Fens and marshes - lowland

Context

Fens and marshes are characterised by a variety of vegetation types that are found on groundwater-fed (minerotrophic), peat, peaty soils, or mineral soils.  These may be permanently, seasonally or periodically waterlogged.  Fens are peatlands which receive water and nutrients from groundwater and surface run-off, as well as from rainfall.  Flushes are associated with lateral water movement, and springs with localised upwelling of water.  Marsh is a general term usually used to imply waterlogged soil; it is used more specifically here to refer to fen meadows and rush-pasture communities on mineral soils and shallow peats.  Swamps are characterised by tall emergent vegetation.  Reedbeds (i.e. swamps dominated by stands of common reed Phragmites australis) are also included in this type.  Lowland is defined as below the level of agricultural enclosure.  The altitude at which this occurs varies across the UK, typically becoming higher as one travels South. 
 
Purple moor grass and rush pastures occur on poorly drained, usually acidic soils in lowland areas.  Their vegetation, which has a distinct character, consists of various species-rich types of fen meadow and rush pasture.  Purple moor-grass Molinia caerulea, and rushes, especially sharp-flowered rush Juncus acutiflorus, are usually abundant.  Just as the best examples of lowland heath contain a wide range of plant communities, so the same is true for this habitat: the characteristic plant communities often occur in a mosaic with one another, together with patches of wet heath, dry grassland, swamp and scrub.  Purple moor-grass and rush pastures are highly susceptible to agricultural modification and reclamation throughout their range.  In Devon and Cornwall, where the habitat is known as Culm grassland, only 8% of that present in 1900 remains, with 62% of sites and 48% of the total area being lost between 1984 and 1991.  Fragmentation and isolation of stands have been common.
 
This habitat type does not include neutral grasslands on floodplains and grazing marshes which are included in the Neutral grassland reporting category, nor ombrotrophic mires (blanket, raised and intermediate bogs) as these are included in the Blanket bogs  and Lowland raised bogs reporting categories.  It also does not include areas of carr (fen woodland dominated by species such as willow Salix spp., alder Alnus glutinosa or birch Betula spp.) as these are covered in the Broadleaved and mixed woodland reporting category.
 
SSSIs can be notified if they qualify under criteria outlined in Chapter 7 Fens of the Guidelines for Selection of Biological SSSIs.  In Northern Ireland, ASSIs are selected on a very similar basis – the Guidelines for the Selection of Biological ASSIs in Northern Ireland is an addendum to the SSSI guidelines rather than an alternative. 
 

Summary statistics

  SAC A/SSSI Total
Favourable condition 18% 41% 38%
Main monitoring coverage E, S, W, NI E, S, NI  
Reported assessments 80 709 789
Completeness of assessments 85% unknown  
Distribution of features     UK
 

Number of assessments reported by country and site type

Country SAC SSSI/ASSI
England 46 446
Scotland 10 222
Wales 19 0
Northern Ireland 5 41
United Kingdom 80 709
 

Natura features

List of Natura 2000 interest features within this reporting category

Interest feature name  
Formal name Informal name No. of assessments reported Total no. of features % assessed
Molinia meadows on calcareous, peaty or clayey-silt-laden soils (Molinion caeruleae) Purple moor-grass meadows 24 30 80%
Alkaline fens Calcium-rich springwater-fed fens 16 19 84%
Calcareous fens with Cladium mariscus and species of the Caricion davallianae Calcium-rich fen dominated by great fen sedge (saw sedge) 11 12 92%
Depressions on peat substrates of the Rhynchosporion Depressions on peat substrates 6 6 100%
Petrifying springs with tufa formation (Cratoneurion) Hard-water springs depositing lime 1 2 50%
Transition mires and quaking bogs Very wet mires often identified by an unstable 'quaking' surface 22 25 88%
 
Natura 2000 comprises Special Protection Areas (under the Birds Directive) and Special Areas for Conservation (under the Habitats and Species Directive). The list presented here includes all of the qualifying interest features under these Directives, and shows the proportion of these features for which a condition assessment has been made.
 

