Community patterns on exposed cliffs in a Mediterranean calcareous mountain

The main focus of this paper is to establish the community diversity pattern of vegetation in exposed-cliffs in the Mediterranean region and the relative importance of some environmental factors. Consequently, a study of a calcareous mesa in C-N Spain has been carried on, based on constrained ordination — CCA. The spatial scale approach for sampling was the patch on the cliff. The total number of taxa was 117 and the average per patch was 15. It is remarkable that the highest frequency plants are not rock specialists (chasmophytes), but generalist nanophanerophytes and chamaephytes.A community pattern has been detected and related to the geomorphology and lithology of the cliff-nine communities. However, those patches of the vertical areas are very heterogeneous in number of taxa and size. Nevertheless, the community pools seem constant for each vertical cliff zone. Based on the ordination results and linear models, this variability may be interpreted as different succession stages of a cyclic process. The primary colonization of the bare rock by chasmophytes leads to the accumulation of soil because of the biological activity and the stock-trampling ability of these specialist plants. After that, the patches may be invaded by generalist chamaephytes (Festuco-Poetalia) and later even by several nanophanerophytes (Sideritido-Salvion lavandulifoliae and Berberidion vulgaris). The root activity of these plants in combination with other erosive events can return the system to the beginning.A second objective included in the paper was related to the capacity of phytosociological approach, widely used in the Mediterranean region, to describe this type of community pattern. The surveyed mountain had previously studied in phytosociological terms. These relevés were compared through an assignation procedure — see text — to our community pattern. Both approaches seem to agree with high correspondence, but there are some differences that must be pointed out. They are related to the fact that spatial/ ecological heterogeneity does not always agree with the idealized phytosociological vegetation models, where only chasmophytic elements are considered.Abbreviations DCA = detrended correspondence analysis - CCA = canonical correspondence analysis