The bracken society forms the most extensive plant community on the island. Ground- ivy is the most regular member of this community, being most abundant where the bracken, after midsummer, provides dense aerial cover. This it does in sheltered parts of the north and east of the island and in dry valleys, and along the borders of the field- walls. Bracken is an encroaching and invading plant on Skomer. During the years of high farming of the island in the last century it was confined to the waste land and the uncultivable foot of the hedge walls. Today the underground extension of its rhizomes goes on apace towards the centre of each field (except in certain fields which we ploughed in 1946, and in some which were ploughed by the owner in 1948).

Bracken cannot thrive where it is exposed to the severest winds, and therefore, as on Skokholm, the western and southern part of the island is almost free from this plant, or when it is present there it is sparse and stunted. Bracken must have a fairly well- drained and deep soil, and is absent from the wet hollows and the rocky outcrops. As, however, it is late in leafing, lesser celandines and ground-ivy are able to flower and seed in the spring sunshine; so also does the buebell (Scilla non-scripta) which follows late in April and May, and is seen to be closely attached to the bracken association wherever its blooms are thickest. The bluebell, normally a woodland plant, enjoys the moisture present in the soil protected from summer drought by the bracken, and its bulbs mature below ground as its spear-like leaves wither under the spreading fronds. This shade in summer and the mat of dead bracken foliage in winter is said to have a toxic effect on other plants in sheltered areas of the mainland, but this is evidently not so pronounced on the islands where the bracken never grows so tall, and where severe gales in winter disperse or flatten the withered foliage; we find, therefore, that many other and later-flowering plants survive (though they may not thrive) in the shade of a dense bracken community. These are especially: wood-sage (Teucrium Scorodonia), Yorkshire fog (Holcus lanatus), and the fescue grasses (Festuca ovina and F. rubra).

Along its perimeter the bracken forms much less than full aerial cover, and shares the ground with the last-mentioned species, which constitute a rough turf before the truer open grassland is reached. Mingled with them, and at times dominating them, are the two sorrels (Rumex Acetosa and R. Acetosella). Patches of nettle (Urtica dioica), ragwort (Senecio Jacobaea), and some buttercup (Rananculus repens) are usually found here close to the entrances of the numerous rabbitand bird-burrows which fringe the bracken, and evidently provide in the excavated soil mingled with animal droppings sufficient nitrogen to satisfy the food requirements of these rank-growing plants.

From time to time Skomer has of late years been grazed by a few cattle and sheep, but not sufficiently to cause any changes in the grassland, and in the year of our survey this was agriculturally very degenerate, and over-grazed by rabbits. Apart from the changes wrought by the steady encroachment of the bracken, it appeared to have reached a stable and mature (or climax) condition, i.e. in equilibrium with the rabbit- grazing. The more level inland pasture is composed principally of grasses: fescue (F. ovina and F. rubra) with Poa annua, P. pratensis and P. trivialis, and Agrostis tenuis. Widely dispersed colonies of ragwort and thistles (Cirsium arvense and C. vulgare) frequently appear. There are in fact few square yards of this pasture which have not some taller plant interrupting the level- grazed sward. Yarrow (Achillea Millefolium) is not uncommon, and small and sometimes pure concentrations of sheep's sorrel (Rumex Acetosella) occur. In the spring dog violets (Viola Riyiniana) brighten the degenerate sward before the grass shoots appear through the winter cushion of moss and withered herbage.

The nature of Skomer's pasture changes where the land rises to a dry wind-swept slope or where it covers thinly the underlying rock. Here we find a springy turf of sheep's fescue, with plants of wild white clover (Trifolium repens), and strong colonies of bird's-foot trefoil (Lotus corniculatus). Associated with the well-drained pasture are the scorpion-grasses (Myosotis collina and M. versicolor), and as summer advances, a host of other dwarf plants come into flower here: we find eyebright (Euphrasia officinalis), two bedstraws (Galium saxatile and G. verum), tormentil (Potentilla erecta common, and P. procumbens), centaury (Centaurium umbellatum), milkworts (Polygala vulgaris, P. serpyllifolia), pearlworts (Sagina subulata, S. procumbens), and speedwells (Veronica officinalis, V. arvensis, V. Chamaedrys). These make a mosaic of tiny low and trailing flowers from late May to the end of July, by which time most of them have seeded, and the area, much dried as a rule by the summer sun and wind, is a brown- green relieved by the yellow discs of the hawkbit (Leontodon Leysseri).

