Observations on the flora and origin of Redgrave and Lopham Fens, summer 1973

OBSERVATIONS O N THE FLORA AND ORIGIN OF REDGRAVE AND LOPHAM FENS S u m m e r 1973 SALLY A . HEATHCOTE

Introduction THE area which is the subject of this paper is a valley-fen associated with the River Waveney. The site lies about miles west of Diss, Norfolk, and runs along both banks of the River Waveney for 11 miles from its source. Little, Middle and Great Lopham Fens, Norfolk, lie on the north bank and Redgrave Fen, Suffolk, on the south bank; together they cover 300 acres. The area described will be referred to as the Fens in the following paper.

The Fens are leased and managed by the Suffolk Naturalists' Trust* and are scheduled as a Site of Special Scientific Interest, since the area contains the best example of valley-fen Vegetation remaining in Suffolk. The area originally escaped destruction by cultivation, on account of its extreme flatness and low elevation in relation to the water table, which makes efficient drainage difficult and expensive. However, man's influence has been feit in several ways; dykes have been cut and embankments of dredging thrown up. T h e partially drained areas behind the dykes have been subjected to the practice of peat cutting known as turbary, and to reed cutting. Also, the area has been damaged by fire.

Field work was carried out on the valley-fen as part of a training scheme for junior members of staff in July and September, 1973, by the Department of Botany, British Museum (Natural History).

It involved a preliminary study of the dominant ecological units in the surface Vegetation, and exploratory peat borings in the fen basin of Middle Fen. Initial data were also collected for the production of a vegetative key to the phanerogamic flora of Redgrave and Lopham Fens, and a check-list of the vascular plants and bryophytes encountered (supplemented from the records of F. J. Bingley and R. Carter) appears as an appendix.

History of the Fens There has been some confusion over the ownership and status of the Fens. Rose and Bellamy (1960) State that designation of the Fens as unenclosed common land has afforded them protection.

However, the Fens have not been designated as common land since the Enclosure Act of 1815-1818. Tithe maps of 1845 and 1847 show Redgrave and South Lopham Fens to be owned by the • N o w called Suffolk T r u s t for Nature Conservation.

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parishioners and to be exempt from tithe payments since the tithe description of the area was turf allotment and fen. W. G. Clarke (1914) describes South Lopham Fen as a 'wet common' known as a 'mowing marsh'.

Today, the Suffolk Naturalists' Trust owns the freehold of Lopham Middle Fen but leases Redgrave Fen, Lopham Little Fen and Lopham Great Fen from the respective village charitable Trusts. The latter were established to administer the Fens as lands for the poor of the local parishes; the Fens were given in exchange for common land to the poor of the area at the time of the Enclosure Act. Origin of the valley-fen The valley-fen at Redgrave and Lopham originates in a shallow Pleistocene valley, in a saucer-like depression with a clay floor.

The water source for the fen has its origin in the underlying chalk and is base rieh. However, in the area of Little Lopham Fen and the western part of Redgrave Fen, the water source is by seepage through the glacial sands, gravels and clays of the area, and the overlying substrate reduces the pH of the ground water and produces conditions which support an acid bog-heath complex.

Water movement in the shallow valley of origin is slow on account of the level terrain and also on account of the fact that water was probably held back in the Waveney valley by delta deposits from tributaries flowing into the valley further east; these factors provided a sequence of events conducive to peat growth and the subsequent development of a valley-fen and its characteristic Vegetation.

The surface Vegetation of Great and Middle Fens A transect through Middle Fen was made along a north-south line (Grid ref. 057805 to 054795) and the cover-density of plants in a metre quadrat listed at 10 m. intervals. The following notes on the ecological units are based on this, and on observations made whilst working on the basin.

1.

