Swyncombe Downs

Site of Special Scientific Interest · 51.6152, -1.0238

Condition (Natural England)

Favourable (3)
UnitFeatureConditionArea (ha)Assessed
SU671915 Favourable 12.38 2019-03-04
SU672911 Favourable 13.43 2019-03-04
SU681908 Favourable 21.25 2019-03-04

Geology & landscape

Rock Type: Chalk

Description

Area, 46.4 hectares 115.1 ac Description A site including an Iron Age hill fort on the escarpment of the Oxfordshire Chilterns, long known for its chalk grassland, scrub and bird communities and subject to ecological studies from as early as 1942. The grasslands include ancient species rich sheep's fescue Festuca ovina turf heavily grazed by rabbits, alternating with rank stands of tall oat grass Arrhenatherum elatius, both occupying slopes of various aspect and gradient. There are also sparse, herb dominated swards indicative of former ploughing on the thinner soils. Notable very local plants include bastard toadflax Thesium humifusum and wild candytuft Iberis amara, while other species of interest are crested hair grass Koeleria macrantha, small scabious Scabiosa columbaria, creeping toadflax Linaria repens, valerian Valeriana officinalis, felwort Gentianella amarella and pyramidal orchid Anacamptis pyramidalis. Parts of the Swyncombe grasslands appear hostile to the invasion of scrub a point of interest in itself but where this has occurred various woody species characteristic of chalk soils are present, though wayfaring tree Viburnum lantana and particularly buckthorn Rhamnus cathartica predominate. Birch Betula pendula also occurs, but of special importance is juniper Juniperus communis, including some quite young specimens; juniper has declined markedly on the majority of its former chalkland sites in southern England. Some of the woodlands, notably the old beech at the eastern end of the Downs, demonstrate the later phases of ecological succession and provide a valuable interface with adjacent scrub and grassland communities. Here the herbaceous flora includes the grasses Brachypodium sylvaticum, Bromus ramosa and Poa nemoralis, together with dog's mercury Mercurialis perennis, enchanter's nightshade Circaea lutetiana, woodruff Galium odoratum and sanicle Sanicula europaea. The site is outstanding for its butterflies and moths. Butterflies include silver spotted, grizzled and dingy skippers Hesperia comma, Pyrgus malvae and Erynnis tages the first of these a national rarity, as well as dark green fritillary Argyn nisaglaia. Day flying moths include the cistus forester Adscita geryon, chimney sweeper Odezia atrata and wood tiger Parasemia plantaginis.

Species mentioned

English name
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Latin name
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IUCN / Red List Type Family
dingy skipper Erynnis tages LC butterfly hesperiidae
silver-spotted skipper Hesperia comma VU butterfly hesperiidae
grizzled skipper Pyrgus malvae VU butterfly hesperiidae
false oat grass Arrhenatherum elatius LC grass poaceae
wood false brome Brachypodium sylvaticum LC grass poaceae
hairy brome Bromus ramosa Not listed in GB list grass poaceae
sheep's fescue Festuca ovina LC grass poaceae
crested hair-grass Koeleria macrantha NT grass poaceae
wood meadow grass Poa nemoralis LC grass poaceae
pyramidal orchid Anacamptis pyramidalis LC herb orchidaceae
enchanter's nightshade Circaea lutetiana LC herb onagraceae
woodruff Galium odoratum LC herb rubiaceae
autumn gentian Gentianella amarella LC herb gentianaceae
wild candytuft Iberis amara VU herb brassicaceae
creeping toadflax Linaria repens VU herb plantaginacea
dog's mercury Mercurialis perennis LC herb euphorbiaceae
sanicle Sanicula europaea LC herb apiaceae
small scabious Scabiosa columbaria LC herb caprifoliaceae
bastard toadflax Thesium humifusum VU herb santalaceae
common valerian Valeriana officinalis LC herb caprifoliaceae
cistus forester Adscita geryon Not listed in GB list moth zygaenidae
chimney sweeper Odezia atrata Not listed in GB list moth geometridae
wood tiger Parasemia plantaginis Not listed in GB list moth erebidae
juniper Juniperus communis CR shrub cupressaceae
buckthorn Rhamnus cathartica LC shrub rhamnaceae
wayfaring tree Viburnum lantana LC shrub caprifoliaceae
birch Betula pendula LC tree betulaceae

Insects to look out for

These moths, butterflies and beetles are known to feed on plants recorded at this site, and carry a notable UK conservation status — but a host-plant being present doesn't mean the insect has actually been recorded here. Treat this as "worth watching for," not a confirmed sighting.

