Changes in the Coast Vegetation near Berrow, Author(s): H. Stuart Thompson Source: Journal of Ecology, Vol. 10, No. 1 (May, 1922), pp. 53-61 Published by: British Ecological Society Stable URL: http://www.jstor.org/stable/2255430 Accessed: 27-06-2016 13:03 UTC

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CHANGES IN THE COAST VEGETATION NEAR BERROW, SOMERSET

BY H. STUART THOMPSON.

(With Map and Plate II.)

The casual observer who has recently walked along the sands or adjoining dunes north of Burnham-on-Sea cannot fail to have noticed a considerable change in the aspect of the mud flats S.W. of Berrow Church, if he had but a few years earlier had the opportunity of observing the same stretch of mud comparatively free from vegetation-at least phanerogamic. In the summer or autumn of 1921 he would have been attracted by a large area of dark green vegetation adjoining the hard strand, and stretching seawards from about 400 yds. N.W. of Burnham lower Lighthouse to 600 yds. S.W. of Berrow Church, which is situated on the. sand-dunes 14 miles from the Lighthouse. The object of this article is to indicate briefly the nature of the new vege- tation, which is about 500 yds. wide, 1500 yds. long (an approximate area of 100 acres) and tapers at both ends; to attempt to fix the date of the inception of the muddy salt marsh formation; to point out certain topographical changes at the mouth of the River Parret; and to incorporate several observations made by Moss, as published in his valuable pamphlet, issued by the Roy. Geog. Soc. in 1906, on the Geographical Distribution of Vegetation in Somerset'. It may also be interesting to make a few remarks on the phanerogamic plants of the line of sand-hills between Burnham and Down. This is based upon a survey made on various dates between July and October 4th, 1921, coupled with observations made and plants collected on that coast on many occasions since 1880. The writer has also in his herbarium a large number of specimens from that part of the coast and from Stert Island, opposite Burnham, gathered by Thomas Clark between 1820 and 1860. Some of these confirm the records in H. C. Watson's New Botanist's Guide, Suppl. 1837, which were chiefly senit by Clark's friend the Rev. J. C. Collins. In Dr Walter Watson's able paper on "Cryptogamic Vegetation of the sand-dunes of the West Coast of " (This JOURNAL, 1918) quite a secondary place was naturally given to the flowering plants of the Somerset sand-dunes. On July 7th, 1921 a Trinity House official informed me that he was changing the position of some of the buoys at the mouth of the Parret, because the channel was altering. This was confirmed in December by the

1 Out of print for some years.

This content downloaded from 142.150.190.39 on Mon, 27 Jun 2016 13:03:24 UTC All use subject to http://about.jstor.org/terms 54 Chianges in the Coast Vegetation near Berrow, Somerset

Harbour Master at , who kindly lent me an emended Admiralty Chart. But in August I observed a new tributary channel some 10 ft. deep and 40 ft. wide near where it enters the Parret about 600 yds. west of the Lighthouse. This is not shown on the 6" Ordnance Map revised in 1904, nor on any map I have seen. The channel drains a portion of the muddy Berrow Flats, and may be the cause of the new vegetation, by diminishing the force of scour over the flat between it and the sand-dunes. It makes a sharp bend westwards when within 460 yds. of the Lighthouse. Its length is nearly a mile, and for a considerable distance it forms at present the western boundary of the Glyceria-Salicornia association. On Oct. 4th, 1921, there was an ex- panse of clean sand, with shells in places, on the west side of this channel. At that date the sand was about two feet higher than the mud on the other side of the channel. The mud is in places furrowed with small irregular channels about two feet deep, which on the west drain into the new channel. The shallower channels nearer the coast remain half full of water, for the mud flats nearest the sand-hills are a foot or two lower. This very liquid mud makes access to the Glyceria-Salicornia association difficult in places. Indeed it would appear from the Admiralty Chart published in 1886, from a survey in 1884-85, that the level of the whole coast near highwater mark is con- siderably lower than that of the major portion of the Flats and of the Gore Sand, which stretches 33 miles to the S.W. The depth in fathoms at high tide was then given as varying from 41 and 52 close to the coast at Berrow, and from 1 and I' at Gore Sand point, to only 2 a fathom 1} mile west of Brean Church, which is two miles north of Berrow Church. A mile west of the last-mentioned sounding the sea was in 1885 about 7 fathoms deep; but even between and the no greater depth than 12 fathoms is indicated. That rocky island is 256 ft. high, or 31 times the greatest depth of water between it and Brean Down point three miles eastward. It is important to remember, as remarked by Moss, that the tides of the Channel rise higher than those of perhaps any other European waters, and that they are slightly higher on the Welsh than the Somerset coast. At Chepstow they occasionally rise to 50 ft. On the Somerset coast the heights of spring tides above Ordnance Datum are approximately: Bridgwater town (14 miles up river) ...... 23 ft. Bridgwater Bar (west of Burnham) ...... 35 ft. Weston-super-Mare ...... 37 ft. Portishead and Avonmouth ...... 42 ft. Bristol (Cumberland Dock Gates) ...... 33 ft. The River Parret is gradually becoming silted up, so that the shipping of the former busy port of Bridgwater has suffered considerably in recent years. The well-known tidal wave or bore which reaches above Bridgwater is caused by the sudden contraction of the river near its mouth. The Harbour Master at Bridgwater informed me of much recent coast

