Nutrient contents, acidity and exchangeable cations in the upper 300 mm of peat beneath lodgepole pine have been compared with those in peat from contiguous unplanted areas at each of six sites. Nitrogen, phosphorus and potassium contents, which are significantly higher in flushed blanket bog peat than in peat from either raised bog or unflushed blanket bog, are not significantly altered by the presence of trees. Calcium and magnesium contents, on the other hand, although similar in peat from different bog types, are lower in peat beneath the tree crop. Exchangeable Ca 2+ Mg 2+ and K 2+ are replaced by Na + and H + in planted peat but the increase in H + content exceeds the loss of base cations, reflecting a higher number of exchange sites. This increase accounts for lower values of both base saturation and pH in planted peat and is attributed to enhanced decomposition promoted by aerobic conditions beneath the tree crop.