The Effect of Habitat Type and Rock Type on Individual Tree Basal Area Growth Response to Nitrogen Fertilization

Individual tree basal area increment models for nitrogen fertilized stands were developed using data from permanent research plots located throughout the Inland Northwest. Results show that tree size, stand density, habitat type, and rock type significantly interact to affect individual tree basal area growth response to nitrogen fertilization. Small trees with high basal area in larger trees growing on moist habitat types and all rock types, except meta-sedimentary, exhibited greater relative response than larger trees with low basal area in larger trees growing in the same stand. Further, small trees with high basal area in larger trees growing on dry sites or on meta-sedimentary rocks showed less relative response than larger trees with low basal area in larger trees. Incorporating the new equations into individual tree growth and yield simulators would provide better representation of N fertilization response differences within a stand