SSSI features

List of SSSI and ASSI interest features in this reporting category

Interest feature name  
Formal name Informal name No. of assessments reported
Alkaline fens Calcium-rich springwater-fed fens 2
Basin fen Basin fen 46
Basin fen-schwingmoor type Basin fen-schwingmoor type 6
Bogs Bogs 39
Calcarous fen Cladium mariscus and species of the Caricion 1
Fen meadow Fen meadow 29
Fen woodland Fen woodland 2
Fen, marsh and swamp Fen, marsh and swamp 407
Fens Calcarous fens 1
Fens Alkaline fens 2
Fens Fens 14
Fens Calcareous fens with Cladium mariscus and species of the Caricion davallianae 2
Flood-plain fen Flood-plain fen 17
Hydromorphological mire range Hydromorphological mire range 11
Laggs of raised bog Laggs of raised bog 2
Lowland Fen Alkaline Fen 1
Lowland fen Lowland fen 4
Open water transition fen Open water transition fen 49
Purple moor-grass and rush pastures Purple moor-grass and rush pastures 12
Reed beds and swamps Reed beds and swamps 2
Spring fen Spring fen 1
Springs (including flushes) Springs (including flushes) 18
Transition grassland Transition grassland 5
Transition ombrotrophic mire Transition ombrotrophic mire 1
Transition open fen Transition open fen 4
Transition saltmarsh Transition saltmarsh 3
Transition sand dune Transition sand dune 1
Valley fen Valley fen 27
 
This list has not been fully standardised at a UK level yet. It is intended to show the principal constituent "feature types" for this reporting category.
 

Maps - distribution

UK distibution of reported interest features

Distribution of reported interest features.

Map showing the locations of the 10km squares in which at least one condition assessment has been reported. It does not show features that have not yet been assessed.

 

Maps - Natura

Distribution of SAC features showing assessments of favourability Condition of SAC features, with those currently reported as unfavourable-recovering shown as favourable
Current condition of SAC features
Distribution of SAC features showing assessments of favourability (where unfavourable-recovering is counted as unfavourable).
Condition of SAC features, with those currently reported as unfavourable-recovering shown as favourable
The implication of the unfavourable-recovering condition assessments is that at some point in the future these features should become favourable. This map shows the effect of that recovery by counting the favourable and unfavourable-recovering assessments together.

 

IMPORTANT NOTE: we do not have information on the timescale of the predicted recovery, which may be influenced by many past, natural and human related factors. A sustained sympathetic management regime is more likely to result in favourable condition being attained.

Key: Proportion of assessed features on 10km squares that are favourable:

Natura map legend - Key: proportion of assessed features on 10km squares that are favourable

 

Details of how these maps were produced

 

Maps - SSSI

Current condition of SSSI/ASSI features Condition of SSSI/ASSI features, with those currently reported as unfavourable-recovering shown as favourable
Current condition of SSSI/ASSI features
Distribution of SSSI/ASSI features showing assessments of favourability (where unfavourable-recovering is counted as unfavourable).
Condition of SSSI/ASSI features, with those currently reported as unfavourable-recovering shown as favourable
The implication of the unfavourable-recovering condition assessments is that at some point in the future these features should become favourable. This map shows the effect of that recovery by counting the favourable and unfavourable-recovering assessments together.

 

IMPORTANT NOTE: we do not have information on the timescale of the predicted recovery, which may be influenced by many past, natural and human related factors. A sustained sympathetic management regime is more likely to result in favourable condition being attained.

Key: Proportion of assessed features on 10km squares that are favourable:

SSSI map legend - Proportion of assessed features on 10km squares that are favourable

 

Details of how these maps were produced

 

Condition summary

Reporting category condition summary on Natura 2000 sites and SSSI

This lists the 10 different condition assessments and presents a bar chart showing the number of features within the SSSI series and the Natura 2000 series (either SPA for bird features or SAC for features other than birds). Note that for Natura 2000 we are able to estimate the number of features that have not been assessed during the 6 year reporting period - we are unable to do this for SSSI/ASSI because we do not have an overall list of notified interest features for these designations.

 

NB favourable unclassified and unfavourable unclassified have been used in this first six year cycle to get around difficulties in identifying trends in condition as common standards monitoring is implemented. It is expected that these categories will not be used for subsequent assessments of a feature.

