Geographical patterns in the radial growth response of Norway spruce provenances to climatic variation

Changing climate is expected to cause range shifts and reduced growth in Norway spruce (Picea abies (L.) Karst). In order to mitigate these changes, genetic variation between populations can be utilized in selecting alternative tree origins that are better suited to the new conditions. The aim of this study was to examine the intraspecific differences in the climatic drivers of radial growth in Norway spruce. We used tree-ring data from seven Norway spruce provenance experiments in Finland, located in different climatic conditions and including a large variety of provenances. The annual ring-width indices were studied with hierarchical clustering, correlation analysis with climate variables, pointer year analysis and linear models to identify the provenance differences in growth variation and its climatic control, and compare them on a latitudinal gradient. The cluster analysis revealed patterns of provenance differences in growth variation: north European and central European provenances were grouped in separate clusters within sites, although with some exceptions. Largest provenance differences in climate-growth responses were found in relation to winter and spring temperatures. In the southern provenances warm winters were typically associated with faster growth whereas for the northern provenances the correlations varied from non-significant to negative. In addition, the pointer year analysis showed negative growth anomalies only in the southern provenances for years with exceptionally cold winters. These patterns may reflect the physiological differences between the provenances relating to, for example, cold tolerance and the timing of spring phenology. As the climate warming in Europe is predicted to be strongest during the winter months, acknowledging the intraspecific growth responses to climate in Norway spruce becomes increasingly important.