C4.1      Flora
     C4.2      Fauna
     C4.3      Introductions and reintroductions
     C4.4      Plant communities

C4.1 Flora

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C4.1.1 Records

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A species list for the Fen, covering the area included in the S.S.S.I., is kept by the Botanical Secretary. This is kept on a card index and on an IBM PC using dBase II. A second copy of the diskette holding the records is held by the Secretary. At present the list includes the following:

Angiosperms (Flowering Plants)............. 403 species
    (including 8 hybrids; 305 spp recorded/confirmed since 1980)
Gymnosperms (Pines etc.)...................   1
Pteridophytes (Ferns and their allies).....  11 (all since 1980)
Musci (Mosses) ............................  85 
Hepaticae (Liverworts) ....................  25 
Charophyta (Stoneworts) ...................  11 
Other Algae .............no precise records available at present

In statements about rarity, 'Cambridgeshire' means the Watsonian Vice-county of Cambridgeshire (V.C.29). This is virtually coincident with the old administrative county but excludes Huntingdonshire and other recent alterations.

C4.1.2 Flowering plants

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Two flowering plant species found at Wicken Fen are national rarities: the Fen Violet (Viola persicifolia) and the Marsh Pea (Lathyrus palustris). A number of other species are locally rare; these are listed in an appendix.

Several species have become extinct since the flora of the Fen was first listed by Babington in 1860; of these, the Great Fen Ragwort (Senecio paludosus) was considered extinct in Britain until rediscovered elsewhere in the Fens in 1972 (it has been reintroduced at Wicken in 1992; see C4.3), and Water Soldier (Stratiotes aloides) is now nationally rare. Species that have apparently become extinct at Wicken are listed in the appendix. The spread of scrub woodland between 1920 and 1960 may have led to the loss of some species. However, the Fen Violet had not been seen at Wicken for 80 years until rediscovered in 1982 by Rowell (1983). Its reappearance, almost certainly from dormant seed, raises the possibility of other species returning from this source, given appropriate management.

C4.1.3 Lower plants

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Wicken is now the richest site in Cambridgeshire (V.C.29) for calcifuge bryophytes, but this richness has declined recently for reasons which are still not clear (Lock, 1990). For several such species, Wicken is the only Cambridgeshire locality. A list of bryophytes rare in the vice-county and occurring at Wicken is given in the appendix.

The Charophytes of Wicken are relatively well-known. Other algae have been little studied recently although there is a recent list of some 200 species resulting from a single visit by an algologist. The rare species Nitella tenusissima has been recorded in turf diggings and, in 1992, in Wicken Lode.

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C4.2.1 Records

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A species list of Fen invertebrates is maintained on a card index. The master copy of this is kept in the Library in the William Thorpe Building at the Fen, and a copy is kept by the Zoological Secretary. The complete list is also held on computer file; the diskette holding the list is kept by the Zoological Secretary. A system has been established whereby specialists co- ordinate records for particular invertebrate groups amd contribute to the species list, which is updated annually.

The Fen is of special interest not only because of its faunal diversity, but also because of the continuity of recording which permits detection of local changes that may reflect national trends. Thus bumblebee records at Wicken over recent decades show losses of species parallelling a national decline, and dragonfly records show the loss of acid-water species that were probably associated with peat diggings. Plant and invertebrate records go back to about 1860, when surrounding fens were drained and natural historians turned their attention to Wicken.

Bird records are few before 1940, but increased following the development of the Charles Raven Reserve and the Mere since 1952. The Wicken Fen Ringing Group has operated since 1968 and publishes regular reports. It attempts, with considerable success, to monitor long-term changes in the numbers of common species by regular trapping.

C4.2.2 Mammals

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Three introduced species (American Mink, Muntjac and Chinese Water Deer) occur at Wicken. Mink have been controlled on the Fen the A.W.A. and Fen staff. Coypu occasionally appeared but were never allowed to become established.