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erosion between Stert Island, a mile from the end of Burnham pier, and Stert Point on the west side of the Parret mouth. This may be the main cause of the silting up of the river. I suggested the planting of Spartina Townsendi. This cord-grass is serving a useful purpose where planted during 1913 on the coast south of , Pieces of Spartina rhizome must have been washed thence by the tide some 14 miles round the promontories of Sand Point, Birnbeck, and Brean Down; for on July 9th, 1921, I noticed three large clumps, two of them 9 ft. across, were well established on the mud at Berrow. One of these is within 20 yds. of the hard sand, and another is about 300 yds. from highwater mark. I photographed them seven weeks later when in full flower. Owing to the drought of 1921 it is probable that horses straying on the mud and wet sand from the dunes had sampled the young shoots of Spartina, for in August that impression was given, and horses were seen on the mud on several of my visits. Subsequently Dr W. Watson told me he had observed the nearest clump of Spartina the previous year.

Glyceria-Salicornia Association. The most interesting feature is the very rapid growth, over scores of muddy acres, of Glyceria maritima Wahlbrg. (Sclerochloa maritima Lindl.) which is now the dominant plant of the area. At present it begins (on the south) some 800 yds. north of the Lighthouse, afterwards in tussocks 12-18 inches high, and extends thickly northwards for about 1000 yds., when it becomes sparsely scattered and in very low patches on the mud and sand. Prostrate isolated patches extend farther northward some 1200 yds., the most northerly units being in a depression of mud and sand five yards east of a ridge or bank of harder sand (with shells) a foot higher. Opposite Berrow a few very detached units of Glyceria, in patches two feet across, extend seawards 1000 yds. from the coast. But this grass, which is the first colonizer on the open mud, does not extend quite so near the new channel as do Salicornia dolichostachya and S. ramosissima. Early in July some of the Glyceria was in flower, though covered at each high tide; but no trace of blossom or seed was observed a month later. Dr Watson saw it in flower July 21st, 1920. WhiteL gives the habitat of this grass as " Salt-marshes, and on the muddy banks of tidal rivers and inlets from the Channel "; and adds " I have seen it sparingly in blown sand near Burnham, a rare position in this country, although on Mediterranean sands it is often abundant." I know of no "Flora" of a county or other district in which the habitats of plants have been described with such care and accuracy. The habitats in this work and Praeger's Tourist's Flora of the West of are in marked contrast with many of those in e.g. Hooker's Student's Flora. Dr E. J. Salisbury tells me that in November 1911 he and Dr Moss were on Berrow Flats. and walked along the mud to Highbridge (near the mouth I Flora of Bristol, p. 659 (1912).

