Distribution Of Plant Species And The Rock Particle Size In Subnival Habitats Of The Central Great Caucasus

Subnival habitats of the Central Caucasus represent typical rocky environments with very sparse soil cover and patchy vegetation. We studied how spatial distribution of plant species in a subnival habitat (alpinenival ecotone) depends on the size of rock particles. We described the distribution patterns of plants and rock particles of various sizes, and examined the possible links between these patterns using correlation analysis and multivariate tests. We found that the largest size class (20-60 cm) was in a strong negative correlation with smaller classes (0.2-0.6 cm, 0.6-2 cm and 2-6 cm), but correlation was insignificant among the largest fragments (6-20 cm) and the soil patches. The CCA included 31 species (frequency >10) and the goodness-of-fit of the obtained ordination was assessed by permutation test. The CCA ordination revealed several species with a clear preference for soils (Carex tristis and Sibbaldia parviflora), while other species preferred midsized (20-60 cm) rock particles (Tephroseris karjaginii, Ziziphora puschkinii, Festuca supina, Minuartia inamoena and Saxifraga juniperifolia). Further, Senecio sosnowskyi and Ziziphora subnivalis tended to colonize large (6-20 cm) rock fragments. Overall, our results show a clear differential preference of species for certain sizes of rock particles that conforms well to the patchy pattern of vegetation typical for subnival habitats: many species that prefer a fine grained substratum might clump together at such fine-grained spots and form the patches of associated plants provided there are facilitative interactions among them; the species that prefer coarser-grained substrata might establish as solitary plants outside of the patches.