Predicting Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) Volume at Age 15 with Early Traits

1990

S. 29-35

2 Abb., 5 Tab., 19 Lit. Ang.

Unselbständiges Werk

200051162

This paper presents data from a Douglas fir provenance progeny test located in southwestern France. This test was planted after intensive site preparation. It was thinned twice before trees were 15 years old (19 years from seed) so that tree crowns can be considered to have grown with little or no competition for light. After 15 years, individual tree volume was found to be twice as large as predicted in forest management tables. The study concentrated on the two fastest growing provenances, namely Darrington and Enumclaw, each being represented by 15 open-pollinated progenies (611 trees all told). Height and girth measurements were taken periodically between ages 2 and 15. All traits, especially girth at breast height, showed high levels of narrow-sense heritability as well as strong additive genetic correlations with stem volume at age 15(V15). Different indirect selection schemes using early traits were explored with the aim of improving V15. At age 8 years after planting, an index combining total height and square girth procured on V15, 90% of the genetic gain which would be obtained on this trait through direct selection. On the contrary, the correlation between family means for total height at age 2 (nursery) and 19 (field) from seed was found weak. Two main consequences are drawn from these results. First, when juvenile-mature correlations are looked at, height and girth growth rates need to be as high as possible in evaluation field trials; in particular, competition between crowns should be avoided. Second, it seems to be possible, under a few constraints, to shorten substantially the length of Douglas fir breeding cycles.