Galeopsis speciosa (Lamiaceae): an Open Vegetation seed bank community at Worsley in Salford (v.c.59), revealed during construction of the new Royal Horticultural Society Garden at Bridgewater

This paper provides a baseline flora for the site of the new garden of the Royal Horticultural Society at Worsley New Hall in Salford (v.c.59). During construction, 35,000 m of top-soil, sub-soil and spoil were stripped and stored onsite; species recruiting from these seed banks were monitored 2017-2020, leading to the description of a new Galeopsis speciosa Open Vegetation plant community. Four commercial wildflower mixes were used during post-construction landscaping in 2019, and their establishment was assessed in 2020. It will be interesting to follow the survival of these introduced species, many of which are not native to the site.

Francis Egerton (1800-1857), 1st Earl of Ellesmere was heir to this fortune. He built Worsley New Hall to a design by Edward Blore. The foundations were started in 1839 but the building was not completed until 1846 (Fig. 1). The formal landscaped gardens were set out while the house was being built in the early 1840s, with further developments over the next 50 years. Landscaping included terrace gardens constructed by William Andrews Nesfield (Fig. 1), who started work on the gardens in 1846. By 1857, there were 6 terraces, separated by stone balustrades, and linked with steps and gravel paths. The top two terraces were set out in a Parterre en Broderie style. A croquet lawn and tennis court were built close to the terraces. To the south lay landscaped parkland and a boating lake. The lake was enlarged by 1875 and featured an island grotto accessible by a footbridge.
To the west of the terraces, woodland separated the grounds of the New Hall from the gardener's cottage and kitchen gardens. The 11 acre walled kitchen gardens were laid out in the early 1840s to provide vegetables, fruit and flowers to the residents of the New Hall. The perimeter red-brick walls were heated by flues using the Trentham wall case design, to create a warmer micro-climate for the fruit trees grown against them. Glasshouses grew cucumbers, melons, grape vines and peach trees. The head gardener's cottage, built in 1834, was also designed by Edward Blore, while The Bothy was erected in the late 19th century to house unmarried gardeners. A boiler in the cellar of the Bothy provided heating to the kitchen garden glasshouses: its chimney is the most prominent surviving feature of the estate. Queen Victoria visited the hall twice, in October 1851 and June 1857. On her second visit, whilst attending the Art Treasures Exhibition, she planted Sequoiadendron giganteum on the lawn of the New Hall in memory of the Duke of Wellington, but the tree did not thrive and was not replaced.
After the New Hall was abandoned by the Earls of Ellesmere in 1914, the gardens fell into disrepair, with the formal gardens becoming overgrown. During World War I, John Egerton, 4th Earl of Ellesmere lent the hall to the British Red Cross, and it was used as a hospital for injured soldiers. The grand rooms of the New Hall were used as wards, with food provided by the kitchen gardens with the terraced gardens and parkland used for recreation. The hospital closed in 1919. In 1920, death duties led the 4th Earl to start auctioning off various items of furniture and fittings from the New Hall: the library, and surplus furniture were sold at auction in April 1921. In 1923, the Worsley estate including the New Hall was sold to Bridgewater Estates Limited, a group of Lancashire businessmen, but their grand plans came to nothing. During World War II, the War Office requisitioned parts of the New Hall and the grounds. The 2nd and 8th Battalions of the Lancashire Fusiliers occupied the site in 1939 and 1940, with around 100 troops based there, using the Hall's basements as air raid shelters, and digging training trenches in the grounds. In 1941 and 1942 the 42nd and 45th County of Lancaster Home Guard Battalions used the site, practising street fighting in the hall, and storehouses for explosives were constructed in the grounds. In September 1943, a fire badly damaged the top floor of the New Hall. The building had suffered during the military occupation, with windows broken and interior furnishings used for firewood. The house was also suffering from dry rot and subsidence due to mining. Calls for tenders to demolish the building were sent out in 1944 and by 1949 the hall had been demolished to ground level, with debris used to fill in the basements. In 1951, the War Office again requisitioned part of the New Hall site and built a reinforced concrete bunker where the servants' wing had been, along with two antiaircraft radar masts. In 1956, the War Office purchased the site of the bunker and it was used by the Royal Navy as a food store. In 1961, the bunker was sold to Salford Corporation, and was used by them and Lancashire County Council as a control centre. In 1968, ownership of the bunker passed to Greater Manchester Fire Service; in 1985 they leased it to a local gun club as a shooting range.
The site of the New Hall and gardens remained in the ownership of Bridgewater Estates Ltd until 1984 when the company was acquired by Peel Holdings, now Peel Land and Property. Worsley Hall Nurseries and Garden Centre continued in business until Peel Holdings bought the Kitchen Garden, Garden Cottage and other buildings in 2008. Over the years there had been various ideas about how the site could be regenerated and put to new use, including a racecourse, hotel and spa.