The dry, short, rabbit-nibbled pastures, so springy and pleasant to walk over, even on mornings of heavy dew, are broken up by the protrusions of rock on higher ground, and only drought-resisting plants survive here. This is a region largely dominated by ling (Calluna vulgaris) and heather (Erica cinerea), but only in very few areas is this heath partnership a pure one. Usually it is shared with other plants of dry situations. Patches of sweet-smelling wild thyme (Thumus Serpyllum) delight the strolling botanist, who observes that it is associated with such other low-growing sun-loving species as English stonecrop (Sedum anglicum), scarlet pimpernel (Anagallis arvensis), lesser skullcap (Scutellaria minor), pearlwort (Sagina procumbens), rock-spurrey (Spergularia rupicola) and occasional colonies of bird's-foot trefoil. But the region of heath is so mixed in topographical character that any attempt to classify the whole into strict ecological communities breaks down; rather it is, like so much of Skomer, a patchwork of minute consociations in which, here and there, the observer finds the same pattern appearing. Thus in a few slightly damper parts of the heath some of the species of the drier ground exist side by side with louse-wort (Pedicularis sylvatica), wood-sage, Yorkshire fog (Holcus lanatus), red fescue (Festuca rubra), and the sorrels. And again, where the rock thrusts clear to the surface, with only shallow pockets of earth to give roothold to the ling and heather, we find wall pennywort (Cotylelon Umbilicus- veneris) (also in damp sites), buck's- horn plantain (Plantago Coronopus), sea stork's bill (Erodium maritimum), and in the autumn the sheep's bit scabious (Jasione montana). Some of the heath extends almost into the marshy areas of the central valleys; some merges into the grassy plateaux above and towards the cliffs, where the fescue grasses fringe the areas of thrift (Armeria maritima). This high ground has few showy plants except in spring, when the charming vernal squill (Scilla verna), a species sufficiently rare in England to make it a special object for English visitors to see, is a common flower on Skomer in such situations.

As the south and west cliffs are approached the typical fescue sward gives way to the thrift, which dominates the cliff-top for a wide distance here in an area covering the burrows of the vast colonies of the puffins. Along the cliff edge the thrift covers this ground frequently in pure huge cushions as much as a yard in diameter and ten to fifteen inches in height. Often these soft masses form a roof of green thatch to the entrances to the homes of the puffins; and they delight the observer with their delicately coloured large blooms in May and June, and at all times provide a most comfortable couch. The dry, windy, salty conditions of the cliff-top are too exacting for most other plants; thrift thrives in spite of the salt rather than, as has been suggested by some botanists, because of it. Thrift grows on the edge of sheltered inland saltings in Pembrokeshire, where it is frequently submerged for short periods by high tides. But it also grows on mountain tops far from salt spray.

Associated with thrift but unable to thrive in dry ground, the seacampion (Silene maritima) occupies the depressions between the sea-pink's cushions. It stands exposure well provided there is sufficient soil and moisture, such as that provided in depressions, crevices, and slopes with a northerly aspect. On Skomer, therefore, it grows most luxuriantly on the Neck and on the eastern and northern slopes, clifftops and ledges, often in association with scurvy-grass (Cochlearie officinalis).

The difference in the wealth and luxuriance of the plant life of the north-east and the south-west cliffs of the island is, in fact, remarkable. The wind- and sun-dried south- west was beautiful while the flowering of the sea- pinks lasted; but afterwards there was little to be seen. An examination of the ground honeycombed by bird-burrows revealed islands of dry turf composed of minute plants of buck'shorn plantain, sea stork's bill and pearlwort (Sagina procumbens and subulata) growing at the landward frontier of the pure societies of thrift. Contrast this with the flora of the broad ledges, about one hundred feet above the sea, which, sheltered by the high castellations of rocks above, run between the Garland Stone and North Haven on the north-east coast. Protected from all but the rare north- east winds, and only receiving the sun's rays early on summer mornings or late in the evening, and much visited by nesting seabirds whose droppings have helped to provide rich plant food, these moist and fertile ledges support in spring a luxuriant concentration of red campion Melandrium dioicum) and sea-campion (Silene maritima), bluebells, scurvy-grass (Cochlearia officinalis) and chickweed (Stellaria media), the last-named selecting the bare nitrogenous patches trodden by gulls and other birds. These are followed by flowering orpine (Sedum telephium), honeysuckle (Lonicera Periclymenum), sea-beet (Beta maritima), buck's- horn plantain (Plantago Coronopus var. maritima) and sea plantain (P. maritima). Ivy (Hedera helix), blackthorn (Prunus spinosa), and blackberry (Rubus fruticosus), with some elder (Sambucus nigra), cover part of the steeper faults or chimneys in the walls of these ledges, and among plants of rank growth noted here we recorded woody nightshade (Solanum Dulcamara), hogweed (Heracleum Sphondylium), hemp agrimony (Eupatorium cannabinum), figwort (Scrophularia nodosa), foxglove (Digitalis purpurea), and ferns: lady fern (Atthyrium Filix femina) and male fern (Dryopteris Filix-mas). The rock- walls were covered with lichens, especially Usnea sp. whose greenish-grey beard- like strands quite disguise the true colour of the basalt.