SpeciesStatusVia host-plant
Chequered skipper
Carterocephalus palaemon
Endangered Brachypodium sylvaticum
The lappet
Gastropacha quercifolia
Endangered Rhamnus cathartica
Scarce vapourer
Orgyia recens
Endangered Betula spp.
The sprawler
Asteroscopus sphinx
Vulnerable Betula spp., Viburnum lantana
Broom moth
Ceramica pisi
Vulnerable Betula spp.
Mottled umber
Erannis defoliaria
Vulnerable Betula spp.
Marsh fritillary
Euphydryas aurinia
Vulnerable Scabiosa columbaria
Juniper pug
Eupithecia pusillata
Vulnerable Juniperus communis, Juniperus spp.
Satyr pug
Eupithecia satyrata
Vulnerable Galium spp.
Grayling
Hipparchia semele
Vulnerable Brachypodium sylvaticum, Festuca ovina
Bedstraw hawk-moth
Hyles gallii
Vulnerable Galium spp.
The lackey
Malacosoma neustria
Vulnerable Betula pendula
Pale brindled
Phigalia pilosaria
Vulnerable Betula pendula, Rhamnus cathartica
Pale eggar
Trichiura crataegi
Vulnerable Betula spp.
Oak hook-tip
Watsonalla binaria
Vulnerable Betula pendula
Flounced chestnut
Agrochola helvola
Near Threatened Betula spp.
Small heath
Coenonympha pamphilus
Near Threatened Festuca spp., Poa spp.
Kentish glory
Endromis versicolora
Near Threatened Betula pendula
Large thorn
Ennomos autumnaria
Near Threatened Betula spp.
September thorn
Ennomos erosaria
Near Threatened Betula spp.
Autumnal rustic
Eugnorisma glareosa
Near Threatened Betula spp., Festuca ovina, Galium spp.
Toadflax pug
Eupithecia linariata
Near Threatened Linaria repens
Double dart
Graphiphora augur
Near Threatened Betula spp.
Silver-spotted skipper
Hesperia comma
Near Threatened Festuca ovina
Wall
Lasiommata megera
Near Threatened Brachypodium sylvaticum
Rosy minor
Litoligia literosa
Near Threatened Arrhenatherum elatius, Festuca ovina
Dark-barred twin-spot carpet
Xanthorhoe ferrugata
Near Threatened Galium spp.
White prominent
Leucodonta bicoloria
Regionally Extinct Betula spp.

Host-plant data: Cook et al. (2025), Traits data for the butterflies and macro-moths of Great Britain and Ireland, 2024, UK Centre for Ecology & Hydrology / Butterfly Conservation; and Padovani et al. (2020), Database of Insects and their Food Plants (DBIF), UK Centre for Ecology & Hydrology (both Open Government Licence). Contains data supplied by UK Centre for Ecology & Hydrology.

Plant communities

W21 — Hedgerow scrub, Mixed scrub

Crataegus monogyna-Hedera helix scrub

Matches 8 species from the description above: Arrhenatherum elatius, Betula pendula, Brachypodium sylvaticum, Circaea lutetiana, Juniperus communis, Mercurialis perennis, Rhamnus cathartica, Viburnum lantana

Hedera helix, Salix cinerea, Acer pseudoplatanus, Ilex aquifolium, Betula pendula, Corylus avellana, Fagus sylvatica, Quercus robur, Fraxinus excelsior, Malus sylvestris, Sorbus aria, Taxus baccata, Ulmus glabra, Ulmus procera, Sambucus nigra, Viburnum lantana, Euonymus europaeus, Cornus sanguinea, Juniperus communis, Ligustrum vulgare, Clematis vitalba, Rhamnus cathartica, Crataegus laevigata, Crataegus monogyna, Prunus spinosa, Juncus effusus, Plagiomnium undulatum, Brachythecium rutabulum, Kindbergia praelonga, Rhynchostegium confertum, Tamus communis, Heracleum sphondylium, Torilis japonica, Arum maculatum, Arctium minus, Cirsium arvense, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Stellaria graminea, Stellaria holostea, Stellaria media agg., Calystegia sepium, Mercurialis perennis, Geranium robertianum, Iris foetidissima, Glechoma hederacea, Lamium purpureum, Origanum vulgare, Stachys sylvatica, Teucrium scorodonia, Allium ursinum, Hyacinthoides non-scripta, Circaea lutetiana, Rumex sanguineus, Anemone nemorosa, Ranunculus repens, Fragaria vesca, Geum urbanum, Potentilla sterilis, Poterium sanguisorba, Rosa arvensis, Rosa canina, Rubia peregrina, Rubus fruticosus agg., Galium aparine, Urtica dioica, Viola riviniana, Anisantha sterilis, Arrhenatherum elatius, Brachypodium pinnatum, Brachypodium sylvaticum, Bromopsis erecta, Dactylis glomerata, Elytrigia repens, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris filix-mas

