Population status and ecology of the globally threatened moss Ditrichum plumbicola Crundw. on the Isle of Man

ABSTRACT Introduction. Ditrichum plumbicola Crundw. is a rare metallophyte that is threatened with global extinction. In this study, its population status and ecology on the Isle of Man were investigated. Methods. Surveys were carried out at all sites where the species may currently occur. Geographical coordinates of colonies were recorded using a GPS unit and counts made of occupied 1 m grid cells. Habitat and community composition were recorded by relevés. The chemical composition of occupied soil was also ascertained. Key results and conclusions. Two subpopulations of the species have occurred, associated with the two main ore bodies on the island. One of the subpopulations has become extinct. The other subpopulation comprises colonies at four nearby disused metal mines. It occurs at each in small quantity, with a total population of 47 occupied 1 m grid cells. The species is confined to open metalliferous spoil with high concentrations of lead. Solenostoma gracillimum is the only frequent associate. Management intervention to re-expose open metalliferous spoil will be required ultimately to save the species from extinction.