A6.1   sedge
A6.2   litter
A6.3   droves and paths
A6.4   reed
A6.5   carr
A6.6   trees
A6.7   ditches
A6.8   turf-digging
A6.9   fire: use and control
A6.10   management of named species

Page index

Description
Sedge (Cladium mariscus) is a widespread but rather uncommon plant of wet places. Detailed studies of its ecology at Wicken have been carried out by Conway (1936-38) and Rowell (1983).

The plant is perennial, with a creeping underground rhizome bearing aerial shoots whose growing points are below ground level except when they flower. The leaves are perennial, remaining green for 2-3 years. They bear rows of sharp siliceous teeth on the margins and on the back of the midrib. Flowering occurs in favourable sites; although warm summers are said to be needed for flowering, fertile shoots can be seen every year at Wicken. Conway never recorded regeneration from seed; Rowell (1983) frequently recorded young seedlings.

Because the leaves of sedge are perennial, annual cutting weakens the plant (Godwin 1941). The rhizome relies for its oxygen supply on diffusion through the air spaces of the older leaves; diffusion into the rhizomes is slow through the bases of the young, growing leaves (Conway 1938). Prolonged flooding which submerges the cut ends, filling the air spaces in the leaf bases and the rhizomes, can cause the death of the plant. Observations at Wicken and elsewhere suggest that young regrowth is frost-sensitive until about 15 cm high.

Sedge management at Wicken
Sedge is a traditional crop at Wicken. Rowell (l983) has found records of harvesting going back to 1414. It is used for thatching, formerly for whole roofs but now only for ridges. Older sedge, unsuitable for thatching, was in the past used as a fuel for bakehouses in Cambridge colleges (Rowell 1983).

There can be little doubt that the vigour of the sedge declined in the 1970s and early 1980s, probably because of over-frequent cutting and cutting late in the year so that the plant had no time to recover before the cold and floods of winter. Falling water levels may also have contributed to the decline. In the 1960s and 1970s water was pumped onto the sedge fields in April-June in preparation for the (rather late) harvest in July-September. This is said to have much improved the growth of the plants immediately before cutting.

There also appears to have been a decline in the area of sedge: compartments 11, 13, 14 and 19 formerly contained harvestable sedge but no longer do so. However, the excellent 1992 season revealed substantial amounts of sedge do occur in cpts 13, 14 and 19.

Cropping interval and seasonal timing
There has been controversy over both the cutting interval and the time of cutting of sedge. The traditional practice was to cut on a four-year rotation; this was changed to a three-year cycle, probably during the 1930s, perhaps to produce a more acceptable material for thatchers (see below).

Current practice is to crop on a four-year cycle. The case for a three-year cycle was presented in 1990 and accepted by the Committee. This has not yet been put fully into practice as it increased the workload beyond the capability of the Fen staff and seemed likely to prove more damaging to ground-nesting birds. However, a 3-year cycle is the overall aim of the work programmes set out in this management plan.

Until 1982, sedge was cut between July and September, but Rowell (l983) produced convincing evidence for earlier cutting as the true traditional practice, and harvesting between May and August was adopted as standard practice in 1983.

Early cutting gives the shoots more time to recover before autumn frosts and may reduce the susceptibility of the plant to flooding. The earlier cutting since 1984 has undoubtedly led to better sedge growth and the spread of sedge where it was previously sparse.

Early summer harvesting has the disadvantage that nests are destroyed, including those of the relatively uncommon Grasshopper Warbler. However, only a small proportion of the nesting habitat is cut in any one year, and early cutting is very beneficial to Milk Parsley (Peucedanum palustre).

Sedge harvesting at Wicken
The sedge is cut with a machine with an offset cutter bar, running so that the cut material falls against the uncut face of the vegetation and is supported by it, making it easier to gather up. Thus the machine must make a single cut, then return to its starting point to make the next cut. It is said to be impossible to cut round and round a block because the sedge tends to be laid in one direction by the prevailing wind. However, at other sites this is not apparently a problem and is likely to be less of a problem with three-year old sedge.

Wicken sedge fields are more level than other commercial sites, where uneven ground may necessitate cutting by scythe or brush-cutter. In 1982, conditions were so wet at Wicken that harvesting was virtually impossible. (At other sites it is normal to cut sedge in very wet conditions, wearing waders).

The cut material is gathered up with a long-handled 4-tined fork, and sorted of rubbish before being bundled into 'yealms'. Until 1991, these each consisted of two halves, one with butts to the left, the other to the right; this 'double yealm' was unique to Wicken. A typical 'single yealm' is now produced; these are faster to produce, but harder to transport. A yealm is secured with a string tie of standard length which also acts as a size gauge. The bundles are stacked to dry on the field and carted to stacks in Lode Lane when dry. The Fen is probably the largest producer of sedge in the country.

Thatchers require material that has been cut green and dried. Material which is already brown when cut is brittle and of little use. The proportion of unusable material increased with the lengthening of the rotation from 3 to 4 years, and there were minor grumbles about quality from the thatchers. Shorter material is also easier to handle.

Quantity of sedge harvested

     YEAR      YEALMS     PRICE PER YEALM     INCOME

     1983      2700           80p            £2160              
     1984      2622           85p            £2228.70
     1985      2250           90p            £2025       
     1986       510           95p             £484.50    
     1987      1877          100p            £1877
     1988      1700          125p            £2125
     1989      1088          140p            £1523.20
     1990      2591          150p            £3886.50
     1991      3540           85p*           £3009.00

* Single yealms. The price per single yealm is, in 1992, 90p.

There is some uncertainty about earlier figures, because bundles of litter may sometimes have been included in the totals (Figure 14).

The future

Every effort should be made to continue the harvest, both because harvested fields of Cladium are now a very rare phenomenon and have considerable conservation interest, and also because the supply of a traditional thatching material depends upon the continuation of the harvest.

However, the time-consuming nature of the harvest means that any attempt to increase the area cut is now unrealistic unless the process can be speeded up a good deal. The recent increase in Cladium in areas which formerly bore carr, but where most Frangula has now died, has effectively increased the area, but these areas are not harvested. Cladium has also increased in those compartments where litter has been cut in spring every two years. The objective (stated in the 1954 Management Plan) of making the whole block bounded by Wicken Lode, Drainer's Dyke, Sedge Fen Drove, and the Windmill Ditch into sedge fields cannot now be regarded as realistic. The Committee should now agree a reasonable area to aim at and compartments to be given priority.

Between 1985 and 1990 the target specified for sedge harvesting was never attained. In view of this the Management Committee has approved (12 Sept.1990) various changes. The following principles will be followed in an attempt to speed up the operation:

1. Sedge is to be cut between April and mid-August only, and, if suitable, on a three-year rotation.

2. Fields are to be surveyed before cutting, and parts where sedge is sparse cut first, and the cuttings stacked to rot. Some localised burning of cut material may be necessary to limit the amount stacked and the damage caused by moving it.