Moles are controlled on the lode banks by the N.R.A.
Foxes are common and an occasional cause of complaint from neighbouring landowners; they have been controlled intermittently, but the response of the Committee has varied over the years. The National Trust reviewed its nationwide policy in 1991-2; guidelines for vermin control are given in Section A6.10.

Otters had disappeared from the Fen, but recent signs have been found that suggest that they might be using the lodes around the Fen margin.

C4.2.3 Birds

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The Fen has consi derable ornithological interest, which has been increased by the construction of the Mere on Adventurers' Fen. Records are kept from day to day by the Warden using a Bird Observatory Logbook system. A revised check-list was published in 1989 (Bennett & Thorne, 1989). Breeding species of interest include Bearded Tits, which have breed annually in recent years, Cetti's Warbler, which had established a colony but was exterminated by the cold of the 1984-85 winter, and Marsh Harriers, which have bred four times, raising five chicks in 1992. Spotted Crakes call in most springs, and may possibly breed, and Montagu's Harriers have bred in the past but no longer do so. Savi's Warblers have held territories several times in recent years, but there is no further evidence of breeding. A River Warbler, a great rarity, was noted in 1992. Four species of owl breed on, or very close to, the Fen, including Long-eared and Barn Owls. Other locally uncommon breeding species include Woodcock, Jay, and both spotted woodpeckers. During the autumn and winter the Fen is an important roosting site for Hen Harriers (up to 12) and thrushes, and up to three Bitterns regularly winter. The mere and surrounding fields provide a valuable refuge for up to 2500 duck, mainly Wigeon and Mallard. During the autumn migration large numbers of Swallows and martins roost in the reed field (see also Section A6.4).

The avifauna of the Charles Raven Reserve is not outstanding, partly due to its small size, but it would rank in the top three or four wetland sites in Cambridgeshire, and perhaps within the top 20-30 in East Anglia.

C4.2.4 Reptiles & Amphibians

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Grass snakes, common lizards, frogs, toads and newts are present. Common lizards appear to have benefitted greatly from the boardwalk and its warm surface and are often seen on it between April and October. Gardiner (1932) recorded Slow-worms in 1926 but the present Head Warden has never seen one. Common Newts occur and Gardiner (1932) records the Great Crested Newt; this species has been seen occasionally during the 1980s and 1990s.

C4.2.5 Fish

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In a recent survey, the Mere was found to be dominated by bream (A.W.A., 1985). The most interesting feature was the presence of a number of hybrid fish; of these, putative Silver Bream X Rudd hybrids would, if confirmed, be a new British record. However, a further survey of the Mere in 1989 failed to reveal any cyprinid fish hybrids, rather surprisingly.

Surveys of the Lode system (A.W.A., 1984; Institute of Freshwater Ecology, 1990; N.R.A., 1991) have shown that the most numerically abundant fish species in Wicken Lode is the Bitterling (Rhodeus amarus), an introduced species dependent on Swan Mussels (Anodonta) for breeding. Eels, Roach and Pike were also abundant, and Dace, Perch, Gudgeon, Rudd and Tench were present.

C4.2.6 Invertebrates

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The original stimulus to the creation of a nature reserve at Wicken Fen was its entomological interest, and the Fen still acts as a focus for a group of zoologists (mainly entomologists) who keep in touch through an annual newsletter: Wicken Fen Biologists' Newsletter.

The various contributors to Gardiner (1923-1932) recorded 2,000 insect, 17 myriapod, 74 crustacean, 170 arachnid, 57 molluscan, 23 annelid, 10 flatworm and 41 protozoan species as present on the Fen, and it was suggested that these constituted only half the species actually present (Eastham, l932). It was recognised that not all of them could be described as "fen species"; thus of the 700 Lepidoptera known in 1932, only 50 were then regarded as being dependent on fen habitats.

Since the publication of Gardiner (l923-32), there have been further surveys of most groups. Some of the most recent are: butterflies and day-flying moths (Smart, l972; updated by Bennett, 1990); microlepidoptera (Emmet, l972); spiders (Duffey, 1970); molluscs (Paul, l967; Bishop, 1974); flatworms (Ball, 1968) and odonates (Bennett & Lohoar, 1990). Although further new records of the larger and better-known insects are unlikely, much remains to be learned of the other invertebrate groups represented in the fauna.

