Shoot length series
A total of 12,528 annual growth increments were measured of 764 branches and 25 shrubs, covering 122 years over the period 1893-2014 (Fig. 2, Table S1). Mean annual shoot length was 5.43 ± 1.90 mm on site level and ranged between 4.26 ± 2.10 mm and 10.20 ± 3.86 mm between shrubs (Table S2). Individual shrub series spanned between 59 (1956-2014) and 122 (1893-2014) years (Fig. S2, Table S2). There were clear similarities in growth variations over time between branch series, especially within, but also between shrubs, as shown by the mean interseries correlation coefficients of 0.53 and 0.42, respectively. The Gini coefficient was 0.19 across all specimen, suggesting intermediate variability in growth, comparable to that found for the same species in the polar desert in northern Greenland . Gini coefficients at the shrub level varied between 0.16 and 0.28, suggesting intermediate to high variability of growth of individual shrubs in comparison to variation in tree-ring widths from mesic to xeric sites .