Newton s ( 2003 ) systematic review of yield responses of white spruce and 3 other North American 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.
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