The Evolution and Colonisation of Tidal Lands

Abstract

THE joint discussion on “The Evolution and Colonisation of Tidal Lands” between the Sections of Botany and Geography during the British Association meeting at Southampton was opened by Prof. F. W. Oliver, who spoke/of the raw materials that go to the making of tidal lands, namely, shingle, sand, and fine silt, and of the transport of these by tide, currents, and wind. Plants can only become established on tidal lands during periods of quiescence. Vegetation thereon arises almost entirely from sea-borne seeds, the sea also bringing drift which in time enriches the ground with humus. Plants as they become established collect and hold silt and blown sand, and are, therefore, in effect creative. In the case of sand dunes, the conditions were traced which lead to permanence. The parts played by Agropyrum junceum and Psamma arenaria in the building of dunes were discussed, it being pointed out that the latter was liable to be killed when invaded by abnormally high tides for some hours. Gales of 60-70 miles an hour stimulated the formation of dunes owing to the consolidation of the sand by wind force. Salt marshes differ markedly in type according to the nature of the ground, being either sandy or slushy or consisting of firm mud. Their proper development requires the concurrence of a number of plants at each successive phase. Reference was made to the almost unique capacity of Spartina Townsendii to occupy the softest muds and to spread rapidly on them. Its efficiency in such ground is comparable to that of marram grass in sand and Suœda fruticosa in shingle.