Changing status of Blysmus compressus (Flat Sedge) in the Sefton Coast sand-dunes, north Merseyside, UK

A 2018 survey of the nationally ‘Vulnerable’ Blysmus compressus (Flat-sedge) in the Sefton Coast sand-dunes, north Merseyside (v.c.59, South Lancashire), aimed to update information collected on distribution and habitats a decade earlier. As in 2008, the plant was mainly found in calcareous dune-slacks of recent origin, with short, open, speciesrich vegetation on gley soils with a relatively high pH. Sites with a lower sward height supported a higher percentage cover of B. compressus. The largest populations were associated with sites that had been disturbed by recreational trampling, occasional vehicle use and/or grazing, especially by rabbits. Twenty-two sites were recorded, seven being new. Overall, the area occupied by B. compressus declined by 17%, two 2008 sites being lost. Similarly, an estimate of 15-20,000 plants in the earlier survey fell to 12,600. Losses were attributed to vegetation overgrowth and scrub development, partly resulting from lower rabbit numbers and reduced management input. The plant occurred in a range of vegetation types but matches to known UK National Vegetation Classification communities were generally poor. Management methods to conserve B. compressus and other vulnerable taxa are discussed.


Introduction
Blysmus compressus (L.) Panz. ex Link (Flat-sedge) (Cyperaceae) (Fig. 1) is a rhizomatous perennial of open vegetation in marshes and fens and in short, sedge-rich, damp grassland, calcareous flushes, dune-slacks, road verges and stream borders that are subject to flooding, especially on base-rich soils. It has also occasionally been found in brackish ditches at the head of saltmarshes and as a constituent of alluvial meadows on stabilised shingle (Graham, 1988;Halliday, 1997;Jermy et al., 2007;Stroh & Walker, 2015;Walker et al., 2017). Ellenberg's indicator values in Hill et al. (2004) show that this species is a light-loving plant (L = 8), associated with constantly moist to wet soils (F = 8) that are base-rich (R = 8) and relatively infertile (N = 3) and that the plant is generally absent from saline sites (S = 0). Blysmus compressus occurs from the temperate zone of Western Europe, north to southern Scandinavia, south to North Africa and east, via Turkey and Lebanon, through southern Siberia, Mongolia, Nepal and the mountains of Central Asia as far as Sichuan in China. This plant has been recorded in most English counties but is now extinct in many, being locally abundant only in the north and west. It is confined to one site in Wales and, in Scotland, is found almost entirely to the south of the Central Belt. The species has not been seen in Ireland.
Due to habitat loss, hydrological change, eutrophication, undergrazing and the spread of competitive species, B. compressus has greatly declined in Britain, having been lost from more than half its pre-1930 hectads by 1962 and, subsequently, from 40% of its post-1930 hectads. Its change index from 1930 to 1999 was -1.28 (Foley & Porter, 2002). A further decline was reported during the Botanical Society of Britain and Ireland's Threatened Plants Project (2008)(2009)(2010)(2011)(2012)(2013), which quantified changes in the distribution of selected populations present after 1970. B. compressus was relocated at 66% of pre-selected sites, which included the Sefton Coast, north Merseyside. The largest populations, with up to 300,000 individuals, were found in flushed grasslands near to streams and rivers in the uplands of Northern England and Southern Scotland (Walker et al., 2017). Reflecting its recent declines, B. compressus, is Red-listed as Vulnerable in the UK and in both England and Wales. B. compressus is also a Species of Principal Importance for the Purpose of Conserving Biodiversity in England and Wales under Section 41of the Natural Environment and Rural Communities Act 2006 and Section 7 of the Environment (Wales) Act 2016, respectively. The plant is Red-listed in many western European countries, including Belgium, Germany, Norway, Croatia, the Czech Republic, Hungary, Finland and Sweden (Cheffings & Farrell, 2005;Dines, 2008;Stroh et al., 2014;Walker et al., 2017). Smith (2009a)

reviewed the distribution of B. compressus in Northwest England
where it is considered a Species of Conservation Importance (Regional Biodiversity Steering Group, 1999). There are records for 69 tetrads in Cumbria, mostly in vicecounty (v.c.) 69, Westmorland (Halliday, 1997

Status on the Sefton Coast
Blysmus compressus has been known from the Sefton Coast since 1801, the first quantitative study of its distribution and habitats being in 2008 as part of the BSBI Threatened Plants Project. Smith (2009a) found the species in 18 calcareous dune-slack and damp grassland sites, occupying a total area of over 3000 m 2 . The estimated total population size was between 15,000 and 20,000 individuals. Most localities were of fairly recent origin and had a history of recreational disturbance and grazing, especially by rabbits (Oryctolagus cuniculus). Analysis of quadrat data gave accordance with UK National Vegetation Classification (NVC) dune-slack communities SD15, SD16 and SD17 and two mesotrophic grassland types (MG8 and MG11) (Rodwell, 1991(Rodwell, -2000, though statistical matches were generally poor to very poor.