3. Trials of mechanical harvesting to be carried out.

4. All aspects of the process described are to be looked at for economies, including the process of 'bushing-out' after harvesting; bush growth may become less severe now that the Fen is wetter.

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Description
The term 'litter' has been variously used at Wicken to mean either a particular group of plant communities (those herbaceous communities not dominated by sedge or reed), or the vegetation developed under a particular style of management. It is a community composed of a large number of species, and not like the virtual monocultures formed by reed and sedge. The term covers at least two major community groups:

1. those dominated by purple moor grass (Molinia caerulea); these tend to occur on sites which have remained open.

2. those with a much more varied composition but in which species of small-reed (Calamagrostis epigejos and C. canescens) are prominent; these usually occupy litter fields which have been re-created by clearance of carr. Death of Frangula in recent years has opened up the carr and allowed a great increase in Calamagrostis beneath it; this poses a potential problem and certainly represents an increased fire risk.

Use and management of litter at Wicken
During the present century, litter has been cut conventionally in the autumn and winter. The harvested crop has been used for thatching ricks, for lining potato clamps, and for providing animal bedding. These are all uses where the nutritional value of the material is unimportant and where maturity and thus resistance to decay are required.

Rowell (l983) has established that a good deal of the litter cutting in the last century and before was done much earlier in the year. It is not clear what the harvest was used for, but it may well be that rather more of it was used for animal feeding, as a sort of rough hay. Some, at least, was used as hay chaff and even sent to London as feed. Nutritional value would then be an important consideration, and since this declines with maturity, harvesting earlier in the year would be logical. Ennion (1949) states that litter was used as a coarse hay for cattle, and that it was cut green, later than meadow hay, as it took longer to mature.

Rowell, Guarino & Harvey (1985) showed that cutting in May or July increased the proportion of dicotyledons in the sward. In line with this, some smaller fields are now cut in May, although the wetness of the Fen makes the operation difficult to mechanise and therefore slow. A programme has also been introduced under which some fields are cut annually, some in alternate years, and some two years in three. The majority of the litter cutting in any year is done in the summer and autumn. The detailed programme is outlined below, and elaborated in the section giving prescriptions for each compartment (Section A3).

Cutting is necessary to maintain the present mix of species, and to prevent the spread of carr. The material is removed to prevent it damaging the vegetation beneath it, and to keep down the nutrient status of the fen vegetation. Cuts at different times help to maintain a steady supply of nectar-bearing flowers throughout the summer, and also spread the work load through the season.

The 'Godwin Plots' in Cpt 10 were set up in the 1920s in order to investigate the role of cutting interval on the composition of the Fen flora (sedge/litter); Godwin, 1941.

Litter was formerly cut with a scythe. The spring cutting is done with a motor scythe because the ground is usually too wet to support a tractor, although in dry years the small Kubota tractor can be used. The cut material is carried off and stacked to rot in heaps at the edge of the carr. The heaps are themselves interesting habitats, but other uses such as composting or drying for feed should be sought for the spring crop.

By July the ground is usually dry enough to support a tractor and allow the use of a tractor-mounted hay cutter and a tractor-mounted hay-sweep. Sometimes the Fen is dry enough to permit the summer litter crop to be baled after cutting. In 1985 several compartments were cut and baled for use on the Trust's farm at Wimpole Hall. 1800 bales were gathered. In the last few years (1990 - 92) much of the July litter crop has been baled and sold as animal feed. Unbaled litter is stacked on standard sites cut in the edge of the carr or burned when safety considerations allow on regular sites. Straw-burning legislation, in force from 1993, does not apply to the burning of litter. Baling and carting off is quicker and reduces the need to store or burn, but burning may prove necessary on annually cut fields, where the accumulation of cut material will be greatest.

The autumn cut is done mainly by tractor, and most of the material is burned, with some being stacked to rot.

The future
The litter fields and the taking of a cut from them are part of the traditional cycle of management at Wicken, and should be continued.

There is obviously scope for extending litter fields by clearance of carr, but, once an area is cleared, it must be managed. The area to be cut is already large (about 24 ha, of which about 12 ha is cut annually), and there can be major problems in cutting and clearing it all in a wet late summer/autumn (August tends to be one of the wetter months in the region). Reliable cutting at a particular time each year requires better control of water levels. The purchase of the Kubota, which has a low ground loading, has improved matters considerably.

The effects of the different cutting regimes should be monitored. There are three different times of cutting (spring, summer, autumn) and three cutting intervals (annual, biennial, and two years in three), giving nine possible combinations, plus the Godwin Plots in winter.

The lack of monitoring means that no detailed changes have been noted under different treatments between 1985 and 1990. No obvious gross changes have been noted, so there is no reason to alter the cutting regime at present. Subjective impressions suggest an increase in Lychnis flos-cuculi (Ragged Robin), Lysmachia vulgaris (Yellow Loosetrife) and Lathyrus palustris (Marsh Pea) in summer- and autumn-cut areas and a general increase in herbaceous plants in all the fields.

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Description
The typical Wicken drove is 5-10 m wide and usually straight, passable by tractor when dry enough, and usually with a regularly-cut portion towards the centre for walking, and margins that are cut less often. Some are public rights of way; there is more information about this aspect in Section C2.2.

Droves provide access routes for the public and for Fen staff and machinery, but they also provide habitats for various plants and animals which do not occur elsewhere. This is especially true of Sedge Fen Drove itself, which has a rich flora containing some species intolerant of competition with taller fen plants, but very tolerant of cutting and trampling. Eleocharis quinqueflora is not known from any other Cambridge-shire (VC 29) locality, and is rare in lowland Britain. The Cyperaceae of the droves deserve careful monitoring as field observations suggest that there is an optimum level of interference for the community to persist and that some local baring of the peat surface is a positive advantage. There is also some evidence of spread of E. quinqueflora on to cross droves, where the cut central strip is of relatively recent origin.

The central strips are mown to allow easy access for visitors, and the lateral strips are cut to give a relatively short and species-rich sward in which attractive species such as marsh orchids appear to thrive, and which are also attractive to various insects and hence to their predators (mainly birds). If the paths and their margins are made easy to follow and attractive, there will be less incentive for visitors to stray from the paths. The minimum width for the central strip is reckoned to be 1.5 m to allow two people to walk side-by-side in comfort. A wider swathe may have to be cut to allow for narrowing of the path by vegetation flopping in from the sides: each successive mowing is usually made a little wider than the last. This will also be necessary on those droves (such as Sedge Fen Drove) along which machinery is taken.

History of the Droves and their management
The old paths on the Fen are those along Wicken Lode, and Sedge Fen Drove. Sedge Fen Drove is at least 300 years old. Other paths undoubtedly existed, and these were probably, at least in part, the basis of the present grid of droves which were first cut earlier this century, starting in 1929, although Professor Godwin is reported to have said that in the early 1920s Sedge Fen Drove and the lode-bank paths were the only ones.

