A SIMULATION-MODEL FOR THE ANNUAL FROST HARDINESS AND FREEZE DAMAGE OF SCOTS PINE

The changes in the frost hardiness of Scots pine were modelled by a dy namic model where the input variables were temperature and photoperiod and the phase of annual development. The damage caused by freezing wa s described by the sigmoidal relationship between the relative needle damage and freezing temperature. The model simulations were carried ou t using temperature data from two sites in central Finland-Suonenjoki and Tampere. The validity of the frost hardiness model was tested with measured frost hardiness data from Suonenjoki. The effects of climati c warming were also simulated by increasing temperature of the long-te rm climatic data. Genotypic differences in chilling requirement, which determines the timing of the reduction of hardening competence, were included in the simulations. The simulated needle damage increased as a result of climatic warming, and the differences in the chilling requ irement had a stronger effect on the amount of damage in the warmed cl imate than in the present climate. A large variation between years was found in the level of damage. (C) 1996 Annals of Botany Company