Since the 2008 study, several new populations of B. compressus have been found in the Sefton dunes. There have also been changes in land-ownership and management. Ten years on, therefore, it was considered appropriate to repeat the 2008 survey, the aims being to establish the current status of this nationally declining and vulnerable plant at one of its important English lowland stations, to clarify its habitat characteristics and make conservation recommendations.

Methods
All known and likely sites for B. compressus in the Sefton Coast sand-dune system were visited in June and July 2018. Populations were marked out using bamboo canes, their areas being measured by tapes or by pacing and number of plants estimated by counting flower spikes individually or in groups of 5 or 100, depending on colony size. National Grid References of sites were determined to an accuracy of about 5 m using a hand-held Garmin Etrex GPS device. For all but the smallest sites, either one or two samples of representative vegetation were recorded in 21 2 m×2 m quadrats using NVC methodology. Reference was made to keys, data tables and community descriptions in Rodwell (1991Rodwell ( -2000 to identify vegetation types. Quadrat samples were also analysed using TABLEFIT to determine the degree of fit to known NVC communities and subcommunities (Hill, 2015). Soil type was assessed in each quadrat by visual inspection and a sub-surface soil sample taken, its pH being measured the same day using a Lutron PH-212 soil pH meter buffered at pH 4 and 7. Notes were also taken on habitat type, condition and current management. Relationships between plant numbers and site area and between vegetation height and percentage cover were analysed using Pearson's correlation coefficient. Vascular plant nomenclature follows Stace (2010) and subsequent updates.

Results
Twenty-two sites supporting B. compressus were found (Fig. 2), extending from Altcar Training Camp in the south to Queen's Jubilee Nature Trail, Southport in the north, a linear distance of about 12 km. They are situated in six tetrads and three hectads of the UK National Grid. As in 2008, most colonies were in four main areas: Altcar Training Camp (four sites), Cabin Hill National Nature Reserve (three), Birkdale frontal dunes (south) (five) and Birkdale frontal dunes (north) (six). Outlying colonies were also located at the Devil's Hole in Ravenmeols Local Nature Reserve (LNR), Royal Birkdale Golf Course, Birkdale Sandhills LNR and Queen's Jubilee Nature Trail. A total of over 12,600 plants was counted (Table 1), with a range of 2 to 5000 and a mean of 600 plants per site. The colonies occupied a total area of nearly 2500 m 2 (range 1-921 m 2 ; mean 119 m 2 ). As might be expected, a positive relationship was found between colony size and area occupied (Fig. 3). A log 10 transformation of both axes was used to give a more symmetrical distribution of data.
