and Buckthorn (Rhamnus cathartica).

 
Traveller's Joy (Clematis vitalba) is a common and conspicuous clambering plant in chalk scrub.
Photograph: Blows Downs, Bedfordshire, 2004.
 


 

ANIMAL LIFE

The principal animal of the downs has to be the Sheep. As noted above, it is the grazing animal that has moulded the nature of the downs for hundreds of years. There is even an ancient breed, the Southdown, that takes its name from the South Downs of Sussex (see Links). Cattle are also grazed on the downs, a 'cow down' being one where this has been the traditional grazing. The importance of rabbits (Oryctolagus cunniculus) has already been mentioned in Part 1 under 'Habitats'.
The Mole (Talpa europaea) commonly burrows in soils that are deep enough, its mounds disrupting the grassland surface.

Two classic birds of the chalklands are the Great Bustard (Otis tarda) and the Stone Curlew (Burhinus oedicnemus).
The Great Bustard is a large, turkey-like bird that once bred in such areas as Salisbury Plain and the Breckland area of East Anglia (the latter being an area of grassy heaths and, locally, chalk heath, rather than downland). It needs large areas of open land and loss of habitat, as well as shooting, led to its extinction by the 1830s. There is currently a trial programme of re-introduction to Salisbury Plain, using birds from Russia.
The Stone Curlew requires similar open ground and still survives in much the same areas, strongholds being Salisbury Plain and the Breckland, but it has suffered a severe decline in recent years and the current UK Biodiversity Action Plan (see Links) gives the total British population as now only 150-160 pairs.

Insect life abounds on the downs. The Chalk is noted as providing important habitat for such groups as the butterflies (Lepidoptera), crickets and grasshoppers (Orthoptera) and bumble bees (Bombus). While not at all restricted to chalklands, the Yellow Hill Ant (Lasius flavus) is often an important member of the insect fauna, the anthills it produces having a significant effect on the morphology of chalk grasslands.

 
     
A butterfly, the Marbled White (Melanargia galathea). While not restricted to chalk downland – it is widespread in rough, grassy habitats in southern Britain – it is especially abundant on chalk and on the southern limestones. The larval foodplants are various grasses and the adult has an interesting preference for purple flowers, such as the Knapweed (Centaurea nigra) it is shown visiting here. There can be large populations on rough, chalk slopes. Despite its colour and name, it is a member of the 'Brown' family of butterflies (now in the Nymphalidae) and is not a relative of the Cabbage White and other 'Whites' (Pieridae).
Photograph: Blows Downs, Bedfordshire, 2004.
     
Adonis Blue (Polyommatus bellargus) (male), a nationally scarce and dazzlingly beautiful butterfly, confined to chalk downs in the south of England, where it is very localised and extinct in many former areas. It is listed as a priority species in the UK Biodiversity Action Plan. It requires warm, south-facing slopes with short turf and good populations of its sole foodplant, Horseshoe Vetch (see photograph above on this page).
Photograph: Isle of Wight, 2004.
     
Red-tailed Bumble Bee (Bombus lapidarius), visiting Horseshoe Vetch on chalk downland. A widespread species in England, though less so in Wales and very local (though also under-recorded) and mainly coastal in Scotland; it shows some apparent preference for the chalk regions.
Photograph: Isle of Wight, 2004.
 
The very similar B. cullumanus occurred only on chalk downland, in scattered localities in southern England, but it has not been recorded for many years and is believed to be extinct in Britain.
     
The nymph stage of a grasshopper, probably the Common Green Grasshopper (Omocestus viridulus) but not certainly identified. A typical species of chalk downland, especially when grazing levels are relatively low, but a common species generally in Britain. Chalk grasslands are important habitat for a diversity of grasshoppers, crickets and their allies (Orthoptera).
Photograph: Blows Downs, Bedfordshire, 2004.


 

MANAGEMENT & CONSERVATION

Where chalk grasslands have survived the threat of ploughing or of 'improvement' by reseeding and use of chemical fertilisers, the critical factor is often the extent of grazing, especially by sheep or rabbits, as discussed in previous sections. Maintenance of a floristically rich, open sward requires regular grazing, though, as shown in the photograph below, grazing management to allow seeding, especially of annuals and short-lived perennials, is also important.

 
Grazing control on downland near Royston, Hertfordshire, June 2002. The area to the right is protected from sheep by electrified temporary fencing, allowing the successful flowering and fruiting of the plants inside the exclosure – this area is noted for its high species diversity and presence of rare species. The fence is later removed to ensure that the area receives the necessary grazing to prevent invasion by coarser grasses and scrub.
 
