The Aquatic and Marsh Vegetation of Esthwaite Water Author(S): W
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The Aquatic and Marsh Vegetation of Esthwaite Water Author(s): W. H. Pearsall Source: Journal of Ecology, Vol. 6, No. 1 (Mar., 1918), pp. 53-74 Published by: British Ecological Society Stable URL: http://www.jstor.org/stable/2255505 Accessed: 27-06-2016 02:42 UTC Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://about.jstor.org/terms JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Wiley, British Ecological Society are collaborating with JSTOR to digitize, preserve and extend access to Journal of Ecology This content downloaded from 128.197.26.12 on Mon, 27 Jun 2016 02:42:23 UTC All use subject to http://about.jstor.org/terms 53 THE AQUATIC AND MARSH VEGETATION OF ESTHWAITE WATER BY W. H. PEARSALL JW4ith twelvefigures in the Text) Continued from Vol. 5, p. 202 V. THE MARSH AND FEN VEGETATION OF ESTHWAITE WATER 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 con- fined 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 arundi- nacea 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. *Ranunculus Flammula f Lythrum Salicaria o Caltha palustris 1 Hydrocotyle vulgaris f Potentilla palustris 1 Achillea Ptarmica f This content downloaded from 128.197.26.12 on Mon, 27 Jun 2016 02:42:23 UTC All use subject to http://about.jstor.org/terms 54 The Aquatic and Marsh Vegetation of Esthwaite Water Senecio aquaticus 1 *J. conglomeratus 1 Hypochaeris radicata o *J. articulatus ab Lysimachia Nummularia 1. ab Carex Goodenowii o Myosotis caespitosa f C. flacca f *Prunella vulgaris f C. flava f Litorella lacustris o *Rhacomitrium heterostichum f Polygonum Hydropiper o *Climacium dendroides I *Juncus effusus f *Hypnum cuspidcitum r The species asterisked are characteristic of exposed places. The sub- stratum is always stable, though wave washed when the water level is high. This community also passes inito fen communities if peat or silt accumulates the transition being marked by an abundance of Agrostis alba, Molinia caerulea and Juncus sylvaticus-and can be termed a colony, since it represents the invasion of a bare area by two or more species. (iii) In many places, woods of Quercus sessilijiora extend almost to the water's edge. The slope is usually rather steep and the substratum of the same type as in the marginal colonies, which are confined to a narrow wave-washed zone near the water. Moisture-loving trees replace the oak along the water margin, and the ground flora beneath them is as follows, the trees themselves being Fraxinus excelsior, Alnus rotundifolia, and Salix cinerea, of which the alder is most abundant. Ranunculus Flammula f Achillea Ptarmica f R. repens o Senecio aquaticus o Caltha palustris f Cnicus palustris 1. ab Meconopsis cambrica r Centaurea nigra r Lychnis dioica f Scrophularia nodosa f L. Flos-cuculi f Rumex obtustfolius o Poterium officinale o R. acetosa 1 Spiraea Ulmaria ab Juncus articulatus o Lythrum Salicaria f J. sylvaticus Id Epilobium montanum o Phalaris arundinacea ld Circaea lutetiana o Agrostis alba, v. coarctata Hofim. 1 Angelica sylvestris 1. ab A. alba, formagigantea 1 Galium Aparine o Deschampsia caespitosa 1. ab Valeriana officinalis f Holcus lanatus o V. sambucifolia 1 Molinia caerulea ld Scabiosa Succisa ab Brachypodium sylvaticum 1. ab Nearer the water and light, Phalaris and Juncus sylvaticus are locally dominant; while further away Molinia, Spiraea and Deschampsia caespitosa become abundant, merging finally into damp oakwood with Mercurialis perennis and Circaea lutetiana. The inner marsh zone is distinguished from the outer by greater shelter, lower water table and weaker light intensity- This content downloaded from 128.197.26.12 on Mon, 27 Jun 2016 02:42:23 UTC All use subject to http://about.jstor.org/terms W. H. PEARSALL 55 which falls from *5 to -05. Definite quantitative determinations of water and humus are not possible owifig to the nature of the