Changes between 1927 and 2004 and effect of rock climbing on occurrence of Saxifraga paniculata and Draba aizoides, two glacial relicts on limestone cliffs of the Swabian Jura, southern Germany

A number of glacial relicts can be found on limestone cliffs of the Swabian Jura in southern Germany. In general, they are rare and endangered, particular on cliffs where rock climbing is allowed. Two glacial relicts, Saxifraga paniculata Mill. and Draba aizoides L., were quantitatively surveyed on 28 cliffs in 2004 to investigate their occurrence compared to former surveys and to analyse the effect of rock climbing on species abundance. Number of cushions per cliff and number of rosettes per cushion were counted, smallest and largest diameter of cushions and rosettes, as well as aspect and inclination were also measured. S. paniculata was found on 75% and D. aizoides on 30% of the cliffs. Up to 150 S. paniculata and 370 D. aizoides cushions were noted per cliff, in total there were 696 S. paniculata and 705 D. aizoides cushions. In cliff areas where rock climbing takes place, S. paniculata was only located in relatively uninfluenced parts of the cliffs. In contrast, D. aizoides was found with at a significantly higher frequency on climbed cliffs, and surprisingly, also at the foot of the cliffs, which means that climbing activities even increased numbers of D. aizoides. Rosettes might have been cut of by trampling and climbing and fell to positions where they established new cushions at the base of the cliff. Compared to earlier studies in 1927 and 1966, a higher number of cliffs containing both glacial relicts were found. It can be assumed that not all cliffs had been surveyed in the past and that cliffs were not surveyed as completely as possible. The former locations were confirmed except for one cliff where D. aizoides did not exist anymore. From the cliffs studied, D. aizoides and S. paniculata do not seem to be directly in danger of disappearance in the near future. Nevertheless, rock climbing or visits of hikers on certain cliffs can be a threat, in particular to S. paniculata. This study provides the groundwork for future quantitative monitoring of these two glacial relicts.