Pre-1928: no detailed records; irregular cutting assumed.

c.1928 - 1948: Two cuts each year with a scythe. Second cut delayed until most flowering finished. Cut material removed.

By 1948: this had been slightly modified to give a central strip cut in June or July, and a broader strip cut in the autumn. Autumn cut removed.

1949-1955: Three cuts annually, June, July, August-October. Allen scythe (motorised) replaced hand scything in 1949.

c.1956 - c.1978: Frequency of cutting increased and first cut taken earlier (April-May). Cutting frequency of central strip depended, essentially, on usage, with the most-used paths on the Sedge Fen being cut every 2-4 weeks, giving 5-8 cuts per year; less-used paths (e.g Verrall's and St.Edmund's Fens) cut 2-4 times each year.

1978 - 1980: Frequency reduced again, partly because of manpower, but also because of a feeling within the Committee that the Fen was acquiring too regimented an appearance.

1980 - present: The central strips are mown at least twice, and, in addition, the whole width is cut in the autumn and the material carried off. The mowing of the central strips is now carried out with a rear-mounted Twose rotary flail cutter mounted on the Kubota mini-tractor, and with this combination the entire network of paths and droves can be cut by one person in one day. The facility and speed afforded by mechanisation allows a greater frequency of cutting to be sustained.

Fig. 10 shows the paths and droves on the Sedge Fen and shows two levels of management; practical details are given in Sections A2.3 and A4.2.4. The basis for this division is as follows:
Level 1 - heavily-used routes

During the vulnerable time of the year, traffic is concentrated on a single circuit, the nature trail, and even later in the summer, when all routes are open, most visitors follow this route (Street 1982). This has the advantage that it protects the central parts of the Sedge Fen and also Verrall's Fen from disturbance. From an educational point of view, it may even be desirable that the 75% of visitors who do not visit the fen primarily for its natural history interest should stick to the nature trail and be guided in their appreciation of it.
Level 2 - less well-used routes

There is an obligation, at least at times of the year when disturbance is of less importance, to keep routes clear enough for access by those interested in natural history. This category of visitor is more likely to be adequately shod and also more likely to accept less well-kept routes. It is also desirable that all the usable routes on the fen should always be clear enough to encourage people to use them rather than to wander at random.

Sedge Fen Drove receives Level 2 management, but is kept wider as it is a major route for taking machinery onto the Fen.

Drove clearance in the autumn, where droves run alongside water-bodies, involves cutting vegetation up to, and sometimes onto, the water, depending on the width of the edge strip. In these cases, the operation is similar to summer brinking (A4.2.6).

Problems


Paths are closed with string when too wet, or when they should not be used because to do so may disturb the fauna and flora. On occasion, strings along each side are used to delimit the part of the path in use. This is particularly important on Sedge Fen Drove during the winter; it cannot be closed as it is a public bridleway, and it becomes extremely muddy. Warning notices are placed at each end. On other paths, duckboards are sometimes placed across bad patches.

At certain times of the year, usually in the spring, some of the paths on the Fen become over-used and break up to give a very muddy surface. This has largely been overcome by concentrating use at critical times onto the peripheral nature trail, and by providing duckboards at vulnerable points on this. At the same time, the droves in the central part of the sedge fen are closed off with string barriers.

When it proves necessary to repair paths, local materials from the Fen itself should be used. Laying of stick walkways is to be encouraged, and turves, if used, should be cut from close to the site. Waste turves from the surface of the demonstration turf-diggings might be used for mending holes in paths.

The lode-side path to the Tower Hide becomes particularly broken-up, and a length of alternative path parallel to the original has been constructed to spread usage. This has proved successful, and may usefully be extended.

On the Sedge Fen (including Verrall's Fen) there are about 10 km of droves. On St Edmund's Fen there are at least 1.7 km.

Future management


The opening of the boardwalk in 1987 has produced considerable changes. A rough estimate suggests that 80% of people follow the boardwalk rather than the longer nature trail; this is currently (1992) being surveyed. This pattern of usage means that the larger numbers of people now visiting the Fen can be accommodated without too many problems, although a busy weekend after a wet spell may still lead to substantial damage to paths.

The development of a short walk, along the eastern edge of Breed Fen to the Brick kiln and Sedge Fen Drove, returning past the windmill, should be considered. This would, however, require careful control of access as it would provide visitors with an alternative entry point onto the Fen.

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Description

Most of our knowledge of the ecology of reed in this country comes from the work of Haslam (1969, 1972, etc.).

The Common Reed (Phragmites australis) is a very widespread grass of wet places. It is a perennial, with large underground stems (rhizomes) which spread extensively and which live for many years. The aerial stems are annual; they appear in the spring (April-May), grow throughout the summer, flower from late July onwards, and then die. The leaves remain on the stems until broken by strong winds following frosts. Spread is mainly by the rhizomes; although seeds are produced, they are said to have a low viability in this country.

Young reed shoots ("colts") are susceptible to frost. This can kill the growing point, which is enclosed by several overlapping leaf sheaths and lies some way behind the apparent tip of the shoot. The young shoots can be protected from light frosts if their bases are covered by water. Death of the shoots through frost or any other agency (fire, trampling, grazing etc.) leads to the growth of extra shoots from lateral buds. The killing of large early colts by frost can produce a more even crop by stimulating the lateral buds.

The responses of reed to nutrients have been discussed by Haslam (1965, 1972). She regards phosphorus as being the most important element controlling reed performance in East Anglia (particularly in Breckland).

Reed requires a moist environment for growth. It can grow in water up to 1 m deep but can survive with the water table permanently below the surface. Flooding is a management device to protect the young colts and also to suppress weedy herbs and shrub growth, which reduces considerably the commercial value of the crop. However, excess flooding, especially later in the year, can cause blackening and rotting of the bases of the stems and can also allow rooting and algal growth above soil level, all of which are unpopular with thatchers.

Reed management at Wicken

The reed field can be flooded in most years from Wicken Lode via the Mere perimeter ditch (the inflowing water does not need to pass through the Mere). Inflow to the field is controlled by blocking and unblocking culverts under Harrisons Drove. Outflow is into Commissioners' Drain, and control is achieved by blocking and unblocking a pipe which leads from the central ditch of the reed field into Commissioners' Drain (see Figure 11, Section A4.2.5).

The standard management since 1983 has been to start flooding the reed field by the end of March to give a water cover and protect the growing colts from frost. Before 1983, flooding began later in the year. If flooding is delayed, soil moisture deficits can build up and it can be difficult to flood the field at all, as happened in 1990 and 1991. Inflow continues until September to maintain a shallow flood. From September onwards the inflow is cut off and the field drained into Commissioners' Drain.