Among the invertebrates are many species for which Wicken is either their only British locality, or one of very few. Twenty species of dragonfly and damselfly have occured (although three of these, Orthetrum coerulescens, Sympetrum danae, and Ceriagrion tenellum are dependent on acid water and are now extinct at Wicken); such diversity is rare in a single site. Brachytron pratense is the rarest species; it probably became extinct in the Fen but has returned in recent years.
A list of rare invertebrate species known to occur at Wicken is given in an appendix.

All too little is known of the ecology of fen insects; in particular, we know little of the minimum areas of habitat that some require. It is possible that in some cases the Fen population is close to the minimum. Several species are known to have become extinct on the Fen, but only one of these, the Swallowtail butterfly, has been well studied. Studies on the Wicken population of the butterfly and its foodplant, the species' demise and attempted reintroduction by Dr. J.P. Dempster and Mrs. M. Hall form the basis for a attempt at reintroducing the Swallowtail to Wicken in 1993.

A butterfly survey has been in progress since 1979 as part of a national monitoring scheme and had yielded much information on population trends, flight times and distribution in relation to management. A second transect was set up in 1991 to cover the newly planted Cpt 68 and northern edge of the Fen.

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The Local Management Committee is opposed to introductions but is sympathetic to reintroductions if a good case is made. Proposals for reintroduction must meet criteria set out in the National Trust's Nature Conservation Subject Paper (see Section A6.10).

The Large Copper and Swallowtail butterflies have been reintroduced in the past, but neither persisted, probably because of changes in the Fen and its vegetation following reintroduction. In both cases, the Fen appears to again afford a suitable habitat; the former species is currently (1993) the subject of a pilot study (Dr. McLean, English Nature) and the latter is being reintroduced in 1993. The Marsh Fritillary is another possible candidate for consideration.

The Fen Ragwort (Senecio paludosus) has been reintroduced in 1992, under English Nature's Species Recovery Programme (Mr. T. Wells). The Water Soldier (Statiotes aloides) and Frogbit (Hydrocharis morsus-ranae) might also be considered if they do not reappear naturally after resumption of ditching and turf- digging.

There are few introduced species on the Fen; the most obvious is the willow, Salix pentandra. Snowdrops (Galanthus nivalis), and apple-trees (Malus sylvestris) occur at the eastern end of Sedge Fen Drove as relics from the brickmakers' cottages. Various other plants were introduced to the Sedge Fen as food plants for insects but only Salix pentandra seems to have persisted. The grove of Alders (Alnus glutinosa) on Evan's Fen was planted around 1950 using material from Chippenham Fen (S.M. Walters, pers. comm.)

About 12 pairs of Canada Geese attempted to breed in 1992, but survival was poor. This introduced species has caused problems in other parts of Britain by excluding other species from its breeding areas; its status should be kept under review at Wicken.

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C4.4.1 Introduction

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Wicken Fen was one of the earliest sites in Britain used for the emerging science of plant ecology (Yapp, 1908; Godwin, 1931, 1941; Godwin & Tansley, 1929; Godwin & Bharucha, 1932). Their work laid the foundations upon which subsequent management of the fen plant communities has been based. Some long-term experiments set up by Godwin in the 1920s are still maintained, although the type of information gathered has altered slightly in recent years, and the cutting regimes have not been maintained continuously for the whole period of the experiment.

The plant communities of the Fen have been described in the past (e.g by Godwin & Tansley, 1929), but these descriptions could not, given the state of knowledge of British vegetation at that time, take much account of vegetation elsewhere. The National Vegetation Classification scheme (NVC) now provides a complete framework into which the Wicken communities can be fitted.

In the following descriptions, the numbers in square brackets are the community numbers ascribable under the NVC.

