In connection with mass burst failure of the birch Betula pendula (R o t h) 1997 in the Ore Mts (North Bohemia), the burst phonology, depending on the sum of effective temperatures, and effects of low temperatures on buds after atypical warming and subsequent frosts (-1.9 to -10.4°C) 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°C, subsequent cooling with the minimum temperature of-10°C 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 resisting well to temperature unusual fluctuations during the winter and late frosts.