Parts of the Main Field may at times be flooded too deeply during the summer, as some of the faults associated with deep flooding (see above) occur. This is difficult to control precisely because the surface of the field is not even.

In 1989, several old ditches within the field were opened up, and a number of blind spurs made leading off them. Although these ditches remained wet in 1989, they dried out in 1990. These ditches were constructed for four reasons:
a) to facilitate the flooding and draining of the reed field;
b) to reduce the total amount of reed harvested;
c) to produce aquatic habitat for reed-dwelling invertebrates

and birds, in particular Bittern;
d) to increase the extent of aquatic habitat on Adventurer's Fen

that is not subject to enrichment by wildfowl.

In the past few years, there has been insufficient water to flood the reed fields adequately. It has been suggested that there is a need for an extra inflow pipe running direct from Wicken Lode to the Reed Field, but such abstraction is not currently allowed by the N.R.A. and would in any case incur a substantial payment. An extra dam on Commissioners' drain downstream of the Conservation Reedbed, installed in late 1989, should help maintain higher levels without affecting the grazing fields when it has been made fully waterproof by the N.R.A.

The reed harvest at Wicken

Small-scale harvesting of reed from the drains and dykes ceased in about 1960. Harvesting from the fields in the Charles Raven Reserve began in the early 1960s. All harvested reed is used for thatching.

Harvesting begins as soon as the leaves ("flag") have been blown off by strong winds, usually early in the New Year. Formerly, harvesting and carting of the crop continued into April and May but these activities now stop by mid-March.

The divisions of the reed field are shown in Figure 11. The Main Field is usually cut first, followed by Scrape, Good Friday and the rest. Harvests from the Main Field were fairly constant between 1981 and 1984. The amounts cut from the others varied more, probably because growth is more variable there. The southern end of Pout Hall field has deteriorated in recent years and has not been cut for several years, but was burned out early in 1990 with a view to bringing it back into production. The whole harvested area is cut annually ('single wale').

The reed is now cut by a machine (Olympia) which bundles the cut reed into rough sheaves. These are carried off the field by fen staff using low ground-pressure vehicles, and stacked on the bank of Wicken Lode.

Since 1988, the employees of a thatcher have taken over the next stages of the work. The sheaves are opened and sorted mechanically; weeds and short, broken and bent reeds are removed, and the clean reeds made into standard bundles. These are banged on a board ("butted") to make a neat lower end to the bundle. and then placed in a slotted box and tied with string. Once tied, the bundles are reasonably water-resistant and are stacked until they are carried to the end of Wicken Lode either by boat or by tractor and trailer. From here, the reed is collected by lorry; it is also possible to collect in this way from Harrison's Drove.

The arrangement whereby the sorting and bundling is done by the thatcher's employees leads to considerable savings in manpower during reed harvest time, but has led to a 50% decrease in income, as costs are shared. This has been partly offset by cutting a larger part of the Reed Field.

Reed must be dry when cut. It is difficult to cut in windy weather because the cut material blows about and does not bunch well. In a spell of good weather it is usual to cut as much reed as possible and carry the rough bundles off the field for processing; the processing can go on in less favourable weather.

Quantity and Quality

The quantities of reed harvested between 1968 and 1992 are shown in Figure 15; this shows a peak of 9,000 bundles in 1975, followed by a general decline through the 1980s. The old standard Wicken reed bundle (30 inches in circumference) has now been abandoned in favour of the normal standard of c. 24 inches.

During this same period, the price of a bundle of reed has increased from 12.5p to 180p (of which the Fen receives 90p). There is some doubt as to the possibility of further increases because the price is depressed by imports of reed from eastern Europe (now sold at 125p per bundle, delivered). Income from reed rose steadily to a peak of £5500 in 1980, and has since declined. Wages, the main component of harvesting costs, have of course continued to rise, and it seems likely that, in strict monetary terms, the reed harvest ceased to be economic in about 1982. This situation altered, however, in 1988 when the thatcher took over the bulk of the work, and it seems likely that the harvest has been genuinely economic from 1989.

Very dry weather in 1990 and 1991 resulted in very poor harvests in 1991 and 1992, as reed growth was suppressed by late frosts while weeds thrived in the drier conditions. In 1992, most of the crop was cut and burned on the field. Since then, Adventurers' Fen has become wetter (the reason for this is not clear) and the prospects for the 1993 harvest seem good, in spite of continued drought.

     YEAR   BUNDLES  PRICE PER    INCOME 
                       BUNDLE     TO FEN
     1986    4020       125p       £5025
     1987    6000        90p       £5400     Bundle size reduced
     1988    5806        60p       £3483.60 ]
     1989    8700        65p       £5655.00 ]
     1990    6527        70p       £4568.90 ] costs split 
     1991    2070        75p       £1352.50 ]
     1992     823        90p        £740.70 ]

Conservation and the reed harvest

Harvesting of the reed undoubtedly has an adverse effect on the fauna of the commercial reed bed, most obviously the birds, but also the diverse assemblage of invertebrates dependent on reed. There is, however, an adjacent field (the Conservation reed field), which is not harvested (although one third is burned off every two years). There are also the extensive reed beds round the Mere, many of them originating when grazing was excluded from the fields adjacent to the Mere in 1981. If the entire commercial reed bed was harvested (and this is usually very far from true), only about 49% of the total reed area at Wicken would be cut. In practice, the total cut is well below 30% in most years.

Birds that depend on reed beds for breeding at Wicken include Bearded Tits and Marsh Harriers. Bearded Tits now have respectable populations in Britain (c. 400 pairs in 1972 (Sharrock 1975) and now seem to be fairly well-established at Wicken in small numbers. They seem to survive adequately in the areas of uncut reed, and also use the reed fields before they are cut.

Marsh Harriers are at the edge of their range in Britain, but are increasing (6 nests rearing 17 young at four sites in 1973 and about 60 pairs rearing c.100 young in 1990; Underhill-Day, 1984 and others). Marsh Harriers bred at Wicken in 1981, 1985, 1991 and 1992, first in the Conservation reed bed, then in the Mere reed beds and most recently in Verrall's Fen. The area of reed at Wicken (44.2 ha, with a maximum of 19 ha cut) is considerably larger than the mean area supporting a single pair (20.7 ha), but a good deal smaller than the mean area for sites with two pairs (71.6 ha) (Underhill-Day, 1984). However, polygynous breeding, with a single male supporting two females, is not uncommon (Underhill-Day, 1984). Given the large area of suitable hunting territory peripheral to the reed, there would be a good chance of polygynous breeding. There might also be a possibility of two pairs breeding if cutting were to be discontinued or reduced to a token area for demonstration purposes, and providing the site could be protected from disturbance by visitors. Two females did attempt to nest in 1992, but one failed before hatching.

Other species which might possibly breed at Wicken, given the right conditions and adequate space, include Bitterns and Savi's Warblers; the latter have bred in the past, and Bitterns regularly winter.