C4.4.2 Aquatics

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Under the NVC, aquatic communities have so far been described in draft outline only. Wicken communities fall into two groups:

Free-floating communities

These belong to the class Lemnetea. Duckweeds (Lemna spp.) are prominent constituents. Most of the Wicken stands can be placed as Lemna minor (duckweed) floating mats (Lemnetum minoris) [A2], with large areas which belong to subcommunities with either Lemna trisulca (ivy duckweed) or Ricciocarpus natans and/or Riccia fluitans. The latter sub-community is an uncommon one, particularly in south-eastern England.

In the past, there may have been stands attributable to species-rich Lemnetea, with Lemna polyrrhiza (large duckweed) and Hydrocharis morsus-ranae (Frog-bit), but neither of these species has been seen in recent years.

Submerged aquatic communities

Some of the brick-pits contain submerged aquatic communities which belong in the class Ceratophylletea. These can provisionally be called species-poor Ceratophyllum demersum pools (Ceratophyllum demersi [A5]). Ceratophyllum (Hornwort) has increased at Wicken in recent years; this may be connected with a rise in the nutrient status of the Fen waters. The Utricularia (bladderwort)-rich pools cannot be classified with certainty as yet, but may represent either the Utricularia vulgaris sub- community of the Juncus bulbosus community [A24a] or one of the species-rich Lemnetea where the floating cover has been lost [A4].

The lodes contain various communities of submerged and floating-leaved aquatics which belong to the class Potametea. Drainers Dyke, and the part of Wicken Lode above its junction with Monks' Lode, contain much Nuphar lutea (Yellow Water-lily), together with Sagittaria sagittifolia (Arrow-head) and Potamogeton lucens (Shining Pondweed). This is the species-poor subcommunity of the Nuphar lutea community [A8a] belonging to the Nymphaeion alliance. The communities of Wicken Lode, on the other hand, have fewer floating-leaved species and a much greater abundance of submerged, slender-leaved species. At present they are best placed somewhere in the Potamogeton pectinatus - Myriophyllum spicatum community (Fennel-leaved Pondweed, Spiked Water Milfoil) [A11] but this section of the classification, the Parvopotamion, is poorly understood as yet.

C4.4.3 Sedge and litter fields

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These are included in the NVC overall category of Swamps and Tall Herb Fens. This section is complete in typescript (Rodwell, 1984) and a copy has been consulted at NCC in Peterborough. The Scheme incorporates earlier work such as that of Wheeler (1980a & b). References in this section are to this document unless stated otherwise.

Litter Fields

The largest areas of open fen vegetation at Wicken belong to Phragmites australis - Peucedanum palustris fen (Common Reed, Milk-Parsley or Hog's Fennel) (Peucedano-Phragmitetum australis [S24]). There are several subcommunities in this association of which the Symphytum officinale subcommunity (Comfrey) is the most abundant at Wicken. It also occurs at Woodwalton Fen, in the Somerset Levels (Catcott Heath), and in the Ham Fens (Kent), although there is considerable variation between sites. It is typical of flood plains and similar sites, outside Broadland, in areas much disturbed and modified in many ways. Calamagrostis species are more typical of alder woodland than of herbaceous fen, but here succeed particularly well in a disturbed environment. This fen type is regarded as occurring in lime-rich but mesotrophic or oligotrophic sites. It is replaced by other fen communities in eutrophic sites; some of these occur at Wicken (see below).

Another fen type which occurs at Wicken is Phragmites australis - Eupatorium cannabinum fen (Common Reed, Hemp Agrimony) (Angelico-Phragmitetum [S25]). This is rather similar to Peucedanum - Phragmites fens but has little or no Peucedanum and Lysimachia vulgaris (Yellow Loosestrife). Eupatorium cannabinum, Angelica sylvestris (Wild Angelica), Lythrum salicaria (Purple Loosestrife), Cirsium palustre (marsh Thistle), Iris pseudacorus (Yellow Flag), and Filipendula ulmaria (Meadowsweet) are all prominent components with reed. It is a widespread community that occurs in moderately eutrophic sites where mineral or organic soils are regularly waterlogged with calcareous waters. Rodwell regards it as not maintained by mowing but similar communities occur in some of the litter fields at Wicken.

