• Wolcott, Michael P.
  Maine Agricultural Experiment Station, University of Maine, Orono, Maine
  
• Shepard, Robert K.
  Maine Agricultural Experiment Station, University of Maine, Orono, Maine
  
• Shottafer, James E.
  Maine Agricultural Experiment Station, University of Maine, Orono, Maine
  

Ten overstory red spruce were selected from a thinned stand at 10 from an unthinned stand. Average age of sample trees was approximately 80 years. A 1.8- to 2.4-m log was removed from the base of each tree and a 5-cm thick diametric flitch, centered on the pith, was cut from each log. A clear, 0.3-m section was removed from each board and cut along the pith to produce two radially opposing sample boards. Microbending specimens and ASTM standard-size test samples were prepared from the sample boards and used for determinations of specific gravity,strength, and stiffness.

Specific gravity reached a maximum at age 53 in the thinned stand and age 72 in the unthinned stand, after which it remained relatively constant. Stiffness reached a maximum at ages 35 and 50, and bending strength at ages 41 and 54; both remained relatively constant with further increases in age. Stiffness showed the largest relative difference between juvenile and mature wood, 22 percent, and specific gravity the smallest difference, 8 percent. Thinning did not adversely affect any of the properties, even though the width of some growth rings was increased by three to four times.

These results suggest that 1) growth of mature red spruce stands can be increased by thinning without affecting wood physical properties, and 2) intensive management practices designed to shorten the rotation age may lead to stands that have not begun to produce mature wood before they are harvested. These short-rotation stands will contain a higher percentage of juvenile wood than stands presently being harvested, which means that pulp yields will decrease and the material will be less suitable for structural lumber.