Rock climbing disturbance severity and abiotic gradients interact to determine cryptogam diversity and community structure

Abstract

Questions: Plant communities are shaped by interactions between natural and anthropogenic disturbances and underlying environmental conditions. We asked how disturbance by rock climbing alters patterns of cryptogam species diversity and composition along elevational abiotic gradients. Location: Red River Gorge, Kentucky, United States of America. Methods: Surveying was completed within 19 climbing routes on sandstone “slabs.” Quadrats were placed at three different vertical positions (elevations) and three different horizontal positions (center of the route, route margin, off-route). The former provides a gradient of light and moisture availability while the latter corresponds to climbing impact. Cryptogam species cover was visually assessed in all quadrats. Quadrat microtopography was quantified as well as route-level Heat Load Index and Climbing Use Intensity. We assessed differences in species richness and Shannon diversity (H) among quadrat positions and evaluated differences in species and cryptogam morphological type abundance and composition. Results: Significant differences existed in richness H, and total cryptogam abundance between quadrat vertical and horizontal positions with a significant interaction between these two factors. Cryptogram abundance was greatest in off-route quadrats and increased with elevation in such settings. Abundance was consistently lower in on-route quadrats and, here, did not change with elevation. Richness and H were greatest in off-route quadrats and declined with increasing elevation in on-route quadrats. Significant differences in community composition existed as a function of vertical and horizontal position. On-route quadrats were associated with crustose and granulose species, while foliose and squamulose lichens, and bryophytes were associated with off-route quadrats. Conclusions: Cryptogam composition and abundance were associated with varying intra-route environmental conditions, and off- to on-route disturbance gradients. There is potential for substantive impacts on the ecology of cliff face ecosystems from climbing. Impacts could be reduced by spacing routes widely and avoiding impacts on upper elevations where diversity and abundance are greatest.