Annex 3 Biodiversity attributes, peat extraction and restoration 1. Diversity as surface patterning and natural range in the UK

1.1. The degree of surface patterning follows a northwest-southeast axis in the UK, with the best-developed hummocks, lawns and pools in the northwest. Protecting the full range of variation is achieved by designating a chosen suite of sites within an Area of Search (AOS), usually a county or other administrative region. It is important to take account of the impact of peat extraction on the UK‟s bog resource as a whole, as well as on individual sites (HAP target 3).

1.2. Recent annexes prepared to accompany the revised LRB HAP have divided

England‟s bogs into a number of priority areas such as the Solway Upper Catchment Mosses1. Extracts from these maps are reproduced within Annexes 4 and 5. They are drawn up in response to the need to have a geographical framework to ensure the full range of examples is protected. Local biodiversity action plans evaluate bogs in the areas they cover and set targets (HAP Target 3).

2. Raised bog structure – natural and degraded

2.1. Emphasis is often placed on the hydrological functionality (see below) as critical to raised bog biodiversity. The science behind this is still developing, but there are some key benchmarks. The way in which the layers of peat build up to form a gently sloping mound with the ability to retain water is particularly important. The commonly-used conceptual model for intact active raised bog (Figure A3.1) is taken from Tansley (1939).

Figure A3.1 Transverse section through a conceptualised raised bog Based on Tansley (1939) Note: the mineral base is variable and may include permeable (sand) and impermeable (clay) materials. The vertical scale is exaggerated compared to the horizontal scale, making slopes appear steeper.

2.2. It is a saturated mound of peat that has formed naturally by the gradual

accumulation of partially decomposed plants. In order to grow, the peat must remain saturated to within about 30cm of its upper surface2. It gives rise to two functional layers in the peat. The large, saturated core is the catotelm; the outer permeable

1 Faber Maunsell (2006) – Lowland Raised Bog Wetland Habitat Action Plan Annexes for English Nature.

2 This figure is not definitive, and estimates of what the saturated water level should be relative to the peat surface

vary.

skin, composed of living and recently dead vegetation is the acrotelm. Rainfall drains, normally very slowly, to the outer margin of the bog through the acrotelm. These attributes are the building-blocks on which conceptual models are often developed for individual sites and determine the types of management works required in achieving HAP targets 1 and 2.

2.3. In practice, very few lowland raised bogs conform to the conceptual model of

Figure 2.1, either because of the unique circumstances in which they have developed in the landscape, or because of the way they have been changed by centuries of drainage and tillage around their edges and by peat cutting into their centres. Whereas the natural lagg3 edge of the bog would follow contours or represent the natural limit of its spread, they may now follow fence lines, which may or may not coincide with the original extent of the peat deposit. This can be seen in Figure A3.2, in which the site outlines within Chat Moss do not follow the edge of the peat deposit.

Figure A3.2 Chat Moss (Manchester) peat deposit, now converted to agriculture, and surviving peatland sites. Adapted from EAU, 1992.

3 The peat bog meets mineral soil around its outer edge and this is known as the lagg.

Astley & Bedford Mosses SSSI and part of a larger SAC. Note that the site boundary follows land ownerships and not the original peat boundary. This is much larger and includes other sites, such as Little Woolden Moss, Astley Moss East and Twelve Yards Road (see Annex 4).

3. Condition classes

3.1. A common set of condition categories4 that arise on raised bogs as a consequence of drainage, peat removal and afforestation (Lindsay & Immirzi, 1996; Figure A3.3) has been based on the conceptual model of Figure A3.1. These „condition classes‟ are useful in evaluating the positive and negative impacts of peat extraction on raised bog (below) because they are based on bog hydrology and have been used widely to underpin Government guidance, such as the Mineral Planning Guidance 13: Guidance for peat provision in England (MPG13) (DoE, 1995a).

Figure A3.3 Lowland raised bog condition classes. From: Lindsay & Immirzi, 1996.

