Effects of Afforestation with Pinus contorta on Nutrient Content, Acidity and Exchangeable Cations in Peat

Nutrient contents, acidity and exchangeable cations in the upper300 mm of peat beneath lodgepole pine have been compared withthose in peat from contiguous unplanted areas at each of sixsites. Nitrogen, phosphorus and potassium contents, which aresignificantly higher in flushed blanket bog peat than in peatfrom either raised bog or unflushed blanket bog, are not significantlyaltered by the presence of trees. Calcium and magnesium contents,on the other hand, although similar in peat from different bogtypes, are lower in peat beneath the tree crop. ExchangeableCa²⁺ Mg²⁺ and K²⁺ are replaced by Na⁺ and H⁺ in planted peatbut the increase in H⁺ content exceeds the loss of base cations,reflecting a higher number of exchange sites. This increaseaccounts for lower values of both base saturation and pH inplanted peat and is attributed to enhanced decomposition promotedby aerobic conditions beneath the tree crop.