Eight-two spruce (Picea rubens Sarg.) sample trees were selcted from eight even-aged stands between 40 and 60 years old in northern Maine. Total height, dbh, crown length, crown diameter at the base and at 1/4, 1/2, and 3/4 of the crown length, and distance between trees were measured for each sample tree and surrounding competitors. Equations expressing 5-year cumulative bole-volume increment as a function of height were developed using stem analysis. The crown surface area displaced (SAD) index best expressed competition as the ratio of actual crown surface area of the sample tree to the sum of the interactions between the ratio of the maximal crown surface area of the sample tree, displaced by the maximal area of the sample tree, weighted by the crown-length rations. Multivariate regression techniques were used to model the 5-year cumulative bole-volume growth to any designated height on the bole of a red spruce tree of known dbh, total height, site index and SAD index. Additional keywords: Picea rubens Sarg., competition.