RHS Involvement at the site
The Director General of the Royal Horticultural Society, Sue Biggs, first visited the site in January 2015 to assess its potential as a location for the RHS's fifth garden. After extensive deliberations, the proposal by RHS Council to develop the fifth RHS Garden at Worsley was announced in October 2015, with the intention of calling it RHS Bridgewater. Planning approval for the development was granted in April 2017 and the Secretary of State signed off the development in June 2017. This enabled completion and exchange of lease agreements between Salford City Council, the RHS and Peel Holdings in July 2017.
Phase 1 of the development involved the restoration of the historic 11-acre walled garden, following a master plan drawn up by Tom Stuart-Smith (Fig. 2). A Chinese Streamside Garden winding through Middle Wood will link a new lake (Worsley Water) to the restored original lake (Ellesmere Water). A new Welcome Building, facing east across Worsley Water includes an events space, a learning centre, offices, café, shop and plant centre. Community gardening projects, developed with and for local people and organisations, are an integral part of the plan.
The aim of this paper is to document the vascular plants present on the site before and during the construction of the new garden, as a baseline for understanding future changes in plant biodiversity. Most of these changes will be a consequence of deliberate horticultural introductions, but some will be legacy effects, and others will be unplanned botanical incursions. The description of the flora is presented in three sections: the species that were growing on the site before its purchase by RHS; the plants exposed during the construction phase, concentrating on the species that were present in the soil seed bank; and postconstruction landscaping, emphasising those areas that were sown or turfed with commercial wildflower mixtures. The main horticultural planting and the development of the arboretum will be documented in later publications.

Methods
The study area comprises 63 ha, as shown in Fig. 3. The boundaries of RHS Bridgewater are defined on the north by Leigh Road and on the south by the Bridgewater Canal. The eastern boundary follows the edge of the slip road of Junction 13 of the M60 motorway, and the western boundary runs from Leigh Road south to the Canal. The site was surveyed for vascular plants on 9 March and 1 September 2016 (pre-purchase), 1 June 2017 (pre-soil-stripping), 10 September 2018 (topsoil mounds), 15 August and 25 September 2019 (topsoil mounds) and 11 July 2020 (post-construction). Comprehensive species lists were made for each plant community, noting the dominant, abundant, frequent, occasional and rare species (dafor; Tansley, 1911), but detailed assessments of plant cover were not undertaken. Nomenclature follows Stace (2019).