4 Precise definition and categorisation are hard to find in studies of raised bogs. No agreed parallels have been

drawn between these condition categories and other ways of describing bogs, or with biodiversity characteristics. For example, in expressing the extent of Natura 2000 Annex 1 categories JNCC advises that he Lowland Raised Bog Inventory condition classes cannot be converted precisely to Annex I categories, and so they do not equate to the total GB resource of active raised bog.

Primary bogs have a complete sequence of peat still in place, there has been no extraction. If undamaged, peat is still forming and the bog is termed ‘active’. Types of damage range from preparative drainage to tree planting or natural scrubbing up

At least some peat has been removed from secondary bogs. If the right conditions survive and bog plants can grow and form peat, it is termed ‘active’.

Damaged bogs with no known prospects for regeneration are

termed ‘archaic’.

3.2. A primary natural bog (or part of a bog) is clearly of great biodiversity importance because, if in a hydrological steady state, it represents an intact functioning ecosystem with the expected species and structure. All primary bogs are of high archaeological and palaeo-environmental importance because they contain an uninterrupted sequence of deposits (pollen, macrofossils, testate amoebae, etc.) that can be used to build up a picture of the past. They are referred to in HAP Target 1.

3.3. In terms of floral and faunal biodiversity (habitat scale), conditions producing

contemporary peat formation (active bog) are more important than a continuous sequence of peat. Consequently, secondary revegetating bog is of great biodiversity importance, though its full potential may remain to be realised if re-vegetation is only at an early stage of development. Revegetating bog is likely to be the most common category on SSSIs and SACs in England for many years to come (HAP Target 2).

3.4. The types of damage (Classes 2–8) illustrated in Figure A3.3 for primary bog

mainly relate to forestry and drainage. The type (cause) of degradation also affects the ease of rehabilitation. For example, it is easier to clear scrub from a drained bog and block drains to rewet it than to clear a commercial stand of forestry and restore the remaining furrowed surface (Anderson, 2001) (HAP Target 3).

3.5. Archaic bog has few or no LRB attributes and its biodiversity importance lies in its

largely unexplored potential for restoration (HAP Target 3). This target emphasizes the need to achieve the full geographical range of LRB habitats and this can only be done if some of the archaic bogs are restored. One extreme example would be Amberley Wild Brooks (West Sussex; source: FenBase 6), now of nature conservation importance because of its grazing marsh vegetation; there are currently no lowland raised bogs in the south east of England.

3.6. The way in which archaic bog peat is managed may also affect the biodiversity on

nearby existing bogs. Many LRB sites designated as SSSI/SAC are surrounded by archaic peat (for example, Astley and Bedford Mosses SSSI/SAC in Greater Manchester (EAU, 1992; Figure A3.2); This archaic peat is likely to have been part of the same bog hydrological unit the past, and to some degree is still often thought by hydrologists to be in hydraulic connection through the peat layer with the remnant bog (see 4.6 of this annex, for example). Its biodiversity importance may be high: firstly to protect the bog it surrounds; and secondly to expand the area of raised bog or fen habitat able to develop into raised bog.

3.7. Conflicts may arise with the established biodiversity of other habitats, such as

coastal and floodplain grazing marsh. The archaic condition occurs (inter alia) when all or some of the peat has been removed and/or treatments have been applied to the surface to make it suitable for agriculture. In terms of restoration to bog, agricultural use will have caused considerable changes, such as adding plant nutrients to the surface layers of remaining peat and this would need to be stripped away before restoration to bog in the short term. Conditions similarly thought of as without any restoration prospects can arise from waste disposal and from forestry.

3.8. The restoration potential of archaic peatlands is complicated by the nature of the

remaining peat. The peat of many large archaic extents is of raised bog origin, with only the bottom few tens of centimetres of fen origin (e.g. Mersey Basin, Greater Manchester and Merseyside) and so potentially suitable for restoration. However, other areas, such as the Somerset peatlands, are largely fen peat. In the latter case, immediate creation of raised bog may be neither practical nor historically appropriate, but fen would be possible and acceptable (Blankenburg & Tonnis (Eds), 2004).

