Effects of manual defoliation treatments and site type on balsam fir, black spruce and white spruce foliage production

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University of New Brunswick


Defoliation level and site type are thought to influence tree response during spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks. We determined the effects of four manual defoliation treatments (0%-100% + bud removal of current foliage) for 3 years on balsam fir, black spruce, and white spruce trees, on four site quality classes (dry/poor, wet/poor, dry/rich, moist/rich), on foliage production. Number of shoots generally increased 12-59% with increasing cumulative defoliation. Shoot length generally decreased by 32% with increasing cumulative defoliation, especially on rich sites. Bud destruction resulted in 47% fewer shoots but 24% longer shoots during a 2-year recovery period. Trees on rich sites had 43% more shoots, 39% longer shoots, and 156% greater needle weight than on poor sites. The effects of site and defoliation varied between and within species, but site quality played an important role in production of shoots and needles and the tree’s ability to withstand defoliation.