Contrasting ecological and biological characteristics of high-altitude populations of Drepanocladus turgescens in the Vanoise national park

Drepanocladus turgescens is a calciphilic arctic-alpine moss species that is highly endangered in central Europe. Lowland populations are at risk of extinction, while high alpine populations have a favourable conservation status. We studied ten high-altitude populations of D. turgescens in Vanoise national park, French Alps, at the south-western margin of its range. The microtopography, substrate depth, vascular plant and bryophyte species cover, and water physico-chemical properties were sampled in the field. Sexuality and branching were studied in the laboratory. In the high alpine area, the moss either thrives on a sparsely vegetated, mineral percolating substrate where female gametangia are regularly produced on mostly unbranched stems or on peaty substrate, where individuals are sterile and tend to branch out. Competition is suggested as the main driver of the species' occurrences. We found neither male gametangia nor any sporophytes, a situation typical for most of the Alps. The high-altitude populations of D. turgescens likely episodically recruit following exceptional sporophyte production in the Alps, and by vegetative fragmentation. Management actions removing competitors may benefit the persistence of the moss in sites where the peat layer exceeds 20 cm deep.