Changes in needle morphology, anatomy, and mineral content during the recovery of protected balsam fir trees initially defoliated by the spruce budworm

Morphological, anatomical, and chemical changes in foliage of 25- to 30-year-old balsam fir trees (Abiesbalsamea (L.) Mill.) that had been completely defoliated in 1977 by the spruce budworm (Choristoneurafumiferana (Clem.)) and then protected for 5 years by insecticide, were compared with foliage from adjacent undefoliated trees. The comparison showed that in 1978, the 1st year of refoliation, needle length, weight, and width were greater in the defoliated trees, while in 1979 they were less. In 1980, needle length was again less, but no difference was observed in needle weight and width. Needle length, weight, and width were similar in the defoliated and undefoliated trees in 1981 and 1982. Needle density in the defoliated trees was lower in 1978, but greater in 1979, while no difference occurred in 1980–1982. Foliar nitrogen content was higher in the defoliated trees in 1978–1980. Foliar phosphorus and potassium content were higher in the defoliated trees only in 1978. Needle and mesophyll cross-sectional areas in the defoliated trees were larger in 1978, but were smaller in 1979. There were no differences during 1980–1982. Mesophyll and needle cross-sectional areas were positively correlated throughout 1978–1982. Relative amounts of total protein were higher, whereas those of total insoluble carbohydrates were lower in 1978–1980 needles from undefoliated trees.