The few areas of
marsh and fenland which remain undrained bear their own
characteristic vegetation of reeds, rushes, sedges, thickets of
alder, birch and willow, and many other plants which grow only in
waterlogged soil. This vegetation is essentially natural, though
its detailed distribution is often determined by human activity.
Thus regular cutting of the reeds and sedges for thatching and leaf
litter prevents the trees and bushes colonising the marsh or fen by
destroying their seedlings and saplings, while the reeds and sedges
spring again from their underground parts.
A very few 'raised
bogs'1 of the kind quite numerous in the central Irish
Plain still survive in the west and north of Britain, and they
possess an extremely distinct and interesting plant population.
Most of them have long since been destroyed by draining and peat
cutting.
The aquatic
vegetation inhabiting rivers, lakes, pools, canals and ponds is
again quite distinct and essentially natural, though many of its
individual habitats, such as canals and ponds, have actually been
provided by man.
Finally there is the
vegetation of the sea coast, of the salt marshes, sand dunes,
shingle beaches and sea cliffs. They bear quite special,
characteristic vegetation, determined by the different kinds of
maritime habitat, wherever it has not been destroyed and replaced
by artificial constructions such as sea walls.
