Sand dunes

Often overlooked in the rush to get to the beach, Scotland's dune systems are among the most valuable of the nation's habitats. The larger systems may have more than one ridge, with depressions or 'slacks' between the ridges that often flood in winter. Scotland is the UK's dune HQ, with over 50,000ha - 71% of Great Britain's coastal sand resource. Though dune systems occur all round the Scottish coast, they are scarcer on the mainland between Glasgow and Kyle of Lochalsh. This total includes machair, as it is difficult to allocate some systems to dune or machair.

A range of dune types

The dune system begins on the beach, on the 'strandline', where seaweed and other debris has provided a growing medium for specialist plants such as orache and sea rocket. Some distance above this, there is sometimes a band of 'foredune' consisting of sand couch grass, before the mobile dune 'proper' is encountered. Here, if the system is large enough, there can be great rolling ridges of mobile sand, held generally in place by marram grass (sometimes lyme grass) but adjusting almost daily to changes in wind direction. This mobility can be extreme in winter when storm events can remove large sections, but these usually return gradually in summer. This mobility is an essential element of dune systems that should not be confused with erosion . Further inland, the dune becomes increasingly 'fixed' by the vegetation. On acid dunes, where there is little seashell in the sand, dune heath can develop, sometimes with so much lichen it is called 'grey dune', but on more alkaline systems (not all of which are machair) the vegetation is dune grassland. The lower-lying areas between ridges have 'dune slack' vegetation that usually requires more moisture, and some slacks are permanently flooded. This sequence from beach to fixed dune is often given in books as the way dunes advance, the 'dune succession'. Though this can be true, and has happened on some systems recently, in most cases the succession is long over, and the sequence should be regarded as zonation rather than succession.

Some dune problems

Of the total of 50,000ha, some 6,000ha have been converted to conifer plantation. The best example of this is at Culbin, where a huge area of drifting sand was afforested. In parts of SE Scotland, significant areas have been colonised by a non-native shrub, sea buckthorn, that was originally planted to combat erosion, but has itself become a problem. There are now programmes in place to control sea buckthorn, along with other non-natives such as pirri-pirri bur Acaena novae-zelandiae, and visitors should ensure that neither their clothes nor their pets carry these burrs from site to site.