Phenological description and thermal time requirements for the seedling phase of three Brazilian native forest species

Understanding the phenological stages and thermal requirements of the seedling phase of forest species is crucial for sustainable nursery management. This study proposed an adaptation of a phenological scale based on the basic Biologische Bundesanstalt, Bundessortenamt, and Chemical industry, associated with the thermal requirement to describe the phenological stages during the seedling phase of three forest species: Cybistax antisyphilitica, Libidibia ferrea, and Platycyamus regnellii. The phenological scale of C. antisyphilitica and L. ferrea was defined and described through 22 seedling development stages ranging from dry seed to 20th visible leaf emitted on the main stem (from 00 to 120) and P. regnellii for 12 leaf development stages, from dry seed to 10th visible leaf emitted on the main stem (from 00 to 110). In addition, the duration (days) and thermal time (°C day) were determined for each seedling development stage. C. antisyphilitica needs to accumulate more energy (and days) to finish the seedling phase (1551.9°C day or 261 days) compared to L. ferrea (1127°C day or 175 days) and P. regnellii (1109.7°C day or 193 days). However, the three forest species exhibit similar energy demands throughout most stages of seedling development, except code 09–12 for C. antisyphilitica. This study provides important information for optimizing silvicultural techniques, evaluating the response of temperature on phenological stages, and assessing the impacts of global warming on forest seedling development.