Climate and signature years in west European oaks

It has been shown that in certain 'signature' years tree-ring chronologies from living oaks throughout much of western Europe exhibit the same characteristic of either increasing or decreasing growth¹. Remarkably, these chronologies, many of which are the product of the recent extension of the European tree-ring network^2-4, are distributed over a latitude span of ∼10°and a longitude span of 20°. This phenomenon means that archaeological series from more distant areas can be compared, increasing the likelihood that gaps in regional dating chronologies can be bridged^5,6. The question arises as to what circumstances could induce trees over such a large area to behave in unison so frequently. We have examined climate departures from modern signature years to determine whether or not there is a typical climate pattern associated with years of large-scale growth increase or decrease. We find that particular climatic conditions affecting the area from which the tree-ring chronologies are drawn can account for the signature years and suggest that this relationship may enable archaeological chronologies to be used in climate reconstruction.