Seven new sites for the target species were located covering 641 m 2 and supporting 3220 plants. B. compressus was not re-found in two of the 2008 sites: a marshy pond edge on Royal Birkdale Golf Course and slack no. 26 Birkdale Sandhills LNR. The former covered 6 m 2 and held 10s of plants in the previous survey, while the latter had 100+ plants within 7 m 2 . Another site was reported in 2008 by P.S. Gateley (personal communication, 2009) in a slack on the fairway of the 12 th hole at Royal Birkdale. However, no plants were found there in 2018. Two sites at Altcar Training Camp's 'I-range' had been mown just before the recording visit and, consequently, only two plants were located in one of them. Previous observations indicated that at least 100 plants were usually present there. While numbers of individuals were only roughly estimated in 2008, site areas were more carefully measured, allowing a direct comparison between the two surveys. Of the sites recorded in both years, nine showed area declines of 23 to 96% while five increased in size from 7 to 144% (Table 1). Greatest area losses were in the Birkdale frontal slacks nos. 31, 49 and 50. All three of the Cabin Hill sites also showed declines in area, while the largest area gains were in Birkdale frontal slacks 32, 27, 28 and 51/52 (Table 1).  Most Sefton Coast sites for B. compressus are dune-slacks that have formed secondarily by wind-erosion or by sand-winning and have a seasonally fluctuating water-table (Smith, 2009b). Using Ranwell's (1972) criteria for classifying slack-types, one site was considered to be semi-aquatic, one semi-aquatic/wet-slack, 13 wet-slack and five dryslack, while two were listed as damp grassland (Table 1). All the soil types were considered to be ground-water gleys of the Greatstone Series as defined by the Soil Survey of England & Wales, though about half approached a peaty-gley condition with large amounts of surface organic matter (Beard et al., 1987). Soil pH was relatively high, ranging from 6.06 to 7.64 with a mean and standard deviation of 7.0±0.51.
compressus, ten of the taxa identified in quadrats are regionally or nationally notable, eight being Red-listed.
Mean vegetation height and standard deviation in quadrats was 18.5±7.5 cm (range 7-35 cm), while percentage cover of B. compressus varied from 3 to 30 (mean 10.3±7.8). Samples with lower vegetation heights tended to have a higher cover of B. compressus (Fig. 4). Shorter swards were found in sites that were either subject to recreational trampling, vehicle passage or, more rarely, rabbit grazing.  (Table 1).
The most unusual locality was the edge of a carpark at Sands Lake, Ainsdale, where 275 plants were counted in a 1 m-wide strip of heavily trampled weedy vegetation only 7 cm tall. This colony was also recorded in 2008, having been first noticed in 1979 (Smith, 2009a). B. compressus was also occasionally found in taller slack vegetation, stems of the plant being up to 47 cm long in slack 28, Birkdale frontals, slightly more than the maximum of 45 cm cited in Jermy et al. (2007). Rodwell (1991Rodwell ( -2000 does not include B. compressus as a constituent of any NVC community. However, reference to his keys, data tables and community descriptions suggested that most quadrats had accordance with SD14: Salix repens-Campylium stellatum dune-slack (3 samples), SD15: Salix repens-Calliergon cuspidatum (now Calliergonella cuspidata) dune-slack (4 samples), SD16: Salix repens-Holcus lanatus dune-slack (4 samples) or SD17: Potentilla anserina-Carex nigra dune-slack (6 samples).
Two quadrats did not key out satisfactorily, while two had similarities to MG5: Cynosurus cristatus-Centaurea nigra grassland or MG6: Lolium perenne-Cynosurus cristatus grassland. TABLEFIT analysis based on percentage cover of vascular taxa (  (Table 2). A re-run of TABLEFIT for vascular species presence gave identical NVC matches but levels of fit were higher, ranging from "very poor" to "very good" (Table 2).

Discussion
Almost all of the B. compressus localities are in seasonally-flooded, calcareous dune-slacks where the plant is subject to occasional inundation by base-rich freshwater.
Waterlogged conditions seem to favour this species (Jermy et al., 2007;Walker et al., 2017), perhaps because tolerating oxygen deficiency in the soil gives it a competitive advantage (Stroh & Walker, 2015). The target species was restricted to about 2500 m 2 of dune-slack and damp grassland. This is a small proportion of the potentially available habitat, the Sefton Coast having over 114 ha of slacks and freshwater wetland, amounting to 33% of the dune-slack resource in England (Edmondson, 2010;Radley, 1994). However, many of the slacks originated over 100 years ago and, being heavily vegetated (Smith, 2009b), are probably unsuitable for B. compressus.
