Soil properties affect the drought susceptibility of Norway spruce

Norway spruce (Picea abies) is considered to be one of the economically most important coniferous tree species in Europe. It is, however, susceptible to drought and there is concern that anticipated climate change may greatly influence its yield potential. In addition to the climate, soil characteristics are known to play a major role in tree growth rates. Detailed knowledge about the relationships between the soil and tree growth in the face of climate change has started to be generated only recently. As a contribution to this field we investigated the influence of soil on the drought susceptibility of Norway spruce by means of dendrochronology. Tree-ring data were acquired from two sites southwest of Munich, Germany, with rather similar climates but different soil textures. By combining multivariate statistics with climate correlation and pointer year analyses, we were able to show a clear differentiation between the two sites with respect to the growth performance of Norway spruce. That is, trees growing on a shallow, well-drained soil grew less and expressed a relatively higher drought sensitivity compared to trees from a site with a deep, silty soil as indicated by higher correlations with drought related indices and more intense droughts in negative pointer years compared to neutral years. Among the considered drought indices the soil water deficit index explained best the multivariate differentiation between the two sites, wherefore we interpret these findings as a significant impact of soil characteristics on Norway spruce performance. In the context of climate change and an increasing risk of extreme droughts during the 21st century, this finding has important implications for forest management activities since the risk of drought induced tree mortality appears to be affected by soil conditions.