3.9. A lowland raised bog site may contain more than one condition category. A site is likely to be a remnant of a once larger peatland, now reduced in area by agricultural or other activities, and in height by drainage with or without peat extraction (Figure A3.2). Parts may still have the original surface, but will no longer be peat-forming; other parts of the same site may have had peat removed but, because the cutover surface has become or been made wet, is now peat-forming.

4. Lowland raised bog hydrology – the quantity and quality of water

4.1. This is particularly important in determining the thickness and type of peat needed for restoration because it determines the options for re-vegetation. These range from non-wetland through various types of fen to immediate raised bog, depending on the ability to control the water level, and to provide water of the required quality.

Water quantity

4.2. Raised bog arises from and is sustained by rainwater (or other atmospheric precipitation) being sufficiently well-supplied to wash out and replace the greater mineral ion and nutrient supply present in groundwater. It does this by accumulating peat so the surface becomes raised above the influence of the groundwater. Peat extraction lowers the surface closer to the groundwater and, in extreme cases, results in the surface being inundated by it.

4.3. In order for raised bog growth to be maintained, the water level within the bog

must not vary more than a few centimetres over the year, and remain close to the surface. This enables the conditions within the bog, from just beneath the surface downwards, to be permanently saturated and anaerobic with a very low throughput of water. Outside influences, such as drainage, result in lowered water levels and moving oxygenated water. Air is drawn in that oxidises the peat and allows greater flow of water through it. Low water levels can interrupt the peat-forming process as the dead plant matter decomposes more quickly in the dry oxic environment. The whole LRBs hydrological unit is important as peat extraction may occur on one part of a peatland and impact on other parts of the bog which are being managed for conservation. It is reflected in the UK‟s SSSI selection guidelines, in the drawing up of site boundaries (JNCC, 1994), where all land necessary to maintain the hydrological function should be included, even if it currently does not bear flora or fauna of special interest.

4.4. Peat deposits are stratified, and the properties of each stratum are determined

(inter alia) by the conditions under which the contributing plant species lived and died. Peat profiles often indicate that the environmental conditions have varied over time at one location. Layers of fen peat (indicative of higher nutrient water) can often be found lower down in the same peat profile as Sphagnum moss peat (which only grows in nutrient poor rain-fed conditions). Similarly, strata which were laid down when trees grew on the bog surface, perhaps in response to a temporarily drier climate, contain much wood. Each type of stratum differs in its ability to hold water or allow it to move. The strata are commonly described as black peat (highly decomposed5 and resistant to water movement) or white peat (slightly decomposed and porous), though actual examples often fall somewhere between these two extremes.

5 This refers to decomposition that occurred when the stratum was at the surface; it would have become very

much slower when incorporated into the saturated lower parts of the bog.

4.5. The ability of a raised bog to retain atmospheric water is determined by two major groups of factors. The first is structures, such as hummocks of Sphagnum moss, that slow down its flow over the surface, the second is the rate at which it can percolate through the peat, away from the surface (comparisons in Table A3.1). A surface from which the vegetation has been cleared has no structures to impede surface water flow, and drainage systems are provided to ensure it is rapid. Percolation through the peat is also speeded up by providing drains at regular intervals to intercept the water within the pores of the peat, enabling it to flow swiftly away from the bog.

4.6. The speed at which water is lost by surface flow and by percolation through the

peat is dependent on the difference in height between the bog surface and the lowest point in the drainage system. Methods exist for estimating the degree of damage arising from drainage, either on or next to the bog. That used by Bragg (1989) is based on the Groundwater Mound Theory first proposed by Ingram (1978). Another more recent generic approach was developed by Morgan-Jones (Capita Symonds, 2005a) to assist in the drawing up of SSSI boundaries to include all land necessary to protect the bog‟s hydrology (JNCC, 1994). It estimates the Hydrological Buffer Zone (HPZ) required around a peatland site to maintain it in a peat-forming state. Blankenburg & Tonnis (Eds; 2004) also provide a formula for calculating an HPZ to protect land around the rewetted peat bog from unwanted water.