The other subcommunities are not represented at Wicken although it is possible that the Shoenus nigricans subcommunity (Bog-rush) of the Peucedano-Phragmitetum may have occurred in the past. The species was last seen at Wicken in 1954. In Norfolk the sub-community occurs on uncut baulks between peat- diggings, and it was on Wicken Poors'Fen that Schoenus was last seen at Wicken.

Sedge Fields

The sedge fields at Wicken belong in the category of Cladium mariscus sedge swamp (sedge) (Cladietum marisci [S2]). This is divided into two subcommunities of which the Cladium mariscus subcommunity is the only one occurring at Wicken. This, like the preceding community, is characteristic of mesotrophic to oligotrophic sites which are none the less rich in calcium. It has been noticed in Broadland that Cladium is most important in those sites which are the most isolated from the rivers. Thus the species is abundant at the isolated Upton Broad, where the substrate is rich in calcium but low in nitrate-nitrogen and phosphorus. This tendency for the species to occur in sites of low nutrient status is even more pronounced in the other sub- community, the Menyanthes trifoliata subcommunity (Bog-bean). Here Cladium is associated with species such as Menyanthes trifoliata and Potentilla palustris (Marsh Cinquefoil) which used to occur between Upware and the Fen proper.

Cladium peforms best in sites where its root system is submerged but where it is not flooded in summer. Winter flooding may help to protect the shoot tips from frost, but if cut ends of leaves are submerged then the root system may be damaged or killed by flooding of the air spaces (Conway, 1936a & b; 1938). It generally occurs in sites with a stable water level, being replaced by Carex elata (Tufted Sedge) communities in sites where water level varies more. It is favoured by summer cutting at long intervals. Phragmites, on the other hand, is severely damaged by summer cutting of its young green shoots but is favoured by winter cutting. Soil pH varies from 6 to 8.5 in Cladium sites, and calcium in the water from 40 to 150 mg/l.

Eutrophication of the Sedge Fen

Some small patches on the Sedge Fen and elsewhere are referable to Rodwell's Phragmites australis - Urtica dioica fen (Common Reed, Nettle) [S26]. This is a species-poor fen type characteristic of sites where eutrophication has taken place due to flooding with water contaminated by agricultural run-off, sewage, or some industrial effluents. It can also appear when a fen surface dries out and allows decomposition of organic matter with consequent nutrient release. In much-improved lowland agricultural landscapes this may be the only surviving fen type. It is related to the Alnus-Urtica fen woodland (Alder, Nettle) (see below). A distinction needs to be drawn here between carr containing the 'stingless', narrow-leaved form of Urtica and that containing the normal form; the former seems to be more-or- less unmodified by enrichment.

C4.4.4 Reed-beds and reedswamps

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The reed field and some patches elsewhere are part of the group Phragmites australis swamps and reed-beds [S4]. These are species-poor communities encouraged by flooding with eutrophic waters. The scheme distinguishes a slightly more species-rich subcommunity in which Galium palustre (Marsh Bedstraw) is frequent, and a species-poor sub-community which is often a virtually pure stand of reed. Both probably occur at Wicken.

The larger ditches are occupied by Sparganium erectum swamp (Burr-reed) [S14]. Some are virtually pure stands and belong to the typical subcommunity; others are more species-rich and are better placed in the Alisma plantago-aquatica subcommunity (Water Plantain) or the richer Mentha aquatica subcommunity (Water Mint).

In the brickpits and elsewhere there are fragments of Typha latifolia swamp (Great Reedmace) [S12], and Typha angustifolia swamp (Lesser Reedmace) [S13], and there are likewise fragments of Carex acutiformis swamp (Lesser Pond Sedge) [S7], and Carex riparia swamp (Great Pond Sedge) [S6] along the lode margins.

Some of the lower-lying and wetter parts of Adventurers' Fen bear a grassy vegetation which is probably Glyceria fluitans swamp (Flote-grass) [S22]. Many of the associates such as Mentha aquatica (Water Mint), Nasturtium officinale (Water-cress), Carex otrubae (False Fox-sedge) and Alisma plantago-aquatica (Water Plantain) are present. Rather surprisingly, the Alopecurus geniculatus sub-community (Marsh Foxtail) of this community, characteristic of washlands, does not occur.

