Struggle zone: alpine shrubs are limited in the Southern Urals by an advancing treeline and insufficient snow depth

Abstract

In recent decades, the rapid climate warming in polar and alpine regions has been accompanied by an expansion of shrub vegetation. However, little is known about how changes in shrub distribution will change as the distribution of tree species and snow cover changes as temperatures rise. In this work, we analyzed the main environmental factors influencing the distribution and structure of Juniperus sibirica, the most common shrub species in the Southern Ural Mountains. Using mapping and digital elevation models, we demonstrated that J. sibirica forms a well-defined vegetation belt mainly between 1100 and 1400 m a.s.l. Within this zone, the abundance and cover of J. sibirica are influenced by factors such as rockiness, slope steepness, water regime and tree (Picea obovata) cover. An analysis of data spanning the past 9 years revealed an upward shift in the distribution of J. sibirica with a decrease in its area. The primary limiting factors for the distribution of J. sibirica were the removal of snow cover by strong winter winds and competition with trees. As a consequence of climatic changes, the tree line and forest limit have shifted upward, further restricting the distribution of J. sibirica to higher elevations where competition for light with trees is reduced and snow cover is sufficiently deep.