Figure A3.4 The application of the HPZ determination to Bowness Common Source: Conservation Objectives for Bowness Common, Natural England, 2 February 2009

4.7. The Hydrological Protection Zone (HPZ) is important in assessing the effects of drainage around a lowland raised bog (see Figure A3.4), such as arising from peat

(numbered)

extraction. Although there is now no peat extraction on or around Bowness Common the Figure illustrates how the width of the HPZ varies with the sub-stratum. The northern edge of Bowness Common is close to the Solway Estuary, and the combination of porous gravels and peat requires a relatively wide HPZ. By contrast, the calculated HPZ is narrow along some lengths of the south side where the SSSI boundary coincides with the edge of the peat and the substratum is glacial till, a much less permeable material. It suggests that drainage activities even within about 200m of the restoration area may reduce the success of bog restoration.

4.8. The HPZ is an important consideration in achieving HAP Target T3 on “chosen

areas of archaic peat to ensure a sustainable hydrological regime for adjacent extant habitat”. Most lowland bog SSSI boundaries were drawn up before the HPZ calculation was developed and no evidence of a review of existing boundaries has been found.

Table A3.1 Hydraulic conductivity (k) of common soil constituents. Adapted from a table in Capita Symonds (2005a). Water quality

4.9. As described above, the bog flora arises in response to the low-nutrient environment sustained by atmospheric water. The removal of peat lowers the surface until peat from the fen that preceded the bog is exposed, and finally the sub-surface of clay, sand or rock that underlies the peat. This has the potential to make groundwater the predominant source, introducing mineral ions and plant nutrients that favour fen rather than raised bog. It means that immediate restoration of raised bog following peat extraction may not be possible, and that it can only occur after a period of fen growth. While each site is likely to present a unique set of circumstances, making accurate prediction of successful bog restoration less certain, a number of generalisations have been made.

4.10. A peat extraction industry standard for the depth of residual peat remaining at the

end of working a site of 0.5m has become established, although it is not supported by specific experimental evidence. It likely to represent the very minimum that should be required (see below and Dargie (2001)). If there is effectively no peat left on a site, restoration to LRB is likely to be much more difficult than if a suitable peat substrate remains. A very thin peat layer (less than 0.5m) will be likely to be breached in

2Hydraulic Conductivities are guidance

values only, based on soil texture, in metres per day.

places due to the imprecise nature of working peat with machines, and the natural variation in the topography of the underlying sediment.

4.11. The requirement for a continuous layer of peat as a precursor to restoration is

supported by a study of primary colonists such as cotton grasses and Sphagnum mosses in relation to residual peat depth and type on Thorne, Crowle & Goole Moors (Dargie, 2001). It showed that very thin or breached peat increased the probability that Soft rush Juncus effusus would form dense stand, rather than a raft of Sphagnum cuspidatum and/or Cotton grass Eriophorum angustifolium. An initial cover of mixed Cotton grasses, Ericaceous species with or without Sphagnum mosses was more likely on deeper, light-coloured peat. There is evidence that, even where Juncus effusus was a vigorous primary colonist, Sphagnum mosses are able to establish amongst rush tussocks after a few years. Extensive over-topping of rush tussocks with Sphagnum fallax and Sphagnum fimbriatum has occurred at Red Moss (Greater Manchester) (Meade, 2007), where, although on peat in excess of 2m, enrichment has occurred from the adjacent landfill site, also over deep peat.

4.12. The principle set out by Wheeler and Shaw (1995) and adopted by the

Government‟s minerals planning guidance (DoE, 1995a) is that a suitable depth of ombrotrophic (white) peat should be left to assist in site rehabilitation. As white peat normally overlays black peat it implies that the underlying black peat should also be left. No specific depth of either is advised, because sites differ in their stratigraphy and juxtaposition of white and black peat, and it is not always possible to assign strata to either category6. Wheeler is subsequently of the view (Wheeler & Money, 1999) that „there is little reason to presume that the acidic low nutrient environment of ombrotrophic surfaces is necessary, or even optimal, for the growth of bog Sphagnum species‟. While this may be true, the important principle is that the Sphagnum mosses must become the principal peat-formers and not be obscured by faster-growing and more vigorous fen plants.

