Vegetation Survey of the Hook Farm Oyster Pond Dolphin Ecological Surveys November 2020

Dolphin Ecological Surveys Edgedown 9 Kammond Avenue Seaford East Sussex BN25 3JL 01323 304180 [email protected] Vegetation Survey of Hook Farm Oyster Pond – Dolphin Ecological Surveys 2020

1.0 INTRODUCTION The owner of Hook Farm in Bosham, West Sussex intends to carry out restoration and reinstatement work on an historic but derelict Oyster Pond on the edge of Chichester Harbour within the grounds of Hook Farm.

The Oyster Pond lies within the boundary of the Chichester Harbour SSSI, Ramsar/SPA and Solent Maritime SAC. A Habitats Regulation Assessment (HRA) will be prepared as part of the restoration proposals.

A vegetation survey of the site was carried out by Kate Ryland BSc, CEnv, MCIEEM as background to this proposal.

The survey consisted of a simple walkover of the land affected on 22nd October 2020. All accessible parts of the site were visited during which plant species were noted and an assessment was made of the plant communities that are present using the National Vegetation Classification (NVC) (Rodwell 2000).

The site description (section 2) makes note of vascular plants that were observed on the site but this does not constitute a comprehensive list for the site.

The survey was subject to minor constraints and limitations.

• Some areas of the site were not safely accessible due to the deep silt around creeks. Despite the limitations on direct access, all parts of the site were visible from stable ground.

• Seasonal constraints exist because the work took place in late October, which is outside the optimum timing for most vegetation surveys. However saltmarsh vegetation tends to comprise a high proportion of perennial species that can readily be identified during the autumn months by an experienced botanist. Although some plants could not be identified with confidence to species level due to the absence of key features, the seasonal constraints were not considered sufficient to reduce the overall accuracy of the vegetation survey and the assessment of vegetation communities present on the site.

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2.0 SITE DESCRIPTION

2.1 Location & Size The Hook Farm Oyster Pond lies on the western edge of Fishbourne Channel in the upper, northeastern reaches of Chichester Harbour at SU83141 02748. The pond is roughly circular with a diameter of approximately 50m and has steep banks on its north, west and eastern sides with a much lower relict embankment on its eastern, harbour side.

The Oyster Pond basin is contiguous with the semi-natural saltmarsh habitats that fringe the harbour and lies on the eastern edge of the garden of Hook Farm. It is surrounded on three sides by extensive areas of mown lawns as well as scattered trees and shrubs.

The area covered by this vegetation survey is shown on the site sketch map. It amounts to approximately 0.5 acre (0.2ha) in total and includes the footprint of the old pond with its neck/inlet channel as well as a representative section of saltmarsh on the harbour’s edge.

The vegetation on the upper banks of the pond forms part of the formal gardens of Hook Farm and was also included in the assessment of the habitat for context.

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View of the Oyster Pond looking west towards Hook Farm

2.2 Oyster Pond Within the pond footprint there is a mosaic of saltmarsh vegetation that reflects the characteristic plant assemblages found on the margins of this part of Chichester Harbour.

The Oyster Pond would once have held more extensive open water but over time there has been a considerable accretion of material which has raised the surface and allowed saltmarsh vegetation to develop. At high tides the pond basin fills via a network of muddy creeks that radiates out from the narrow inlet channel in the southeast of the pond.

The inlet to the Oyster Pond

Large areas of the pond basin are dominated by dense stands of sea-purslane Atriplex portulacoides and annual sea-blite Suaeda maritima. This is a typical, species-poor community that is widespread on the harbour’s edge.

The network of deep, silty creeks are more sparsely vegetated being subject to higher levels of tidal friction and accretion. These linear features tend to support pioneer vegetation comprising stands of common cord-

4 Vegetation Survey of Hook Farm Oyster Pond – Dolphin Ecological Surveys 2020 grass Spartina anglica with annual glassworts Salicornia spp. Perennial glasswort Sarcocornia perennis is present on more stable muddy areas within the pond basin.

