Relationship between throughfall (TF, % of total precipitation) and basal area (G, in m² ha⁻¹) according to stand age (young: 20 to 50 years old; old: more than 50 years old). Points are grouped by intervals of 15 successive G values, and the y -axis presents percentiles of the TF values of these groups based on a normal approximation (median and 95% confidence interval, cf. Harrell, 2001), placed at the median group values for G on the x -axis. Point grouping was performed to render the plot more readable (Harrell, 2001).