Editing Tree breeding (section)

==Tree improvement==

A genetically variable population and a method of selecting genetically superior individuals provide the basis for tree improvement by breeding. In essence, a tree improvement program sets out to isolate and evaluate the genetic component of variation in one or more characters of interest. In the simplest procedure, cycles of selection reduce the available population in a particular direction to enhance desirable traits, then breeding from selections to expand the population with improved characteristics. Breeding strategies vary with species and objectives, but all use mating designs to generate information and new material. Choice of a suitable breeding strategy and mating design is a key decision in any breeding program. Kiss (1986)<ref name="kiss3">Kiss, G.K. 1986. Genetic improvement of white and Engelmann spruce in British Columbia 1983–85. p. 191–193 ''in ''Yeatman, C.W.; Boyle, T.J.B. (Eds.), Proc. 20th Meet. Can. Tree Improv. Assoc. Part 1, Quebec QC.</ref> used a 2-level design in British Columbia to study variation within and between separate populations of [[white spruce]], both within British Columbia and from eastern North America.

The breeding program for white spruce initiated in 1986 by the Canadian Forestry Service in the Maritimes employed 2 kinds of mating: polycross, to test clones for general combining ability; and pair-mating, to generate material for second generation selections (Fowler et al. 1988).<ref name="fowler">Fowler, D.P., Bonga, J.M., Park, Y.S., Simpson, J.D., and Smith, R.F. 1988. Tree breeding at the Canadian Forestry Service – Maritimes 1985 and 1986. p. 31–36 ''in'' Morgenstern, E.K.; Boyle, T.J.B. (Eds.). Tree Improvement – Progressing Together Sympos., Truro NS, Aug. 1987. Proc. Part 1, 21st Meet. Can. Tree Improv. Assoc.</ref>

Newton's (2003)<ref name="newton">Newton, P.F. 2003. Systematic review of yield responses of four North American conifers to forest tree improvement practices. For. Ecol. Manage. 172:29–51.</ref> systematic review of yield responses of white spruce and 3 other North American [[Pinophyta|conifers]] to forest tree improvement practices indicated that correct provenance-progeny selection could yield juvenile height growth gains of about 12% at 20 years for white spruce, and a corresponding merchantable productivity (mean annual merchantable volume increment) gain of 26% at 50 years for plantations established at nominal initial densities on medium-to-good quality sites. Also, preliminary estimates derived from individual case studies indicated that first generational selection strategies for white spruce could increase merchantable productivity by approximately 20% at 45 years.{{cn|date=September 2024}}