Extended Data Fig. 8: Age-related shift in the air temperature offset under the forest canopy.

The data show the below-canopy air temperature (Ta_bc) offset, which values were calculated as the difference between the mean temperature measured during May–August in each forest stand and the corresponding temperature statistic derived from the mean values recorded in the 3 youngest forest stands (5–7 years old). This latter temperature represented the air conditions outside the forest stands. Negative Ta_bc offset values indicate cooler air temperatures inside than outside the forest stands. The panel a) shows the Ta_bc offset during the baseline period 2016–2017 (BL_16–17) and the drought year 2018 (D₁₈), while the panel b) shows the absolute anomaly of Ta_bc offset (∆Ta_bc) during D₁₈ relative to BL_16–17. Circular open symbols indicate the values for each forest stand, while circular closed symbols indicate the means for each of the stand age classes, including initiation (I), young (Y), middle-aged (Ma), mature (M), and old-growth (O). The horizontal and vertical bars represent the 95% confidence intervals, while the solid lines show the best-fit regressions. The equation form and coefficient of determination (R²) of the linear regressions are also shown. Equations and associated goodness-of-fit statistics are derived from the individual forest stand data (n = 49). The p-values for the non-parametric Kruskal–Wallis rank sum test comparing the differences between the stand age class means are also shown.