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This study examines the effects of visitors on vegetation of natural semi-arid areas of Mediterranean basin using controlled experimental trampling. Impacts were assessed on days 1, 5, 15 and 30 examining presence of plant species, their cover and height in linear transects suffering a constant trampling intensity (25, 75, 100 and 200 passes/day). In addition, the study included the analysis of factors such as plant species, trampling intensity, the cumulative impact (day effect) and the type of footwear on plant variables. The results showed a decrease on plant cover and height influenced by cumulative (day) effect, an effect of trampling intensity and a different effect for each species. In contrast, shoe type affected only slightly the decrease in plant height. The evolution of plant cover revealed which species were most resistant to trampling. The disappearance of plant individuals during trampling appeared to be an impact index better than plant cover, because cover increased in some species when they were trampled thus introducing a bias.

Abstract& Key message Shrub cover has visible effects on Pinus nigra Arn ssp. salzmannii seedling emergence, but only in drier years under moderate basal area (25-30 m 2 ha −1 ). In the wetter year, shrub cover favours seedling survival without basal area influence. & Context Shrubs are known to favour tree seedling recruitment in difficult climate environments, but facilitation may prove optimal in intermediate-level rather than harsh conditions, although such an effect remains to be specified. & Aims The main aim of this work was to evaluate the influence of stand basal area (15-20, 25-30 and 35-40 m 2 ha −1 ) × with/without shrub facilitation on seedling recruitment in Spanish black pine (P. nigra Arn. ssp. salzmannii), which has been struggling to regenerate natural forests since the late nineteenth century, sometimes jeopardizing stand persistence. & Methods In spring 2012 and 2013, 72 subplots of 25 × 25 cm were established in Cuenca Mountains, centraleastern Spain (four replicates, each counting three subplots × 2 shrub conditions, both under and outside shrub cover, in three different stand basal areas). All plots were randomly distributed at least 500 m apart within each stand basal area. Each subplot comprised 20 seeds previously collected at the experimental forest site. Seedling emergence and early survival were monitored every month in 2012 and 2013. Handling Editor: Laurent BergèsContribution of the co-authors ME Lucas-Borja and D Candel-Pérez conceived the research, obtained the field data, run the data analysis and wrote the manuscript. PA Tíscar, T Onkelinx and P Balandier run the data analysis and wrote the manuscript. FA García Morote obtained the field data and wrote the manuscript.