Results
The flora when the site was purchased: 1) semi-natural habitats Woodland -The main block of woodland comprised East Wood, Leigh Road Woods, Middle Wood and Bothy Wood and represents a species-poor remnant of W10 (Rodwell, 1991a), with the canopy dominated by self-sown Acer pseudoplatanus and the shrub layer by thickets of Rhododendron ponticum naturalised from rootstocks planted in the late 19 th century to support choice cultivars as grafts. The dense shade excluded all ground flora from much of the area. The composite species list is shown in Table 1a, where the most conspicuous ground-layer plants were Dryopteris dilatata and D. filix-mas (Table 1a). For such a grand garden (Brookes, 1857) there is a surprising lack of ornamental conifers and veteran native trees. Scrub -A zone of scrub ranging between 5 and 20 m wide surrounded Victoria Meadow and Arboretum Meadow (Fig. 3). The flora (Table 1b) was intermediate between woodland and grassland, and while the woodland component was reduced in species-richness, the grassland component had more species (both of grasses and forbs; MG1, Rodwell 1992) than the adjacent meadow, dominated as this was by Lolium multiflorum. In damper areas, sallow (Salix cinerea subsp. oleifera and hybrids) and Impatiens glandulifera were conspicuous.
Wetland -There were small patches of wetland all along the southern boundary, next to the Bridgewater canal, with a Reedmace swamp (S12; Rodwell 1995) in the south-eastern corner. The most extensive wetland was at the eastern end of the man-made Ellesmere Lake which had been a focal feature of the original garden, at the foot of the steep terraces, south of the grand house. The eastern half of the lake had long-since silted up, and the former lake bed supported a wet woodland, with Acer pseudoplatanus, Alnus glutinosa, Athyrium filix-femina, Betula pubescens, Carex pendula, Crataegus monogyna, Dactylis glomerata, Dryopteris dilatata, Dryopteris filix-mas, Fagus sylvatica, Impatiens glandulifera, Phalaris arundinacea, Phragmites australis, Quercus robur, Ribes rubrum, Rumex sanguineus, Salix x fragilis, Solanum dulcamara and Urtica dioica. The ground layer was dominated by Carex remota (as in W2; Rodwell 1991a).
The Moss -Nothing remained of the Sphagnum mires (M18; Rodwell 1991b) that once dominated the lower ground on the south of the site (the grey area in Fig. 3) which would have supported species like Erica tetralix, Andromeda polifolia, Drosera intermedia, D. anglica, Rhynchospora alba, Myrica gale and Osmunda regalis (Savidge et al., 1963). These mires were probably drained in the mid 18 th century before the canal was built. The ghost of the mire survives in the form of black, peaty soils underlying the improved grasslands that stretch from South Moss to Victoria Meadow.
The Lake -Before it was drained for dredging (2018)     The seed bank of the black peaty soils of The Moss was sufficiently consistent and distinctive to merit description as a new category of Open Vegetation (Galeopsis speciosa community; Table 2). The early country floras of Cheshire (Warren 1899) and Lancashire (Wheldon & Wilson, 1907) as well as the metropolitan floras of Liverpool (Dickinson 1851) and Manchester (Wood, 1840, Grindon 1859) agree that Galeopsis speciosa was a locally abundant component of the seed bank of root crops on black, peaty soils. Curtis (1777-98) considered it to be "One of the most splendid of our native wild flowers". An early description of this seed bank was by Price Evans (1923) from Carrington Moss, just south of the RiverMersey in Cheshire. Prior to 1886 this had been a well-stocked grouse-moor, over 600 acres in extent, forming part of the estates of the Earl of Stamford. In 1886 the Moss was purchased by the Manchester Corporation to be used primarily as a dumping-ground for town refuse. It was then systematically drained as the first step towards creating valuable agricultural land. Hundreds of thousands of tons of night-soil, with cinders, were dumped on the virgin moss, but after the introduction of modern methods of sanitation this practice was discontinued. Subsequently, street-sweepings were supplemented by sulphate of potash, sulphate of ammonia and super-phosphate. This created a soil that could be worked and tilled in all weathers; it never got too wet and, on the other hand, never too dry (Price Evans, 1923). He described the seed bank as follows: abundant Achillea millefolium, Atriplex patula, Chenopodium album, Elymus repens, Galeopsis speciosa, Persicaria maculosa, Rumex acetosella, Stellaria media, Tussilago farfara, Veronica hederifolia; frequent Capsella bursapastoris, Fallopia convolvulus, Holcus mollis, Mentha arvensis, Myosotis arvensis, Papaver dubium, Plantago major, Poa annua, Poa trivialis, Rorippa palustris, Senecio vulgaris, Sinapis arvensis, Spergula arvensis, Stachys palustris, Symphytum officinale, Trifolium spp., Veronica arvensis; 29 further species were listed as occasional or rare. He observed that "Galeopsis speciosa is perhaps the most conspicuous weed on the arable ground on the Moss, and it can only be held in check by a vigorous or 'smothering' crop" like potato.

Physiognamy
A spring-germinating ruderal community with a diverse, long-lived seed bank producing a dense cover of species-rich vegetation by late summer. Galeopsis speciosa has a strong dormancy that is sufficiently alleviated during the winter to allow germination of only part of a seed batch each spring; hence a stepwise germination pattern occurs over a period of several years (Karlsson et al., 2006).

Habitat
Peaty soils, of the kind developed during the 18 th and 19 th centuries on lowland 'mosses' in the north-west of England. Driven by the fashion for agricultural improvement, the bog was drained, then copious quantities of night soil were applied to surface of the peat each year. Today these habitats have black peaty loam soils with a pH around 6.2.

Zonation and Succession
The community appears following disturbance of the perennial vegetation by ploughing or during construction work. It disappears after 2-4 years of secondary succession, replaced by rank grassland, then scrub.

Distribution
Not yet documented, but necessarily restricted to the distribution of the nominate species on lowland peaty soils in western Wales, north-west and eastern England, lowland Scotland and Northern Ireland (Fig 5).

