Dune slack habitat is located primarily in two distinct areas of the reserve; the Freshwater Marsh, and the slacks of the East Dunes, with minor areas in the West Dunes.  Water tables are reliant upon precipitation.  None of the Gibraltar Point communities exhibit Salix repens, although Salix caprea represents the climax stage in the East Dunes.  Dune slack is typified by open damp grassland on sandy soils, invariably in the low trough between dune ridges.  Standing water may be extensive during the winter period, with damp conditions persisting into the summer months.  This feature is floristically rich and the following NVC community is significant:

SD17 Potentilla anserina - Carex nigra (silver-weed - common/brown sedge) dune slack community.

The key areas are described below;

1.    The Freshwater Marsh area comprises a 16 acre grazing meadow (compt 1/31/A) with a low- lying damp plateaux interrupted by dune ridges and the slacks which run north into Measures 40 Acres (compt 1/95).  The grazing meadow was claimed from saltmarsh through the building of the Bulldog Bank at the turn of the century.  This effectively served to truncate the transition from upper saltmarsh through to freshwater habitats, although tidal inundation during storm conditions occurred until as recently as January 1978.  After this last event, the bank was raised and strengthened.  Certain saltmarsh plants still thrive here, for example sea milkwort Glaux maritima, sea aster Aster tripolium and saltmarsh rush Juncus gerardii.  The 1999 NVC survey (Weaver) identified extensive tracts of communities consistent with inundation grassland, dune slack and swamp on the Freshwater Marsh and Measures; notably MG10, MG11, SD 17b and S21.

2.    The East Dunes is comprised of a series of dune ridges with three areas of slack in between. They are discussed, from east to west.

a)  Main east dune slack (compt 1/25)

This eastern-most slack is the most significant in terms of its extent and water table and includes the compartments known as Army Swathe (1/25/A) and ‘Buckthorn’ (1/25/G).  The majority of this slack was scrub-dominated by the 1960’s with the exception of a relict 2 acres of open grassland.  Army Swathe was cleared by military activities, during a check for ordnance.  As with Army Swathe, ‘Buckthorn’ as its compartment name implies was a canopy of dense scrub by the 1960’s, with full succession to Salix carr well established by the 1980’s.  It is possible that the establishment of Salix caprea along ride edges was promoted by bird ringers to attract warblers to net rides.  Narrow ringing rides have always been maintained in ‘Buckthorn’ and in places this has allowed a representation of dune slack flora to persist.

b)  Natterjack slack (1/25/B)

At its southern extreme, this slack meets the Old Saltmarsh and there is an interesting zone of transition where tidal inundation is infrequent.  Distant sedge Carex distans, lesser centaury Centaurium pulchellum and sea milkwort Glaux maritima are characteristic of the sward.

To the south, scirpus pool and celery pool are very small pockets of almost fresh water, presumably created during military activities.  Their juxtaposition along the saltmarsh dune interface makes this hydrology difficult to understand.

c)  Willey’s slack (1/25/F)

A very narrow strip of wet slack, which holds standing freshwater throughout the winter months and well into the spring.  This slack also meets the Old Saltmarsh at its southern extreme, where a tidal slack shows developing sea club rush swamp.  However, a low artificial bund prevents tidal inundation north up the slack that would otherwise occur on the highest springs, although percolation may exert some saline influence through the substrate.  The removal of this bund would allow a rare example of upper saltmarsh transition to be fully reinstated.

3.  West Dunes

Whilst there are no extensive slacks on this system, there is an interesting area of open water and ephemeral pools at the southern extreme.  Roadside Pool was apparently excavated during military occupation and may have been a fuel dump.  It is notably saline and is fed via percolation during the spring tide sequences.  The water table increases in tandem with the highest tides.  The pool frequently dried completely during the summer months but with the instatement of dams on Jackson's Marsh, water levels are generally held higher during the year across this part of the reserve.  Sea club rush Bolboschoenus maritima, orache sp and annual sea blite Suaeda maritima are found around the otherwise bare margins.  To the north, there is no natural standing water in this dune.  Park pool and Mill Pond are both man-made.

Currently the NVC communities are present in suitable proportions and total extent.  Water tables are favourable, active management is continuing through grazing and scrub removal.  It is anticipated that favourable status will be maintained for the duration of this plan.