Fig. 1.

Schematic overview of transverse sections prepared from a specimen in tree 1. Illustration of the wood developmental zones defined as phloem, cambium, expansion zone and xylem, similar to illustrations in Hertzberg et al. (2001) [3] and Mahboubi et al. (2013). For details about the anatomical characterization and sampling scheme see (Additional file 1: Tables S1.1–4). Blue arrows indicate progressive trends across the series of development zones in the sampled wood (Symbols: C/P, cambium-phloem transition: C/E, cambium -expansion transition: E/X1, expansion-xylemX1 transition: X1/X2, xylemX1–X2 transition: X2/X3, xylemX2–X3 transition: X3/X4, xylemX3–X4 transition