Effects of climatic warming on northern trees: Testing the frost damage hypothesis with meteorological data from provenance transfer experiments

According to a hypothesis presented recently the predicted climatic warming will cause premature bud burst of trees in Finnish conditions during mild spells in mid-winter and heavy frost damage during subsequent periods of frost. The full stocking and high productivity of northern Finnish provenances of Picea abies (L.) Karst. grown in central and southern Finland for several decades seemed to conflict with the frost damage hypothesis, because the increase in the annual mean temperature involved in the most distant provenance transfers exceeded the predicted increase in the annual mean temperature in northern Finland. A calculation method using air temperature data from provenance transfer experiments was developed for testing the frost damage hypothesis. The method was applied with temperature data from Finnish provenence transfer experiments, assuming for northern Finland both (1) a uniform warming scenario of 4.7 degrees C throughout the year and (2) a non-uniform warming scenario in which the same mean annual temperature increase is applied more to winter than to summer. The results revealed that the present air temperature conditions in central and southern Finland do not correspond to those of either of the scenario climates in northern Finland; thus the frost damage hypothesis was not falsified. The calculation method developed can be used in testing the frost damage hypothesis in the case of other tree species, locations, and warming scenarios by altering the specifications applied in the method.