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(1) Budburst and leaf expansion up to maximal leaf area index were followed from 1976 to 1983 in a 120-year-old Quercus petraea stand. (2) A phonological model was formulated to predict the date of budburst and the increase in leaf area as a function of cumulative temperature and of day-length. Budburst occurs when the temperature sum of the past 10 days exceeds a given threshold, which is a decreasing function of day-length. Leaf area increases with the temperature sum since budburst, and reaches its greatest value when the temperature sum exceeds a given threshold, which is also a function of day-length. (3) The model was tested during the growing season of 1982 and 1983. Simulated dates of budburst and leaf area index development were in close agreement with the measurements.
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Nizinski et al. (1988) studied this question.
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