Of the four bird species mentioned, the two large ones are very susceptible to disturbance during the breeding season, especially during the period when territories are being established. The smaller ones appear to be less fussy. Descriptions of the habitat of Savi's Warbler suggest that it is more likely to breed in wet sedge-fields than in reedbeds, and indeed a singing bird in 1990 (and subsequent possible breeding) was in sedge.

At least a dozen species of British moths are dependent on reed as their larval foodplant. Among these is the Reed Leopard (Phragmataecia castaneae), which takes 3-4 years to complete its life-cycle. Obviously, annually cropped reed will not support a population of such species, but the six-year rotation of management of the Conservation reed field is designed to ensure that an expanse of more permanent habitat is always available.

Future management

Large-scale reed harvesting is not a traditional element of management at Wicken. However, reed was certainly one of the traditional natural crops taken from the fen margins, and the continuation of a traditional practice of this kind should be encouraged. Wicken Fen is the only site in the area where traditional reed-haresting can be seen. Furthermore, reed harvesting has been, and to a lesser extent still is, a valuable source of income. The demand for good quality reed is likely to continue.

The present management of the reed-beds at Wicken is a compromise between maintaining the traditional activity of reed harvesting, and attempting to attract certain bird species that are now breeding in the fens for the first time in many years. The old motive for cropping commercially, financial gain, has receded as other sources of income (especially from visitors) have increased.

The recent changes in practice have led to a speeding up of the harvest so that it ends before the critical spring period during which birds are susceptible to disturbance. However, it is not possible to conserve the reed-bed fauna by non-intervention: even on the Conservation reed-beds, there is a need for some kind of management, whether cutting or burning, to control bush invasion.

Some increase in the area of uncut reed-beds may be considered as part of the development of the Charles Raven Reserve.

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Description

Carr is a scrub woodland, dominated at Wicken by Alder Buckthorn (Frangula alnus), with the willow Salix cinerea an important subsidiary component. In drier sites there is a tendency for Purging Buckthorn (Rhamnus catharticus) and Hawthorn (Crataegus monogyna) to become dominant. A fuller account of community structure is given in Section C.4.4.

At present about 75% of the area of the Sedge Fen (including Verrall's Fen) is covered by carr. Early accounts definitely show that this has mostly developed since the beginning of this century, replacing sedge and litter as cutting ceased or became infrequent. As the Fen has become drier, there is little doubt that carr has become the natural vegetation of the whole fen and that herbaceous vegetation can be maintained only by management to control the development of carr.

The plants of sedge and litter fields persist for some time under carr but eventually die out. The recent death of much of the Frangula has opened the canopy and given a new lease of life to some of the fen species beneath, and allowed the appearance of much Calamagrostis. New surveys to determine the extent of the survival of sedge under carr are needed.

Carr provides a valuable habitat for some birds and mammals. Owls, including Long- eared Owls, do well at Wicken. Other woodland species, such as Bullfinches, Long-tailed Tits and Jays are also well represented at Wicken, and Sparrow-hawks have bred in recent years. In spite of these interesting species, Wicken is not a reserve that exists to protect woodland, and there is a strong case for clearing more carr and increasing the area of sedge and litter.

The Frangula dieback

Since 1980 there has been a dramatic decline in Frangula for reasons which are not well understood. A previous dieback episode in 1928-1933 was then connected with the fungi Nectria cinnabarina and Fusarium sp. (R.E.D. Baker in Godwin 1936). The rust Puccinia coronata was also present but was probably not lethal (M.R. Brown in Godwin 1936). The symptoms of the recent attack are similar to those described from the earlier one, but no fungi have been definitely identified although a rust is present on the shoot tips in June-July and the blackening of the under surface of the bark linked previously with Fusarium infection is particularly clear. It was suggested (Godwin 1936) that the widespread death of Frangula would lead to its replacement by Rhamnus catharticus, but this has not happened.

It is not certain, however, that the fungi are the prime cause of the dieback; two other factors may be involved. First, trees of various species have died in many parts of the Fen in recent years; high water levels can be definitely blamed in some areas and Frangula may be similarly affected. Secondly, virtually the entire Frangula population of the Fen was coppiced during the 1939-45 War to provide charcoal for gunpowder, and regeneration was very vigorous from the cut bases (W.P. Barnes). The above-ground parts of most of the present population are therefore of approximately the same age and may be reaching the end of their natural life. However, Frangula has also died on Wicken Poors' Fen, where the plants were much younger. Older plants appear to be attacked and die first (T.J. Bennett).

The death of Frangula has had important effects on its associated species. While there has not been time for the appearance of new willow bushes, the death of the buckthorn has thrown them into prominence and made it clear how abundant they are. The understorey of herbs, formerly rather sparse, is now very much more vigorous; this has probably contributed to the decline of calcifuge mosses, which were widespread in the 1970s.

By 1990 the disease appears largely to have run its course. Plenty of seed parents remain at the edge of the fen, and Frangula regeneration is widespread and the species remains the most vigorous colonizer of sedge and litter fields. There is evidence of Rhamnus catharticus plants also having been killed (T.J. Bennett).

Carr clearance

Trials were carried out in the 1960s by Dr N.W. Moore and colleagues from Monks Wood Experimental Station to determine the efficacy and safety of using herbicides for stump treatment. The treatment used was found to have no undesirable side effects, but, at Wicken, manual clearance proved more effective because stumps had to be cleared anyway to allow mowing. The experiments, though not applicable at Wicken, provided results which have been successfully applied elsewhere.

Clearance is done mainly by volunteer labour which is most often available in the summer between July and September. However, the best time for clearance is November- December, when the herbaceous vegetation has died down and the ground is drier, but when volunteers are not often available. Later than this, the fen is usually too wet.

The herbaceous vegetation is cleared from round the bush bases, which are then grubbed out with spades and axes. The waste is built into stick piles which are burned at a suitable time when they are dry and the ground is wet. After clearance, the ground surface tends to sink, and hollows disappear fairly quickly. The acquisition of the Glencoe and its winch in early 1990 opened up possibilities for much more extensive clearance by Fen staff.

The carr is 'faced-up' where it borders on open fields and paths to obtain a fairly straight or gently curved edge which can be maintained with a tractor. The vertical edge so produced is, however, a less favourable habitat for insects than a broad sloping boundary. This problem is partly solved by the increased amount of herbaceous vegetation now growing amongst the carr.

Encroachment should not, however, be allowed onto sedge fields, and bush fringe development should also not be allowed in sites where there is enough sedge to raise hopes of ultimate development of sedge fields.

Future management

There is no definite plan for the total area of carr that should ultimately by achieved, except that it is acknowledged that the extent of clearance must be constrained by the manpower available to maintain the cleared areas. Suggestions as to which areas should next be cleared are made in Section A3 on the management of the Sedge Fen. The priorities would seem to be:


1. to complete the Parish Strip (subject to agreement and 
   prior delimitation);
2. the western end of Cpt 13 towards Sedge Fen Drove;
3. possibly also the areas adjacent to the existing sedge field
   in 02, 03 and 05 (subject to surveys of their sedge content).
4. to develop a management strategy that produces a mosaic of
   uneven-aged stands of carr.

