Burst phenology and birch bud resistance to frost

In connection willi mass burst failure of the birch Betula pendula (R o t h ) 1997 in the Ore Mts (North Bohemia), the burst phenology, depending on th e sum of effective temperatures, and effects of low temperatures on buds af ter atypical warming and subsequent frosts (-1.9 to -10.4 degreesC) during the winter period (9.2.-4.3.1998) were investigated. The birch responded by growth activities in buds at the sum of effective temperatures of 31 degre esC, subsequent cooling with the minimum temperature of - 10 degreesC only stopped the growth bud did not damage buds. If the birch is not exposed to other stress factors disturbing the bud physiology, it is a tree sort resis ting well to temperature unusual fluctuations during the winter and late fr osts.