C4.4.5 Turf diggings (Rodwell, 1991b)

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A community which now exists only in small and impoverished fragments at Wicken, but which may have been more abundant in the past, is the Carex diandra - Calliergon giganteum sub- community of the Carex rostrata - Calliergon mire [M9]. This moss-mat community occurs in old peat diggings. In Norfolk it is the habitat of several local and national rarities including Liparis loeselii (Fen Orchid), Anagallis tenella (Bog Pimpernel), Drosera anglica (Great Sundew), Parnassia palustris (Grass of Parnassus), and Hypericum elodes (Marsh St.John's Wort). Of these, the first two formerly occurred at Wicken.

C4.4.6 Woodlands, including Fen Carr (Rodwell, 1991a)

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The carr at Wicken is included in Salix cinerea - Betula pubescens - Phragmites australis woodland (Sallow, Birch, Common Reed) [W2]. This is a typical form of scrubby woodland of such sites, although there is considerable variation from site to site, due perhaps more to chance dispersal and the presence of seed parents than to differences in environment. The abundance of Frangula alnus (Alder Buckthorn) and Rhamnus catharticus (Purging Buckthorn) at Wicken, and the virtual absence of Alder (Alnus glutinosa) are examples of this.

Within this woodland type, Rodwell distinguishes two sub- communities, differing mainly in their ground floras:
the Alnus glutinosa - Filipendula ulmaria sub-community is characterised by a richer ground flora in which fen species such as Filipendula ulmaria (Meadowsweet) and Eupatorium cannabinum (Hemp Agrimony), together with Urtica dioica (Nettle), are generally abundant, at least locally. Ferns are scarce, and Sphagnum (Bog-moss)is absent. This sub-community is widespread on the fen;
the Sphagnum sub-community, has a more open field layer,with scattered grasses and sedges often prominent, and with many ferns in the best-developed stands. Species of Sphagnum are often abundant, as are other calcifuge mosses such as Mnium hornum and Aulacomnium palustre. This sub-community appeared to be developing over large areas of the Fen, but, since the early 1980s, it has regressed for reasons which are poorly understood, but in which high water tables and the death of Frangula may play a part.

The differences between these two sub-communities are explained by Rodwell mainly in terms of the groundwater regime. The first occurs where the surface is still flooded at times by calcareous ground water, and the second where the surface remains damp yet isolated from the calcareous groundwater. Drying of the surface allows breakdown of the peat, with nutrient release, leading to a drier type of Alnus - Urtica woodland [W6], lacking fen herbs but with much Urtica (Nettle) and Sambucus (Elder). Woodland of this type, with birch trees, appears to be developing in the angle between Sedge Fen Drove and Drainers Dyke, behind the patch of Myrica (Bog Myrtle). However, these birches were originally planted, and roosting birds may be at least partially responsible for the nutrient enrichment.

C4.4.7 Adventurers' Fen

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Compared with the Sedge Fen, the vegetation of the Charles Raven Reserve has been poorly documented. The following are the main sources of information:

Vegetation of the mere -            Dr.S.M.Walters (late 1950s)
Small areas of grassland -          Dr H.J.Harvey (early 1970s)
Characeae in new boundary ditches -                 Mrs J.Moore
                                         (B.M.N.H., late 1970s)
Vegetation of boundary ditches -        Dr D.E.Coombe (1979-80)
'A Survey of the Flowering Plants on the National Trust
Property to the South of Wicken Fen (i.e. Adventurers' Fen)'    
                  -   A.D. Mills (Report in Fen Archives, 1981)
General notes on flora and vegetation -   Dr.J.M.Lock (1984-85)

The summary that follows is taken from Dr Harvey's paper to the Committee (1981), with modifications, and on more recent observations by Dr.J.M. Lock. Dr Harvey's account was based on his casual observations over the years. The vegetation is mapped in Fig.. A new survey is in progress in 1992.

