1.      In addition to colonisation by invasive plants, the factor which most influences the grey dune communities, is the rabbit population.  Fundamentally, rabbits have undoubtedly been important in suppressing scrub colonisation across fixed dune systems.  Damage to pioneer growth can be extensive during late winter in heavily populated areas. Further, they are important in creating and maintaining structural and species diversity in the dune sward in the absence of any native grazing animals.  There is no evidence to suggest that livestock were extensively grazed on the dunes.  Historical accounts indicate that occasional sheep grazing was practiced probably along the southern extreme of the West Dunes until the 1920's.  Rabbits however, have long been established. Indeed early references to the Gibraltar Point dunes termed them ‘the great rabbit warren south of Skegness’. Rabbit would have constituted a significant food source for the community which existed until the 1950’s.  Rabbit trappers sold meat in Skegness until the late ‘30’s.  During the 1950’s the advent of myxomatosis effectively eradicated the rabbit population on the reserve.  The resulting prevalence of coarse grassland and scrub, may have resulted in the demise of certain invertebrates, possibly including the brown argus. 

Photos from 1974, (Payne) show the resumption of heavy rabbit grazing pressure again on the West Dunes.  However, outbreaks of the virus persisted, keeping the rabbit population in check.  Coupled with this, control was carried out in the dunes periodically.  Rabbit control was relaxed from the early to mid 1990’s. During the latter part of this period, it was noted that immunity to myxomatosis was widespread in the population.  Whilst the symptoms of the virus could still be seen, particularly during late summer and autumn, there were no resulting fatalities.  The population grew accordingly and the resulting grazing pressure was heavy over large tracts of dune grassland, with the resulting impoverishment of sward structure etc and a tendency for uniformity.  Although no quantitative assessment of rabbit grazing is available, grazing pressure is visually assessed and judged to be either light, moderate or heavy, based on the following landscape characteristics.

2.  There is no evidence to suggest that livestock were extensively grazed on the dunes at any time.  However, sheep grazing is known to have occurred patchily at the southern end of the West Dunes, but not after the 1920’s.  Sheep-grazing was established again from 1985, when the mid- section of the West Dunes was grazed and this was extended across the West Dunes the following summer.  Inevitably, rabbits moved in to the grazed areas and negated the need for annual livestock grazing during most of the 1990's.

3.  Occasional burns have occurred on the dunes, attributable to arson incidents.  One such incident on West Dunes in 1990, involved a quick burn over a half acre of roadside dune at middle car park.  It is interesting to note that whilst occasional buckthorn bushes were killed, the turf recovered quickly and well, including marram.  Deeper burn incidents may have resulted in the spread of rosebay willowherb across the dunes.

4.  Trampling by human activity has also shaped some of the dune communities, particularly where in conjunction with rabbit grazing.  The main West Dune track (compt 1/22) for example shows cornsalad Valerianella locusta, parsley piert Aphanes arvensis, buck’s-horn plantain Plantago coronopus, whitlowgrass Erophila verna, early forget-me-not Myosotis ramosissima, dove’s-foot crane’s-bill Geranium molle and stork’s-bill Erodium cicutarium.  The latter being the favoured foodplant of the brown argus.  Human activity on the visitor centre lawn may be responsible for the perpetuation of rue-leaved saxifrage Saxifraga tridactylites.  This grey dune compartment (1/41/C) is periodically fenced off however, to allow turf recovery, when large areas are worn down to bare sand.

5.  A variety of alien plants have appeared on the grey dune, particularly on the West Dunes where most originated from fly- tipping of garden waste and unofficial plantings.  Species include lesser periwinkle Vinca minor, daffodil Narsissus sp. and snowberry Symphoricarpos sp. Management has curbed the spread of most of these species. The origins of the alien spring beauty Montia perfoliata are unclear.  This species is largely shade- tolerating and proliferates under the scrub canopy.  It can also occur in dense patches across open grey dune.

