During the active growing season, A–Ci response curves at temperature 10, 15, 20, 25, 30, 35 and 40 °C were generated in July 2015 at the Watford and Deville plantation sites (respectively the easiest to access among southern and northern sites) and again in July 2016 at the Watford plantation site. The A–Ci response curve measurements were taken after 20 min of steady-state conditions at the ambient atmospheric CO2 partial pressure (Ca = 400 µmol mol−1) and at saturated photosynthetic active radiation (PAR = 1000 µmol m−2 s−1). Thereafter, for a given temperature, the reference CO2 (Ca) was changed in the following order: 400, 350, 300, 250, 200, 100, 50, 400, 500, 600, 700, 800, 1000, 1200, 1400 and 1500 µmol mol−1. Values were recorded based on the stability of photosynthesis, stomatal conductance, CO2 and water vapour concentrations. For each foliage sample, data collections to build the A–Ci–T curves were completed within two or three consecutive days. Most of the A–Ci curves at 35 and 40 °C measured in 2015 at the Watford and Deville sites failed to converge and estimates could not be obtained. All measured gas exchange were corrected based on the measured projected needles area (see below).