This section is from the book "British Wild Flowers - In Their Natural Haunts Vol2-4", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Zonal Character of the Coastal Vegetation. The vegetation of the sea-coast differs from every other type of vegetation in that it is entirely restricted to the junction of the sea with the land. This causes at once a more or less uniform altitude, the sole difference in this respect being defined by the rockiness or otherwise of the seaboard. Thus the maritime plants are at once confined to a fringe along the coast of little extent, rarely encroaching inland more than half a mile, or a little more where salt marshes, which are secondary products of the coastal vegetation, are concerned. It is, in fact, the marginal action of the sea, with its saline waters and peculiar deposits, that determines the formation of maritime vegetation.
There are two limits to the action of the sea, high-water mark and low-water mark, and as regards flowering plants these have little or no effect upon distribution. It is on the deposits thrown up and conserved above the high-water mark that the maritime plants are especially found, and these form the first zone, which may in the case of a low shore line be of sand or shingle. Where there are cliffs lashed at high tide by the sea there is a single zone, the rocks and cliffs. But on a low shore there are usually parallel with the first sandy shore or shingle beach dunes of aeolian origin, whilst a third zone is constituted by the salt marshes on the landward side of the dunes, though these may not everywhere be present, nor are dunes always developed on a low shore. To leeward of the salt marshes there may be a second line of dunes, and then inland vegetation. There are normally three or four zones of vegetation on the sea-coast.
One feature of most maritime tracts is the almost universal absence of trees. This is due to the regular occurrence of sea breezes and land breezes, which constantly subject the coast to unusual wind force, so that trees are unable to flourish except in a dwarfed state, and generally have their branches blown landwards. The exposed nature of the sea-coast also, apart from the wind, contributes to the absence of trees. Another reason is the character of the soil, which is saline, and usually of coarse texture unsuited to tree growth.
The fact that along most coasts there are relics of ancient submerged forests does not denote that the maritime border was formerly more suited to such conditions, but is an indication of the great amount of submergence or sagging that has occurred. Such forests were originally not only above the sea-level but a good distance inland. The maritime formations are thus without any native forests of their own. From this cause there is generally a relative absence of humus in the soil, except in the salt marshes where semi-marine peat is formed.
An exception must be made to the foregoing general rule in the case of sheltered coves and estuaries, as in Devonshire, Somerset, etc, where trees grow down to the sea margin, at any rate on rocky coasts. There are some shrubs that are characteristic of the sea-coast, such as Tamarisk, Sea Buckthorn, Coton-easter, and Elder is in many places common, as also the Tea Plant.