Sand dune - State 2 - Open/Semi-mobile

The dunes describe here as being in an Open/Semi-stable state are considered to be those where grazing and/or 'natural' processes are sustaining the balance of vegetation types from early successional stages to mature grassland and/or heathland and scrub. The key to this state lies in the continuing presence of grazing animals including domestic stock and rabbits, which have helped create and sustain the characteristics and value of the dune. These are particularly important on calcareous dunes where grazing pressure helps to maintain the close-cropped sward with a typically species-rich dune grassland.

Caption: Typical open/semi-mobile dune. This site (from the west coast of Ireland) appears to be stabilising following a period of instability. The presence of marram Ammophila arenaria within the body of the dune is indicative of this process. Note the eroding dunes towards the rear of the system, suggesting that the dynamic processes are continuing.

In acid dunes, heathland, a priority habitat under the EU Habitats and Species Directive, can be the dominant form. In this state scrub may develop but, so long as grazing animals are present, this does so in relatively small patches, without reaching fixed (State 3) and adds to the structure and biodiversity of the dune.

Comment: This state depends on there being sufficient grazing pressure to retain the open vegetation. Where grazing is absent or reduced then instability becomes a much more important factor in maintaining the range of plant and animal communities. Included within this state are sites where erosion occurs in cycles as for example as 'blow-outs' within the body of the dune which can act as precursors to dune slacks. Overall the proportion of bare sand remains the same, but can vary in both time and space.