GENETIC EVALUATION, MULTIPLE-TRAIT SELECTION CRITERIA AND GENETIC THINNING OF PINUS-CONTORTA VAR LATIFOLIA SEED ORCHARDS IN SWEDEN

Seedling seed orchards were established in Sweden with 1112 open polli nated progenies of Pinus contorta Douglas ex Loudon plus-trees, select ed from 88 wild stands in western Canada. The progenies were also grow n in Swedish test plantations. Breeding values (best linear unbiased p redictors) were calculated for tree condition, height, and ramicorn wh orl frequency, assessed at ages ranging between 8 and 12 yrs. On the h arshest sites, damage caused by weather and fungi, e.g. Gremmeniella a bietina, were also evaluated. Categorical data were transformed into v alues on a normal score scale to improve the efficiency of the evaluat ion. Breeding values for all assessed traits were combined to form tot al-value indices. These indices were then used to guide the genetic th inning of the seed orchards, where single trees were selected from gro ups of four. The genetic gains resulting from the thinning operations on 1010 of the progenies were estimated to range from 2% for the milde r utilization areas to 6% for the harshest. It should be possible to d ouble or triple gains by harvesting seed selectively from the five sup erior families.