 
Field Fleawort (Tephroseris integrifolia) is one of the species protected by the grazing control shown in the photograph above. It is a nationally scarce species that has shown a marked decline through loss of habitat, by ploughing and destruction of downland and also through reduction in grazing leading to invasion by coarse grasses and scrub (Rose, in Stewart et al., 1994). It is perennial, but short-lived, so successful seed-set is vital for population survival.
Photograph: near Royston, Hertfordshire, 2002.
 
Early Gentian (Gentianella anglica) is a British endemic (i.e. not found outside Britain) and is rated 'nationally scarce' here and given full protection under the Wildlife & Countryside Act, Schedule 8, and under European directives. It is confined to the south of England, with most populations in closely grazed turf on chalk downs, but has declined substantially through loss of habitat and cessation of grazing. Remaining populations are mostly in SSSIs or nature reserves, but it is "still threatened because of the practical difficulties of grazing grassland fragments, cliff edges and coastal slopes." (Chatters, in Stewart et al., 1994).
Photograph: Isle of Wight, 2004.

A principal threat of reduced grazing is the spread of coarser grasses, such as Upright Brome (Bromopsis erecta), Tor-grass (Brachypodium pinnatum), or, sometimes, False Oat-grass (Arrhenatherum elatius). Spread of Bromopsis erecta is said to be reversible, effectively this is a dynamic situation with the proportion of B. erecta in the grassland responding to increases or decreases in grazing pressure. As stated in Rodwell et al. (1992), the spread of B. pinnatum is by no means so easily countered. This tough, invasive species is regarded as a major problem, has spread generally on the chalk in recent decades and needs labour-intensive control.

It should not be forgotten, however, that Brachypodium pinnatum grassland is a habitat itself and is favoured over the shorter turf by most crickets and grasshoppers. Marshall and Haes (1988) note the loss of one of the few remaining British populations of a nationally rare cricket, the Wart-biter (Decticus verrucivorus), as an apparent result of clearance of coarse grasses to promote more species-rich turf.
B. pinnatum is also the foodplant of the Lulworth Skipper (Thymelicus acteon), a small butterfly that is widespread but declining in Europe and which, in Britain, is now confined to coastal chalk and limestone grassland in the county of Dorset. Within its restricted area its populations appear stable (Asher et al., 2001), but maintenance of its Tor-grass habitat is essential
Conservation often has its conflicts and requires the fullest possible information.

Spread of scrub can also cause serious damage to a site. Grubb and Key (cited from Rackham, 1986) found that clearance of recent hawthorn scrub on the Devil's Dyke in Cambridgeshire did not restore the previous species-rich grassland, but instead a coarse vegetation with thistles and other plants that indicated a nutrient-enriched soil, with high levels of nitrate and phosphate.

Lowland calcareous grassland is a priority habitat included in the UK Biodiversity Action Plan (see link below).


References
•   Asher, J., et al. (2001). The millennium atlas of butterflies in Britain and Ireland, Oxford University Press, Oxford.
•   Marshall, J.A., & Haes, E.C.M., (2001). Grasshoppers and allied insects of Great Britain and Ireland, Harley Books, Colchester.
•   Rackham, O., (1986). The history of the countryside, J.M. Dent & Sons, London.
•   Rodwell, J.S., et al. (1992). British plant communities, 3: Grasslands and montane communities, Cambridge Univ. Press, Cambridge.
•   Stewart, A., Pearman, D.A., & Preston, C.D., (eds.) (1994). Scarce plants in Britain, JNCC, Peterborough.
•   Wigginton, M.J. (ed.), (1999). British red data books. 1. Vascular plants (3rd ed.), JNCC, Peterborough.


Links
•   UK Biodiversity Action Plan - Lowland calcareous grassland
    http://www.ukbap.org.uk/UKPlans.aspx?ID=12
    The 'official' current statement on the British conservation status of lowland chalk and limestone grasslands, with links to BAP accounts of individual species of these habitats.
 
•   UK Biodiversity Action Plan - Stone Curlew (Burhinus oedicnemus)
    http://www.ukbap.org.uk/UKPlans.aspx?ID=175
    The 'official' current statement on the British conservation status and BAP for this species.
 
•   The Chalk of Portsdown Hill ('Hilma')
    http://www.bbm.me.uk/portsdown/PH_310_Chalk.htm
    A very nicely put together webpage on chalk rock and its features, with an excellent subsidiary page on coccoliths.
 
•   Revival of the Southdown (Southdown Sheep Society)
    http://www.southdownsheepsociety.co.uk/ark.htm
    A well illustrated page summarising the history, near extinction and revival of the Southdown breed of sheep, part of a large site for enthusiasts for this ancient breed of the downs.
 
•   Chalk Downland Insects (David Element)
    http://www.david.element.ukgateway.net/chalkdownlandinsects.htm
    A selection of photographs; part of his extensive photographic site covering insects and other wildlife.


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© A.J. Silverside
e-mail: alan.silverside@uws.ac.uk
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