Selecting trees for structural timber

Twenty-eight cubic metres of timber (i.e. a total of 2248 boards) cut from 108 Pinus radiata trees from two 25-year-old plantations from Canterbury and Nelson in the South Island of New Zealand were tested in tension. Within- and between-tree variations of stiffness, strength and density were examined. Comparisons between density and stiffness for selecting trees for structural timber indicated that stiffness is the better parameter for selecting superior trees within the natural population of a forest stand; and the quality and grade recovery of structural timber would be increased significantly if trees were to be selected on the basis of stiffness. These conclusions apply to both stands although regional differences are evident with the Nelson timber being somewhat stiffer.