Martí March-Salas, Felipe Morales-Armijo, Juan Antonio Hernández-Agüero, Eduardo Estrada-Castillón, Andrea Sobrevilla-Covarrubias, José Ramón Arevalo, J F Scheepens, Juan Lorite

Cliffs are unique ecosystems with an outstanding but relatively unknown plant diversity, harboring rare, endemic and threatened species, but also common and dominant species. The rising popularity of climbing represents an increasing threat to cliff biota, potentially diminishing diversity and species associations, and affecting the community composition. We used a novel closely paired sampling design in climbing routes with different climbing intensities in El Potrero Chico (Nuevo León, Mexico), differentiating plant species and analyzing species associations and community composition in climbed and unclimbed plots. Diversity on the sampled cliffs was high, even greater than in other regional ecosystems. We found reduced abundance, cover, and diversity in climbed plots, irrespective of the climbing intensity. Dominant species were the most negatively affected by rock climbing in terms of abundance, and some locally rare species, comprising endemics and endangered species, were entirely absent from climbed plots. Co-occurrence analysis showed that the number of associations between pairs of dominant and common species were greatly reduced in climbed plots, and that positive associations between locally rare species existed in unclimbed plots but not in climbed plots, which may contribute to the disappearance of endemic and threatened species. Finally, NDMS analysis revealed that the community composition significantly changed due to climbing. Our results indicates that conservation science should convince stakeholders of the need for a holistic conservation of cliff ecosystems and not only focus on emblematic or rare species, since the plant community dynamics and preservation depends on the coexistence and interactions between different plant species.