Monitoring habitat extent

The extent of the vegetated shingle is a fundamental attribute to be assessed in determining condition of the vegetated shingle feature. The target is no decrease in extent from the established baseline with the caveat 'subject to natural change'. There is a need to ensure that natural processes govern the system, and that the geomorphological 'health' of the feature is considered. However, the extent of the vegetation may be subject to periodic and seasonal variation, as natural processes re-distribute shingle sediments and change sediment composition. Extent of the driftline may be particularly difficult to assess as the community can vary enormously from year to year. The sparse nature of the vegetation and its seasonal appearance makes it difficult to detect on aerial photographs, but remote sensing images may be available. Driftlines on essentially sandy beaches are assessed within the sequence of sand dune communities. The aim is to identify anthropogenic from natural processes which may be causing the feature to move away from favourable condition.

Shingle deposits are dynamic and will adjust and respond to climatic changes (such as a rise in sea level) or local changes in wind and wave energy in an attempt to reach 'geomorphological equilibrium', which may include landward transgression. If this response is constrained by anthropogenic constructions such as fixed sea defences or infrastructures, natural habitat migration is prevented ('coastal squeeze'). The ensuing loss of extent would fail the extent attribute, as the feature is prevented reaching a natural geomorphological equilibrium. However, if landward migration is prevented by a feature such as higher ground, we would consider this to be favourable for the extent attribute (the shingle deposits are free to respond and reach a natural geomorphological equilibrium). The shingle structure might breach in response to ambient and storm effects, which would constitute 'roll over' - literally over landward habitat types including saltmarsh or sand dune.
The amount of offshore sediment available will also determine response of the system to such changes. There are other activities which may affect sediment supply, such as dredging for offshore aggregates.