Modelling relation of first shoot emergence in various tree species to meteorological parameters in Slovenia

The relation of first shoot emergence in various tree species (birch, beech, oak and spruce) to meteorological parameters was studied on the basis of phenological and meteorological observations at five locations in Slovenia during 1967–1986. A physical model was developed using tree branch temperature obtained by the energy balance equation. The gained linear dependence of first shoot emergence on effective tree branch temperature was compared with the results obtained by multiple regression analysis among first shoot emergence, effective temperature, global radiation, wind velocity and precipitation. A new method was developed to define the proper biological temperature threshold which was used for effective temperature calculations. Results of the physical model and of the multiple regression analysis are statistically significant and give similar correlations between first shoot emergence and meteorological parameters.