4.13. Blankenburg & Tonnis (Eds; 2004) describe scenarios in which thin residual peat

may be underlain by acidic, neutral or calcareous material that may or may not bear higher concentrations of plant nutrients. While immediate restoration to acid bog plant communities is listed for thin (<0.5m) peat over sub-strata of acid reaction, neutral and calcareous locations are described as suitable for fen types.

4.14. Even though the influence of a thin peat residue on the subsequent growth of bog

plants is not entirely clear, there is little doubt that a sufficient thickness of undisturbed peat is required to prevent downwards loss of water, especially where the peat is underlain by a porous material such as sand (Blankenburg & Tonnis (Eds), 2004).

4.15. The opinions expressed above show just how difficult it is to set out generic

standards that would lead to successful bog restoration on all sites. Individual outcomes are influenced by a wide range of factors that make accurate prediction of restoration very difficult. The difficulty is compounded by the desire, driven by SSSI condition criteria and by the requirements of HAP targets, to restore raised bog immediately rather than following on from fen. It is of importance to note that Blankenburg & Tonnis (Eds, 2004), in providing peatland restoration advice on behalf of leading research workers and the European peat industry via the BRIDGE project (BRItish, Dutch, GErman), recognise the variety of wetland habitats achievable on cutover peatlands. These contribute to the HAP targets for fen, reedbed, coastal &

6 Dividing peat into white and black is analogous to applying the same dichotomy to types of bread; it has limited

predictive value in respect of texture or palatability.

floodplain grazing marsh and wet woodland as well as to lowland raised bog in the short term, and to even more lowland raised bog in the longer term if given the necessary management. Recognition of the range of wetland habitats restorable after peat extraction, many of which are peat-forming, places less restriction on the amount of peat that can be taken.

5. The living biodiversity of lowland raised bogs - flora, fauna, vegetation and the

peat archive

5.1. The vegetation expected on lowland raised bog depends on its geographical location, but there is similarity throughout the UK, and even the world. Ericaceous shrubs such as Ling Calluna vulgaris and Cross-leaved heath Erica tetralix form a matrix with the Harestail cotton grass Eriophorum vaginatum and/or Deergrass Scirpus cespitosus and have a ground layer of Sphagnum mosses, particularly Sphagnum papillosum, S. magellanicum and S. capillifolium. There are rarer species, such as Bog Rosemary Andromeda polifolia and Cranberry Vaccinium oxycoccos.

5.2. Describing the vegetation for intact bog surfaces in these terms masks the fact

that change has occurred over time. The majority of bogs began to form a few thousand years ago and have reached a stable stage of their development long before peat extraction. For example, the plant remains in the peat show that some developed over a tree-covered landscape, and wet woodland was a natural part of their development. The woodland died off as conditions became even wetter, perhaps as a consequence of climatic change, and were then preserved in the peat beneath a much-changed flora of ericaceous shrubs, cotton grasses and Sphagnum mosses.

5.3. The plant species are distributed between the surface elements, such as pool,

lawn and hummock, and are often involved in their formation; mosses use the support of the higher plants to build up their hummocks. The species found and the types of patterning are dependent on their position within the bog: wettest in the centre (mire expanse) and drier at the sloping edge (rand). Invertebrates such as the Large heath butterfly Coenonympha tullia and the Bog bush cricket Metrioptera brachyptera and breeding waders find food plants and niches within this structure.

5.4. The National Vegetation Classification is normally used to describe vegetation in

the UK (NVC; Rodwell, (Ed.), et al., 1991-2000). It gives collective names to groups of species found to occur together, describing them as plant communities. Some communities are associated with relatively intact bog, others with degraded bog. The NVC plant communities are used to set benchmarks what should be there, and its quality. Those expected in the various parts of the bog are described in Table A.3.2. The communities thought of as natural in some geographical locations may not extend to others. While M18 (Table A3.2) might be the norm in the north and west of the UK, it might be the exception in the south east and be replaced by sub-communities of M19 or M20, in which cotton grasses are dominant and in which there is less Sphagnum moss. It is important to take account of broad natural geographic variation when setting biodiversity expectations.

