A bryophyte flora of sarsen stones and an assessment of their bryological interest.

Abstract

Sarsen stones, hard acidic rock fragments, are restricted to just six sites in southern England but they provide an important habitat for both lichens and bryophytes. The bryophytes of sarsen stones have received less attention than the lichens but they include many species that are. either rare or absent throughout the region, or occur only in man-made habitats such as in churchyards or on roofs. Members of the Grimmiaceae are well represented including Grimmia decipiens, G. laevigata, G. trichophylla and Racomitrium heterostichum. Other notable species include Hedwigia ciliata s.s., H. stellata, Pterogonium gracile and Porella obtusata. Unlike the lichen flora there is no maritime element among the bryophytes of sarsen stones, but shared with the lichens is a clear upland element. Thisis in a large part a reflection of the scarcity of hard acidic rock outcrops in southern England; many of the notable species occurring on sarsen stones are more common in the upland areas of west and north Britain where suitable rock is extensive. A comparative assessment of the status of some of the more notable species in southern England demonstrates the high bryological importance of sarsen stones. Although the existing sarsen stone sites are to some degree protected, they occur within a farmed landscape and the widespread use of agricultural chemicals and the impact of grazing need to be carefully monitored. Air pollution may also be a contributory factor in the decline and loss of certain sarsen stone species.