Prescribed burning in montane Nardus grasslands: Fire frequency is key to balance vegetation structure and diversity

Semi-natural grasslands are increasingly threatened by abandonment and intensification, highlighting the need for effective management tools. Here, prescribed burning (PB) is tested as a cost-effective and easily accessible alternative to animal-bound grassland management for maintaining not only the openness of grassland fallows: Our study investigates the effectiveness of different PB frequencies for the conservation management of montane Nardus grasslands. We experimentally tested the effects of recurrent application of prescribed burning at three different frequencies on diversity, vegetation structure and soil parameters of two Nardus grassland communities (species-poor and species-rich) compared to fallows in the central German Rhön Mountains over 8 years. We showed that PB effectively mitigates negative effects of secondary succession on vegetation structure, mainly by reducing moss cover and litter accumulation. While frequent PB slightly reduces species richness and promotes a few dominant species, less frequent burning (e.g. burning every 3 years) prevents these negative effects. PB had minimal effects on soil parameters of our study sites. Different PB effects on species-rich and species-poor communities, respectively indicate that the initial species composition plays an important role in mediating fire effects. Our findings indicate that late winter/early spring fires at low frequencies can act as appropriate tools for maintaining a favourable conservation state of montane Nardus grasslands, but that the initial species composition has to be carefully considered before application.