Fig. 5From: Drought sensitivity of Norway spruce is higher than that of silver fir along an altitudinal gradient in southwestern GermanyBootstrapped correlation coefficients between standardized chronologies of spruce and fir and sc-PDSI in July as a function of altitude. The horizontal dotted line denotes the 95% confidence limit. Asterisks indicate significance levels of linear regressions, *P < 0.05, **P < 0.01Back to article page