Table A3.2 National Vegetation Classification plant communities commonly found on lowland raised bogs. Adapted from JNCC (2004).

Zone Plant community

Mire expanse M17 Scirpus cespitosus (Trichophorum cespitosum)-Eriophorum vaginatum blanket mire; M18 Erica tetralix-Sphagnum papillosum raised and blanket mire; M19 Calluna vulgaris-Eriophorum vaginatum blanket mire; M20 Eriophorum vaginatum blanket and raised mire.

Bog pools (wettest part of surface patterning)

M1 Sphagnum auriculatum (denticulatum) bog pool community; M2 Sphagnum cuspidatum/recurvum (fallax) bog pool community; M3 Eriophorum angustifolium bog pool community.

Lagg fen M4 Carex rostrata-Sphagnum recurvum recurvum (fallax) mire; M6 Carex echinata-Sphagnum recurvum/auriculatum (Sphagnum fallax/denticulatum) mire; M22 Juncus subnodulosus-Cirsium palustre fen meadow; M23 Juncus effusus/acutiflorus-Galium palustre rush pasture; M24 Molinia caerulea-Cirsium dissectum fen meadow; M25 Molinia caerulea-Potentilla erecta mire; M27 Filipendula ulmaria-Angelica sylvestris mire; S4 Phragmites australis swamp and reed-beds; W4 Betula pubescens-Molinia caerulea woodland; W5 Alnus glutinosa-Carex paniculata woodland; W6 Alnus glutinosa-Urtica dioica woodland;

5.5. The peat stratigraphy of most bogs show that conditions and the predominant

plant communities may have changed over time; and that one particular „community‟ is unlikely to have covered the bog surface over the whole of its past. It is likely that changes will also occur on bogs under restoration management and that the development of the more mature condition may take decades.

5.6. Many bogs, and probably the greater part of most in England, currently bear

communities indicative of degradation. The communities result from past drainage, with or without subsequent peat extraction, and have been left with a typical watertable tens of centimetres below the peat surface. Expansion of Purple moor-grass and birch trees (analogous to NVC communities M25 and W4) has exacerbated the effect through increased evapo-transpiration. It is fundamental to improving LRB biodiversity to manage sites so that these communities are replaced by those characteristic of natural raised bog, as appropriate to the geographical characteristics described above.

Links with SAPs

5.7. Links between the LRB HAP and individual species in Species Action Plans (SAPs) are important. The lowland raised bog habitat hosts rare invertebrates such as the Large heath butterfly (Coenonympha tullia), the Bog bush cricket (Metrioptera brachyptera) and the Mire pill beetle (Curimopsis nigrita). Some sites, probably due to their heath-like structure rather than any unique bog properties, support significant populations of Nightjar (Caprimulgus europaeus). Possible losses have to be balanced against possible gains. For example, the rare beetle Bembidion humerale on Thorne Moors (Skidmore et al., 1985) is associated with algae found growing on bare peat in and around pools (pers. comm.. R. Key, Entomology Specialist, English Nature, 2005); it is likely that the suitable habitat area was increased by certain techniques for peat extraction in creating shallow open water and bare peat, and these would be changed when peat-forming Sphagnum mosses replace the bare

peat and algae. The large and diverse invertebrate fauna of Thorne Moors, South Yorkshire, may be a consequence of the fen and grassland habitats created within the former raised bog by peat extraction, providing a refuge a the original fen habitat was lost from the surrounding agricultural land. It could be argued that peat extraction had benefited the conservation of these species.

5.8. Some peat deposits are important type locations for Holocene features within the

Geological Conservation Review (i.e. locations where the geological strata are well represented and can help define the geological succession). These are already designated as SSSIs.