Post-construction Landscaping
Four different wildflower mixes were employed (2 seed mixtures and 2 as turves): their botanical compositions are described in Table 3. The plant communities that developed where these mixtures were planted, indicate which of the sown species showed themselves in 2020, plus the local seed bank and unintentionally introduced species that recruited along with them ( Table 4). The strip along the northern boundary to the east of the new entrance was sown with seeds of Emorsgate EM3 Meadow Mixture in 2018. Wildflower turf was laid in all the swales (e.g. down the western edge of the main drive, and through the main car park), around Moss Basin and as a strip along the southern wall of the walled garden in 2019. The western end of Victoria Meadow was sown with DLF Seeds Wildflower Seed Mix for Acidic Soil in late 2020 (but after the survey; it will be monitored for the first time in 2021).
Green manures, including Phacelia tanacetifolia and Sinapis alba were sown as weed suppressors in beds that were destined to lie fallow for one or more growing seasons (e.g. The Outer Walled Garden).
Details of the planting of the Paradise Garden, Kitchen Garden, New Orchard, Chinese Streamside Garden and the Arboretum will be published elsewhere.  The construction work associated with building the new RHS garden involved the movement and temporary storage of vast quantities of topsoil and this provided an opportunity to study the seed banks beneath contrasting habitats within the Warley New Hall estate. The black, peaty soils from The Moss in the south-west corner of the site proved to have a highly distinctive seed bank with Galeopsis speciosa as a major component. This is described here as a new Open Vegetation community (not in Rodwell, 2000; see Table 2). It will be interesting to see from the results of future work, over what part of the geographic range of G. speciosa (Fig. 5) the community occurs. A notable feature of this seed bank was the co-occurrence of closely related taxa: Persicaria lapathifolia along with P. maculosa and Galeopsis bifida with G. tetrahit. Persicaria amphibia was reported by as a pernicious weed on some of the arable soils on Carrington Moss (Price Evans, 1923), and was locally frequent on the soil piles in the south-western corner of RHS Bridgewater.
This fertile soil was used to fill many of the beds in the Paradise Garden and all the beds in the Kitchen Garden. It was also used in landscaping the ground at the newly-constructed Welcome Building and around the adjacent new lake (Worsley Water). These works will have spread the seed of Galeopsis speciosa over most of the non-wooded parts of the estate.
In assessing the flora of soil piles, there is inevitably a degree of uncertainty about the origin of the seed of the species that appear (e.g. did they come from the seed bank or by contemporary inward dispersal). Some of the more obvious nonseed-bank species were the alien fleabanes (the recently arrived Erigeron sumatrensis and E. floribunda and the longer-established E. canadensis). These typically peaked in abundance in the first year after topsoil dumping, germinating in an essentially competition-free substrate, but declined dramatically in abundance in the 2 nd and 3 rd years as competition from perennial grasses increased. Their likely origin was the embankment of the M60 motorway slip-road. Other species recorded from the soil piles had clearly come from spilled seed used in the wildflower mixtures (e.g. Anthemis austriaca, Eschscholzia californica, Leucanthemum vulgare, Linaria vulgaris, Lotus pedunculatus, Medicago sativa subsp. sativa, Mentha spicata, Origanum vulgare, Papaver dubium subsp. dubium).
The use of wildflower mixtures in semi-natural habitats outside a horticultural setting has become controversial in recent decades (May, 1994), especially where it has been shown that species being sold as native wildflowers were actually alien species (e.g. Cota austriaca instead of Anthemis arvensis), alien subspecies (e.g. Poterium sanguisorba subsp. balearicum) or alien varieties (e.g. Lotus corniculatus var. sativus) purchased cheaply overseas from agricultural suppliers and sold at considerable profit in Britain. The extensive use of well-documented seed mixtures in landscaping at RHS Bridgewater affords an opportunity to follow the establishment and subsequent survival of a set of British native species that were not previously part of the flora of the estate. It will be particularly interesting to follow the fate of any of these introduced species that become naturalised and increase in abundance, indicating that previously their recruitment had been seed-limited (Turnbull et al., 2000). None of the sown species has any reputation for invasiveness (see Stace & Crawley, 2015).
The plan is to record and publish details of the horticultural planting as the garden develops over the years, so that we can tease apart the origins of the botanical changes that are bound to occur: planned introductions, legacy effects and unintended arrivals. This will form a unique archive on the interaction between horticulture and ecology.