Grassland

Ai - (Brett's Piece). Agrostis stolonifera (Creeping Bent) and Festuca rubra (Red Fescue), with much rush (Juncus spp.) The latter has been controlled by cutting and heavy autumn grazing. Some parts liable to flooding.

Aii - Similar to the above but with more Juncus. Once again, some control has been achieved by cutting and late grazing. Often very wet in places.

Aiii - (Trevelyan's Piece). Again rather similar, with much Agrostis and Festuca. Formerly badly infested with ragwort and thistles but these have been well controlled by hand pulling. The south-eastern corner is a shallow scrape, usually bare of vegetation but with a fringe of rushes.

Aiv - (Rothschild's Lapwing). Lolium perenne (Ryegrass) and Agrostis stolonifera and Festuca rubra. Very few rushes, and not much ragwort or thistle. Probably the best grazing area.

Av - (Evans' Fen). Earlier infestation by thistle and ragwort has now largely been overcome but constant control needed.

Avi - The lode banks have a diverse flora, including a number of species characteristic of better-drained sites.

Swamp

Bi - This area has now been divided into two. The western two- thirds has been fenced off and reed allowed to take over. The eastern third is wet grassland with a lot of rushes. At the time of the 1981 account the whole area was wet grassland with much rush and some reed.

Bii - This area contains the four old brickpits. The vegetation is wet cow-trampled grass with much rush. The cow trampling is probably an important component of the environment as it maintains open habitats for the Lesser Water-plantain (Baldellia ranunculoides).

Reed

Ci - (Commercial reed-bed). Virtually pure reed (Phragmites communis), with Calamagrostis (Small-reed) and Phalaris (Reed- grass) in slightly better-drained sites. Some invasion by willow bushes, mainly on the eastern edge.

Cii - (Conservation reed-bed). Reed is abundant at the north- east end, but thins out towards Commissioners' Drain and is then largely replaced by Juncus and Phalaris.

Ciii - (Outer Mere fringe). Reed, with patches of grassy vegetation on higher patches. This has largely developed since the 1980 report as a result of the exclusion of grazing from these compartments.

Civ - (Mere fringe). Reed, with occasional willow bushes. Some grassy vegetation on high spots. Reed is most vigorous close to the open water.

Scrub

This occurs mainly at the foot of the bank of Wicken Lode, and consists of Crataegus (Hawthorn), Rosa (Wild Rose) and Salix (Willow). Overgrown hedges along Harrison's Drove and elsewhere contain the same species, together with some Frangula (Alder Buckthorn), Rhamnus (Purging Buckthorn) and Viburnum (Guelder Rose).

Woodland

The only compact areas of trees (and these are small) are the Alder plantation on Evans' Fen and the Willow and Hawthorn thicket on the Mere Island.The hedges of the Conservation Reed Bed contain some large willows. Some dense thickets of Elm that survived the epidemic of Dutch Elm Disease are now over 6m high.

Ditches

Most of the ditches are choked with vegetation, and the ditch round the Mere is now heavily shaded by reed. In some places there are large patches of Rumex hydrolapathum (Great Water Dock), and there are a few clumps of sedge (Cladium mariscus). No records are yet available for the grid of new ditches created in the Commercial reed field in 1989.

Open water

The Mere is very poor in aquatic macrophytes, probably because of grazing and defaecation by waterfowl. The old brickpits contain a few species, particularly those ponds which are not excessively shaded. The ponds dug in 1969 and 1971 seem poor in aquatics. No records are yet available for the Borrow Pit (1989).

General

Dr. Harvey commented on the richness of the aquatic vegetation in his paper. Since then many of the ditches have become overgrown and there may be a case for a roding and slubbing programme to be started, along the same lines as the programme implemented on the Sedge Fen (see Sections A2.7, A4.2.5, A6.7). The new ditch close to the junction of Monk's Lode and Wicken Lode is rich is species, as is Commissioners' Drain, which used regularly to be cleaned by Swaffham Internal Drainage Board (until 1989).