6. Biodiversity attributes - evaluating quality and condition

6.1. The JNCC‟s Common Standards for Monitoring (CSM) sets out quality standards for monitoring the condition of lowland raised bogs (JNCC, 2004). It is based on an expected extent (area) of the structural sub-components of mire expanse (most of the bog), the rand (sloping edge) and lagg (wet area usually with fen where peat water mixes with that of the surrounding mineral soil). The mire expanse and lagg on Bowness Common, Cumbria, are shown in Figure A3.4. The vegetation quality attributes require an adequate representation of ericaceous shrubs, cotton grasses and Sphagnum mosses; negative attributes include excessive scrub or tree cover, drying indicators, and indicators of nutritional enrichment, such as Reedmace Typha latifolia.

6.2. Although there may be some discretion based on specific sites, a site is deemed

to be in unfavourable condition if it fails on any of the tests. The way in which a site has become defined by its designated boundary may not coincide with all the land necessary to provide hydrological stability, or with the original (pre-drainage) extent of the peat body (Figures A3.2 & A3.3), possibly due to the difficulty of identifying such land before a method for calculating Hydrological Protection Zones (HPZs; see Figure A3.4) was developed in 2005. It is important to take account of the way in which site boundaries relate to the larger original extents of peat when assessing the potential of future peat extraction scenarios for biodiversity gain (or loss). Where future extraction may be adjacent to and have hydrological connection with the bog under restoration, the extraction (and associated drainage) can hinder the restoration area achieving favourable condition.

6.3. Conversely, peat working on land around a site under restoration management

may provide opportunities for eventually raising the water level within the calculated HPZ. It is also possible that slowing down the rate of peat extraction by reducing consumption delays the date at which restoration measures can be implemented. These are important considerations within the working and restoration conditions attached to planning consents.

7. Damage caused by peat extraction

7.1. Site preparation dewaters the catotelm, and the division into the two functional layers (acrotelm and catotelm)7 no longer occurs. The active peat forming and recent vegetation layer of the acrotelm is completely removed. Surface water no longer takes many pathways through the surface vegetation, in a diffuse flow pattern which

7 Wheeler & Shaw (1995) comment that the loose structure of white peat may compensate for the loss of the

natural acrotelm (Figure 2.1) to some degree.

sustains the bog plants (Schouten, 2002), but is concentrated into runnels and drains. The peat between drains is progressively dewatered and the air entering the pores in place of the water carries oxygen that enables the peat to decay, release carbon dioxide, fissure and shrink. This leads to a change in plant species from the mixed Ericaceous-Cotton grass-Sphagnum mix (typical of the lowland raised bog mire expanse) to others dominated by single Ericaceous shrubs, Purple moor-grass or birch scrub and woodland, more typical of the lagg of an intact bog.

7.2. The combined effect of dewatering and oxidation is for the peat to slump,

particularly around the edges of the peat body. This is evidenced by the steep slopes of bogs such as Glasson Moss and next to the north edge (Newton Arlosh Awards) of Wedholme Flow, Cumbria, where peat cutting has occurred. Many relict areas of peat are still domed, but are dramatically over-steepened compared with the contours of undrained bogs. One consequence of over-steepening is that, due to gravity, surface water runs off even more quickly. These changes in topography affect the hydrology that underpins the floral and faunal biodiversity and also the prospects for retaining water on the surface during restoration.

7.3. Some of the plants that made up the bog surface when in its natural state may

survive in small wet niches around the peat extraction site. Heathers (Calluna vulgaris and Erica tetralix) and the two species of cotton grass (Eriophorum angustifolium and E. vaginatum) typically occupy the sides of tracks and shallow drains; a few species of Sphagnum moss, particularly Sphagnum cuspidatum and S. fallax, may also survive on damp peat and in the drains. It is less likely that the „quality‟ indicators such as Marsh Andromeda Andromeda polifolia, Cranberry Vaccinium oxycoccos and Sundew Drosera rotundifolia will survive.

7.4. The „irreplaceable record‟ in the undisturbed peat layers, of considerable

importance to archaeology and an understanding of past climatic change, is at risk from peat extraction and from attempts to improve the biodiversity. Apart from revealing artifacts, such as the Sweet Track in Somerset and Lindow Man in Cheshire, peat extraction destroys the archaeological and palaeo-environmental information, which cannot be replaced (Coles, 1995).

