1.      Rabbit grazing is a valuable management option in some areas (see natterjack toad factor). In some areas it is not desirable at all, as controlled grazing by livestock is carried out, as on the freshwater marsh.  In the east dune slack, from 1997, a temporary rabbit exclosure has been instated to conserve a 30 x 20m representation of slack sward.  This is rich indeed, supporting meadow vetchling Lathyrus pratensis, common fleabane Pulicaria dysenterica, adders-tongue fern Ophioglossum vulgatumand some 300 spikes of southern marsh orchid Dactyloriza praetermissa (in 2000) amongst typical slack constants such as silverweed Potentilla anserina and common sedge Carex nigra.  The level of rabbit grazing is a difficult issue, as elements like myxomatosis, weather conditions, level of control and perceived optimum vegetation structure all have to be taken into account.

2.  Controlled grazing by livestock is the ideal management tool for this feature, particularly the freshwater marsh area, where cattle are the preferred animal.  Sheep are utilised to maintain open conditions at the four acre enclosure at Army Swathe.  By 2001, under the Trust’s ownership, the potential to stock-fence the entire Measure’s compartment is being pursued.  This will enable livestock to maintain the slack grassland within the mosaic of open dune and scrub.  The exact history of grazing on the Freshwater Marsh (compt 1/31/A) is unclear, although it is believed that cattle were regularly grazed during the first two decades of the century.  However, military occupation during the First World War served to evict the graziers and there is no evidence of subsequent grazing until well after the establishment of the nature reserve.  Under the Trust’s management, late summer cattle grazing was re-instated from 1974 and has been carried out annually since 1976.  Cattle grazing was permitted in temporary fencing around three acres of the central slack in Measures 40 acres (compt 1/95/A) from 1992.  At the south- western extreme of the Freshwater Marsh, Mere Meadow 1/32/B has been managed as a traditional hay meadow, with aftermath sheep grazing.

3.  The water table is fundamental for its influence on the vegetative communities on the freshwater marsh.  There is no controllable input of fresh water.  The water table is governed through precipitation and any subsequent drainage or evaporation.  For the most part the water table range during the year is in the order of 60-90 centimetres on the Freshwater Marsh.  A network of man- made pools, ditches and dykes has been created on the Freshwater Marsh over time.  Most have been created to enhance the nature conservation interest of the site; others for educational use (Eric’s and Oval), or resulting from military operations.  Mill Pond was dug as a proposed water supply for the Tennyson Glen Estate; a housing complex which was curtailed in the 1930’s.

4.  The well-documented tidal inundation of 1953, impacted heavily on the freshwater ecology.  The demise of amphibians and some plants eg bee orchid Ophrys apifera were attributed to this event.  Repeated inundation through the 60’s and 70’s, coupled with the drought years (particularly 1976) led to an unstable and quite inhospitable environment for a range of flora and fauna on the Freshwater Marsh.  More recently, the drought years of 1989- 91 have led to a freshwater deficit.  Saline ingress was apparent in some pools on the Freshwater Marsh where an increase in up to 2 ppt was recorded during the period.  Local water abstraction may have exarcebated the situation.  The Borrow Pits (compt 1/32/D) were created when material was excavated to build up the Bulldog Bank; most recently, to strengthen the bank after the 1978 tidal breach.  The salinity of the water here varies and may be influenced by hydrodynamic pressure, particularly during spring tides.  The East Dune slacks show some variation in salinity from Army Swathe which is totally fresh, to Natterjack Slack which meets the Old Saltmarsh and tidal inundation occurs rarely on the highest spring tides.  Conversely, the adjacent ‘tidal slack’ compt 1/3/B becomes quite fresh during winter eg 5.3 ppt (1/2/2001).

5.  Following the above-mentioned tidal inundations, measures were taken to restore common amphibian populations during the mid 1980’s.  The importation of frogspawn may have been responsible for the accidental introduction of Crassula helmsii to the Freshwater Marsh.  This pernicious alien was found when already quite established in two main areas. A prolonged and aggressive campaign of eradication began in 1995.

