Berkshire: Greenham Common

11 July 2013
Half to all day                               OS Landranger 174: Newbury & Wantage

 

Greenham Common is a former airbase that is now an open access area and nature reserve.  Basically acid heath on gravels, it also contains calcareous patches from the concrete and other structures introduced by man.  Many of the plants are quite dwarf and need a slow pace to spot, so we spent most of the day wandering over the area, although we also explored the wetlands at Goldfinch Bottom in the SE corner and some of the roadsides off the common near there.  Bowdown Woods BBOWT reserve is just north of the common, but this is also extensive and we did not find it feasible to explore both adequately in one day, so that was left to another time.

          There are several car parks near the north edge of the common, which is centred at SU500645.  We started from the centre of the north side and walked towards the centre of the common, which is basically one large runway running east-west.  We strolled to the west end and then returned along the south side past the former airport buildings that have been converted into a business park.

          We found we were a little late for many plants, as a week of hot dry weather had parched the thin soil and most were now brown, although there was still much of interest.  The common is also excellent for insects, which we did not have time to explore as well, but we noted in passing the following:

Common blue damselfly Enallagma cyathigerum (male)

Moth Pyrausta purpuralis

Six-spot burnet moth

 Other common insects included the hoverfly Helophilus pendulus, broad-bodied chaser Libellula depressa, cinnabar moth caterpillars, and butterflies meadow brown, marbled white, common blue, speckled wood, small tortoiseshell, and painted lady.

 In terms of the flora, common centaury Centaurium erythraea was one of the most conspicuous at this time, being in full flower and scattered everywhere, including some white ones.

Common centaury, white form

 Heath speedwell Veronica officinalis was also quite dominant, although towards the end of its flowering period, along with other expected heathland species like mat-grass Nardus stricta, heather Calluna vulgaris, bell heather Erica cinerea, and lesser stitchwort Stellaria graminea.  Other common plants, however, were familiar members of the chalk grassland community - eg fairy flax Linum catharticum, salad burnet Sanguisorba minor, carline thistle Carlina vulgaris, tiny wild strawberries Fragaria vesca, and upright brome Bromus erectus.  There was also little mouse-ear Cerastium semidecandrum, a plant which seems happy with sandy and limy substrates.  Musk mallow Malva moschata was frequent and showy, along with viper's bugloss Echium vulgare.  More scattered were biting stonecrop Sedum acre, common storksbill Erodium cicutarium,  field madder Sherardia arvensis, blue fleabane Erigeron acer, bee orchid Ophrys apifera, pyramidal orchid Anacamptis pyramidalis, kidney vetch Anthyllis vulneraria, dwarf thistle Cirsium acaule, and common broomrape Orobanche minor (gone over).  The dry grey "stag's moss" lichen Cladonia portentosa was another major part of the ground "flora".

Heath speedwell

Musk mallow

Viper's bugloss

 One young viper's bugloss away from other clumps had pinker flowers with only two stamens exserted and corollas hairy on the veins rather than all over, which should make it (using Stace's key) purple viper's bugloss Echium plantagineum, which rarely occurs as a garden or crop escape, but the upper leaves did not have cordate bases as described by CTW (the original Flora of the British Isles) and we were therefore uncertain about its identification.

Odd viper's bugloss

 Less common were patches of common cudweed Filago vulgaris, so short we thought at first they were small cudweed.  Nearby were fruited specimens of the equally diminutive silver hair-grass Aira caryophyllea and the uncommon fine-leaved sandwort Minuartia hybrid.

Common cudweed in bud

Common cudweed in flower

 There was also a little sulphur cinquefoil Potentilla recta, which has probably colonised fairly recently, as the Berks flora does not mention it here (although it does have a record from the roadside just to the north).  The pale flowers and toothed finger-like leaflets identify it easily.

Sulphur cinquefoil

 We saw one conspicuous bush of small-flowered sweetbriar Rosa micrantha.

Small-flowered sweetbriar

Various ponds, seemingly created as pools for the cattle used to graze the common from time to time, have been massively invaded by New Zealand pigmyweed Crassula helmsii, excluding virtually all other pond-side vegetation.  At the time of the latest Berks flora (2005) this plant had been recorded at many sites (not Greenham Common) but was not yet seen as a problem.  However, that has obviously changed.  Some water-plants were still surviving in small numbers, such as water-plantain Alisma plantago-aquatica.

At the SW corner of the common are remains of alder Alnus glutinosa woods, but they were relatively impenetrable.  The galls caused by the mite Aceria nalepai were prevalent on the leaves.

Galls on alder of Aceria nalepai

 In this area we saw a dark green fritillary.

Dark green fritillary on greater knapweed

Past the business park in the south-east section of the common we approached the woodlands of Goldfinch Bottom.  Here on a rough bank was a large stand of cut-leaved teasel Dipsacus laciniatus, a plant recorded in the Berks flora as rare on waste ground, with only two records cited.  It is perhaps increasing, although we have not seen it elsewhere.

Cut-leaved teasels

Nearby were plants of Italian eryngo Eryngium amethystinum, a species not recorded in the Berks flora at all.  We have only seen it once before on dunes in one place on the North Wales coast.

Italian eryngo

This area had once hosted another alien, skunkweed Navarretia squarrosa, mentioned in the Berks flora, but we did not come across any specimens and Stace says that it was "naturalised for some years" in Berks.  It is interesting that although the species change over time this location seems to be consistent in hosting unusual aliens.  Native species in the same area included mouse-ear hawkweed Pilosella officinarum, common bent Agrostis capillaris, wild parsnip Pastinaca sativa and (in bud) woolly thistle Cirsium eriophorum.

Common bent grass

Woolly thistle in bud

After a degraded strip of woodland separating the common from new houses, we came to a path leading down to a stream with a boardwalk, where a completely different set of plants was on view.  Here were slender StJohn's-wort Hypericum pulchrum, the attractive wispy fronds of wood horsetail Equisetum sylvaticum, marsh horsetail Equisetum palustre,  marsh thistle Cirsium palustre, marsh figwort Scrophularia auriculata (with the distinctive little weevil Cionus tuberculosus typical of this plant), bog pimpernel Anagallis tenella, royal fern Osmunda regalis, wild angelica Angelica syvestris, bogbean Menyanthes trifoliata; many sedges such as common yellow sedge Carex viridula oedocarpa, greater tussock sedge Carex paniculata, smooth-stalked sedge Carex laevigata, and spiked sedge Carex spicata; and three introduced species - sensitive fern Onoclea sensibilis, elecampane Inula helenium (in bud, with its evenly-toothed cordate leaves and artichoke-like flower-heads) and white stonecrop Sedum album.  The sensitive fern, which has separate spore-bearing spikes like royal and hard ferns, was beside the boardwalk, where some cattle had invaded and unfortunately smashed most of it down.

Sensitive fern

Wood horsetail

Elecampane in bud

Marsh thistle

At the far east end of the common we emerged into a lane leading south downhill to another road.  Across this road in the hedgerow was a good colony of fodder vetch Vicia villosa. 

Fodder vetch

A lane, now closed to traffic, goes right off this road to a former ford and footbridge across the River Enborne, where there are Indian balsam Impatiens glandulifera and hemlock water-dropwort Oenanthe crocata.  Back on the road just after this turning were plants of broad-leaved helleborine Epipactis helleborine in the verge.  From here we returned to Greenham Common and walked along the north side back to the car.  Along here we added weld Reseda luteola and sand spurrey Spergularia rubra.