Habitat Assessment, Phytosociology and Conservation of the Tunbridge Filmy-fern Hymenophyllum tunbrigense (L) Sm. in its Isolated Locations in the Vosges Mountains
The Tunbridge Filmy-fern, Hymenophyllum tunbrigense, has been discovered within the last 10 years in several places in a 15 km long by 2 km wide area located in the western part of the Vosges Mountains. After the disappearance of the Saxony and Ardennes sites, these Vosgian locations have to be considered as one of the last continental areas for this fern in Europe, meriting the same level of interest as the well-known Luxembourg locations. In its Vosgian area, the fern occurs in Abies alba forests on small (less than 2.5 m high) and moist sandstone rocks, generally located near running water in wet valleys, at altitudes between 400 and 640 meters a.s.l. As assessed through the impact of the 26 December 1999 storm on one Hymenophyllum location, this fern appears to be sensitive to direct sunlight in the Vosges mountains. Therefore the main measure to ensure its conservation would be to maintain a dense and permanent forest canopy above the Hymenophyllum sites in order to avoid any direct sunlight.