This content downloaded from 142.150.190.39 on Mon, 27 Jun 2016 13:03:24 UTC All use subject to http://about.jstor.org/terms 56 Chianges in the Coast Vegetation near Berrow, Somerset of the Brue where are salt marshes). It was only some way up the estuary south of Burnham and near the Brue mouth that they saw a little Glyceria maritima, "very patchy." The following extract (Moss, loc. cit. p. 8) is very noteworthy: "The Berrow Flats at low spring tides are four miles in width. Owing to the constant movements of the surface, caused by the ebb and flow of the tides, the flats possess no vegetation. The prevailing westerly and south-westerly winds, blowing over the flats, drive tiny particles of sand onwards; anid in times of high winds sand blizzards are frequent." My own observations fully confirm the statement about the constant movement of the surface. Changes were noticed even from day to day, e.g. one day a clump of Spartina was half embedded in fresh blown sand. On the mud of Berrow Flats Salicornia is at least subdominant. S. ramo- sissima and S. herbacea forma stricta, begin in units and small colonies 400 yds. north of the Lighthouse, and the Salicornietum soon becomes much thicker. These two species are here and there interspersed with S. dolichostachya, some of which consisted of a single long spike of 8-12 cm. on an unbranched stem of similar length. This well-marked species was not previously recorded from the . The habitat in Camb. Brit. Flora is " gravelly foreshores and portions of salt marshes subject to much wave action." At Berrow it chiefly frequents the wettest mud, and especially the sides of shallow furrows, and is usually associated with Glyceria maritima and other species of Salicornia. At present it extends north to within six yards of the most northerly clump of Spartina; but there are large areas from which it is absent. In places the Glyceria is so thick that nothing else will grow. I have not yet at Berrow detected G. distans which probably occurs with it, for White records it: "By the Channel at Burnham 1882, 1888 and 1905." Another Salicornia, which puzzled the late Cedric Bucknall and myself, has the outward aspect of S. lignosa; but after Bucknall saw it growing on Oct. 4th he thought it an undescribed, large woody form of S. Smithiana with very long lower branches. Few of these were seen, some were a foot long, and they mostly broke off as if rotten at the top of the rootstock. Dr E. J. Salisbury has since seen my specimens sent to the Watson Bot. Exch. Club and con- siders they are probably Smithiana x ramosissima. By Oct. 4th many S. dolichostachya were "in seed," dried up and looking almost like large dried up specimens of Euphrasia or Bartsia; while others were turning golden, and bright red patches of tall S. ramosissima decorated the landscape. At present there is at Berrow li-ttle of the true S. herbacea; unless, as Marshall says in his Suppl. to Flora of Somerset, forma stricta is "the type." Moss remarked, in reference to the Somerset coast generally, that "between the limits of neap tides the mud is stirred up at every tide, and the ground is consequently bare of vegetation. At the limit of high neap tides, where

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vegetation makes its appearance, an open association of Salicornia herbacea occurs. The plant is not merely the dominant, but often the only species that occurs, though occasionally Zostera marina is found." Zostera is rare on the Somerset coast, though possibly overlooked. Very little was observed in one or two small pools on Berrow Flats. I have seen only two small plants of Suaeda maritima on the Berrow Flats; and no Spergularia-1, Statice or Armeria yet. The absence of these plants, so common on older salt marshes, tends to prove how recent is the vegetation in question. Aster Tripolium is present in places, and in August one large clump in particular was a beautiful sight. It appears in one of the photo- graphs. Unlike the usual form of tidal river banks and muddy salt marshes (var. discoideus) the mauve ray florets were well developed. Triglochin mari- timum is more widely spread, and some of the huge tufts are so tall and conspicuous that they may easily be taken for Spartina from a distance. Seedling Triglochin maritimum of about five inches in height is a most puzzling plant to determine, until one becomes accustomed to it. It has much the aspect of some seaside Isoetes! To sum up; of Moss's "General Salt Marsh Association, which occurs on the landward side of the two preceding associations" (that of Salicornia herbacea and that of Glyceria and Triglochin), we have none at Berrow; because for its development the mud must be "scarcely ever tide-washed, and hence the conditions of plant life are much more favourable." Of the five dominant and subdominant species of the "General Salt Marsh Association" Glyceria maritima and Aster Tripolium alone are as yet present. Statice Limonium, Armeria maritima and I believe Plantago maritima are absent. Of the eight "abundant species" only Suaeda maritima, in extremely small quantity, and Triglochin maritimum locally figure. Nor do any of the "occasional species" of this association occur at Berrow Flats. This association "has a dominant halophytic form, and with both halophytes and hemi-halophytes among the secondary and dependent species."

Association of Strand Plants. As pointed out by Moss (loc. cit. p. 9), on the foreshore at highwater mark a fringe of plants often occurs. Most of the species are rather fleshy, and may be termed hemi-halophytes; and many of them belong to the natural order Chenopodiaceae. Beta maritima is an occasional strand plant not mentioned in 1906. They are not only exposed to the westerly gales, and to sand blasts at low tide, but to occasional submergence at the highest tides. They are chiefly annuals with tap roots, and possess no power of growing upwards when buried beneath sand. In that particular Moss shows that they differ from the association of Sea Couch Grass (Agropyron or Triticum junceum) and from the association of Marram Grass (Psamma arenaria).

