British & Irish Botany 3(2): 136-151, 2021 Current status of the rare British endemic Gentianella amarella subsp. occidentalis, Dune Gentian (Gentianaceae) Lyn D.I. Evans¹* & Timothy C.G. Rich2 ¹Department of Countryside Management, Bridgend College, U.K; ²Cardiff, U.K. *Corresponding author: Lyn Evans [email protected] This pdf constitutes the Version of Record published on 26th July 2021 Abstract Gentianella amarella subsp. occidentalis, Dune Gentian, is a rare annual of dune slacks endemic to Western Britain. Its current status was compared to historic records. A maximum of 2250 plants were found in ten subpopulations in four sites in 2019-2020. It was not refound in three sites and 15 subpopulations. It is assessed as IUCN threat category ‘Endangered’. Its primary vegetation type is SD14d Salix repens - Campylium stellatum dune slack Festuca rubra subcommunity, within which it favours short, open structure on dry, low nutrient soils. Conservation requires managing and creating its niche in the dune slacks. Keywords: Dune slack; Endangered; England; IUCN threat criteria; Wales. Introduction Gentianella amarella subsp. occidentalis T.C.G. Rich & McVeigh, Dune Gentian, is a small, summer annual of dune slacks endemic to South Wales and North Devon in Western Britain (Rich & McVeigh, 2019; Stace, 2019; Figs. 1 & 2). Historically referred to as Gentianella uliginosa (Willd.) Börner in Britain, it was recently recognised as a morphologically distinct taxon related to the biennial G. amarella subsp. amarella (Rich et al., 2018). A short video showing the plant and its habitat prior to the work reported here is given by Rich (2019). Rich & McVeigh (2019) noted Dune Gentian had been recorded from seven sites in four vice-counties (North Devon, Glamorgan, Carmarthenshire and Pembrokeshire) and gave its IUCN threat category as ‘Vulnerable’. Following concern that it was declining, a comprehensive survey of all its sites in 2019-2020 was undertaken, its IUCN threat category re-assessed, the habitat described and recommendations made for its conservation. The results are summarised here; fuller details are given in Evans (2020). Methods Historical data on its distribution, abundance and habitat were compiled from herbaria (ABD, BIRM, BM, CGE, HDD, K, LTR, NMW, OXF, RNG), literature, the BSBI Distribution Database (https://database.bsbi.org/, accessed January 2019), Aderyn/LERC Wales (accessed January 2019) and data held by Natural Resources Wales. The population counts from the last 50 years presented in the figures have been compiled from Vaughan et al. (1972), Elias (1981), Youngson (1986), Jones 136 (1992, 1993, 1994), Kay & John (1995), Rich (2004), Dockerty (2010), the BSBI database and our personal observations. Figure 1. Gentianella amarella subsp. occidentalis. 137 Figure 2: Sites from which Gentianella amarella ssp. occidentalis has been recorded. Basemap © Google maps L. Evans with the help of M. Breeds, N. Ferris, R. Harding, T.C.G. Rich and J. Woodman searched all sites except for one subpopulation in August and September 2019, and most of the Welsh sites were searched again in August and September 2020 including the missing subpopulation. Populations were counted by careful searching, and taking care to distinguish plants from G. amarella subsp. amarella with which it often grows (Rich & McVeigh, 2019). Hybrids reported as G. amarella x uliginosa are no longer accepted and most such plants are depauperate subsp. amarella (Rich & McVeigh, 2019). IUCN (2001, 2019) threat categories were determined by assessing the site and population data against the IUCN criteria, using the highest recent population count where two counts were available. Estimates of extent and occupancy were calculated using MAGIC maps (DEFRA, 2013). Vegetation data were recorded using 2 x 2 m quadrats following the NVC protocol but also with percentage cover (Rodwell, 2000, 2006). Additional quadrats from surrounding dune slacks and slopes approximately 1 m altitude above and below the Gentianella population were recorded to provide comparative data. NVC community types were allocated using the floristic tables and keys in Rodwell (2000) and ‘MAVIS’ software (Smart, 2000). Ellenberg indicator values (Hill et al., 2004) were calculated for each quadrat in MAVIS. Mean values were calculated by combining quadrat data at, below and above the level of the target species; these values were analysed using one-way ANOVA to determine which variables differed significantly. Ellenberg values for each 138 population were compared to those derived from the ‘standard’ associated NVC community data from Rodwell (2000); as the NVC tables give Domin scores, percentage cover required by MAVIS was calculated by taking the median Domin value from the cited range and calculating (Domin)2.6/4 to correct for underestimation