3.1 | Environmental data
We first present seasonal variations of the precipitation, PPFD, temperature and VPDZ in 2012 and 2013, which were typical of boreal forests (Figure 1). The annual mean temperature during 2012 and 2013 was 1.6 °C and 3.3 °C, and the total precipitation 796 mm and 542 mm, respectively. Precipitation was relatively high during the thermal growing season limiting the potential for drought during the growth period. The light level increased almost three months before the start of the thermal growing season and the maximum values were in June before they decreased until winter. The temperatures were the highest in July-August and reached very low values in winter. Temperatures stayed below zero for several months. Finally, VPDZ was highest during the thermal growing season although its increase started around March for both years. VPDZ showed high variability over the whole year.