Silver Fir Defoliation Likelihood Is Related to Negative Growth Trends and High Warming Sensitivity at Their Southernmost Distribution Limit

Figure 4

Best predictors of silver fir decline obtained by logistic regression models. Variables are plotted for declining and non-declining trees. The growth sensitivity to climate was estimated as the determination coefficient between basal area increment (BAI) and annual climatic variables (SPI, standardized precipitation index; P-ETP, annual values of the difference between precipitation—P—and potential evapotranspiration—ETP). The percentages displayed near the boxes indicate the frequency of declining (trees with percentage of crown defoliation above 50%) and non-declining trees which were correctly classified. In the box plots, error bars represent the 5th/95th percentiles, boxes indicate the standard errors, solid lines are the medians, dashed lines are the means, and points are outliers.