 

Condition assessment - Natura 2000 features

The number and proportion of assessments for Natura 2000 (SAC and SPA) interest features falling into each of the condition categories
The number and proportion of assessments for Natura 2000 (SAC and SPA) interest features falling into each of the condition categories. Note that the �unfavourable� category includes all reports of unfavourable condition except �unfavourable recovering� which is shown as a separate segment.
 

Condition assessment - SSSI features

The number and proportion of assessments for SSSI/ASSI interest features falling into each of the condition categories
The number and proportion of assessments for SSSI/ASSI interest features falling into each of the condition categories. Note that the �unfavourable� category includes all reports of unfavourable condition except �unfavourable recovering� which is shown as a separate segment.
 

Adverse activities

The number of interest features where an activity has been reported as being implicated in the "unfavourable" condition of a feature
The number of interest features where an activity has been reported as being implicated in the "unfavourable" condition of a feature. More than one adverse activity may be reported for each feature.
 

Management measures

The measures summary bar chart lists the management measures relevant to the reporting category
For each "measure" the chart shows the number of interest features where that measure has been taken on a site to improve or maintain the condition of an interest feature. More than one measure may be reported for each feature assessed.
 

Interpretation

 
Overall, 38% of lowland fen marsh and swamp features reported are in favourable condition.  This is about the average for terrestrial habitats, but below the average for all habitats or all features combined together.  41% of A/SSSI features and 18% of SAC features reported are in favourable condition.  21% of A/SSSI and 39% of SAC features reported are unfavourable-recovering. 
 
A sample of English fen, marsh and swamp sites was split into topographic types.  They showed that the category with the highest proportion in favourable condition was spring fen (40%) followed by water fringe fen (30%), then basin fen (29%), floodplain fen (27%), and valley fen (26%).  The more favourable condition of spring fen may reflect the higher quality of the groundwater on which they depend, as opposed to more nutrient-enriched surface water capable of entering the other categories.  There is also the implication in the comparison of these figures that fen condition in England is worse than elsewhere in the UK.
 
The main reasons for features not being in favourable condition are lack of remedial management, under-grazing, water management, invasive species, and water quality.  This may reflect a number of issues commonly encountered in relation to fens.  For example, it is natural for open fens to change spontaneously into wooded fens, and management, such as scrub clearance and grazing, is required to prevent this.  The management of surface and groundwater is clearly crucial to providing the surface:groundwater requirements of each type of fen, as are its constituents, for example basic ions such as calcium, its pH, and quantity of the plant nutrients nitrogen and phosphorus.
 
Air pollution is not listed as a cause of unfavourable condition in fens.  It is likely that surveyors would attribute its effects to other causes, such as drainage.  Critical loads of sulphur are still being exceeded for some types of wetland, and are predicted to do so at least until 2010.  Dry deposition of ammonia is still very high in most parts of England, Wales and Northern Ireland.  Apart from the inhibitory effect of bisulphite on some Sphagnum moss species, deposition of nitrogen encourages rank competitors such as the purple moor-grass Molinia caerulea.  It should be borne in mind that several fen types bear similar vegetation to lowland raised bog and blanket mire, so that observations appropriate to them in respect of air quality would also apply.
 

Purple moor-grass and rush pastures

Under a third of purple moor-grass and rush pasture features reported are in favourable condition (30% of A/SSSI, and 4% of SAC features).  There is some variation between countries, with Scottish SSSIs (62% favourable) in rather better condition than those in Northern Ireland (42% favourable) or England (22% favourable). 
 
The unfavourable-recovering category accounts for a significant proportion of assessments reported (32% of A/SSSI features, 56% of SACs), particularly in England.  Under-management is the main cause of unfavourable condition, specifically under-grazing and abandonment.  Scrub encroachment is the common result, sometimes together with invasive species problems. 
 
Purple moor-grass and rush pastures are also affected by overgrazing and nutrient enrichment.  Underlying causes of under-management are still thought to be largely due to current agricultural economics and policies, exacerbated by e.g. BSE and Foot & Mouth disease, leading to a reluctance to keep stock (large stock in particular) on pasture perceived to have little nutritional value.  In addition, the extent to which atmospheric nutrient deposition is affecting the composition of grassland sites is a largely unknown quantity.