Distances between the three groups of sites supporting the plant are approximately 12 km and 2.8 km, suggesting that dispersal and establishment of new colonies may be problematic. Little seems to be known about dispersal mechanisms in this species (Stroh & Walker, 2015), though Pignotti & Mariotti (2004) described particularly long perianth bristles surrounding the nut that may assist attachment to mammals and birds. Smith (2009a) reported "encouraging findings" that fewer than ten sites in the  (Rodwell, 1991(Rodwell, -2000Davy et al., 2006). B. compressus is therefore likely to decline in older slacks unless these are managed to maintain short swards which this study has shown are associated with higher frequencies of the plant.
An Ellenberg N value of 3 indicates adaptation of B. compressus to infertile conditions (Hill et al., 2004). Millington et al. (2010) showed that Sefton dune soils generally have relatively low nitrogen levels which tends to increase in the older parts of the system. Increases in nitrogen and other nutrients in dune-slack soils during succession is well-established (e.g. Grootjans et al., 1998;Olff et al., 1993), probably making older slacks less suitable for B. compressus. Eutrophication is likely to be exacerbated by aerial deposition of nitrogen from industrial and agricultural sources (Jones et al., 2004).
Although Walker et al. (2017) highlight soil compaction and trampling damage as a threat to the plant, Smith (2009a) found that human trampling benefited B. compressus by reducing sward height and the dominance of Salix repens. This was also apparent in the current study, the heavily trampled slack 32 in the Birkdale frontals ( Fig. 5) having both the largest population of B. compressus and the greatest increase since 2008. Vegetation height at the important colony at Birkdale slack 13 was similarly reduced by recreational pressure (Fig. 6). As in 2008, several sites were associated with the edges of informal footpaths where vegetation, especially S. repens, has been suppressed ( Fig. 9). Examples include the Birkdale pipeline slack, frontal slacks 27, 28, 33 and 51/52 and the heavily disturbed fringe of Sands Lake carpark. Smith (2009a) described the latter site as "sub-optimal" for B. compressus, expressing surprise that the plant had survived here since 1979. He also found that it had persisted and increased after severe churning by illegal motor-cycling in the northern Birkdale frontal slacks during the late 1970s and early 1980s. Occasional passage of military vehicles similarly created more open, disturbed swards at some of the Altcar sites (Fig. 7), while off-road vehicle damage to Birkdale slacks 27 and 28 in 2014 (Fig. 8) was followed by an increase in B. compressus. The loss of the Birkdale slack 26 population and declines at slacks 49, 50 and 31 seem to be partly associated with reduced footfall and the overgrowth of informal footpaths by coarse vegetation dominated by tall S. repens. K. Walker (personal communication, 2008) reported that the densest populations of B. compressus he found in the Yorkshire Dales National Park, including thousands of plants at Gordale Scar campsite, were hard-grazed or kept open by trampling. It was also apparent that four sites in the Birkdale frontals (slacks 30, 31, 50 and 51/52) were being colonised by larger shrub species: Hippophae rhamnoides (Sea Buckthorn) and Salix cinerea (Grey Willow) (Fig. 10). This may have contributed to declines of B. compressus at slacks 31 and 50. Smith (2009a) also drew attention to the growth of larger willow taxa as a potential threat to B. compressus.
Annual late-summer mowing of sites at Altcar Rifle Range, Ainsdale slack 49 and Royal Birkdale was highlighted by Smith (2009a) as a way of maintaining lower sward heights. Mowing has continued at Altcar "I" range and Royal Birkdale but seemingly did not prevent a decline of B. compressus at the golf course 5 th fairway. This grassland is rarely inundated in winter and may now be too dry for the plant to thrive.
