The 'Dynamic Model' of chilling accumulation: its structure and performance under simulated and real thermal regimes

The major features of the 'Dynamic Model' (Fishman S., Erez A., Couvillon G.A., 1987 - J. Theor. Biol. 124:273), which evaluates the temperature dependence of bud rest breaking, are briefly analyzed and discussed. The chilling accumulation calculated according to this new approach is compared with that predicted by the 'Utah Model' and by counting the total number of hours below 7 °C. Results obtained by simulations show some differences, occurring mainly during periods with steady high or freezing temperatures. The 'Dynamic Model' proved to be able to account for chilling enhancement due to short exposures to high temperatures. However, differences tend to cancel out, when the models are applied to a set of real temperature records. While it seems possible that greater differences wiould come out in milder cilmates, the need for a stronger linking to physiological events is finally emphasized.