Context-dependent associations of climbing intensity and abiotic characteristics with cliff vegetation on limestone cliffs in Freyr, Belgium

Sarane Coen , Georgia R. Harrison, Amre van den Maagdenberg, Christophe Metsu, Laura M. Bogges, Francisco Velasquez-Espin, Martí March-Salas, Kobe Burdack, Elias P. Goossens, Koenraad Van Meerbeek , Jonas J. Lembrechts

Cliff ecosystems support diverse vascular plant communities due to high abiotic heterogeneity and their historical role as climatic refugia. However, cliffs are increasingly exposed to disturbances from recreational rock climbing. The ecological effects of climbing likely depend on abiotic cliff characteristics—such as slope, aspect, and microtopography—but these context-dependent relationships have not been consistently evaluated. We investigated how plant diversity, community composition, and community-level functional tendencies vary with climbing intensity and abiotic characteristics on limestone cliff faces in Freyr, Belgium. Vegetation was surveyed using a standardised protocol across 248 1-m² subplots along 13 vertical transects spanning unclimbed, low-intensity, and high-intensity climbing routes. We quantified species richness, vegetation cover, Shannon diversity, community composition, and community-weighted means of Grime’s competitive, stress-tolerant, and ruderal strategies. We recorded 103 vascular plant species. Species richness etc. were more consistently associated with abiotic characteristics than with climbing intensity, whereas climbing intensity was mainly associated with community composition and functional strategies. Species richness and vegetation cover were highest at moderate microtopography and lower on steep slopes, and cover was lower on south-facing cliffs. The association between climbing intensity and richness depended on microtopography: richness peaked at low climbing intensity on cliffs with pronounced microtopography, consistent with the intermediate disturbance hypothesis. Competitive species were more abundant on unclimbed cliffs, whereas ruderal species were more abundant on climbed cliffs. Unclimbed cliffs were also associated with threatened (red-listed) indicator species, suggesting vulnerable vegetation may be at risk under increasing climbing pressure.