Status, conservation and ecology of the exceptionally rare metallophyte Cornish Path-moss (Ditrichum cornubicumPaton)

Cornish Path-moss is one of the world’s rarest bryophytes, presently known from just three sites, former copper mines in the UK and Ireland. Covering the two UK sites, for the first time this study provides a set of location coordinates (x-, y- and z-axis) that is comprehensive, accurate and precise, in addition to investigating aspects of its ecology and assessing the success of trial habitat management plots. The species is shown to be rare, with a total population occupying 490 Ordnance Survey (OS) 10 cm grid cells, 77% at Phoenix United Mine and the remainder at South Caradon Mine, confined to bare patches of metalliferous soil that are especially high in the phytotoxins arsenic, cobalt and copper. Whilst the hostile chemical environment limits competition, various tolerant and larger bryophytes, lichens and vascular plants are shown to occupy the same niche, so that competitive exclusion is a constant threat. Turf-stripping of trial habitat management plots using a mechanical excavator at Phoenix United Mine, re-exposing bare metalliferous ground, is shown to be remarkably successful, providing a 20-fold increase in the population, presently making it the most important site for the plant in the world. Priorities for future survey and research are considered.