THE DIFFERENTIAL SENSITIVITY OF RED PINE AND QUAKING ASPEN TO COMPETITION

Growth of red pine (Pinus resinosa Ait.) and quaking aspen (Populus tr emuloides Michx.) target trees with varying degrees of competition by neighboring aspen was measured in a 7-year-old clearcut in northeaster n Minnesota. Competitive conditions were measured using indices of res ource availability (percent open sky) and neighborhood stand density. Three-year diameter growth of target trees was reduced by more than 50 % in both species because of competition from neighboring quaking aspe n. The last 2 year's height growth was also reduced by approximately 3 0% for both species. The relationship between growth and percent open sky was convex for red pine and concave for quaking aspen, potentially indicating a greater sensitivity in aspen to any reduction below opti mal resource availability. Competition reduced crown size in both spec ies, but self-pruning occurred only in quaking aspen. Needle and leaf size were not affected by competition, but red pine needle density was lower in highly competitive environments. Red pine had a higher speci fic gravity when growing under competition, partially offsetting the r eduction in wood volume.