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Thinning and Nitrogen Fertilization in a Grand Fir Stand Infested with Western Spruce Budworm. Part II: Tree Growth Response

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The effects of thinning and nitrogen fertilization on tree growth in a grand fir (Abies grandis [Dougl.] Forbes) stand infested with western spruce budworm (Choristoneura occidentalis Freeman) were evaluated over 5 years by a replicated split-plot experiment. Fertilization treatments resulted in significantly reduced defoliation and significantly heavier biomass of shoots and foliage for the last 3 years of the study. There were, however, 30% fewer buds on fertilized grand fir midcrown branches at the end of the study. Height growth of fertilized trees was significantly greater than unfertilized trees 3 to 5 years after treatment and was almost double that of controls. Radial growth measured at breast height and base of live crown was significantly greater for fertilized trees 3 to 5 years after treatment; 5 years after treatment, radial growth of thinned trees also was significantly greater than the controls. Trees thinned and fertilized had almost double the growth of controls 2 to 5 years after treatment. Fertilized trees apparently produced fewer buds m-2 of foliage but more foliage per shoot than budworm larvae could destroy, and this resulted in significantly increased tree growth. The results of the study have implications for using fertilization as a management option for some budworm outbreaks. For. Sci 38(2):252-264.

Keywords: Abies grandis; defoliation; foliage production

Document Type: Journal Article

Affiliations: Forestry Technician, Forestry and Range Sciences Laboratory, 1401 Gekeler Lane, La Grande, OR 97850

Publication date: April 1, 1992

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