Carr and woodland The fact that the Fens have escaped cultivation does not mean that they will automatically remain in their natural vegetational State as a reed-sedge complex. The effect of man through land use is greater than people realise, and the type of management practised is the dominant factor in determining the survival of the reed-sedge complex on the Fens. Carr, a subclimax Vegetation of shrubs and young trees and often an intermediate stage between the fen Vegetation and true woodland, borders the Fens on the north and south boundaries. Unmanaged fen rapidly becomes colonised by carr whenever the spring water table is not above the

FLORA OF REDGRAVE AND LOPHAM FENS

41

stools of the sedges, allowing seeds of carr species to lodge and germinate. The typically dominant carr species seen on the northern boundary are Alnus glutinosa, Salix alba and Fraxinus excelsior, with Acer pseudoplatanus, Crataegus monogyna and Quercus robur. The Sycamore, Ash and Oak, once established, form a woodland with a typical canopy and under-storey of Hawthorn and Eider, Sambucus nigra. There is a ground layer of herbs such as Aegopodium podagraria, Cirsium vulgare, Dryopteris austriaca, Geranium robertianum, Heracleum sphondylium, Listera ovata, Lonicera periclymenum, Solanum nigrum, Stachys sylvatica and Galium uliginosum, with Pteridium aquilinum in the more drier open sites.

Freshwater Community The freshwater Community, in the area studied, includes both plants growing in the drainage dykes and those in the River Waveney. Those growing in the immediate vicinity of water such as on the banks which at times may be subject to submergence are also included in this Community. Lemna minor floats on the surface of the still water of the dykes, while other plants are partially or totally submerged. Hottonia palustris adopts a floating habit in the dykes, and sometimes roots on the bed of the watercourse. The pondweeds, Groenlandia densa and Potamogeton crispus are prevalent in these freshwater habitats, and both species are totally submerged. Other aquatics include, Potamogeton coloratus, with floating leaves and indicative of a base-rich water (a species which is often confused with P. polygonifolius, a plant of acid pools and bogs) and Hippuris vulgaris.

These plants are fairly frequent in the dykes and river.

2.

Reed/sedge communities The greater part of the Fens is made up of a reed-sedge complex with Phragmites australis and Cladium mariscus as the dominant members; Cladium mariscus can adapt well to an unstable ecosystem, where there are marked changes in water level. jfuncus subnodulosus and Carex elata are common throughout this Community and they are good indicators of the basic ground water and deep peat. Juncus subnodulosus rapidly spreads into areas where Cladium and Phragmites have been cut, and is especially successful where annual cutting is practised. Calamagrostis canescens also secures a hold where the reeds and sedges are cut annually. The species prefers damp sites but often occurs with Arrhenatherum elatius on drier sites. Molinia caerulea is abundant in slightly drier sites which are also more acid, occurring as tussocks when the influence of the basic ground water is feit to a lesser extent. It is associated with a clay substrate and thrives in sites where much of the surface peat has been removed by 3.

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turbary, and also when downwash from surrounding arable lands introduces clays and silts onto the Fens. It should be mentioned, that particularly in the 19th Century, turbary was widely and intensively practised on the Fens. The peat was gathered for fuel and as bedding for stables, and it was at this stage that Molinia was able to secure a hold over the basin. Peat cutting on these Fens probably ceased around 1920. Herbs such as Galium palustre, Lotus uliginosus and Lathyrus pratensis are also common over the basin and Succisa pratensis is abundant throughout the Phragmites-Cladium complex.

4.

Acid wet heath community The fourth ecological unit is that on Lopham Little Fen and the western part of Redgrave Fen, namely an acid wet-heath Community. The site was the subject of a paper by Bellamy and Rose (1960) and the original aim of our survey had been to produce a comparative study of this site. However, the area in question had been extensively damaged by fire in the spring of 1973 and had not recovered sufficiently for an accurate or effective comparison to be made at the time of our investigation.

The site is of particular interest because it is an area which supports both plants preferring an acid habitat and those which require a basic habitat occurring in close proximity. The River Waveney rises in this part of the Fen basin, and the river bed although largely dry at the time of our visits, was dominated by Schoenus nigricans, Carex panicea and C. lepidocarpa. These species are all indicators of the basic ground water to be found on this Fen. However, within a few yards of them a number of calcifuges thrive. The reason for these diverse floral elements growing in such close proximity to one another is the presence of two undulations of a sandy substrate which run through the area. Ground water under normal conditions flows around these ridges without influencing the substrate and leaves 'islands' of sandy soil which, being acid, support the entirely different flora described above. In the winter and spring when the water table is higher and water flows over the 'islands', the water, although base-rich, has very little influence in reducing the acidity, because of the rapid rate of percolation through the glacial sands and gravels.

