A pilot experiment of forest fertilization during an outbreak of the western spruce budworm in northeastern Oregon.

Abstract

Mixed-conifer stands of grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), and ponderosa pine (Pinus ponderosa Dougl. ex Laws.) were fertilized with nitrogen and combination treatments of nitrogen, phosphorus, potassium, and sulfur to test their effects on trees and associated insects during an outbreak of the western spruce budworm (Choristoneura occidentalis Freeman). None of the treatments significantly influenced the impact of defoliation on foliage and shoot growth, radial increment, or tree mortality. The only significant effects of fertilization on insects were a higher survival of budworm larvae and an increase in pupal weight the first year after treatment. Many of the sampled variables, however, were significantly affected by the year of measurement and tree species. The lack of a more significant measurable response of trees to fertilization was attributed to the variability of site conditions and the extreme densities of budworm larvae that severely impacted growth of grand fir and Douglas-fir during the experiment.

Citation

Mason, R.R.; Wickman, B.E.; Paul, H.G.; Torgersen, T.R. 1998. A pilot experiment of forest fertilization during an outbreak of the western spruce budworm in northeastern Oregon. USDA Forest Service PNW Research Paper No. 506: 25 p