Tree rings are recognized as a strong archive for the reconstruction of environmental changes, retrospectively for different time epochs and spatially for different regions. The combination of stable isotopes (Carbon, Oxygen, Deuterium and increasingly Nitrogen) from tree rings with classical dendrochronological data (tree ring width and density) is well established and widely used for the reconstruction of past climatic eras. Detailed studies of distinct epochs in the past (e.g. severe volcano eruptions or anomalous climatic events) and in particular for the last decades, however, show an increasing difficulty to correlate tree ring proxies with climatic data. There are strong indications that temperature anomalies or for the latest decades the increase in ambient CO2 along with the emission of nitrogen compounds and other air pollutants impact the physiology of trees, and thus mask the climatic signals. This calls for a deepened investigation of the interaction between tree physiological processes and the environmental impacts. This challenge on the other hand is an opportunity to refine the natural archive "tree ring" as a sensitive indicator for environmental changes.

For this session we invite contributions using stable (C, O, D, N) and radiogenic isotopes (14C) in tree rings as indicators for climatic and environmental changes.