Changes in a primary resistance parameter of lodgepole pine to bark beetle attack one year following fertilization and thinning

Abstract

Many of the forest soils in the Intermountain West are deficient in several nutrients, including nitrogen (N), potassium (K), sulfur (S) and boron (B) and these deficiencies may impact tree resistance to insect attack. Two potential techniques for manipulating tree resistance are fertilization and thinning. We examined fertilization (both alone and in conjunction with stand thinning). Conifer resistance to bark beetles involves a three-step response, the first stage of which is resin flow. Rapid resin flow can prevent the colonization of bark beetles within a tree. Fertilization with low levels of N resulted in an increase in resin flow while high levels of N did not significantly increase resin flow in treated trees. Thinning did not result in higher concentrations of foliar K or B but did result in higher concentrations of foliar N and S. The highest concentrations of foliar N and S consistently occurred in the trees from thinned treatments, regardless of fertilization. There was a negative correlation between tree growth and resin flow one year following treatments. Increasing available nutrient levels to trees (either through fertilization or stand density management) may result in modified resistance parameters that must be considered when making management decisions.