These delightful cliff-gardens of Skomer were the frequent resort of observers who sought to escape for a while from the blustering south-westerly gales; the ornithologist who wandered there in the spring found himself looking up at the grey rock face where gull, raven, chough, peregrine falcon and fulmar petrel patrolled; and below him the sheer cliffs were filled with the cries and flighting of nesting kittiwakes, guillemots and razorbills. The spongy turf itself contained the burrows of puffin and shearwater, although the entrances to these underground nests were partly or wholly concealed by the vigorous growth of the plant community.

These ledges, too, had been discovered by the cattle which in 1946 were pastured on Skomer; and their owner had great difficulty in preventing the descent of the beasts to this shelter and rich grazing. He had experienced several losses due to the heavy animals slipping or jostling each other when turning on the unfenced edges of the precipice. The effect of the tramp!ing and dunging by the cattle was plain in the virile growth of the vegetation; the nitrogen content had been increased in a soil already well supplied with seabird guano, and with the moisture and humus provided by layers of decaying vegetation laid down each winter.

Another cliff plant association is to be found between the extremes of the luxuriant flora of the north-east and the xeromorphic vegetation of the exposed south-west. In partly sheltered situations such as those offered by breaks in the cliffs (usually occurring on the exposed west and south coasts), wherever there is sufficient moisture conserved by some shade and by natural water collecting in the rocky soil of declivities, there appears in spring a community which temporarily covers a surface that had been swept bare of living vegetation by salt storms and perhaps by surface water in winter: chickweeds (Cerastium viscosum and Stellaria media), mayweed (Matricaria inodora fleshy form), shoreweed (Littorella uniflora), Poa annua and the cliff- loving orache (Atriplex hastata and A. Portulacoides). Each of these species may occur as pure societies in such a terrain. They are also found as members of other plant communities elsewhere on the island. Stellaria media occurred in a great variety of situations, but usually where the soil had been bared and enriched by vertebrate droppings. Darling found that Stellaria media exhibited 'a refulgent growth of about twenty acres growing to a foot in height' on North Rona where Atlantic seals had trampled and bred in previous autumns. In situations with sufficient soil mantle over the rocks where seabirds breed on Skomer (notably also on Middleholm where there is a large colonrof breeding gulls) this chickweed grows with a like abundance, especially during and after a spell of wet weather.

Next we may consider the region of boggy heath and wet land which is a marked feature of the two chief valleys or declivities in the central plateau of the island, which we called the north and the south valleys. In each there is a headwater pond, feeding a small stream flowing in an easterly direction, that of the north valley being the greater, and never drying completely in years of drought. This north pond has some of the commoner plants usually found on exposed waters: yellow flag (Iris Pseudacorus), a water crowfoot (Rananculus sp.), amphibious persicaria (Polygonum amphibium), floating pond-weed (Potamogeton polygonifolius), water purslane (Peplis portula), marshworts (Apium noliflorum and var. ochreatum), and floating club-rush (Scirpus fluitans). The water of this pond was much disturbed by constant wind and by great numbers of gulls which visited it all day long for the purpose of washing their plumage; its shore was a well- trampled mud during the breeding season of the gulls in 1946 as the water receded in summer. On both sides of the little stream flowing from this pond, however, there was a region of wet spongy ground full of varied plant life. Here mosses and rushes dominated: Juncus articulatus, an extremely variable species, seemed to be as numerous as the common rush (J. communis) of which the closely related J. conglomeratus and J. effusus were collected by Dr. W. J. L. Sladen.

Associated with the rushes were the delicate pink bog pimpernel (Anagallis tenella), marsh St. John's-wort (Hypericum eloles), cuckoo-flower (Carlamine pratensis), marsh bedstraw (Galium palustre), marsh pennywort (Hydrocotyle vulgaris), water- mint (Mentha aquatica) bog stitchwort (Stellaria alsine), water- pepper (Polygonum Hydropiper), skullcaps (Scutellaria galericulata and S. minor), and some club-rushes listed in Appendix 2. There were patches of moor-grass (Molinia caerulea) in this community of the stream-side rushes, but in general Molinia seems to prefer land which is slightly less waterlogged (at least in summer); near the south pond there was a large region dominated by the Molinia, with other plants of the rush community much less in evidence.

