Survival of the critically endangered Ditrichum cornubicum and dependence on conservation management intervention.

Ditrichum cornubicum is one of the world's rarest bryophytes and is undergoing a long-term decline as its habitat is gradually lost to vegetation succession in derelict mining areas. This study investigates short-term changes in abundance of the species at two sites in Cornwall (UK), including within trial management plots where turf-stripping occurred in September 2015. A detailed survey of D. cornubicum was undertaken in January 2020, and locations recorded using high accuracy GPS. The species has declined dramatically in trial management plots since January 2018, illustrated by a 93% loss in occupied 0.1 m grid cells. Outside trial management plots, such a decline did not occur over the same period. Within trial management plots, D. cornubicum underwent an initial dramatic increase soon after turf-stripping in September 2015, quickly followed by a rapid decline. Initial colonisation likely arose from germination of rhizoidal gemmae in the diaspore bank, exposed by turf-stripping. The subsequent decline is at least partly due to competitive exclusion by other colonists of exposed mine spoil, especially Ceratodon purpureus, and perhaps also changes in chemistry at the spoil surface, for example due to leaching. The life-strategy of D. cornubicum is poorly suited to the undisturbed conditions of derelict mining areas, and the species is critically dependent on conservation management interventions that re-expose areas of metalliferous substrate. Without such management, the long-term survival of the species is in serious jeopardy. [ABSTRACT FROM AUTHOR]