Spruce budworm defoliation and growth loss in young balsam fir: recovery of growth in spaced stands

Trees defoliated by the spruce budworm (Choristoneurafumiferana (Clem.)) for 1 to 4 years and subsequently protected rapidly regained foliar biomass. Three plots of 25- to 30-year-old balsam fir (Abiesbalsamga (L.) Mill.) trees, on the Cape Breton Highlands of Nova Scotia, were studied. Two major factors contributed to the rapid growth recovery rates: the ability to produce epicormic shoots, combined with increased retention of older age-classes of needles, and the development of new foliage at the expense of volume growth. A complete recovery of volume increment occurred after 2 years of extreme defoliation, but not after 4 years of severe defoliation. Epicormic shoot production was only associated with shoot and bud destruction and therefore, growth recovery was slow after partial defoliation of only current foliage. In all plots studied, there was a lag of 2 to 3 years between increased foliar biomass and significant increases in volume increment.