The species found on the acid 'islands' are typical of a wet acid heathland, and include Calluna vulgaris, Erica tetralix, Drosera rotundifolia, Molinia caerulea and Hydrocotyle vulgaris. As stated, severe fire had largely destroyed the flora of this area some months before our visits but young seedlings of the above-mentioned species were observed. Other seedlings present were those typical of the first colonisers of an area following fire, such as

FLORA OF REDGRAVE AND LOPHAM FENS

43

Betula pendula and Chamaenerion angustifolium. Gymnade conopsea was also present at a site in an area influenced by basic ground water.

The East Anglian Water Company is pumping water from a borehole situated half way along and just off the southern boundary of Redgrave Fen. The effect of this water extraction, averaging 20 million gallons a month and a total of 243 million gallons in 1973, has beeil to reduce the overall level of the water table, and consequently to reduce this unique site of wet acid heathland to a dry heath.

Liparis loeselii, known to have been present on the wet fen peats of the basin, is now believed to have disappeared from the area. This may not be directly as a result of the drawing-off of water, but this practice, if it is not controlled and if the water level is not replenished rapidly, will certainly not encourage the re-establishment of this increasingly rare orchid.

The Suffolk Naturalists' Trust has permission to draw back water to build up the water table to its original level but, replenishment quantities are unknown until the completion of hydrogeological surveys, which are planned for the spring of 1975, by The Nature Conservancy and The Anglian Water Authority.

There are alsofinancialproblems of sinking a bore and obtaining a pump for drawing back water. But, as indicated the urgency to establish this process is obvious, for the adverse effects of the reduced water level have been immediate and any further delay in replenishing the water level will have a drastic effect on the overall ecology of the Fens.

5. Ruderal or weed associations

Thefloraof the dyke margins is made up of species which elsewhere in East Anglia (e.g. the Broads district) thrive in reed swamp communities. Examples of such plants are, Lycopus europaeus, Equisetumfluviatile,Apium nodiflorum, Myosotis scorpioides, Ranunculus lingua and Iris pseudacorus. Weed specie which are colonisers of newly bare ground, find excellent opportunities for colonisation on the newly dredged material from the dykes which is deposited on the banks. These species include Equisetum arvense, Chenopodium album and Epilobiutn hirsu The paths along the dyke and river margins are habitats for common weed species such as Artemisia vulgaris, Arctium minus, Briza media, Bromus mollis and Calystegia sepium.

Artemisia is an interesting genus whose pollen is often found in peat deposits. Tallantire (1953) reports that pollen sampling from peat cores from the fen basin indicate that this genus has been present on the Redgrave-Lopham site since the Late Glacial

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times, around 10,000 years B.C. T h e presence of the pollen of Artemisia, a plant which now grows as a weed, suggests that the area now occupied by the valley-fen once contained open habitats in the Late Glacial period. T h e presence of the pollen in more recent deposits is probably indicative of the appearance of man and bis arable practices.

Results of peat borings in the f e n basin T h e borings were made at 10 m. intervals along the transect line previously described, using a Hiller peat borer with a 33 cm.

Chamber. T h e general stratigraphy is shown in the diagrammatic cross section (see figure). T h e extensive deposit of mud, formed from the deposition of planktonic organisms, suggests the Fens have formed over a lake basin, previously described by Tallantire (1953). Tallantire's section was taken through a basin further upstream but essentially shows the same picture.

T h e origin of these basins is not fully established but is likely to be from water in the Waveney Valley held back by delta deposits from tributaries flowing in from the north, in this case between Great Fen and Bressingham Fen. There are siliceous grains in the mud suggesting there was a constant downwash from the upland into the lake. Eventually the substrate rose sufficiently above a descending water table to allow swamp and then fen Vegetation to establish itself.