substratum. The slightly acid soil waters probably account for the presence of such species as Molinia caerulea, Juncus sylvaticus, Rumex acetosa and Deschampsia caespitosa. The two marsh zones are probably no more than societies (cf. Clements) of the oakwood community. (iv) At the South end of the lake, there is a bank of morainic material, which, formerly submerged and superficially eroded, is now covered with vegetation. This bank has a maximum elevation of 2-75 m. above summer water level, a gradual slope 1 in 15-and its vegetation is divided into five well marked zones according to its distance from the water. At the water's edge, the gravel is unstable, and forms a slope about 1 m. wide, at the top ot which a sparse marginal colony is developing. Pushing out on to this colony, Carex elata occupies the next zone, where the gravel is quite stable. During floods the Carex acts as a breakwater for the zones behind it, and normally aflords a drier habitat for Scabiosa Succisa, Caltha palustris, Lythrum Salicaria, and Valeriana sambucifolia. The water level of the Carex zone varies between 7 and 14 cm. Behind this zone there is a dense sward, on stable gravel, of the following: Hydrocotyle vulgaris f Juncus articulatus 1. ab Carex panicea ab J. effusus o C. echinata f Prunella vulgaris f Ranunculus repens f Potentilla palustris o R. Flammula ab Lythrum Salicaria f Viola palustris f Molinia caerulea f Spiraea Ulmaria if These are beyond the reach of wave wash, and as peat accumulates, Molinia and Myrica, Gale extend downwards from the zone above, where they are dominant. The highest zone is a closed thicket of small trees: Betula tomentosa ab Rhamnus frangula f Salix cinerea ab Coryllus avellana 1 Alnus rotundifolia ab Quercus sessiliflora o Fraxinus excelsior 1 This is extending on to the Molinia-Myrica zone, and will ultimately cover the lower zones as the water level gradually falls, owing to the cutting back of the outlet. Lt is a natural extension of an adjacent oakwood, and the respective zones will probably ultimately pass into oakwood societies akin to those described in (iii). B. The Fen Successions. Fens at Esthwaite succeed the aquatic sere and are developed on peaty or sedimentary soils. The communities are de- scribed under this name because of their close floristic resemblance to those described in Types of British Vegetation. The fens at the north of the lake, This content downloaded from 128.197.26.12 on Mon, 27 Jun 2016 02:42:23 UTC All use subject to http://about.jstor.org/terms 56 The Aquatic and Marsh Vegetation of Esthwaite Water being most characteristic and instructive, will be considered first. Their development is chiefly due to the abundance of silt brought down by the Black Beck, of which the current is sufficient to transport stonies to within 270 m. of the lake. Hence all the finer sediments;-considerable in quantity, are dropped in the lake or in the fen round the beck mouth. In 1888, the lake water reached a point at least 25 m. further inland than it does today, giving an extension of almost 1 m. per annum. This rapid silting is in part due to the heavy annual rainfall, which at Esthwaite Mount was 71-3 ins. (175 cm.) for the period 1900-1909. At Black Fell, further up the valley, it was 81>3 ins. (200 cm.) during the same period. (British Rainfall.) Heavv rainfall and rapid silting are therefore, two of the conditions under which this fen has developed. Also important, probably, is the acidity of the waters of the stream, lake and fen soil-in reaction to phenol-phthalein. Of these, three factors, the deposition of sediment is most important.t It is obvious that it will be most rapid round the beck mouth and will decrease to the right or left of the line of flow. This gives the clue to the conditions under which the fen soils are developed. Those along the stream side were built up rapidly of inorganic silt. Those furthest from it receive least silt and show a greater proportion of organic remains.