The Cabin Hill NNR sites and Birkdale slack 13 are winter-grazed by livestock but a large rabbit population at Cabin Hill that helped to maintain shorter swards throughout the year has declined to near extinction, probably due to disease. Formerly supporting the largest duneland population of B. compressus, the number of plants at Cabin Hill's site 1 has fallen by about 90%. This site was mowed on four occasions in the 1990s but less often since and most recently in 2011/12 and 2017/18. Birkdale frontal slack 49, which has lost 92% of its colony area, was mowed annually, with removal of arisings, from 1996 to about 2010 but not subsequently. Slack 49 had a moderate rabbit population in 2008 (Smith, 2009a) but rabbit activity was noted only at Devil's Hole during the 2018 survey. These grazers are known to have a major influence on sanddune vegetation, including seed dispersal (Dellafiore et al., 2010;Potter & Hosie, 2001) but tend to be excluded once coarse vegetation becomes established (Drees & Olff, 2001). Relatively high values for soil pH measured in this study are similar to those published by Millington et al. (2010) for Sefton Coast dune-slacks, reflecting the presence of calcium carbonate derived from marine mollusc shells. However, these authors included a number of older and more acidic slacks in their samples. Their mean pH value of 6.7 is therefore lower than the 7.0 found in the younger slacks supporting B. compressus. An Ellenberg reaction value of 8 (Hill et al., 2004) confirms the association of this plant with base-rich soils, as reported more widely (Stroh & Walker, 2015;Walker et al., 2017).
Blysmus compressus habitats were found to support a diverse plant community, 80 associated vascular taxa being recorded in 21 quadrats, compared with 90 in 51 quadrats during the 2008 survey. Of the most frequent associates, all except Plantago lanceolata were also ubiquitous in the 2008 quadrats (Smith, 2009a). A high speciesrichness is characteristic of many younger dune-slacks on the Sefton Coast (Smith, 2006). The slacks are also renowned for their rare plants, nine associated taxa in 2018 (11%) being regionally or nationally notable, the comparable figure in 2008 being 12 (13%). Remarkably, only two taxa (2.5%) found were non-native, in contrast to the Sefton sand-dune flora as a whole, which has about 37% alien vascular plants (Smith, 2015). The allocation of most 2018 quadrats to SD14, SD15, SD16 or SD17 accords with the earlier survey which found that 37% of samples equated to SD16, 27% to SD15 and 18% to SD17 (Smith, 2009a). That study also recorded a small number of samples with a best fit to MG11: Festuca rubra-Agrostis stolonifera-Potentilla anserina grassland or MG8: Cynosurus cristatus-Caltha palustris grassland (Rodwell, 1991(Rodwell, -2000. However, most of the matches were "poor" or "very poor". As previously noted, B. compressus is not given as a component of NVC sand-dune slack communities by Rodwell (1991Rodwell ( -2000. Walker et al. (2017) report that most populations of B. compressus recorded during the Threatened Plants Project were in fen meadows and rush pastures, especially M22: Juncus subnodulosus-Cirsium palustre fen-meadow, M24: Molinia caerulea-Cirsium dissectum fen meadow, M26: Molinia caerulea-Crepis paludosa mire and MG8: Cynosurus cristatus-Caltha palustris grassland. Fen meadows and rush pastures are not typically associated with calcareous sand-dunes (Rodwell, 1991(Rodwell, -2000. The 2003/04 NVC survey of the Sefton Coast mapped only 0.03 ha of M22, consisting of dense patches of Juncus subnodulosus (Blunt-flowered Rush) (Gateley & Michell, 2004). The present study noted a few stems of B. compressus on the edge of one of these patches at the Devil's Hole but this association was not found during a coastwide survey of J. subnodulosus in 2013 . B. compressus seems unlikely to be able to compete with dense stands of J. subnodulosus (Walker et al., 2017). TABLEFIT analysis determined one 2018 sample (Birkdale slack 27) as M22 but statistical matches were "very poor" for both percentage cover and species only. Hill (2015) recommends that if goodness-of-fit is "very poor" the vegetation should probably not be assigned to any NVC type. The same should perhaps apply to the two OV communities ascribed by TABLEFIT to Birkdale slack 13. Percentage cover gave "very poor" fits while, for species only, the matches were "poor" to "very poor".
Poor statistical fits to NVC communities have been found in several previous studies of Sefton Coast vegetation (Smith, 2017b). This may be due to the complex environmental gradients that operate in dune systems, to the difficulty in selecting "typical" stands in the mosaic of dune vegetation and the fact that the data used to derive dune NVC communities were based on a limited number of quadrats and may not be particularly representative (Natural England, 2014).