Whilst remains of certain dominant species could be identified in quantity in this fen peat, no obvious stratification of largescale peat beds could be delimited to suggest a clear-cutsuccession.

Phragmites was present in quantity throughout, and patches of orange-red-brown peat of Cladium, yellow-brown peat suggestive of Carex elata and occasional grass nodes indicative of Calamagrostis canescens were found in the top metre. Pockets of nekron mud and granular dark red-brown peat (brushwood) and the presence of twigs and boughs of birch (reddish or pink-brown wood) and sallow (a yellowish wood) suggest that throughout the whole period of peat deposition, open swamps with pools and sedge mires alternated with islands of bushes. For some ecological or perhaps anthropogenic reason the bushes never established a lasting carr or woodland sufficient to lay down deep and pure brushwood peat. T h e practice of turbary should be considered here, since peat digging around the 19th Century or earlier may have removed the brushwood peat. T h e subsequent 'hollow' may have been a wet semi-swamp or swamp Community similar to those seen today around Scottish lochs and tarns in northern England (see Holdgate, 1955).

Silt and mud pockets seen at depth indicate the presence of former pools of open water which were formed as the changes in water level occurred during the formation of the valley-fen.

DIAGRAMMATIC CROSS SECTION OF LOPHAM AND REDGRAVE

FENS

R. WAVENEY

SOUTH

? ? ??

twwvtwV

I carr

fen peat

brushwood peat

mud

X " silt and clay

represents20cm.

represents20m.

SAH

FLORA OF REDGRAVE AND LOPHAM FENS

45

The silt and mud pockets which are generally thicker and occurring nearer the surface owe their origin to peat cutting and the subsequent fluctuations in water level. Newly made pools resulting from turbary would eventually be encroached upon by Cladium, and as the site became drier, by Phragmites, Calamagrostis and Juncus. Many seeds of Menyantlics were found in the peat cores, suggesting that this was a common plant on the lake or in the surrounding swamp, and possibly occurred with Potentilla palustris and Carex rostrata.

Summary A survey of the main ecological units (carr oak-ash woodland, freshwater communities, the reed-sedge Community, the acid wet heath Community and the ruderal or weed associations) was undertaken and a series of peat borings were made in Middle Fen. T h e results show the presence of another lake basin similar to that described by Tallantire (1953) as a Late Glacial lake.

No pollen analyses were carried out on the cores from Middle Fen but it was seen probable that there was a series of lakes in the Waveney Valley during the Late Glacial period. T h e importance of turbary is discussed in relation to the present-day pattern of Vegetation.

Finally the factors affecting the present-day status of the Fens were examined. Water movements have been instrumental in the formation of the valley-fen and changes in the ground water at the present time were seen to be the primary factors in the future ecological status of the natural Vegetation of the Fens. It was realised that action must soon be taken to restore the water table to its correct level otherwise Redgrave and Lopham Fens will cease to exist as an area of true valley-fen Vegetation in Suffolk.

APPENDIX

Preliminary check-list of the flora of R e d g r a v e and L o p h a m Fens It is likely that the check-list which follows is incomplete and further records will be welcomed for inclusion.

Acer pseudoplatanus L .

Adoxa moschatellina L .

Aegopodium podagraria L .

Agropyron repens (L.) Beauv.

Agrostis stolonifera L. Alisma plontago-aquatica L. Alliaria petiolata (Bieb.) Cavara & Grande Alnus glutinosa (L.) Gaertn.

Angelica sylvestris L. Anthoxanthum odoralum L. Apium nodiflorum (L.) Lag.

Arctium minus Bernh.

Arrhenatherum elatius (L.) J. & C. Presl Artemisia vulgaris L .

Atriplex patula L. Betula pendula Roth Briza media L. Bromus mollis L. Bryonia dioica Jacq.

Calamagrostis canescens (Weber) Roth Callitriche stagnalis Scop.

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Suffolk Natural History, Vol. 17, Part 1

J. subnodulosus Schrank Calluna vulgaris (L.) Hull Calystegia sepium (L.) R. Br. Latnitim album L. Lapsana communis L. Carex demissa Hรถrnern.

