Climate sensitivity is affected by growth differentiation along the length of Juniperus communis L. shrub stems in the Ural Mountains

Arctic and alpine shrubs are valuable for future dendro-ecological and dendro-climatological studies in regions where trees are sparse or absent. A commonly accepted procedure of sampling shrub stem disks is at the root collar. However many shrub studies report low inter-series correlations in radial measurements as compared to trees. Many studies also report cross-dating difficulties with radial measurements from shrubs within a stand and commonly attribute this to differential growth along the length of the stem. So does one stem disk entirely represent the environmental parameters the shrub might be reacting to? Does change in sampling location of the stem disk affect the subsequent ring-width chronologies and climate sensitivity? To tackle these questions, we investigated Juniperus communis L. - a species wide spread in the circumpolar arctic - across a latitudinal gradient in the Ural Mountains. Based on traditional radial ring-width measurements we assessed growth synchronicity along the length of shrub stems. We also compared ring width chronologies representing different stem heights with respect to their relationships with temperature and the standardized precipitation evapotranspiration index (SPEI). Growth patterns often varied significantly among stems disks of the same shrubs, resulting in dissimilar climate-growth relationships of stem disk chronologies. For correlations with temperature, stem disks at 20 cm distance from the root collar captured the best signal. For correlations with SPEI data we could not find any specific stem disk chronology with highest sensitivity. At least in our dataset, no “perfect sampling height” with high climate sensitivity exists and our results thus highlight that a single stem disk from a shrub may not completely represent the shrub's growth response to climate parameters.