Conservation
Colonies of B. compressus on the Sefton Coast are mostly found in younger duneslacks, in which succession is likely to reduce habitat suitability over time. Due to overstabilisation, there is a low rate of slack formation on the Sefton Coast (Smith, 2009b), with limited potential for suitable new habitat to form without human intervention. Since the mid-1980s, a 66 ha mosaic of saltmarsh, embryo dunes and slacks, known as Birkdale Green Beach, has developed on the shore between Birkdale and Ainsdale (Smith, 2007). Smith (2009a) suggested that this might provide suitable habitat for B. compressus. However, despite careful searches, only the related B. rufus (Saltmarsh Flat-sedge) has been found there.
As more than 60% of the B. compressus colonies known in 2008 have declined over the last decade, active management is likely to be needed to prevent further losses. Walker et al. (2017) recommend maintaining an open, short sward, a dynamic hydrological regime and reducing eutrophication. The current study suggests that these approaches could help to conserve B. compressus in the Sefton dunes and would have wider benefits, as the slack habitat supporting B compressus is rich in other biota (Smith, 2009b).
Shorter swards in slacks can be achieved by livestock grazing and mowing (Houston, 2008), while the present study shows that light to moderate recreational trampling or low levels of vehicle use can have the same effect. However, only four of the 22 sites recorded in 2018 are within Sefton duneland units grazed by livestock. Rabbits have greatly declined in recent years and resources for mowing slacks have been much reduced since about 2010. Tramping tends to be concentrated near to access points and its intensity is difficult to manage, over-use being deleterious (Walker et al., 2017). Colonies threatened by scrub invasion, especially of Hippophae rhamnoides, Salix cinerea and S. repens require targeted scrub control. In recent years, this has relied increasingly on volunteers using hand-tools, rather than the machinery needed to tackle older and larger scrub patches.
Turf-stripping to return slacks to an earlier successional stage has been used on the Sefton Coast to create over 50 small breeding pools (scrapes) for Natterjack Toads (Epidalea calamita) (Smith, 2009b). This has benefited some early successional stage slack plants, such as Carex oederi (Small-fruited Yellow-sedge) (Smith, 2017b). Decleer (2008) reports the appearance of B. compressus after large-scale restoration of dune slacks in Belgium, suggesting colonisation from a long-lived seed-bank. However, the plant was found in only four Sefton scrapes and not as a pioneer. Turf-stripping, mowing and grazing may help to counter eutrophication, though Plassmann et al. (2009) showed that, while it helped to keep competitive grasses in check and maintain species-rich swards, duneland grazing did not mitigate all the negative effects of Ndeposition.
Detailed hydrological studies provide no evidence of a consistent decline in the Sefton sand-dune water-table over the last 46 years (Clarke & Sanitwong Na Ayutthaya, 2010). However, Natural England (2014) found a 36% and 44% reduction in wetland area at Ainsdale and Birkdale respectively between 1989 and 2012 due to slack habitats becoming drier. Climate change may cause average dune water-levels to fall by as much as 1.5 m by the end of the century (Clarke & Sanitwong Na Ayutthaya, 2010), giving rise to concerns for the long-term future of slack species, including B. compressus.
It is hoped that two coast-wide projects will augment funding for dune management and contribute to conservation of B. compressus and other threatened Sefton dune biota. Part of the Back from the Brink project supported by Heritage Lottery (HLF) and other partners, Gems in the Dunes targets six Section 41 species for recovery management in the dunes. B. compressus is one of the secondary targets for the project which runs from 2017 to 2020. Relevant management includes scrub control, small-scale turf-stripping and scrape creation, as well as public engagement to encourage survey work, monitoring and volunteer recruitment. Dynamic Dunescapes is a joint HLF and EU Life project covering seven coastal dune systems in England and Wales, including the Sefton Coast. The delivery phase, from 2019 to 2023, proposes capital works, such as re-mobilisation, turf-stripping, mowing and scrub control. There is also an emphasis on public involvement and citizen science. However, both these initiatives are time-limited. A longer-term vision for duneland management is provided by the Sefton Coast Plan (https://indd.adobe.com/view/88432262-8368-42b2-8d91-97ef25ddec4c) and a Nature Conservation Strategy, currently being developed by the Sefton Coast Landscape Partnership.