8. Options in peatland restoration following peat extraction General

8.1. Peat formation is not restricted to raised bogs. The possibilities for wetland habitat creation on the full range of cutover surfaces are described by Blankenburg & Tonnis (Eds, 2004). Peat deposits contain the remains of fen plants such as reeds and sedges, and these are particularly common at the base of raised bog peat profiles. The sometimes fen-like bog pool vegetation that is established early in restoration lies within NVC communities M1, M2 and M3, whereas poor fen communities, perhaps associated with the lagg, include M4, M5, M6, M9, M21 and S27 (see Table A3.2). All of these communities include species of Sphagnum moss, though not all of them are normally found on active raised bogs (Rodwell (Ed) 1991-2000).

8.2. Peat deposits show that poor fen communities have developed into raised bog

over the course of time (decades to centuries) in response to the hydrological changes associated with the build-up of peat. Condition monitoring protocols (4.4) and the description of Natura 2000 habitat types (EU, 1996; 4.2) require the earliest possible re-establishment of a raised bog flora (within 30 years in EU (1996) for Degraded raised bog (still capable of natural regeneration). This may be why

Government guidance (MPG 138) and restoration plans using the guidance require the provision of the right conditions for bog pool communities by leaving a sufficient thickness of in situ peat and excluding minerotrophic and nutrient-enriched surface water rather than taking a longer view with a preliminary period of poor fen (Table A3.2).

8.3. The successional relationship between fen and bog is of importance because

some planning requirements on peat extraction sites ask for a range of wetland types rather than the immediate raised bog precursors (e.g. Solway Moss; Annex 4, Figure A4.13). Although this may be judged by conservation bodies to be less than ideal, and may not have been acceptable on designated sites such as Thorne Moors (Annex 4, Figure A4.14), its value as a longer-term precursor of raised bog and interim contribution to the Fen HAP creation targets is a material consideration in determining the consequences of peat extraction for biodiversity.

Specific requirements for raised bog restoration

8.4. The early practitioners of bog restoration in Germany (e.g. Eigner & Schmatzler, 1991) believe it is important to store the „top spit‟ or layer initially containing viable plant fragments, spores and seeds for the restoration phase, with the aim of restoring active bog, where past land use has not already destroyed it. The importance of refugia is recognized in MPG13 (DoE, 1995; Table 4.1). Overall, the effect of peat cutting on the bog flora is to eliminate many important species, such as the full range of peat-forming Sphagnum mosses, and to drive others into small corners from which it may take years to spread back onto an extensive restoration surface.

8.5. If the peat bog formed over saturated sand, and if the level of water in the sand

aquifer has now fallen9, water that would otherwise keep the peat wet will escape downwards. The upper layers, often referred to as white peat (described above), have a greater water-holding capacity than the black peat, but it is more porous and permeable. Some authorities on the subject of bog restoration (e.g. Eigner & Schmatzler, 1980; Nick, 1985) claim that white peat provides a better growing medium for lowland raised bog plants during restoration, apparently because of its physical properties, such as loose structure and, in particular, its greater water storage capacity (Schouwenaars & Vink, 1992). This is challenged by others, such as Blankenburg (In: Wheeler & Shaw, 1995), on the grounds that the additional nutrients found in more humified peat are helpful in re-establishing the vegetation.

8.6. A sufficient thickness of peat (see 4.12 - 4.14 of this annex) also needs to be

retained so that there is enough left to construct the baulks and dams for water retention without causing weak points where the water can drain away into the substratum, or for the substratum to affect water quality detrimentally (Blankenburg & Tonnis, (Eds) 2004).

8 Generic principles for bog restoration are provided in MPG13 (DoE, 1995) and follow the principle of immediate

restoration to raised bog vegetation. These guidelines are important because of their status within the UK‟s planning process and act as a benchmark against which planning decisions and concomitant events can be measured. 9

The water level in aquifers may fall for reasons such as extraction for potable supplies.