Secondary ion mass spectroscopy and synchrotron X-ray fluorescence analysis have been used to document the changes in metal content across the ring system of trees from northern Canada. The results show a seasonal qualitative variation in the uptake of Na, Al, K, Ca, Cr, Mn, Fe, Cu, and Zn. Diffusional models show that locally elevated concentrations of selected metals are sufficiently stable within individual rings that variations in content among rings remain at detectable levels for at least a century.