Chalk grasslands develop on shallow lime-rich soils, notably on the downland of south-east England. The habitat supports a wealth of wildflowers and a wide array of butterflies, grasshoppers and other invertebrates, many of which are restricted to chalk soils.

In London, chalk grassland is largely restricted to the southern edge of the metropolitan boundary. Here parts of the North Downs lie within the Boroughs of Sutton, Croydon and Bromley. Another area of chalk lies on the extreme north-western edge, in the Borough of Hillingdon, where outliers of the Chiltern Hills are just within the Greater London boundary. Further small patches of grassland containing species typical of the chalk can be found scattered throughout London growing on artificial calcareous substrates such as railway ballast and fly ash.

There are approximately 320 ha of calcareous grassland in Greater London. The approximate figures for each borough are given in Table 1and represented by the Map. There are approximately 9,560 hectares of calcareous grassland in south-east England.

These totals have also been broken down into individual sites within the 5 boroughs. Click for Bromley and Sutton or Croydon, Hillingdon and Lewisham. For the purposes of future updates of the audit, a grid reference is included along with the LEU Habitat Survey Parcel number.

Greater London’s chalk grassland supports a number of nationally rare species. Many of these are continental in distribution and occur in Britain only on the downland of the Southeast, where climatic conditions are comparable to those of mainland Europe.

The London Boroughs of Sutton and Croydon support populations of the extremely rare and specially protected greater yellow rattle Rhinanthus serotinus. The populations found in Sutton, Croydon and in nearby parts of Surrey represent the national stronghold for this species. The London Borough of Bromley holds Britain’s largest colony of the nationally rare Kentish milkwort Polygala amarella.

Greater London’s chalk grassland also support a number of other rare or local plant species such as knapweed broomrape Orobanche elatior, lesser calamint Clinopodium calamintha, man orchid Aceras anthropophorum and fragrant orchid Gymnadenia conopsea. Other species typical of chalk grassland which are indicative of the habitat in Greater London are salad burnet Sanguisorbia minor ssp. minor and kidney vetch Anthyllis vulneraria.

This rich and diverse habitat supports numerous invertebrates, with some sites recording as many as 43 butterfly species, some of which are also nationally rare. These include the small blue and chalkhill blue. Most chalk grasslands also support a range of other uncommon or declining species such as skylark, linnet, goldfinch, slow worm and common lizard.

All these factors have led to a reduction in the extent and distribution of this habitat and continue to threaten remaining chalk grassland. The fragmented, isolated nature of the remaining sites makes further decline in their nature conservation interest more likely, particularly the loss of small populations of vulnerable animal species.

Opportunities
Efforts to reverse this trend have been made on a number of sites with some success, particularly through the removal of invasive scrub and restoration of grazing. Where former chalk grassland has been lost to previous arable conversion, there is the potential for reversion to grassland which can become quite species rich. Arable reversion can provide an opportunity for linking together isolated chalk grasslands by providing stepping stones, habitat corridors or extensions to existing habitat.

Old mineral workings and quarries such as those found in Hillingdon and Croydon, may also contain valuable calcareous communities, With suitable management and protection, these often neglected sites represent considerable opportunity for the conservation of species associated with chalk grassland.

Protection from development should be ensured to prevent further losses of this valuable habitat and the UDP status of all chalk grassland sites should be assessed. The potential for LNR status (and SSSI status for all sites where greater yellow rattle occurs) should be fully investigated.

The audit was conducted using the best available data. Some figures used are estimates and the quality of the data may vary from site to site. For many of the sites there is no recent data; consequently the data will include some inaccuracies when compared with the present day situation. Habitat areas have been rounded to the nearest hectare to avoid misleading precision in the figures.

The audit should be used as a guide and not as a definitive statement of Greater London’s chalk grassland resource. Each borough could refine the audit by comprehensive re-survey.

Much of the data collected was taken from the London Wildlife Habitat Survey (1984/5). This survey represents the most fully comprehensive survey to date. The survey data have been cross-referenced and updated by re-surveys carried out by the LEU and others.

The data was further cross-referenced with the ‘Phase 2’ chalk grassland survey undertaken by the Nature Conservancy Council (1988) and the Greater London Grassland Inventory (English Nature 1996). However, JNCC’s 1988 survey used stricter criteria in identification of chalk grassland. The distinction between calcicolous and mesotrophic grassland can be uncertain and can lead to double accounting or even omission of sites which would benefit from the Chalk Grassland Habitat Action Plan.

In view of the above, the 1988 data has replaced the 1984/5 data when the area of chalk grassland had increased, but not when chalk grassland area had been reduced or sites omitted. Although this may lead to an inflated estimate of the resource, it is an attempt to provide a comprehensive list of Greater London’s chalk grassland in its widest context and to include all potentially applicable habitat in the Habitat Action Plan.