6.  A number of pernicious weeds persist on the areas, notably ragwort Senecio jacobaea, and creeping thistle Cirsium arvense.

7.  The drought and some scrub invasion may have discouraged nesting attempts by lapwing Vanellus vanellus which had previously been a feature of the site. This species has declined by 49% in 11 years (BTO).  It is something of a ‘flagship’ species for the freshwater marsh.

8.  The drier reaches of such grassland, where ribwort plantain Plantago lanceolata thrives, may provide a niche for the rare marsh moth.  This species UK range has contracted to possibly only two sites on the Lincolnshire coast.  It has been sparsely recorded at Gibraltar Point through the 1990’s.  Piles of cut grass are left in strategic locations, as these are favoured by the larvae.

9.  The feature supports a range of Orthoptera, including two species of groundhopper (Tetrix sp).  The most important species is the short- winged conehead Conocephalus dorsalis, which can be found on emergent strands of sea club rush Bolboschoenus maritimus and other rank marginal vegetation along the network of pools and dykes.

10. The natterjack toad survived at Gibraltar Point until possibly as recently as the 1940’s.  It was reportedly seen in numbers in 1911 (LNU).  Its subsequent extinction here is probably linked to the extensive scrubbing over of much of the dunes, including the slacks where the animals presumably spawned in shallow warm waters.  The advance of scrub will also have facilitated the movement of the competitive common toad into breeding sites.  It is possible that natterjacks may have bred on the upper reaches of saltmarsh where met by freshwater slacks.  The installation of the Bulldog Bank therefore may have had a significant effect on the natterjack toad. Attempted re- establishment failed during the 1960’s and 70’s largely due to a lack of understanding of the species ecology.  Gaps in knowledge were later addressed and in 1990, the site was sanctioned for inclusion in EN’s Species Recovery Programme.  By this time, significant progress had been made with the restoration of the open slack through scrub clearance.  Coupland’s pond had been dug in 1986 with the characteristics of an optimum breeding pool, ie shallow, with gradually shelving sandy margins.  A second slack pool, the Barrow, was cleared of scrub and re-profiled.  It is important for natterjacks to have a variety of pools to broaden the population base and ensure good productivity in at least occasional years.  Productivity in Coupland’s Pond and the Barrow seems limited by colonisation of odonata (particularly Sympetrum striolatum) and coleoptera larvae, which are assumed to predate heavily on the natterjack tadpoles.  The notable Dytiscus circumflexus is probably a major predator in Coupland’s Pond.  In the ‘Natterjack Slack’ the land quickly rises to the north, well proud of the water table and there is no standing water at any time of year.  Scrub clearance was carried out to the north to reinstate grey dune and suppress the migration of common toads into Riseholme Pond, which was created as a natterjack pool.  The characteristics of this pool offer better prospects for natterjacks than any other.  The proximity of scrub, the late-summer drying and occasional winter inundation assist with suppression of serious predators/competitors. Oppressive scrub has been removed from the margins of Scirpus Pool and it’s potential for colonisation by natterjacks may be realised in the future.

11. Water voles occur in various water bodies on the Freshwater Marsh on the Freshwater Mere, which was created in 1973, providing 0.95 ha of open water.  There is a small population of water voles present on the borrow pits.  Water voles are a national and county BAP species.

12. The Mere being the reserve’s largest freshwater body, is an important nucleus of the regionally important odonata assemblage.  Of the 12 species which breed on the site, 8 are believed to breed at the Mere, some of which colonised the site as recently as the 1980’s and 1990’s.  On the borrow pits there is sufficient freshwater influence to support a range of Odonata, such as emerald damselfly Lestes sponsa.

13. Through the mid-1980’s, the term marsh was something of a misnomer.  Predominantly dry conditions prevailed and the sward was consistent with a fine dune meadow.  The increasingly dry conditions culminated in the drought years of 1989-1991.  Immediately following the drought years, 1992 yielded over 700mm of rainfall (compared to 416mm in 1991) and subsequently there followed a return to at least average rainfall.  Standing water then became a feature of the habitat in most winters.