The land occupied by the rush community drained into the stream which had, during winter rains, cut for itself a track over the bedrock, and nearer the sea the valley assumed the appearance of a miniature gorge, complete with waterfalls. Tall vegetation existed in the shelter of the gorge; where moisture was abundant hemlock dropwort (Oenenthe crocata), hogweed (Heracleum Sphondylium), wild angelica (Angelica sylvestris), meadowsweet (Filipenlula Ulmaria), and marsh thistle (Cirsium palustre) flourished, together with many ferns and some purple loosestrife (Lythrum Salicaria). The slopes above the stream were well drained, dry and sheltered, and here grew the tallest vegetation on the island: stunted elder and blackthorn bushes, mingled with trailing bramble, tall bracken, and a few ancient furze bushes (Ulex europaeus). There were many foxgloves (Digitalis purpurea) in both the north and south valleys, and about the rocky outcrops.

In the stream itself watercress (Nasturtium officinale), brookweed (Samolus Valerandi), water-starwort (Callitriche sp.) and water-blinks (Montia chondrosperma) were found in suitable sites. Many small plants grew among mosses on the banks overhanging parts of the island streams. The eye was pleased with showy masses of primroses from early spring until well into June. Water forget-me-not (Myosotis caespitosa) mingled with lesser spearwort (Ranunculus Flammula) in a harmonious blue and yellow pattern. There were ragged robin (Lychnis Flos-cuculi), and cross-leaved heath (Erica Tetralix) to be found, but not abundantly. Where the ground was moist but not saturated, even far from streams, silverweed (Potentilla anserina) was locally dominant. The common yellow sedge (Carex flava) and the carnation sedge (C. panicea), together with the field wood- rush (Luzula campestris), were found here in spring.

The last but not the least variable environment which there is space to describe here is that of the human habitation- the island farmhouse, buildings and yards. When we lived on Skomer these had been abandoned completely for five years and there was little trace left of the 'artificial' flora which springs up wherever man and his domestic animals settle. One fuchsia bush (Fuchsia sp.) and one black poplar(Populus sp.) were the only surviving trees in the courtyard facing the house, but a great number of cultivated narcissi (Narcissus pseudo- narcissus) flourished exceedingly, and gladdened our hearts on our arrival in March when all else about these buildings was a scene of neglect and decay, and armies of rank weeds were springing up everywhere. Hemlock (Conium maculatum), hogweed (Heracleum Sphondylium), burdock (Arctium sp.), great dock (Rumex crispus), ragwort (Senecio Jacobaea), and nettle (Urtica dioica) would have choked the entrances and exits to the yards and buildings if we had not cut down much of this growth during the summer.

The garden at the back of the house was taken in hand and tractor-ploughed by the chief warden, supported by two keen farmer-gardeners in Joan Keighley and the skipper. It was harrowed with a wooden 'scrubber' made out of driftwood planks, cleaned, and planted with potatoes, lettuces, cabbages, etc. But throughout the summer an interesting if exasperating struggle ensued with two aggressive plants which had persisted since the last cultivations years before: false oatgrass (Arrhenatherum elatius) and lesser swine-cress (Coronopus didymus). The cultivations in fact brought them to light and life just when they were on the point of being overpowered by the thickening tussocks of cock's foot grass (Dactylis glomerata) and Yorkshire fog (Holcus lanatus). As summer advanced, a few plants of groundsel (Senecio vulgaris), petty spurge (Euphorbia Peplus), charlock (Brassica sp.) and red dead-nettle (Lamium purpureum), appeared, together with quite a representative collection of the mouse-ear chickweeds (Cerastium viscosum, C. semidecandrum, C. tetrandrum and C. vulgatum).

On the yard walls, both tops and sides, inaccessible to rabbits and grazing animals, in the cracks between the stones and the lime mortar, flourished a typical dry, rock- loving flora. This consisted of English stonecrop (Sedum anglicum), rock- spurrey (Spergularia rupicola), long-rooted cat's-ear (Hypochaeris radicata), dandelion (Taraxacum officinale), buck's-horn plantain (Plantago coronopus), ribwort plantain (P. Ianceolata), Danish scurvy-grass (Cochlearia danica), pennywort (Cotyledon Umbilicus- veneris), wild thyme (Thymus Serpyllum) and lesser clover (Trifolium dubium) - these last two probably benefit from the lime content of the mortar. Two grasses were common on these walls - Poa annua and sweet vernal grass (Anthoxanthum odoratum), and some spleenworts: maiden-hair spleenwort (Asplenium Trichomanes) and wall-rue (A. Ruta- muraria).