EFFECTS OF CROWN REDUCTION ON NEEDLE NUTRIENT STATUS OF SCLERODERRIS-CANKER-DISEASED AND GREEN-PRUNED SCOTS PINE

The effects of green crown reduction (needle loss) on the nutrient status of needles were studied in Scots pine (Pinus sylvestris L.) in Finland. Trees were either diseased with scleroderris canker (Gremmeniella abietina (Lagerb.) Morelet) or had been green pruned. The concentrations of 15 different elements were determined in needles collected in March 1987 from 120 trees in six young Scots pine stands. Four of the stands had suffered from scleroderris canker over the last 10 years, whereas the other two stands were healthy and had been pruned about 2 years before sampling. To eliminate the effects of soil and environmental factors, sample trees were chosen in pairs. Each pair contained one tree with a severely reduced crown (about a 50% reduction in crown length as a result of disease or pruning) and an adjacent tree (control) with an unaffected crown. Compared with the control trees, concentrations of foliar B, Ca, N, and S were significantly higher in both diseased and pruned trees, while Mn was higher only in diseased trees and Na and Cu, only in pruned trees. Foliar Fe and Mg concentrations were lower in diseased trees than in control trees. In many stands there was a significant correlation between needle element concentrations and severity of crown reduction, suggesting that differences in foliar elemental concentration in Scots pine needles depend on the extent of crown reduction. This phenomenon should be considered when interpreting foliar analyses of recently defoliated conifers, particularly before conclusions are made about the need for fertilization, nutritional disturbances, or the effects of air pollution.