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Woodland is often assumed to be the climax state of the hydrosere occurring at Wicken, and in a few places there are signs that this final stage may be being reached. Near the Brickpits there are oak and ash trees, some quite old. On St Edmund's Fen there was a substantial grove of ash trees (in 1990 these are largely moribund), and scattered trees, mostly ash, occur on the northern side of Verrall's Fen.

Some of the trees in all these areas are dying. Deaths on Verrall's Fen can definitely be attributed to the high water levels caused by the opening of New Dyke, and those on St Edmund's Fen to flooding caused by the new earth bank outside the Fen (see section on St Edmund's Fen for details). There is no clear evidence of raised water levels in the Brickpits area (although the dam by the William Thorpe Building could possibly be implicated), but the springs of 1982 and other recent years were wet, and it is possible that the problem is the same here. Isolated trees and shrubs have also died in other parts of the fen at this time. This may reflect a national trend, especially among Ash; a survey of the health of trees in the British countryside is being carried out by English Nature and the Forestry Commission.

Trees have been planted in various places on the Fen in the past. Birches and alders were planted at the beginning of this century at the western end of Sedge Fen Drove. Birch spread between 1970 and 1980 but may now be in decline or spreading less. This period of spread coincided with the maximum development of surface acidity as shown by records of calcifuge mosses. Major spread of birch is undesirable and should be monitored; no control has been found necessary recently, and, indeed, some regeneration is needed to replace the older trees, many of which are now dying, probably of old age. The role of these trees in the landscape should be considered as part of a management strategy for carr and trees on the Fen.

Alder has long been held not to regenerate at Wicken for reasons which are obscure; the seedlings fail to survive. However, the present Head Warden reports that some regeneration is occurring, most obviously in the area of the birch glade at the far end of Sedge Fen Drove, where many of the more mature birch have died.

There are the planted willows (Salix pentandra) to the north of the eastern end of Sedge Fen Drove. These are all male and do not regenerate from seed although cuttings, and branches that touch the ground, root readily. There are, however, provisional records, which need checking, of hybrid saplings (on Record Cards in Archives). The Salix pentandra are becoming decrepit and, although introduced, should be conserved, as they include the individuals with the 1st, 2nd and 4th largest girths in the country.

Finally there are willows, mostly Salix alba, in many places at the edge of the Fen. Some of these are large. There are also various trees in the middle section of Little Breed Fen, including elms, which are mostly dead, and various apple and plum trees which are relics from the long-demolished brickmakers' cottage gardens.

Management


Dead trees provide a valuable habitat for insects and for birds and should be left standing unless they are an immediate threat to the visiting public. The safety of trees on the property is regularly monitored in accordance with NT policy on all its properties. A number of willows around the education field and some oaks along the boardwalk have been pollarded or felled for safety reasons in 1990-91.

There is a good case for pollarding some of the large Salix alba on and around the Fen. This is a traditional method of maintaining the vigour of the trees while taking a useful crop from them; old pollards are also a valuable wildlife habitat. This has been done around the Education area in 1990 and the same treatment has been applied to some of the Salix pentandra trees which have responded very well. There is evidence from work at Hatfield Forest that large branches should be removed in rotation from old trees that have not been pollarded for many years, rather than removing all at once; trials are recommended. Priority should be given to any trees which have been pollarded in the past.

The planting of trees is not generally needed as regeneration of most species is good. Exceptions arise where a screen is needed quickly, as may be the case in the future on the Charles Raven Reserve. Already some willows have been planted close to the Mere Hide using local stock.

In 1989, Cpt.68, an arable field on clay last cultivated in 1987, was planted with a mix of native deciduous species. The planting was planned to provide a sinuous outline and a number of rides and glades. The field is not part of the main Fen.

Disposal of cleared wood


Dead wood provides a valuable habitat for many insects, and at least some of the timber cleared during normal operations on the fen should be stacked and allowed to rot, preferably in the shade, but with some in full sunlight (to encourage aculeate Hymenoptera). In general, it is the larger timber which is best treated in this way.

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The system of dykes at Wicken is shown in Figure 12 (Section A4.2.6). Apart from Drainers' Dyke, the dykes appear to have been dug mainly as boundary markers. In the past a distinction has been drawn between 'major ditches' and 'internal ditches'. The former included Drainers', Malcarse, Cross, New, Howe's,and Spinney Bank Dyke; the latter, various small internal dykes, none of them open at the time but some now opened. Wicken Lode and Monks' Lode are maintained and controlled by the National Rivers Authority in consultation with English Nature and the National Trust. The dykes on Adventurers' Fen are considered separately.

Management Techniques


Three different techniques are used:
1. Brinking

The marginal vegetation, both in the water's edge and on the slope of the bank, is cut to prevent the water surface from becoming heavily shaded and to give a view of the water. Autumn drove clearance will also remove bankside vegetation where droves run alongside water-bodies.
2. Roding

Formerly, the emergent vegetation was cut in conjunction with the taking of a reed harvest from the ditches. The practice continued as part of ditch management: a first cut removed the reed; a subsequent cut, below water level, removed the submerged parts. Roding is an inefficient method of keeping down reed growth in ditches and is damaging to the reed fauna. It has been largely discontinued at Wicken Fen, in line with English Nature policy. It may be continued on Wicken Lode, where a reed-free stretch of water is desirable for its visual effect. Winter cutting in the Brickpits may also be desirable at times.
3. Slubbing-out

Accumulated sediment, organic and inorganic, is removed mechanically from the bottom of the ditch. It is carried out about every four to twelve years depending on the rate of accumulation. Timing: the drier winter period (Nov-Jan).

The slope of the bank (the 'batter') also influences the communities which develop; alteration of the batter of the existing Wicken dykes would be a complex operation and is not practicable at the present time. However, a sloping batter on one side can be created when re-excavating former ditches; this has been done on the eastern side of North Dyke (1991) and its effects on the recolonising flora and fauna is being monitored.

Spoil is generally disposed of on one bank, whichever least interferes with public access, and levelled before it is colonised by vegetation.

Recent history of the Dykes

1. Drainers' Dyke (75)

Apparently passable dry-shod until cleared out in 1962. Slubbed-out in 1979. Reasonably clear in 1985 but with some reed growth. Northern end slubbed out in 1989. Alternate 55m stretches of the entire length were due to be slubbed in 1991 (Section A4.2.6), but this has been delayed for one year.

2. Malcarse Drain (71)


No documented history. In 1985, fairly densely filled with reed and burr-reed (Sparganium). Completely slubbed-out from southern side in late 1991.

