The aim of this work was to evaluate the effect of thermal time methods and to identify the phyllochron and photoperiod response in seedlings of two forest species: Corymbia citriodora and Eucalyptus urophylla. A field experiment was installed under a completely randomized design, in a 2 × 11 factorial scheme, with two forest species and eleven sowing dates (E). Phyllochron is influenced by thermal time methods. The best thermal time method is the one that considers the base and optimum temperature and compares them with daily extreme temperatures. In addition, the influence of photoperiod and air temperature on phyllochron values was also verified. The lowest value occurred in E1 (Corymbia citriodora: 24.6 and Eucalyptus urophylla: 13.2 °C day leaf-1) and the highest in E10 (Corymbia citriodora: 46.4 °C day leaf-1) and E7 (Eucalyptus urophylla: 29.2 °C day leaf-1), suggesting that the phyllochron is influenced by sowing dates.
