The New International Encyclopædia/Swamp
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 Hydrophytes.) Thus undrained swamps are hydrophytic with respect to soil moisture, but xerophytic with respect to plant structures. See Xerophytes.
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 Mangrove.) 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.