3. Cross Dyke (73)


No documented history. In 1985, densely filled with reed, burr-reed and water-lilies. Roded autumn 1985. Slubbed out in 1989 and again, in alternate 55m sections in late 1991. At the Drainers' Dyke end, the dyke should be stopped by an earth dam, maintaining a controllable culvert connection with Drainers' (1993).

4. New Dyke (70)


No documented history until 1982 when, after clearance of the line of the dyke from trees and shrubs, re-opening started at the Wicken Lode end. It soon appeared that the area at the north end of the dyke was low-lying and water began to flow in from Wicken Lode. Operations were suspended and the dyke blocked with a wooden dam. A second dam was added in 1985. After the restoration of Howe's Bank in 1987, these dams became redundant and they were removed in 1991, prior to slubbing out two 65m sections (half the total length).

5. North Dyke (72)


No documented history. The line of the dyke has been completely cleared of woody vegetation in the mid 1980s. It existed till late 1991 only as a depression, with the margin on each side being treated as level 2 droves. It was then completely redug, with a sloping batter on the east side. The resulting spoil has been left unlevelled.

6. Howe's Dyke (87a)


This was completely dug out 1937 and 1949. By 1985, most of it was passable dry-shod, at least during the summer. The opening of New Dyke showed Howe's Bank to be very weak. In 1987-88 the ditch was re-excavated further into the Fen and the additional spoil used to build up the bank. At the same time a
4 m-deep trench was excavated in the middle of the bank and a polythene sheet inserted before back-filling. The bank is now waterproof, and the ditch cannot be crossed. The bank has been officially adopted by the NRA as the north bank of Wicken Lode.

7. Spinney Bank Dyke (87b-d)


It appears that this was cleared in 1952. By 1985 most of it was very overgrown and passable dry-shod for most of the year. In 1988-89 it was treated in the same way as Howes Bank, with polythene sheeting being inserted over much of its length. The ditch is now impassable on foot. It was slubbed out again from the north end to the pumping station in November 1991.

8. Gardiner's Dyke (91a-d)


This name is given to the dyke excavated in 1980 along the line of a pre-existing dyke beside Gardiner's Drove. The spoil was deposited on the northern side and levelled along some of its length.

At the western end there is a connection to Drainers' Dyke which was opened in 1990. However, permanent connection to Drainers Dyke should await studies of the latter's nutrient content, and should be formalised by the construction of a board dam, or penstock valve, possibly with a buffer pool in which barley straw bales could be placed to absorb excess nutrients. Water can be pumped into the eastern end from the windpump ditch, but this should be reserved for times of very low water levels when the ditch flora and fauna are in danger of desiccation.

The ditch is effectively divided into lengths by droves. Alternate sections between the droves were roded until 1985; since then, the southern margins of the various sections have been brinked on a rolling biennial programme. The sections are botanically distinct, some sections having much Fen Pondweed (Potamogeton coloratus) and stonewort (Chara spp.), and Great Spearwort (Ranunculus lingua) was prominent in some parts in 1991 and 1992. The rare water beetle Hydraena palustris was found in section 4 in 1992; as a result, section 4 will not be slubbed in 1992/3, but may be inserted into the rotation later.

9. Thomson's Dyke (95)


This is another recently-dug dyke (1980), on the line of an older one. It is lightly overgrown with reed, but is very much overhung with brambles growing on the spoil bank to the south.

10. Windpump Dyke (78d)


This dyke leads from Wicken Lode to the Brickpits. It was slubbed out in 1983, and roded from 1984. It contains a little reed and much submerged aquatic vegetation. It has been managed since 1985 as two separate sections, brinking alternate sections on a biennial basis, to preserve dragonfly populations. To be slubbed in rotation from 1993. A dam will be placed across the ditch just beyond the windpump, to ensure that any water drawn from the ditch into Gardiner's comes from the direction of the Lode and not from the Brickpits. A dam protects the brickpit 78f from any water entering the Fen from the north (see below).

11. Sedge Fen Drove - Spinney Bank connecting dyke (78g)


This small dyke was dug out using Fen machinery in 1983 and roded in 1985. After the redigging of Spinney Bank Ditch, there is no longer any connection. This is a good thing because there is a potential connection between Spinney Bank ditch and the Spinney Abbey farm slurry pits, which may have led to pollution in the past. Alternate lengths of both banks are roded on a biennial basis.

12. Sedge Fen Drove ditches (90a and 90b)


These ditches are virtually dry, but are wettest at the east end. Here 90a has Ranunculus lingua; the southern ditch 90b has a distinctive 'old ditch' fauna.

Why actively manage ditches?

1. There may be, as in the case of Drainers' Dyke, a drainage

obligation.
2. Open waters provide habitat for certain elements of the Fen

flora and fauna.
3. Pure stands of reed (Phragmites) are relatively poor in

invertebrate species.
4. Regular clearance maintains the early stages of the hydrosere

for demonstration purposes.
5. Reopening of some dry ditches may release from dormancy the

seeds and other resting stages of fenland plants which were

formerly abundant but are now rare.
6. Open waterways are part of the traditional fenland scene.

Historically the ditches appear to have been kept free of

vegetation by use.
7. Ditches allow some control of visitor access and movement.
8. Water-filled ditches provide sources of water for fire

fighting and act as fire-breaks.
9. Open ditches may be used to conduct water into the Fen in dry

conditions.
10. Ditches maintain a stable high water table in their near

vicinity.
11. Open waters are visually attractive to visitors.

These reasons should, however, be tempered by the following considerations:

1. Dykes may drain the central parts of the Fen, which are best

kept wet during the dry months of the year, if inflow and

outflow are not controlled by sluices or dams.
2. Wholesale clearance would destroy the 'old ditch' habitats of

later stages of the hydrosere and prevent them from

developing. Some rare species (e.g. the beetle Hydraena

palustris) are associated with heavily overgrown ditches.
3. Clearance of reed destroys a proportion of nesting habitat of

some bird species (e.g. Reed Warbler), if the timing is

wrong.
4. Clearance of water-weed beds on a large scale may destroy

entire populations of aquatic invertebrates.
5. Ditches can make access to some parts of the fen difficult

for machinery and necessitate the construction and

maintenance of strong bridges or solid earth banks for

access.

(See also H.J. Harvey's three papers to the Committee of 12/77, 9/78 & 12/78).

In 1992, a new management plan for ditches and dykes was initiated which should allow the advantages to be achieved while minimising the disadvantages. This plan aims to:

1. Re-open some of the former ditches, now dry.
2. Leave untouched some other old ditches pending a study of


their fauna.
3. To begin regular cycles of management for the majority of

ditches on the Fen.
4. Manage these ditches in short stretches on a rotational

basis.
5. Match the length of the cycle for an individual ditch not

only to the rate of accumulation of material, but also to the

conservation aims for that ditch.
6. Allow some cleared ditches to undergo natural succession.

