Coastal vegetated shingle and shingle heath
Shingle is a mobile and transient habitat, rarely stable in the long term, and many of the world's shingle features are bare of vegetation.
Most shingle beaches are within reach of storm waves so much of the vegetation is restricted to things that can grow on the strand-line. Shingle structures stable enough to support perennial vegetation are rare even in Britain, which has around a third of all the vegetated shingle in Europe (4,000 to 5,000ha).
Shingle features are under increasing threat from development and gravel extraction, as well as from ‘coastal squeeze’ in the form of rising sea levels and coastal erosion. The increasing leisure use of coastal areas and the consequent damage and disturbance is also degrading our vegetated shingle.
The ridges and valleys evident on Orford Ness have been deposited over many centuries by the action of the sea, in particular by longshore drift (the process of strong tidal currents moving material along the shore, in this case in a mainly southerly direction) and wave patterns. The ridges are a visual record of the evolution of this complex landform, with each ridge showing the position of an ancient shoreline. However, unlike the growth rings of a tree, shingle ridges don't necessarily show a progressive sequence of time. In many places an older series of ridges has been destroyed and replaced by a new series. So the date of formation of Orford Ness still confounds the experts.
Colonisation of shingle is dependent on three main factors – degree of disturbance and mobility of shingle due to factors such as wave action; presence or absence of ‘fines’ in the shingle matrix; and the availability of moisture. Shingle ridges are formed by wave action (in particular storm waves) against a beach and as the shingle is laid down it is naturally sorted and graded by size, with the larger stones lying in the valleys and the smaller ones on top of the ridges.
The finer (<5mm) fraction on the ridge improves seed and water retention, and although not essential allows some organic debris to be trapped and held. The presence of the 'fines' is thus crucial to the germination, establishment and survival of shingle plants, which depend on this matrix of shingle, with finer material mixed in with coarser particles.
The result of this colonisation is the distinctive strips of vegetated shingle for which Orford Ness is famous. It has highly specialised and important flora communities which include significant plants, for example the nationally scarce sea pea (Lathyrus japonicus), which is particularly mentioned in the European Union Special Area for Conservation (SAC) designation, and grows mainly along the drift line.
Coastal vegetated shingle habitats are extremely fragile; the damaging effects of access on foot, and particularly by vehicles, have degraded many areas on the Ness, with loss of vegetation. Military use of Orford Ness has now ceased, but walkers and fishermen can still access the beaches. Such disturbance by humans can also have detrimental effects on breeding, feeding and roosting bird populations, which also have to contend with ground predators and very high tides. For example ‘loose’ colonies of little tern are under severe pressure on Orford Ness from all these causes of disturbance.
Acid shingle heath is one of the rarest habitats in Britain, with Orford Ness having the second largest area.
It is dominated by dense mats of sea campion (Silene uniflora), which are pierced by the taller growth of false oat grass (Arrhenatherum elatius). These plants are interspersed with continuous crusts of spiky, branched and brittle lichens.
To date, 116 species of lichen have been recorded on Orford Ness, some of which are extremely rare. Lichens are unique, as they are not plants but part fungi and part algae. Lichens are slow growing (approx. 1mm a year) and extremely sensitive to aerial pollution.
Shingle heath manages to survive the hostile windy and salty conditions of Orford Ness, in areas no further than 250m from the sea.