Despite the attention that climate change has attracted in the forestry sector, the effects of temperature and precipitation changes on sensitive phases of the life cycle, including seed germination, have been virtually ignored. This study investigated the variation in temperature requirements (including chilling requirements) and moisture requirements for germination of the shallowly dormant seeds of Pinus sylvestris, and used a chill unit model and thermal time
model to predict germination under different conditions.
The base temperature for germination (Tb) varied from 3.5°C to 7.5°C among seed sources (provenances and seed orchard crops), while the optimum temperature (To) was around 20°C for all seed sources; the maximum temperature (Tc) could not be determined but was above 35°C. Thermal time to 50 % germination (θ50) varied from 70 degree-days to 175 degree-days among seed sources. There were significant differences among provenances in germination capacity, germination rate, chilling requirements for dormancy breakage and tolerance of moisture stress. Southern European provenances required considerably less chilling, had a higher germination capacity and rate, and germinated over a wider range of temperatures than northern European provenances. Provenances from high elevations were more susceptible to moisture stress than provenances from low elevations. There were significant differences in germination capacity and rate among seed crops collected in different years from a clonal seed orchard, suggesting that the environment experienced by mother trees during seed maturation can affect germination characteristics.
A new chill unit model for predicting germination capacity from accumulated chill units gave R² values of 80-94 %. A thermal time model used estimates of Tb and θ50 to predict germination under current and future climatic conditions in southern England. Under the increasing temperatures predicted by the IPCC A2 scenario, seeds of all provenances are expected to start and complete germination earlier.