14. The water table deficit has been possibly exacerbated by land drainage through arable operations to the west and abstraction to the north.  In 1995, positive benefits for the water table were realised when farm drains on Jackson’s Marsh and Tennyson’s Sands were blocked.  This has ensured that drainage from the NNR which ultimately goes into the Cowbank Drain, has been curtailed.  However, the water table range remains extensive during the year and low summer levels cannot be compensated for through any controllable freshwater input. The effects of any local water table abstraction need to be fully investigated.

15. Payne documented the decline of the great crested newt Triturus cristatus at its remaining breeding pools in the mid-late 1970’s.  Tidal inundations and summer droughts during this period saw the population dwindle and it was subsequently believed extinct until a spate of records in the 1990’s.

16. Amphibian populations suffered from a series of tidal inundations from the early 1950’s. During the mid-1980’s, a programme of re-establishment was carried out for common frog Rana temporaria and smooth newt Triturus vulgaris.  The toad population appeared to have fared better although was not subject to re-introduction.

17. Dune slack communities are not particularly robust in terms of visitor pressure. Repeated trampling has caused damage to the dune slack turf and promoted the spread of undesirable species.  Isolated incidents of orchid picking and trampling of natterjack toadlets have occurred.  Fortunately, most of the key sites are in discrete parts of the reserve or public access is discouraged where fencing has been instated for stock-grazing purposes.

18. The extent of scrub is a major factor.  Efforts to restore open dune slack in ‘Buckthorn’ (compt 1/25/G), commenced in the mid-1990’s, concentrating around the existing ringing rides.  A network of broad rides and glades were established and maintained through annual cutting.  The dominance of the sallow canopy has increased rapidly.  Its value to a wide range of invertebrates both as foodplant and early nectar source cannot be understated.  Its value to nesting and migrant birds is therefore also high.  However, due to its status, likely effects on the slack via evapo-transpiration and succession over floristically rich slack communities, management intervention has been initiated to restore open dune slack. Much of the Measures slacks were under a sea buckthorn canopy by the early 1990’s when the Trust was able to negotiate an annual management agreement with the landowner Mrs Measures. Scrub clearance was undertaken to restore areas of open slack, although established scrub remains in parts and obscures some of the slack/dune transition.  An annual mowing programme has been instated for the Measures ride and glade system and this maintains some of the smaller areas of slack.

19. Juncus is a widespread species on the freshwater marsh.  Whilst indicative of damp conditions it can become invasive.

20. The Freshwater Marsh is an important area for breeding birds, with the mosaic of damp grassland, ponds, dykes, ditches and marginal vegetation.  The assemblage includes reed, sedge and occasional grasshopper warbler and possibly water rail.

During the autumn and winter, the Mere provides an important refuge for passage and wintering wildfowl including teal and wigeon.

1.  Total extent of both areas.  Extent will be measured once during the reporting cycle. There should be no decrease in the area of open slack/Freshwater Marsh habitat.

2.  Characteristic vegetation.  The dune slacks and freshwater marsh will be surveyed at least once during the reporting cycle, for the presence of key species and range of NVC communities.  Natural change/transition may dictate some variation in extent of specific communities as a proportion of the habitat resource, particularly where changes in hydrological regime are attributable to rainfall.

 

3.      The water table in the East Dune slacks is believed to be entirely dependent upon precipitation and there are no control mechanisms.  The water table on the Freshwater Marsh is surveyed via the Mere depth gauge.  The levels of which should be tied into the depth gauges of Tennyson’s Sands, Jackson’s Marsh etc to increase understanding of the hydrology.  Mere readings are measured on a weekly basis.

4.  Vegetation negative indicators

Negative indicator species include aggressive ruderals eg creeping thistle and nettle which may exploit bare ground or enriched areas or scrub, which may colonise the dune slack or Freshwater Marsh from established stands.  On the Freshwater Marsh, Juncus may be deemed a negative indicator species and will be managed between 1-5% coverage.