Phytosociological studies in the southern Isles of Shetland

Abstract

Over 500 samples were collected from as wide a variety of vegetation types as possible. The principles of the Zurich Montpellier School of phytosociology were followed to form the data into a species-releve matrix for each vegetation type. The CLUSTAN package of computer programs was utilised, using Ward's Error Sum of Squares as a sorting routine, to produce differentiated data tables. 72 groups were identified, and described and compared with units recognised in Britain and North-West Europe. 38 groups were assigned to 21 Associations and the remainder were left as noda of doubtful status within alliances and orders. All communities were classified into higher syntaxa following, with only a few exceptions, the scheme of Westhoff and Den Held (1969). The Classes and Alliances used to contain the communities are as follows: Cakiletea maritimae atriplicion littoralis open communities (of mainly annual species) of shingle beaches and strandlines Agropyretea pungentis Honkenyo-Crambion maritimae Open, unstable, halonitrophile communities of biennials and perennisals and shingle beaches and strandlines Agropyrion pungentis Stable communities in maritime areas subject to disturbance. Ammophileta Agropyrion boreoatlanticum Unstable pioneer communties on sand. Ammophilion borealis Moile dune communities. Plantaginetea majoris Agropyro-Runicion crispi Disturbance communities of transitional and relatively unstable habitats. Phragmitetea Magnocaricion Large sedge communiies. Koeleric-Corynephoretea Galio-Koelerion Dry grasslands on acidic soils in the atlantic sector Festuco-Brometes Mesobromion erecti Semi-dry calcareous grasslands. Saginetea maritimae Saginion maritimae closed maritime grasslands on sandy soils in the upper saltmarsh regions. Asteretes tripolii Puccinellion maritimae Halophyte communities of lower saltmarshes. Elecharion uniglumis Communal sedge communities of saltmarsh boundaries. Puccinellio-Spergularion salines Disturbed maritime communities on sand and gravel Molinio-Arrhenatheretea Calthion Palustris Fen meadow vegetation.Cynosurion cristatti Communities of graged, lowland pastures and simliar habitats. Montio-Cardaminetea Cratoneurion Chalk and limestone spring communities. Parvocaricetea Caricion curto-nigrae Small sedge communities in habitats near springs. Caricion devallianae Small sedge vegetation of base-rich habitats. Scheuchzerietea Rhyncosporion albae Species poor vegetation in pools in poor fens and mires Caricion Lasiocarpae Communities of pools in moderatley rish fans and mires. Oxycocco-Sphagnetea Ericion tetralicis Wet heath communities on shallow peat. Erico-Sphagnion Bog Communities. Nardo-Callunetea Violion caninae rough grasslands. Ulicion Nanae Oceanic heaths. Caricetea curvula Arctostaphyleto-Centrarion nivalis Chionophobous montane grass and dwarf-shrub heath communities. The occurrence and interrelation ships of the plant communities of the Southern Isles are discussed, and the potential pressures on Shetland vegetation are examined.