Similar growth responses to climatic variations in Norway spruce ( Picea abies ) and European beech ( Fagus sylvatica ) at the northern range limit of beech

In south-east Norway, in the hemiboreal vegetation zone, beech reaches its northern distribution limit and typically occupies the same type of sites as spruce. Under future climate change, this area is projected to fall within the temperate zone and beech to increase its distribution towards the north at the expense of spruce. However, such forecasts are based on very broad scale estimates and the knowledge of climatic adaptation and the competitive potential of the beech and spruce populations at these latitudes is scarce. Here, we use a dendrochronological approach to study the growth performance of neighbouring spruce and beech trees to climate variability over a period of 70 years. The two species responded quite similarly to variations in climate in the study area. Both showed increased incremental growth in response to high precipitation both in the previous and present year June, indicating that water is a limiting resource. In addition, beech showed a negative response to high temperatures in previous July and August, which is probably connected with growth reductions due to masting. Overall, spruce and beech in the hemiboreal zone show comparable responses to climatic variations as in the temperate zone. Due to the different drought-handling strategies of the two species, we suggest that the intensity of summer droughts and the variability between years are likely factors that would be decisive for which of them that will be more successful under future climatic conditions.