Stabililty and change in ultramafic fellfield vegatation at the Keen of Hamar, Shetland, Scotland

Abstract

The paper reports 15 years' monitoring of erosion rates of drift soil deposits, fluctuations in vegetation cover, effects of nutrient addition and the population dynamics of rare species from the Keen of Hamar's fellfield habitat. Normal successional models do not apply on the fellfield since closed vegetation cover is restricted to soils on glacial deposits that once removed cannot be reconstituted from the underlying ultramafic parent material. The successional processes that occur are so slow and on so small a scale that it is concluded that the fellfield plant communities are stable. Eutrophication related to agricultural activity led to a temporary increase in plant cover and loss of habitat for the rare species. The numbers of individuals of the rare species have fluctuated locally from year to year but during the time of the observations the populations were relatively stable over the entire site. This means that the rarities have migrated within the site and this has important implications for their conservation. It is concluded that the Keen debris has retained more of its primeval appearance and vegetation than perhaps any other inland lowland area in the British Isles.