I Frequent further south. A Stert Island example is dated 1817.

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Watson (loc. cit. p. 136) remarked that on this coast "the association of strand plants was little evident for several years (probably owing to storms and high tides), but in 1916 appeared to be regaining its former conspicuousness." Of the ten strand plants given by Moss in this district, Glaucium flavum and Polygonum Razi described as "rare" have become rarer: there is now very little Yellow Horned Poppy south of Brean. Cakile maritima and Arenaria peploides ("not common") are now quite scarce. In 1921 Salsola Kali, one of the " abundant" species in 1906, was less so at Berrow, but abundant about Brean, and particularly where it has invaded the Marram Grass on the lower windward slopes of the shifting dunes. Salsola, which varies much in quantity from year to year, does not appear at all in Moss's Marram Grass association. Eryngium maritimum was a frequent strand plant between Burnham and Brean 30 or 40 years ago, but it has become rare on the whole coast. Moss gave it as an " occasional" species of the Sea Couch Grass (Agropyron junceum) association. It may now be considered a somewhat rare species of the associa- tion of Marram Grass S.W. of Berrow Church, and rarely seen farther N. Probably this plant and the Horned Poppy have suffered more from the depredations of visitors than by the natural consequences of storm and flood.

Blown Sands and mobile dunes. South-west of Berrow Church, and immediately behind highwater mark and the occasional line of strand plants, there are at present for several hundred yards towards Burnham three more or less distinct belts of vegeta- tion on the shifting sands (A, B and C on plan). BELT A. Association of Sea Couch Grass. This zone of blown sand 35- 50 yds. wide, taken locally, has no vegetation but Agropyronjunceum (Triticum junceum) in places here and there; and thus bears out the statement of Moss (who gave Carex arenaria as a subdominant species) that "Frequently the dominant plant occurs to the exclusion of all others." But at Berrow a distinct Carex arenaria belt (B) is formed between (A) and the Marram Grass zone. BELT B is 35-40 yds. wide, and of slightly higher sand.

DOMINANT SPECIES. Carex arenaria and Ammophila arundinacea.

OCCASIONAL SPECIES. Arenaria peploides. Euphorbia Paralias. Rumex crispus. Atriplex sp. BELT C, 50-60 yds. wide and a foot or two higher, extends to the be- ginning of the sand-hills proper. It forms the windward part of the Associa- tion of Marram Grass (Ammophila arundinacea Psamma arenaria).

DOMINANT SPECIES. A mmophila arundinacea.

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SETCH MAP oi BERROW FLATS YFONTYe FCLYM AKIO ADJOIN IN& COASTLINhE. * @ M >B 1 SURVE-YED AUTUMN 192,1 ; 01b'S; lf4 SC LE 0 300 6(yards ;|, i ,:- SCALE)~~~ I.i!}

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This content downloaded from 142.150.190.39 on Mon, 27 Jun 2016 13:03:24 UTC All use subject to http://about.jstor.org/terms 60 Changes in the, C(oast Vegetation near Beri'ow, Somerset

ABUNDANT SPECIES.

Euphorbia Paralias perhaps subdominant. Carex arenaria Festuca uniglumis. F. rubra var. arenaria.

FREQUENT SPECIES. Viola ericetorum. Taraxacum erythrospermum. Erodium cicutarium. Crepis virens. Senecio Jacobaea. Cynoglossum officinale. Hypochaeris radicata. Phleum arenartum. Leontodon hirtus.

OCCASIONAL SPECIES. Eryngiurt maritimum. Lycopsis arvensts. Calystegia Soldanella. Agropyron junceum.

The planted Hippophae rhamnoides, forming a low scrub or sometimes 15 ft. high, hardly extends to this zone, but is above and behind it. As already stated, Salsola is abundant among the Marram Grass on the windward side of the shifting dunes about Brean. And a little Salsola reappears close to the Lighthouse, but it cannot be considered a typical plant of this association. Beyond the crest of this belt the Marram Grass Association is continued in a less open formation; and in places the Sea Buckthorn (HippophaW) thickly covers the slopes.