of the means (Currall, 1987). Vascular plant nomenclature follows Stace (2019). NVC types follow Rodwell (2006). Results Population sizes 1. Braunton Burrows (v.c.4) It was first collected at Braunton Burrows in 1843 but was only rediscovered recently (Holyoak, 1999). It been recorded as widely distributed in five slacks but never in quantity; Holyoak (1999) recorded ‘over 130 plants’, BSBI records mention ‘several plants’ and an unpublished Natural England report from 2012 states ‘half a dozen plants’. In 2019, a total of 43 plants were found in four slacks, again all in small quantity (Table 1) including two new subpopulations. It was not refound in three historic subpopulations (one slack was suitable but two were not) giving a total of seven locations within the Burrows. 2. Northam Burrows (v.c.4) It was only recorded once at Northam Burrows in 1882 (Rich, 1996). No plants were found in 2019 or on three previous searches by T. Rich 2004-2008. Northam Burrows is now a golf course and only one small slack remains with generally unsuitable habitat. 3. Oxwich Bay (v.c.41) It was first recorded at Oxwich in 1927 and subpopulations have been recorded at up to seven slacks (Lousley, 1950; Kay, 1973; Elias, 1981; Table 1). The recent population data traced are summarised in Fig. 3. Jones (1994) noted populations recorded by Morgan (1988) in three slacks had gone by 1993. In the early 1990s, the large population in Slack 21 was nearly destroyed by construction of a dune scrape (Q.O.N. Kay, pers. comm. 1995); it has taken over 20 years for this population to recover. In 2019, one good population of 478 plants was found on the scraped edges of Slack 21, with a few isolated plants in the centre. In 2020, 998 plants were present (Table 1). The six slacks with historic records now all have coarse vegetation or scrub and no plants were found in them. 4. Whiteford Burrows (v.c.41) It was first recorded at Whiteford in 1934 and has been recorded in at least seven widely distributed slacks (Lousley, 1950; Kay, 1973; Table 1). In 2019, 280 plants were found in four slacks, with over two-thirds of the population in Slack 19. Slacks 7 and 9, which had records of several hundred plants in 2003-2004, had only several dozen plants despite having suitable habitat at the time of survey. At Slack 60 where it was recorded as ‘occasional’ in 2015, one diminutive plant was found. In 2020, a total of c.1200 plants were found in Slacks 9 and 19, the latter again with the largest subpopulation. Many of the slacks on the east side of the dunes with records from 139 the 1970s have scrubbed over with Salix spp. and Betula pubescens. The recent population data traced are summarised in Fig. 4. 7000 6000 5000 4000 3000 PopulationCount 2000 1000 0 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 Year Figure 3. Population counts of Gentianella amarella subsp. occidentalis at Oxwich. A trend line (dotted) is also given. 1400 1200 1000 800 600 PopulationCount 400 200 0 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 Year Figure 4. Population counts of Gentianella amarella subsp. occidentalis at Whiteford. A trend line (dotted) is also given. 5. Pendine Burrows (v.c.44) It was first recorded at Pendine in 1944 (Vaughan et al., 1972) and has occurred in two locations, on tractor ruts in a slack and beside a test track. A possible third subpopulation at SN284072 (Jones, 1993) has not been confirmed and no plants were found there in 2020. It was last recorded in 1992 when seed was collected and no plants were reported in 1993 (Jones, 1994). In 2019 and 2020, no plants were found; the slack has become unsuitable with coarse slack vegetation (though there had been some recent scrub clearance) and the test track has only a modicum of suitable slack vegetation. 140 6. Pembrey Burrows (v.c.44) It was first recorded at Pembrey in 1961 and has been recorded at three locations. The recent population data traced are summarised in Fig. 5. In 2019, only nine plants were found in an area of short turf, which had seven plants in 2020 (Table 1). It was not re-located on a trackway where previously noted as ‘occasional’ and where suitable habitat was present, or the helipad where it was frequent in 2003 but was dominated by coarse vegetation in 2019. Figure 5. Population counts of Gentianella amarella subsp. occidentalis at Pembrey. A trend line (dotted) is also given. 7. Penally Burrows, Tenby (v.c.45) It was first recorded at Penally in 1923 and was recorded in damp sandy pastures and a dune slack; the former may have been destroyed by construction of the golf course in 1946 and by 1950 and 1971 was restricted to one slack (Pugsley, 1924; Lousley, 1950; Vaughan et al., 1972). A population of 58 plants was recorded in 1993 (Jones 1994) and it was last recorded in 1994. The population data traced are summarised in Fig.