CROWN RELEASE IMPROVES GROWTH OF 20-YEAR-OLD BETULA-ALLEGHANIENSIS INTOLERANT NORTHERN HARDWOOD STANDS

Twenty-year-old overstocked naturally regenerated yellow birch (Betula alleghaniensis Britton) were thinned near Thessalon, Ontario. Treatme nts consisted of either a control, or the removal of all competing tre es at 1, 2, 3, or 4 m around the boles of the crop trees, The size of the openings created around the crop tree crowns was found to be more strongly correlated to diameter, clear bole length, and crown incremen t than the removal of competing trees using fixed distance from the st em. Crop trees responded well to thinning. Five-year diameter incremen t and crown diameter growth were positively correlated to size of the opening created around the crop tree crown. However, the relationship between height growth and size of canopy opening was weak. Clear bole length was found to be negatively correlated to the size of canopy ope ning. Few epicormic sprouts developed on the stems when all competing trees were removed at 1, 2, or 3 m around the crop tree boles. However , release at 4 m greatly increased the number and size of epicormic sp routs. Providing about a 15-m(2) opening around the crop tree crown, c orresponding to approximately a 3-m removal of competing trees around the bole, provided a good balance between diameter increment and stem quality maintenance.