Genetic evaluation, multiple‐trait selection criteria and genetic thinning ofpinus contortavar.latifoliaseed orchards in sweden

Seedling seed orchards were established in Sweden with 1112 open pollinated progenies of Pinus contorta Douglas ex Loudon plus‐trees, selected from 88 wild stands in western Canada. The progenies were also grown in Swedish test plantations. Breeding values (best linear unbiased predictors) were calculated for tree condition, height, and ramicorn whorl frequency, assessed at ages ranging between 8 and 12 yrs. On the harshest sites, damage caused by weather and fungi, e.g. Gremmeniella abietina, were also evaluated. Categorical data were transformed into values on a normal score scale to improve the efficiency of the evaluation. Breeding values for all assessed traits were combined to form total‐value indices. These indices were then used to guide the genetic thinning of the seed orchards, where single trees were selected from groups of four. The genetic gains resulting from the thinning operations on 1010 of the progenies were estimated to range from 2% for the milder utilization areas to 6% for the harshest. It should be possible to double or triple gains by harvesting seed selectively from the five superior families.