Seasonal variation in the frost hardiness of Scots pine and Norway spruce in old provenance experiments in Finland

Temperature is one of the major factors regulating the acclimation of forest trees to winter conditions in the boreal zone. The projected climate warming may therefore affect the overwintering pattern of trees. In this study, old provenance trials with Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) were used to simulate the effects of a warmer climate on the seasonal variation in frost hardiness. In both species, there were differences between northern and southern provenances in the timing of bud and needle hardening during autumn. The northern provenances hardened earlier. During the dehardening phase in spring, no significant difference was found between the provenances. For buds of Norway spruce, fluctuations in hardiness that coincided rather well with fluctuations in the ambient temperature were observed during mid-winter. The results of this study do not support the theory that climate warming will increase the risk of frost damage in Scots pine and Norway spruce in boreal areas. Further research is recommended. (C) 1998 Elsevier Science B.V.