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A soil resampling approach has detected an early stage of recovery in the cation chemistry of spruce forest soil due to reductions in acid deposition. That approach is limited by the lack of soil data and archived soil samples prior to major increases in acid deposition during the latter half of the 20th century. An alternative approach is the dendrochemical analysis of dated wood to detect temporal changes in base cations back into the 19th century. To infer environmental change from dendrochemical patterns of essential base cations, internal factors that affect cation chemistry such as the maturation of sapwood and the spread of wood infection need to be recognized. Potassium concentration was a useful marker of these internal maturation and infection that could affect the concentration of essential base cations in wood. Dendrochemical patterns in samples of red spruce in the eastern United States and Norway spruce in northwestern Russia were used to determine how internal changes in base cations can be separated from external changes in root-zone soil to date major changes in the availability of essential base cations associated with a changing environment. [ABSTRACT FROM AUTHOR]