W20 — Montane scrub

Salix lapponum-Luzula sylvatica scrub

Matches 2 species from the description above: Festuca ovina, Valeriana officinalis

Salix arbuscula, Salix cinerea, Salix lapponum, Salix myrsinites, Salix phylicifolia, Salix reticulata, Empetrum nigrum, Calluna vulgaris, Salix lanata, Vaccinium myrtillus, Vaccinium uliginosum, Carex atrata, Carex bigelowii, Carex binervis, Carex flacca, Luzula multiflora, Luzula sylvatica, Huperzia selago, Selaginella selaginoides, Aulacomnium palustre, Mnium hornum, Philonotis fontana, Plagiomnium undulatum, Rhizomnium punctatum, Dicranum bonjeanii, Dicranum majus, Dicranum scoparium, Fissidens adianthoides, Racomitrium lanuginosum, Calliergonell cuspidatum, Ctenidium molluscum, Hylocomium splendens, Hypnum callichroum, Hypnum cupressiforme, Palustriella commutatum, Plagiothecium denticulatum, Plagiothecium undulatum, Pleurozium schreberi, Ptilium crista-castrensis, Rhytidiadelphus loreus, Rhytidiadelphus squarrosus, Rhytidiadelphus triquetrus, Sanionia uncinata, Scorpidium revolvens, Thuidium tamariscinum, Atrichum undulatum, Polytrichastrum alpinum, Sphagnum capillifolium, Sphagnum fallax, Sphagnum girgensohnii, Sphagnum palustre, Sphagnum russowii, Sphagnum squarrosum, Sphagnum subnitens, Sphagnum teres, Barbilophozia barbata, Chiloscyphus polyanthos, Diplophyllum albicans, Lophocolea bidentata, Plagiochila porelloides, Ptilidium ciliare, Scapania undulata, Cladonia squamosa, Peltigera canina, Angelica sylvestris, Caltha palustris, Hieraclium spp., Saussurea alpina, Solidago virgaurea, Campanula rotundifolia, Succisa pratensis, Valeriana officinalis, Rhodiola rosea, Vaccinium vitis-idaea, Thymus praecox, Epilobium anagallidifolium, Dactylorhiza viridis, Euphrasia officinalis, Rhinanthus minor, Oxalis acetosella, Oxyria digyna, Polygonum viviparum, Rumex acetosa, Anemone nemorosa, Ranunculus acris, Thalictrum alpinum, Alchemilla alpina, Alchemilla glabra, Filipendula ulmaria, Geum rivale, Galium boreale, Galium saxatile, Saxifraga aizoides, Saxifraga hypnoides, Saxifraga oppositifolia, Saxifraga stellaris, Viola riviniana, Agrostis canina, Agrostis capillaris, Anthoxanthum odoratum, Deschampsia cespitosa, Deschampsia flexuosa, Festuca ovina, Festuca rubra, Nardus stricta, Dryopteris dilatata, Phegopteris connectilis

W22 — Hedgerow scrub, Mixed scrub

Prunus spinosa-Rubus fruticosus scrub

Matches 2 species from the description above: Brachypodium sylvaticum, Mercurialis perennis

Hedera helix, Acer campestre, Corylus avellana, Ulex europaeus, Prunus spinosa, Plagiomnium undulatum, Brachythecium rutabulum, Eurhynchium striatum, Kindbergia praelonga, Thuidium tamariscinum, Atrichum undulatum, Lophocolea bidentata, Achillea millefolium, Cardamine flexuosa, Lonicera periclymenum, Moehringia trinervia, Silene dioica, Silene uniflora, Stellaria media agg., Mercurialis perennis, Geranium robertianum, Stachys sylvatica, Teucrium scorodonia, Hyacinthoides non-scripta, Oxalis acetosella, Digitalis purpurea, Plantago lanceolata, Veronica chamaedrys, Armeria maritima, Rumex acetosa, Filipendula ulmaria, Geum urbanum, Rosa canina, Rubus fruticosus agg., Rubus idaeus, Galium aparine, Urtica dioica, Viola riviniana, Agrostis capillaris, Brachypodium sylvaticum, Dactylis glomerata, Festuca rubra, Holcus lanatus, Holcus mollis, Poa trivialis, Asplenium scolopendrium, Pteridium aquilinum, Dryopteris borreri, Dryopteris filix-mas