The result of 3 - 6 should be the maintenance of habitat of

all ages, both within individual ditches and over the Fen as

a whole. The cycles of management are described in Section

A4.2.6.

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Definitions
'Peat'    -    the material in the ground;
'Turf'    -    peat once extracted for use; plural = 'Turf';
'Top'     -    the poor-quality black top soil;
'Moor'    -    the peat suitable for digging turf;
'Turf     -    the dug moor.

Turf-digging has been an important activity at Wicken in the past, but it ceased in the early part of this century.
Fig. 16 (from Rowell; 1983) shows the distribution of past diggings on Wicken Sedge Fen, based on ground survey and on patterns visible in aerial photographs. Much of the digging appears to have been relatively small-scale and occurred in the 18th and early 19th centuries. Large-scale commercial digging took place on Burwell, Reach and Swaffham Fens (of which only North Adventurers' Fen is part of Wicken Fen) from the 18th century up to 1939. Large-scale digging on North Adventurers' Fen had largely ceased by the 1920s.

Five episodes of turf-digging have occurred on Sedge Fen and Verrall's Fen this century:

1. in the late 1930s, Barnes' Mere was created in Cpt. 05, to  
   encourage wildlife, and not primarily as a turf-digging site; 
2. in the 1950s, diggings were made in Cpt 19 (these were found 
   to contain the rare stonewort Nitella tenuissima in 1957). 
3. in the 1970s, some scattered non-traditional diggings were 
   made in Cpt 19, just outside the William Thorpe Building, to 
   supply peat to the Cambridge Botanic Garden for creation of 
   the fen display. These diggings were filled in during 1992. 
4. In 1980, similar diggings were made in Cpts. 12 and 18 for 
   colonisation studies. These are now completely overgrown with 
   carr;
5. in 1989, a trial, using traditional methods, was carried out 
   in Cpt 18 at the junction of Thomson's Drove and Gardiner's 
   Drove and adjacent to the boardwalk. A programme of further 
   digging is underway in this area (see A4.7).

Turf-digging should continue for historical reasons, as part of the Fen's Education programme. A booklet by G. Lohoar and S. Ballard 'Turf-digging at Wicken Fen' (1992) is available for sale at the Fen, the new diggings are included in the Boardwalk Trail, and have an explanatory notice alongside. It is hoped to carry out digging in June and July for the benefit of visitors. It is also hoped that the product will be used at the Fen in a traditional manner: either being burned on the hearth in the Fen Cottage, or being used to fuel the bread oven, and so become part of the social history display at the Cottage. Cut turf should be stacked on the Fen to dry and may be stored in the shed of the Cottage.

Turf-digging also creates additional habitat types on the Fen. The uneven surface produced by alternating pits and top spoil heaps creates variation in soil and water pH, due to the local oxidation of peat when exposed to the air and drained. These conditions are favoured by certain flora and fauna. Former peat cuttings supported some plant species that no longer occur at Wicken; it is hoped that these may reappear from buried seed or spores. However, the acid-loving dragonflies may have to be reintroduced, if conditions allow, in the future (see Section A6.10).

Turf-digging should be continue only on a small scale and by traditional methods; it is unlikely to prove economic, even if the produce was considered suitable for sale. Any future digging should be carried out for the reasons described above.
It should occur only in areas where digging has already occurred and new diggings should align with old pits, in order to preserve the remaining undisturbed peat profiles.

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The burning of large tracts of standing vegetation is a standard management tool in certain vegetation types but there is no tradition of its use at Wicken. Burning has the advantage of rapidly removing large amounts of material but has the associated risks of damaging certain species in the community, and of unintentional spread to communities which should not, for biological or management reasons, be burnt. Extensive fires have generally been considered a hazard on the Sedge Fen, although burning has been proposed from time to time as a management tool. It has been used to assist in localised bush clearance, normally of very small areas, since the war.

Major accidental fires occurred in 1929 and 1952. In April 1980, the standing litter in Cpt 05 was burned, but the fire got out of control and spread across Cross Dyke to Cpt 03. Much of the northern third of 05 was burnt-out, many bushed were killed and the sedge crop lost. In 1989, a smouldering litter heap on the western edge of Cpt 03 flared up after hours, and in 1991, a similar incident led to a major fire in Cpt 04.

The deliberate burning of standing vegetation is likely to be a rare event, and should only be considered for specific areas with careful precautions and when no other management is appropriate. It should take place only in the winter or early spring. The natural state of affairs in a fen is for much of the litter produced each year to accumulate as peat. Burning halts this process and also leads to the release of nutrients that would otherwise remain bound in the peat.

Burning is the current management policy for the Conservation Reed Bed; one third of this is burned every other year (Section A4.2.5). It is possible that more extensive burning of reeds round the Mere and elsewhere may become necessary for economic control of bush invasion.

Stick and rubbish piles have been burned on the Sedge Fen for at least 20 years, and this will continue. Where possible, specific sites should be set aside for such fires, because of the different vegetation which develops on fire sites. Spring-cut litter is probably best burned in small heaps on the field itself; if left to dry out for a few days before burning, the ash produced, and therefore the nutrients released, is very slight. There is little risk in burning at this time of year, as the surrounding ground is very damp and the vegetation lush.

Straw-burning legislation comes into force in 1993. It is specific in banning the burning of agricultural by-products, such as cereal straw, and will not prevent the burning of litter heaps or the residue from carr clearance, nor the burning-off of reed fields.

A detailed Fire Plan, to be implemented in case of emergency, has been drawn up and circulated to staff; this was amended, in the light of experience during the 1991 fire, by the Deputy Head Warden. Fire-beaters have been sited at strategic points on the Fen and a fire tender has been developed for the Glencoe. Some further training for staff would be beneficial.

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The National Trust's Nature Conservation Advisor should be consulted in the case of reintroductions. Guidelines have been issued as follows:

Key criteria for reintroduction

i    evidence of the former natural occurrence of the species;
ii   species is known to have been lost from the site;
iii  an understanding of the reasons for the loss;
iv   a low chance of natural recolonisation;
v    the presence of a sufficient area of suitable habitat;
vi   a source of individuals for reintroduction of appropriate                                                                                                                                                                        genetic form;
vii  a population from which individuals may be taken for
     reintroduction without risk to the source population.

Key recommendations for implementing predator control

i  there must be a clear and fully justified reason for the  
   proposed control; there must be clear evidence that the 
   target species is having an undesirable impact;
ii the native and local status of the target species must be  
   considered;
iii alternative ways of solving the problem must be evaluated;
iv the proposed method of control must be humane and acceptable   
   in respect of the Trust's other obligations;
v  it must be shown that control measures will reduce the size 
   of the target population;
vi the control programme must also be shown to reduce the damage 
   or nuisance attributed to the target species (reduction of 
   the target population alone is not an adequate criterion of  
   success);
vii the results of any cull should be carefully monitored.