Association of Dune Sward-forming Plants. Many further notes upon the phanerogamic vegetation of the sand-dunes must be postponed. Suffice it to say that this denser association, intermediate between the open and the closed type, has a richer flora. The association is of a more complex type, and in almost all particulars the dominant, sub- dominant and abundant species of phanerogams are as given by Moss in 1906. In 1921, however, Carex arenaria is the only dominant species of this association at Berrow; Festuca rubra var. arenaria is not more than sub- dominant; and Iris foetidissima but occasional. On the south slopes of the sand-hills nearer Brean the Iris is much more abundant. All the " abundant" species of 1906 are still so. To them we should now add Erodium cicutarium. Lycopsis arvensis figures at Berrow in this association as well as in the previous one, though, like the Erodium, relegated by Moss to his (next) association of "Dune Pasture Plants," an association in which he placed Ononis repens var. horrida as having become dominant with Carex arenaria and Festuca rubra var. arenaria. Elymus arenarius, given as an "occasional species" of the dune pasture plants, is extremely rare on any part of the Somerset coast.

This content downloaded from 142.150.190.39 on Mon, 27 Jun 2016 13:03:24 UTC All use subject to http://about.jstor.org/terms JOURNAL OF ECOLOGY VOL. X, PLATE 11

| l | l | Aw a ... .w.. x ... . ,. .:.z.X..:W..~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ....

| -_-- ? ...... 0.. FIG. i. Glycer-ia mari/irna, at first in tussocks 12 i8 i,nches high, becoming domninant iooo yds. N .W. of Lighthouse. Salicornia, chiefly S. dolhJlos/achya, on wet mud in foreground.

------

FIG. 2. Aster T)iz5olium and clumps of Triglochiln mari/imumll on beds of G/yce?ria mar'i/ima and Salicornzia. Large clump of Spar/ina Townsendi on horizon S.W. of Berrow Church.

THMSNCAGSI H OS EEAINNA ERW OEST

FIG 3 Trig/ochin mari/irnum, small tuft of Sfiar/a Townsendi, and dwarf Aster TrintI oiimy amidst Glycera on wet mud ca 1350 yds N.W of Lighthouse. Seawards is the present western limit of vegetation on the 11 Gore Sand." Clean sand beyond, on Aug. _31St, 192 1.

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DOMINANT SPECIES. Carex arenaria.

SUBDOMINANT SPECIES. Ononis repens var. horrida Lange. Galium verum. Lotus corniculatus. Festuca rubra var. arenaria. Sedum acre. FREQUENT OR ABUNDANT-SPECIES. Erophila vulgaris. Potentilla reptans. Sisymbrium Thalianum. Senecio Jacobaea. Viola ericetorum. Crepis virens. Cerastium semidecandrum. Cynoglossum officinale. Arenaria serpyllifolia and var. viscidula Lycopsis arvensts. Roth. (earliest in Herb. dated 1836). Myosotis collina. Erodium cicutarium. Iris foetidtsstma. Medicago sativa. Phleum arenartum. Trifolium arvense. Festuca uniglumis. OCCASIONAL SPECIES. Cerastium tetrandrum. Calystegia Soldanella. Oenothera bjennis and Oe. odorata. Agrostis alba 1.

Whereas Glauciumflavum, Reseda alba, Eryngium maritimum and several other plants are less common about Burnham and Berrow than 30 or 40 years ago, it is gratifying to notice an increased amount of Calystegia Soldanella, which in 1912 was thought to be "gradually disappearing from the district." And although White expressed in 1912 (loc. cit. p. 347) the fear that Oenothera odorata had become extinct from extension of building and enclosure, this is by no means the case. The earliest specimens of this Patagonian species gathered at Burnham (by Thos. Clark) are dated 1859. The earliest record for Oe. biennis at Burnham is 1834 (Dr A. Gapper, in Bath and Bristol Mag. third and last vol.). Clark's specimens are dated 1842. To fix exactly the date of the inception of the Berrow Flats colonisation is difficult. Salisbury suggests that it can be safely put at about 1910. Watson is inclined to go a few years further back, for in 1912, when most of his work on the sand-dunes was done, he observed considerable vegetation on the mud, and in 1916 Triglochin, Aster, Glyceria were present; but he agrees on their greater development during recent years. Several local observant and re- liable persons, though not ecologists, maintain that nearly all the present vegetation on the mud has come within the last three or four years. Doubtless the great mass of it has developed as recently. My thanks are due for kind help in the course of this work to Messrs 0. V. Darbishire, W. W. Jervis, W. Watson, E. J. Salisbury, A. G. Tansley) and the late C. Bucknall. 1 var. stolonifera.

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