Fig. 2

Preparation process to measure δ¹⁸O of α-cellulose in each tree ring: a cutting an increment core of 1 mm thickness (C: cross plane, R: radial plane, T: tangential plane); b vial with a thin wood plate fixed between Teflon-punch sheets; c chemical treatment to extract lignin and hemicellulose in solutions of NaClO₂ and NaOH in a water bath at temperature 70 and 80 °C, respectively; d separating α-cellulose from each tree ring of same width from early- to latewood at 120–250 μg, and e wrapped α-cellulose in a thin silver foil