摘要
Diphasiastrum tristachyum, which is a rare Pteridophyte under national protection in France, has been discovered in several places in the Vosges Mountains during the last two decades. With its 20 currently existing populations in these mountains, it appears to be the Diphasiastrum species with the largest current distribution in the Vosges. This species mainly occurs on Vosgian sandstone substrate, in northern or northeastern exposures up to 600 m a.s.l., corresponding to the lower and middle montane levels in the Vosges Mountains. The main habitat (16 sites) are forest track borders. Only in single cases could D. tristachyum be found in other habitats such as a skiing track, a heath submitted to regular fire, an abandoned quarry and a limit of a forest plantation weeded with herbicides. All of these sites are secondary places of young anthropic origin. No really natural and primary habitats of D. tristachyum in the Vosges Mountains could be found. All localities show fragments or beginnings of heath communities belonging to the Genistion alliance. Because of the progressive succession of these communities towards forests if no human regulation occurs, D. tristachyum may have only ephemeral existence in such secondary Vosgian sites. This shows the need for a conservation and management programme which comprises measures like keeping open growing sites by the removal of invading trees, controlled pruning of dwarf shrubs and removal of the soil vegetation and the humus layer. A long-term stabilisation of the Vosgian populations of D. tristachyum may only be possible in this way.
