Rock climbing alters plant species composition, cover, and richness in Mediterranean limestone cliffs

Rock climbing is among the outdoor activities that have undergone the highest growth since the second half of the 20th century. As a result, cliff habitats, historically one of the least disturbed by human colonization worldwide, are facing more intense human pressure than ever before. However, there is little data on the impact of this activity in plant-communities, and such information is indispensable for adequate manager decision-making. The goal of this study was to determine the impact of rock climbing on plant communities in terms of cover, richness, and composition in relation to climbing intensity on typical Mediterranean limestone cliffs. Three rock-climbing sites were selected in the Baetic range (SE Spain), corresponding to qualitative categories of climbing frequentation: i) "low" (low frequentation with intermittent climbing), ii) "medium" (high frequentation without overcrowding), and iii) "high" (high frequentation with overcrowding). Within each site, we selected climbing routes and adjacent areas free of climbing, then we carried out a photoplot-based sampling by rappelling. We analysed the images to calculate: richness, species cover, and total cover. This study shows that rock climbing negatively affected the cliff plant community at all three study sites. A significant decrease in plant cover, species richness and a shift in the community composition were recorded for climbed areas, the cover being the variable most sensitive to rock climbing. Impact observed proved to be related to the frequentation level. Low-frequentation sites, with usually more specialized climbers, underwent relatively mild damages, whereas at high frequentation sites the impact was severe and the conservation of the species, especially rare ones, became jeopardized. Our study is the first one available to investigate climbing impact on plant communities in Mediterranean areas, but more research on the impact of rock climbing is needed to assess the regulation of this activity. Regarding management guidelines, we propose a management guideline protocol to evaluate climbing routes and design: i) "Sites free of climbing", ii) "Strictly regulated climbing routes", iii) "Mildly regulated climbing routes", or iv) "Free climbing routes".