A soil heat sum model for predicting seed germination

Mediterranean mountain species face exacting ecological conditions of rainy, cold winters and arid, hot summers, which affect seed germination phenology. Porceddu et al. quantify the thermal requirements for seed dormancy release and germination of Rhamnus persicifolia, an endemic tree species restricted to mountain streams. They find that seeds exhibit physiological dormancy, with base temperature (T_b) and thermal time requirements (θ₅₀) for germination decreasing systematically with cold stratification. By integrating T_b and θ₅₀ values with soil heat sum estimates, spring emergence in the field can be successfully predicted, both underneath and outside of the tree canopy, and the model may be of use for predicting in situ germination of other species.