Vegetation in the pond basin

Where the woody canopy of sea-purslane is sparse a slightly more diverse range of saltmarsh species occurs. This is most obviously in a small area at the foot of the bank in the southwest of the pond basin. Common sea-lavender Limonium vulgare, sea aster Tripolium vulgare, sea arrowgrass Triglochin maritimum, greater sea-spurrey Spergularia media, saltmarsh-grass Puccinellia sp. and shrubby sea-blite Suaeda vera were recorded in such areas.

2.3 Embankments & Harbour’s Edge Zone On the eastern edge of the Oyster Pond there are two narrow, parallel embankments with an area of lower- lying land between them. A small channel is present at the foot of the eastern, harbourside embankment.

The embankments looking north from the inlet

The vegetation in this part of the site is very similar to that within the pond basin and is dominated by dense stands of sea-purslane and annual sea-blite. This saltmarsh plant assemblage occurs in the area

5 Vegetation Survey of Hook Farm Oyster Pond – Dolphin Ecological Surveys 2020 between the two embankments and extends further eastwards towards the pioneer vegetation and mudflats on the harbour’s edge.

The western embankment is a little higher than the one to its east but both have a strip of grassy vegetation along their top edges and a concentration of couch-grass Elymus sp. on their sides, which suggests they are only rarely inundated for prolonged periods.

The embankments and woody debris looking east

The accumulated woody debris on the western face of the inland embankment and the presence of a small hawthorn Crataegus monogyna shrub on its southern tip also suggests that the top of this relict feature still lies above the usual high tide level.

2.3 Oyster Pond Banks On the drier, less brackish ground to the west of the pond, there is a dense stand of common reed Phragmites australis with sea-beet Beta vulgaris ssp.maritima on its margins that extends up towards the garden lawns. This stand of vegetation lies near the bottom of the pond bank but is above the level of the more typical saltmarsh plants.

The upper banks of the Oyster Pond are, for the most part, of minimal botanical interest. They support either mown, improved grassland or occasional coarse and ruderal species such as docks Rumex spp., nettle Urtica dioica, common cleavers Galium aparine and white dead-nettle Lamium album interspersed with areas of bare ground.

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Oyster pond banks showing common reed and trees/shrubs on the northern edge

There are scattered trees and shrubs in places along the banktops. These include hawthorn, field maple Acer campestre and mature ash Fraxinus excelsior to the south and west whilst to the north there are patches of scrubby English elm Ulmus procera and bare ground mixed below a group of mature trees.

View of the southern pond bank

2.4 Summary & Saltmarsh NVC Assessment The Hook Farm Oyster Pond contains a mixture of pioneer and low saltmarsh vegetation that can be referred to two NVC community types. These are:

• SM6 Spartina anglica saltmarsh, which is mostly associated with the creek edges but also occurs in patches across the pond basin.

• SM14 Halimione portulacoides (now Atriplex portulacoides) saltmarsh, which occupies the majority of the pond basin, the embankments and extends toward the edge of the harbour.

SM6 Spartina anglica vegetation is typically found on silt and mud substrates of the seaward fringes of saltmarsh and on creek sides. It is widespread around the English and Welsh coasts.

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SM14 Atriplex (Halimione) portulacoides vegetation is typically a species-poor community with sea-purslane and common saltmarsh-grass as the only constant components. The Oyster Pond supports the most species-poor sub-community (SM14a sub-community with Halimione portulacoides dominant). This type of saltmarsh vegetation is widespread and extensive in the SE of England.

Whilst some saltmarsh NVC communities are typically species-poor, they usually occur within a mosaic of other community types. It is the combined diversity of vegetation across the whole saltmarsh and its international rarity that is at the root of its high conservation value. Coastal Saltmarsh is a Priority Habitat under Section 41 of the Natural Environment and Rural Communities (NERC) Act 2006 – Habitats and Species of Principal Importance in England.

References Adnitt, C. et.al. 2007. Saltmarsh Management Manual. Technical Report SC030220. Environment Agency

Rodwell, J.S. (ed) 2000. British Plant Communities volume 5. Maritime communities and vegetation of open habitats. CUP. Cambridge

Stace, C. 2019. New Flora of the British Isles. 4th Edition. C & M Floristics

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