Limestone cliffs in the Jura Mountains harbour species-rich plant and animal communities including rare species. Sport climbing has recently increased in popularity in this habitat and several studies have reported damage to cliff biodiversity. However, so far how damage levels vary with climbing intensity has not been investigated. We evaluated the effects of climbing intensity on the diversity of vascular plants and land snails in 35 limestone cliff sectors in the Northern Swiss Jura Mountains. Mixed-effects models were used to examine whether species richness of plants and land snails differ between cliff sectors with low and high climbing intensity and unclimbed cliff sectors (controls) taking into account potential influences of cliff characteristics (aspect, cliff height, rock microtopography). At the cliff base, the best fit model revealed that plant species richness was affected by climbing intensity and cliff aspect. Plant species richness was reduced by 12.2% and 13.1%, respectively, in cliff sectors with low and high climbing intensity compared to unclimbed cliff sectors. On the cliff face, plant species richness was only influenced by climbing intensity (species richness reduction by 24.3% and 28.1%). Combining data from cliff base, face and plateau, the best fit model revealed that land snail species richness was only affected by climbing intensity (species richness reduction by 2.0% and 13.7%). In both organism groups, species composition was increasingly altered by increasing climbing intensity. Our study provides evidence that even low climbing intensity reduces cliff biodiversity and that damage becomes more pronounced with increasing climbing intensity.