Lathyrus pratensis L. C. elata All. Lemna minor L. C.flaccaSchreb.

Linaria vulgaris Mill.

C. lepidocarpa Tausch.

Listera ovata (L.) R. Br. C. panicea L. Lolium perenne L. Centaurea nigra L. Lonicera periclymenum L. Chamaenerion angustifolium (L.) Lotus corniculatus L. Scop.

L. uliginosus Schkuhr.

Chenopodium album L. Luzula multiflora (Retz.) Lej. C. rubrum L. Lychnisflos-cuculiL. Cirsium arvense (L.) Scop.

Lycopus europaeus L. C. dissectum (L.) Hill Lysimachia vulgaris L. C. palustre (L.) Scop.

Lythrum salicaria L. C. vulgare (SavH Ten. Cladium mariscus (L.) Pohl Mentha aquatica L. Crataegus monogyna Jacq. Moehringia trinervis (L.) Clairv.

Molinia caerulea (L.) Moench Dactylis glomerata L. Myosotis scorpioides L. Deschampsia cespitosa (L.) Beauv.

Myosoton aquaticum (L.) Moen Drosera rotundifolia L. Dryopteris austriaca (Jacq.) Nasturtium officinale R. Br. Parnassia palustris L. Woynar Pedicularis palustris L. Epilobium hirsutum L. Phalaris arundinacea L. E. palustre L. pratense L. Epipactis palustris (L.) Crantz. Phleum Phragmites australis (Cav.) Tri Equisetum arvense L. ex Steudel E.fluviatileh.

Plantago lanceolata L. E. palustre L. P. major L. Erica cinerea L. Erysimum cheiranthoides L. Poa trivialis L. Eupatorium cannabinum L. Polygala vulgaris L. Festuca arundinacea Schreb. Polygonum amphibium 1..

P. convolvulus L. F. ovina L. L. FUipendula ulmaria (L.) MaximP. . hydropiper P. lapathifolium L. Galeopsis tetrahit L. P. persicaria L. Galium aparine L. Potamogeton coloratus Hรถrner G. uliginosum L. P. crispus L. G. verum I/.

Potentilla anserina L. Geranium robertianum L. P. erecta (L.) Rauschel Geum urbanum L. P. palustris (L.) Scop.

Glechoma hederacea L. Groenlandia densa (L.) Fourr. P. reptans L. aquilinum (L.) Kuhn Gymnadenia conopsea (L.) R.Pteridium Br. Pulicaria dysenterica (L.) Bern Hedera helix L. Heracleum spondylium L. Quercus robur L. Ranunculus acris L. Hieracium pilosella L. Ii. lingua L. Hippuris vulgaris L. R. repens L. Holcus lanatus L. Reseda lutea L. Hottonia palustris L. Rorippa islandica (Oeder) Borba Humulus lupulus L. Rosa canina agg.

Hydrocotyle vulgaris L. Rubus caesius L. Hypericum perforatum L. R. idaeus L. H. pulchrum L. R. fruticosus L. sensu lato H. tetrapterum Fr. R. ulmifolius Schott Hypochoeris radicata L. Rumex acetosa L. Iris pseudacorus L. R. hydrolapathum Hudson Juncus articulatus L. Ii. maritimus L. J. effusus L. Ii. obtusifolius L. J. inflexus L.

FLORA OF REDGRAVE A N D L O P H A M FENS

R. sanguineus L. Salix alba L. S. aurita L .

S. caprea L. S. cinerea L .

S. repens L. Sambucus nigra L. Samolus valerandi L. Schoenus nigricans L .

Scrophularia aquatica L. Senecio erucifolius L. S. vulgaris L. Solanum nigrum L. Sonchus arvensis L .

S. asper (L.) Hill S. oleraceus L .

Stachys ambigua Sm. S. sylvatica L .

Stellaria media (L.) Vill.

Succisa pratensis Moench Tamus communis L .

Taraxacum officinale Weber Thalictrum flavum L. Trifolium arvense L .

