Natural variation of stable isotopes is used to understand element cycling in forest ecosystems altered by acid rain. Strontium
(Sr) isotopes are used as a proxy for calcium (Ca) to discriminate between atmospheric and mineral weathering sources of Ca in tree
nutrition. The coupling of this isotopic method with the archive properties of tree-rings (dendrochemistry) adds an important
piece to the knowledge of the soil acidification story. Other isotopic tracers (multi-isotopic approach: Sr-Pb-Nd) are currently being
tested.