 

6.      Another threat to the species diversity of grey dune has been the invasion of rosebay willowherb.  In contrast to dune systems at Saltfleetby, Holme and Holkham where it grows in isolated clumps, the Gibraltar Point scenario has involved extensive monotypic stands, spreading over the grey dune.  On the East Dunes in particular, occasional stands of rosebay were over 100 square metres at 3ft high. The blaze of pink across the dunes was actually quite striking and visitors commented on the aesthetics!  So much of the East Dunes has been disturbed by military activity and large areas of dune between Mill Hill and the Ringing Hollow were occupied by military buildings until they were demolished between the late 1940’s and 1960’s.  The buildings and associated military activity has clearly affected the development of the dune grassland and promoted the spread of rosebay. Rabbits preferentially avoid rosebay and ragwort, which in a heavily grazed environment can lead to dominance of either.  In rank dune grassland, both species are somewhat suppressed via competition with coarse grasses.  The status of rosebay in the UK is somewhat dubious.  Ragwort however, is an important component of the native dune flora. Whilst it grows extensively, it does not grow as densely as rosebay and even at highest density the shade cast is less significant on grassland communities.  The basal leaves can constitute significant ground cover though. Ragwort is a key source of nectar for invertebrates in the heavily rabbit-grazed dune landscape, which may be devoid of alternative flowers.  The flowers are favoured by some of our specialist coastal lepidoptera such as Platytes alpinalla(Goater) and sand dart Agrostis ripae for example.  As a foodplant it is also important for hosting a range of notable monophagus species nationwide.  The cinnabar moth population is so large in some years, that caterpillars consume not only the leaves, but also the whole flowering head, leaving a series of woody stalks.  This form of ‘biological’ control can be locally very effective.

7.  Heavy rabbit grazing in some areas of the fixed grey dune has resulted in ‘lawns’ where lichens (Cladonia and Peltigera sp) and mosses are prominent.  This is an important component of the dune habitats and may be lost as a result of decreased grazing pressure or colonisation by rosebay and scrub.

8.  Grey dunes are important for a wide range of lepidoptera, many of which may be reliant upon grassland herbs as larval foodplants or nectaring source for adult moths or butterflies. Some species may also be dependant upon the proximity of scrub or saltmarsh for various stages of their generations.  Bare sand is sought by several butterfly species for basking. Some of the noteworthy moth species are mentioned above.  Of the butterflies, the brown argus and green hairstreak are of regional significance.  The marsh moth may favour the transitional zone between damp slack and grey dune, where it is presumed to depend upon ribwort plantain Plantago lanceolata as its foodplant.

9.      Many of the specialist invertebrate communities are reliant upon rabbit grazing activity to maintain short swards and open ground.  Bare sand is again important for the aculeate hymenoptera.  The NNR has national significance for this group with over 120 species recorded. Whilst some species are solitary, eg the impressive red-tailed sand wasp Ammophila sabulosa, other species form extensive colonies.  South-facing sandy banks or cliffs are important for these colonies.

10. Heavily grazed dunes with resultant short sward provide optimum foraging habitat for the natterjack toad Bufo calamita, and are somewhat inhospitable to its chief competitor, the common toad Bufo bufo.  Natterjacks also require areas of open sand to burrow into, and have been seen emerging from rabbit burrows.

11. Grey dune habitat supports a most diverse range of flora and fauna.  Many species occurring on the NNR are of national or regional importance including red-tailed sand wasp, natterjack toad, marsh moth and rue-leaved saxifrage.  Populations of some sp will be determined through routine survey work.  For other species, specific surveys are necessary and may require external specialists.

12. At Gibraltar Point NNR, large tracts of grey dune have been colonised by sea buckthorn scrub.  To some extent, this has been suppressed by rabbit browsing, and more recently by management intervention.  In 1968, the Trust undertook a programme of scrub removal on the West Dunes and a fairly open aspect has thus been maintained here.  Clearance has been carried out on a smaller scale on the southern sector of the East Dunes, mostly associated with dune slack clearance and in contrast, the northern sector of this ridge has developed a natural response.  Once sea buckthorn has become established on grey dune, the local soil characteristics will change.  In particular, nitrogen enrichment results from the species ability to fix atmospheric nitrogen in root- nodules and an extensive litter layer, raises the soil organic content and thus also adds enrichment.  As the scrub canopy develops, typical grey dune turf species become shaded out and are replaced by a weedy flora comprising few species.

13. The low nutrient, free-draining and calcareous status of the dune soils are fundamental in governing the vegetation communities.  Changes in nutrient status as mentioned above will cause a response in vegetation.  Increased nitrogen is a negative factor for the grey dune and in addition to the fixing by sea buckthorn, atmospheric levels may in any event be increasing.  Similarly, precipitation may effect a lowering of soil pH attributable to atmospheric pollution, oxides etc. There is no mobile sand on these fixed dunes and most are beyond the reach of fresh windborne material to replenish the mix of sand and shell fragments and maintain pH.