T. repens L .

Ulex europaeus L. Ulmits glabra H u d s o n Urtica dioica L. Valeriana dioica L. V. officinale L .

Veronica anagallis-aquatica L. V. chamaedrys L. V. scutella L .

Viburnum opulus L. Viccia cracca L. Viola odorata L. V. riviniana Rchb.

Acrocladium cordifolium ( H e d w ) Richs. et Wall.

A. cuspidatum (Hedw.) L i n d b .

Atrichum undulatum (Hedw.) P. Beauv.

Aulacomnium androgynum (Hedw.)

Schwaegr.

A. palustre (Hedw.) Schwaegr.

Brachythecium rutabulum (Hedw.)

B., S. & G .

B. salebrosum (Web. et Mohr) B., S. & G .

Bryum pseudotriquetrum (Hedw.)

Schwaegr.

B. rubens Mitt.

Calypogeia fissa (L.) Raddi

47

C. muelleriana (Schiffn.) K . Mull Campvlopus fragilis (Brid.) B., S. & G. C. pyriformis (Schultz.) Brid.

Cephalozia bicuspidata (L.) D u m .

C. connivens (Dicks.) Lindb.

Ceratodon purpureus (Hedw.)

Brid.

Chiloscyphus pallescens (Ehrh.)

Dum. Ctenidium molluscum (Hedw.)

Mitt.

Dicranella heteromalla Hedw.

Dicranoweisia cirrata (Hedw.)

Lindb.

Dicranum scoparium Hedw.

Drepanocladus fluitans var. intermedius Warnst Eurhynchium praelongum (Hedw.)

B., S. & G .

Fissidens adiantoides Hedw.

Hypnum cupressiforme var. ericetorum B., S. & G .

Lepidozia setacea (Web.) Mitt.

Leucobryum glaucum (Hedw.)

Aongstr.

Lophocolea cuspidata (Nees) Limpr.

L. heterophylla (Schrad.) D u m .

Lophosia ventricosa (Dicks.) D u m .

Marchantia polymorpha L. Mnium hornum Hedw.

M. punctatum Schreb. ex Hedw.

Moerckia flotoviana (Nees) Schiffn.

Pellia epiphylla (L.) Corda Pohlia nutans (Hedw.) Lindeb.

Polytrichum juniperinum Weed. ex Hedw.

P. piliferum Schreb. ex Hedw.

Preissia quadrata (Scop.) Nees Pseudoscleropodium purum (Hedw.)

Fleisch Riccardia multifida (L.) Gray R. pinguis (L.) Gray R. sinuata (Dicks.) Trev.

Scorpidium scorpioides (Hedw.)

Limpr.

Sphagnum fimbriatum Wils.

5 . palustre L. S. plumulosum Roell S. russowii Warnst.

Tortula muralis Hedw.

Acknowledgements F. J. Bingley, Fiatford Mill Field Centre.

R. Carter, Queen Mary College, London.

Suffolk

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History,

Vol. 17, Part 1

Secretary for t h e N o r f o l k Research C o m m i t t e e , for t h e loan of the borer.

P. A. W r i g h t , T h e N a t u r e C o n s e r v a n c y Council.

References Bellamv, David J. and Rose, Francis (1960). T h e Waveney-Ouse Valley Fens of the Suffolk-Norfolk border. Trans. Suffolk Nat. Soc. 11, 367.

Clarke, W. G. (1914). On the common lands of Norfolk. Trans. Norf.

Norw. Nat. Soc. IX, 52.

Doubleday, H. Arthur (Gen. Editor) (1901). The Victoria History of the County of Norfolk 1.

Holdgate, M. W. (1955). T h e Vegetation of some British upland fens.

J. Ecol. 43, 389.

Page, William (Gen. Editor) (1911). The Victoria History of the County of Suffolk 1.

Tallantire, P. A. (1953). Studies of the Post-Glacial history of British Vegetation. X I I . Lopham Little Fen, a Late Glacial site in Central East Anglia. J. Ecol. 41, 361.

Sally

A.

Heathcote,

Department (Natural

of

Botany,

History).

British

Museum