Phytosociological studies in the northern isles of Shetland

Abstract

In this thesis an attempt is made to detect, define and characterise, on the basis of their floristic composition, the principal types of vegetation occurring in the Northern Isles of Shetland. Some 600 samples were taken from as wide a variety of vegetation types as possible, and from as many parts of the Northern Isles as possible. The data was processed using a computer assisted hand-sorting routine (which simulated traditional Zurich-Montpellier methods of analysis) , leading to the production of structured species-sample tables. Fourty-seven Groups were identified and described and compared with related units recognised from Britain and North-west Europe. Thirty-eight of the Groups were arranged into 17 Associations, of which one represents a new syntaxon. The remainder were left as noda of uncertain status. The communities were all classified into higher ayntaxa essentially following the scheme used by Westhoff & Den Held (1969).The Classes and Alliances used to contain the communities as as follows:- Cakiletea maritimae Atriplicion littoralis Open communities (of mainly annual species) of shingle beaches and strandlines. Agropyretea pungentis Honkenyo-Crambion maritimae. Open and often unstable communities of biennial or perennial species of shingle beaches and strandlines. Agropyrion pungentis. Perennial, generally closed communities of shingle beaches and strandlines. Ammophiletea arenariae Agropyrion boreoatlanticum. Fore-dune communities. Festuco-Brometea Mesobromion erecti. Semi-dry calcareous grasslands. Asteretea tripolii Puccinellion maritimae. Halophyte communities of the lower parts of salt marshes. Armerion maritimae. Halophyte communities of the lower parts of saltmarshes. Armerion maritimae Halophyte communities of the mid and upper zones of salt marshes. Silenion maritimae. Cliff-top grasslands. Molinio-Arrhenatheretea Cyanosurion cristati. Communities of lowland grazed pastures and related habitats. Calthion. Fen meadow vegetation. Parvocaricetea Caricion davallianae. Low-growing sedge vegetation of base-rich mire. Scheuchzerietea Rhynchosporion albae. Communities of bog hollows and pools. Oxycocco-Sphagnetea Erico-Sphagnion. Bog Communities. Nardo-Callunetea Violion Caninae. Rough grasslands. Ulicion nanae. Heaths. Caricetea curvulae Arctostaphyleto-Cetrarion nivalis. Chinophobus montane grass and dwarf-shrub heaths of poor soils. Thlaspeetea rotundifolii Arenarion norvegicae. Communities of calcareous montane screes. The new Association described is the Empetrum-Rhytidiadelghus loreus Association of the Erico-Sphagnion. A short account of the occurrence and interrelation ships of these vegetation in the Northern Isles is given.