Thlaspi alliaceum L. (Garlic Penny-cress) in Combe Valley Countryside Park (v.c

is no long-term decline in this vegetation type. This monitoring, comprising 15.4km of the beach at Dungeness between Jury’s Gap (TQ99261798) and the town of Lydd-on-Sea (TR09441839), and the control site of Rye Harbour beach (TQ91861612 to TQ95011797), has been ongoing since 2003 and provides a long-term insight into the distribution, dynamics and composition of this vegetation. The survey is contained within the hectads TQ91 and TR01.

At Dungeness the AVDL is a very species poor vegetation type, formed mainly of Atriplex glabriuscula (Babington’s Orache). This was the only species reported in Ferry, Lodge & Waters’ (1990) definitive account of the vegetation of Dungeness, and a similar situation was noted on two 2017 visits by the BSBI Atriplex referee John Akeroyd (pers. comm.). Atriplex glabriuscula is the only species referred to in the Dungeness Special Area of Conservation (SAC) supplementary advice on conservation objectives (Natural England, 2019), which draws together information from a range of sources. Atriplex glabriuscula seems uniquely well-adapted to survive the conditions of the strandline on shingle beaches; there is little doubt that it is the primary species in this community, and the most consistently successful.

It is difficult to find previous confirmed reports of other oraches at Dungeness, although there is reference to an unnamed hybrid recorded in 2018 (Jacobs, 2018). The BSBI DDb contains just over 80 records of A. prostrata (Spear-leaved Orache) for the relevant hectads, but none of these records has a grid reference or comment that suggest they are from the drift line. Monitoring in 2019–2021 has allowed the authors the opportunity to make a detailed examination of the Atriplex species present in the drift line community. Our observations showed that both A. glabriuscula and A. prostrata are present. This was confirmed by John Akeroyd from photos of a range of material. Atriplex glabriuscula is the most common species, representing 81% of Atriplex records (199 of 234) from the 2021 annual monitoring, the remainder being A. prostrata.

Another Atriplex which occurs very occasionally on the drift line at Dungeness is A. laciniata (Frosted Orache). This was recorded by the authors in one year out of three at Jury’s Gap, with additional records in the DDb from drift line around the boat mooring area on the south-eastern corner of Dungeness in 2017 and at Jury’s Gap in 2014. Atriplex laciniata is more common on the drift line of the neighbouring sandy beach of Camber Sands that lies between the shingle of Rye Harbour and Dungeness.

Given the definitive statements on the presence of only A. glabriuscula on previous occasions, it seems likely that A. prostrata is either not present every year, which would fit with the known variability of drift line composition, or else is a recent addition to the drift line in this area. Both would be ecologically interesting and, given the lack of clear definition from old reports, the best test will be to see if A. prostrata is consistently present in future years.

Occasionally, other species occur along the drift line. Tripleurospermum maritimum (Sea Mayweed) and Galium aparine (Cleavers) are the only two recorded on more than one occasion in the previous three years, both occurring on <5% of the strandline. Beta vulgaris var. maritima (Sea Beet) was noted on one occasion and is much more common amongst the pioneer perennial vegetation. In 2018 some Cakile maritima (Sea Rocket) was recorded in the AVDL where some sand accumulation amongst the shingle was noted, but this species has not been seen in subsequent years.

Despite the presence of both species in some areas of strandline, checking of over 50 specimens has failed to identify the uncommon hybrid between A. prostrata and A. glabriuscula, which is unknown from the two hectads. However, in 2021 John Akeroyd was able to confirm the hybrid Atriplex × taschereaui (A. glabriuscula × longipes) from the Dungeness beach near Jury’s Gap. This hybrid is known from Rye Harbour Nature Reserve, where the DDb contains records of it as part of the strandline from 2003. It has not been previously recorded from Dungeness.

Atriplex longipes (Long-stalked Orache) is not known from either site, but the hybrids are well-known to occur in the absence of this parent (Stace et al., 2015). This specimen occurred on the landward side of the main crest, in an area where the sea has washed over the main crest (see ‘overwash zones’ below) close to the line of perennial vegetation in conditions that are likely to be less severe than the true strandline.

Sometimes pioneer perennial species are found amongst the drift, presumably where the shingle has remained sufficiently stable for long enough. Most commonly this is Crambe maritima (Sea Kale) which forms the distinctive first line of perennial vegetation. This ‘C2’ vegetation (also referred to as pioneer perennial vegetation) of Ferry et al. (1990) is considered to represent Annex 1 Perennial Vegetation of Shingle Banks (PVSB). The diversity of species rapidly increases (from two to more than ten) as the vegetation transitions to better developed pioneer PVSB. Notable coastal species including Glaucium flavum (Yellow Horned-poppy) and Lathyrus japonicus (Sea Pea) occur in these pioneer stands as the shingle becomes increasingly stable, alongside the distinctive glaucous leaves of Crambe maritima and scattered Crithmum maritimum (Rock Samphire).

The AVDL develops along the strandline, and the plants are often seen emerging from amongst the drift. In undisturbed sections of the beach, it often forms just below the highest beach crest, typically on the seaward side, and sometimes on lower ridges near the top of the beach where there is net accretion. This can lead to the appearance of up to three distinctive lines of AVDL, a feature noted on the drift lines at Sefton (Smith, 2022).

AVDL also occurs behind the main beach crest in areas where large waves have broken over it, creating overwash zones. In places these are marked by characteristic fans of shingle, that vary in size; small ones a few square metres in area just over the crests to others nearly half a hectare in area stretching from the crests down to, and occasionally covering, the

Transition to pioneer perennial vegetation is marked by a zone of Crambe maritima (Sea Kale).

A band of AVDL on a beach ridge at the southeastern beach corner with the distinctive Dungeness boats in the background.

Atriplex on the landward side of the main beach crest where breaking waves have thrown and washed material from the seaward side. Note the vehicle tracks on the right hand side of the image which are impinging on the AVDL.

PVSB. In these places the conditions are perhaps more stable, and a denser cover of AVDL species can develop earlier in the year.

Although species poor, the drift lines at Dungeness and Rye Harbour are dynamic and important habitats. Atriplex glabriuscula is the main species in this habitat, but the relatively extensive presence of a second species of Atriplex raises interesting questions regarding permanent versus dynamic changes in this vegetation, and the importance of long-term monitoring of sufficient intensity to understand the inter-factorial relationships that lead to the observed changes in the species composition.

We are grateful to Dr John Akeroyd for reviewing photographs of the plants and commenting on a draft of this article, and to Geoffrey Kitchener for providing access to the DDb records. We are also grateful to the Environment Agency for funding and facilitating the work. We are grateful to Elizabeth Cooke for commenting on a draft of this article. Fieldwork was completed as part of the authors’ work at JBA Consulting.

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