Variable soil pH can drive changes in slope aspect preference of plants in alpine desert of the Central Great Caucasus (Kazbegi district, Georgia)

Abstract

Alpine deserts are noteworthy habitats in temperate high mountain systems such as the Caucasus. Botanically this biome is well studied, yet little is known about its vegetation patterns in quantitative terms, whilst the role of soil pH in species distributions is particularly unexplored. Here we describe and quantitatively analyse vegetation patterns and soil pH in an alpine desert along elevation range (3000–4000 m a.s.l.) on two contrasting slope aspects (N versus S) of Mt. Kazbegi, the Central Greater Caucasus, Georgia. We sampled vegetation with standardized stratified-random design and collected soil samples for measuring pH; the collected data were analyzed using multivariate ordination methods. Overall, 63 species were recorded and, as expected, strong dependence of species distribution on elevation and between slopes was observed. However, we also found that soil pH increased monotonically and more steeply on N than on S slope, and many relatively abundant species changed their preference to slope aspect from N to S in parallel with the increasing difference in soil pH between N and S slopes. Our results suggest that the observed shift in slope preference from N to S, at least in part, can be explained by the differences in soil pH gradient between N and S slopes.