The hill vegetation of North Hoy, Orkney

North Hoy is an area containing a remarkable diversity of vegetation in a small area. A phytosociological account of the hill vegetation of North Hoy is presented, making use of an ordination method to clarify the inter‐relationships of the moorland vegetation types, as well as traditional methods. It has proved very interesting to compare the vegetation with the account of Scottish Highland vegetation by McVean and Ratcliffe (1962). Birks' (1973) account of the vegetation of Skye has also been drawn on, particularly as a source for a system of classes, orders and alliances applicable to Scottish vegetation. The environmental background (climate, topography, geology, patterned ground phenomena, animal populations and past and present land‐use) is summarized. Several important general features of the vegetation of North Hoy deserve emphasis, especially from a conservation point of view. Many good examples of noda characteristic of strongly basic soils, especially mires and grasslands, are found. Some of these have a rather restricted distribution in Scotland. Small areas of woodland, including one very species‐rich wood, are found in sheltered ravines. These are well‐developed and regenerating, and represent the northernmost occurrence of woodland in Britain. Many species and many types of vegetation occur at unusually low altitudes (as is also observed in northernmost Sutherland, Caithness and Shetland). Particularly interesting are certain montane dwarf heaths, which are associated with well‐developed patterned ground features. The area contains both occurrences of ‘Atlantic’ bryophytes and well–developed stands of lichen heath and lichen‐rich bog, which have a strongly ‘continental’ distribution in Scotland. This apparent paradox is discussed but not resolved. The low level of sheep‐grazing and absence of burning in recent years have led to some unusual vegetation features. Phytosociological tables are presented in an appendix. A second appendix lists the lichens collected, as identified by P. W. James, with a short note on the occurrence of each.