VARIATION IN TEMPERATURE SUM REQUIREMENT FOR FLUSHING OF BEECH PROVENANCES

The time of bud-burst of provenances of beech (Fagus sylvatica L.) is important especially on sites with frequently occurring late frosts. O n a field trial in the nursery of the Institute of Forest Genetics at Grosshansdorf, Germany, the time of bud-burst was scored in 2 differen t ways on 158 3 year old provenances representing most part of the nat ural distribution of beech. Also the air temperatures were logged to c alculate temperature sums at the time of bud-burst. A dine became evid ent with provenances from the east and south-eastern part of the range of distribution to flush early and provenances of the western part of the range to flush late. Also provenances from higher elevations tend to burst bud earlier than those from lower elevations. At a base temp erature of 5 degrees C starting from January Ist early flushing proven ances require 8,500 degree hours for bud-burst whereas late flushing p rovenances require 11,000 degree hours. Averagely 9,750 degree hours w ere required for bud-burst. The first single trees to flush required 7 ,600, the last 14,750 degree hours before bursting bud. According to t he local risk of late frost occurrence during the period when the fres hly flushing beech leaves are prone to frost it can be predicted which provenances could be potentially planted without late frost risk at a certain site and for which the late frost risk is too high.