Fig. 4

Density distributions of all tracheid diameters grouped per standardized precipitation-evapotranspiration index (SPEI) of prior year August. Negative and positive SPEI indicate dryness and wetness, respectively. The density distributions were calculated with a Gaussian smoothing and the “nrd0” bandwidth using the “density” function of R (R Development Core Team, 2013). Tracheid data from 6, 13, 6 years were included in the classes of SPEI − 1, 0, and 1 respectively. Lines for the SPEI − 2 and 2 are not shown since only found in 2 and 3 years