Ecological and Developmental Aspects of Multi-Stemmed Clusters of Siberian Spruce (Picea obovata Ledeb.) in the Southern Urals

The tree-line ecotone in the Southern Urals is mostly formed by monospecific stands of Siberian spruce (Picea obovata Ledeb.). Spruce is an ecologically plastic, cold-tolerant species that presents various growth forms. Moreover, its growth is further affected by stressful environment factors, including low temperatures, snowless winters, and strong winds. Thus, the morphological variability of individual trees can be due to climate-driven transformations, and represents a manifestation of biological plasticity. It was found that multi-stemmed clusters were formed by the rooting of groundlevel branches of formerly single-stemmed trees. Age analysis performed for 771 samples taken from 70 tree clusters demonstrated that mass rooting of branches started in the beginning of the 20th century and is ongoing. Dendroclimatic analysis did not demonstrate any significant links between the dynamics of stem formation and climatic data. The average biological age of mass rooting coincides with the period at which soil nutrition would have declined severely and the main root system would have become non-functional. This research shows that dendrochronological research can be used to help understand the ecophysiology of plants.