Varied growth response of high alpine Rhododendron myrtifolium and forest zone tree species to climate warming in the Eastern Carpathians, Ukraine

Plants growing along altitudinal transects in alpine and mountainous areas respond differently to climatic conditions. The present study is centred on the unique and ecologically significant species, Rhododendron myrtifolium Schott & Kotschy, an evergreen clump-forming or prostrate dwarf shrub. This high-mountain endemic plant grows at several localities in isolated massifs of the Eastern Carpathians, but the greatest numbers of sites can be found in the subalpine and alpine belts of the Chornohora range. The main objectives of this study were (1) to assess the dendrochronological potential of Rhododendron myrtifolium as a new species in dendrochronological research and (2) to compare the growth response of R. myrtifolium (sampling elevation: 1800–1950 m a.s.l.) with Picea abies Karst. (1350–1500 m a.s.l.) and Abies alba Mill. (950–1050 m a.s.l.) collected from the upper and lower forest belts. Tree-ring material from 97 trees and shrubs enabled the construction of three site chronologies from sites located within the altitudinal transect. The longest chronology, covering the previous 184 years, was developed for fir. The chronology for the rhododendron was the shortest at 66 years. This species is the most sensitive of the three species analysed. The highest positive r-value (r=0.71) was obtained between the rhododendron chronology and the warm-season temperature (from March to July). Also, the growth of this species was significantly positively correlated with the summer temperature (r=0.50). In contrast, fir and spruce demonstrated a similar inverse relationship with August temperatures.