The Aquatic and Marsh Vegetation of Esthwaite Water

Abstract

The terrestrial hydrophytic vegetation at Esthwaite falls naturally into two subdivisions: A. The purely zonal plant communities bearing no relation to the aquatic succession.B. The communities succeeding aquatic plants as the mud gets above the water level.I propose to refer to these two types of communities respectively as marsh andfen types, since the habitats, plant communities, and biotic relationships of each are widely different.A. The marsh vegetation occurs in zones near the water, and is confined to substrata composed of the primitive rounded morainic stones of which the shores are built.Locally, these are superficially eroded, or masked by thin peat, but these variations produce little difference in the vegetation, which is apparently chiefly controlled by the stony substratum and the slightly acid waters of the lake.The following communities are distinguished.(i) Along sheltered, slightly eroded and unsilted parts of the shore, local communities of Eleocharis palustris or Phalaris arundinacea occur, extending sometimes below the summer level, and to about 10-15 cm.above it, with Lythrum Salicaria frequent.All three species have tough rhizomes capable of penetrating the interstices of the hard substratum.Where peat accumulates or silting sets in, these communities pass into the Phragmites consocies.The communities being developmental and having one dominant each, can be termed respectively the Eleocharis palustris consocies and Phalaris arundinacea consocies.(ii) Where pasture land abuts on the lake, an open community of the following species occurs, usually at levels of 10-30 cm.above the summer water level.