SWAMP (AS. swamm, swam, swamp, Goth. swamms, sponge, swumsl, ditch, OHG. swam, MHG. swam, swamp, Ger. Schwamm, sponge; connected with OHG. sumpft, Ger. Sumpf, swamp, and with Gk. σομφός, somphos, spongy). An area of wet ground usually covered with certain coarse grasses, trees, and other plants peculiar to such land. While the direct cause for differences between typical swamps has not been fully worked out, drainage seems to be the principal controlling factor. It seems probable that in undrained swamps, such as peat bogs, the products of plant decay, including various acids, necessarily accumulate and that aeration is imperfect. Hence it seems reasonable to believe that only xerophytic plants can grow in such places. On the other hand, river swamps, which are comparatively well drained, may show reverse conditions. Since they are hydrophytic, as habitats they maintain plants whose structures are hydrophytic. (See .) Thus undrained swamps are hydrophytic with respect to soil moisture, but xerophytic with respect to plant structures. See .
Perhaps no type of plant society better
illustrates the order of succession or encroachment
of one zone upon another than the most
xerophytic swamps, the peat bogs or moors. A typical
bog, for instance, may show a central pond
with water lilies and other aquatics, surrounded
by bulrushes, behind which may be a zone of
sedges, and then grasses or swamp forests, e.g. of
tamarack or arborvitæ. Since each of these zones
in turn advances toward and encroaches upon the
centre, the swamp gradually becomes filled and
drained naturally in a few years.
Other characteristic xerophytic swamps are
salt marshes, both the typical northern salt
meadows and the mangrove swamps of the
tropics. Plants of salt marshes (halophytes, q.v.) are very largely succulent. In many cases the coarse grasses resemble those of the prairies. In mangrove swamps xerophytic structures, represented typically by the mangrove leaf, are not the sole interesting features. Above the foul water many plants develop knee-like processes which supposedly are of advantage in aeration; and vivipary (q.v.) here reaches its highest expression. (See .) A closely allied type is the so-called cypress swamp of the Southern United States.
All swamps may be considered as ephemeral
plant societies, developing either into prairies
or mesophytic forests as they become better
drained. Climate doubtless plays some part
in this development, since the prairie rather than
the forest is likely to develop in the prairie
regions or in the forest regions adjoining the
prairie, whereas in the heart of the forest regions
most swamps eventually become covered with
trees. This, is, however, not a universal
explanation, since some swamps in forest regions
never become sylvan.