Salt-marsh vegetation in the Shetland Islands

Abstract

Details are given of a preliminary study of salt marshes near Sullom Voe, Mainland, Shetland, using 50 × 50 cm quadrats placed systematically along transects. Computer-generated clusters are shown to match well against generally accepted syntaxa, whilst high-similarity clusters in certain alliances possess internal structure related to dominance and to effects of freshwater irrigation. The syntaxa provisionally identified are the Eleocharion uniglumis, Armerion maritimae, Puccinellion maritimae, and grazed cliff top grasslands showing affinity to the Puccinellio-Spergularion salinae. Computer clusters with Puccinellia maritima and much Fucus muscoides are associated with active pioneer grass growth and with slumping and erosion on wet marshes, whilst more species-rich clusters reflect a loss of vigour in Puccinellia maritima at higher elevations. Drier stonier marshes also display depositional and erosional features, the former being associated with active Puccinellia maritima growth at lower levels on the marsh. It is suggested that most of these processes involve the recycling of local marsh sediment material.

Nomenclature follows Clapham et al. (1981) for the angiosperms, Parke & Dixon (1976) for the algae, and Adam (1981) for plant communities.

My thanks are due to the Shetland Oil Terminal Environmental Advisory Group for allowing me to make use of data obtained during contract work for them at Sullom Voe, and to the Nature Conservancy Council and Institute of Terrestrial Ecology for permission to refer to their report on Shetland cliffs and salt marshes. Thanks are due to the Central Research Fund of the University of London and to the Department of Pure and Applied Biology, Imperial College for financial assistance. Computing was done at the Imperial College Computer Centre. I would also like to thank R. G. Davies for lending me some of his FORTRAN IV programs, and my wife for assistance with the field work.