Systematic review of yield responses of four North American conifers to forest tree improvement practices

Abstract

The objective of this review was to summarize the expected yield gains of black spruce ( Picea mariana (Mill.) B.S.P.), jack pine ( Pinus banksiana Lamb.), white spruce ( Picea glauca (Moench) Voss) and red pine ( Pinus resinosa Ait.), to correct provenance-progeny selection, first generational selection strategies and second generational selection strategies, based on a systematic assessment of the scientific literature. The procedure consisted of four sequential steps: (1) searching electronic databases for relevant forest tree improvement studies employing a meta-analytical protocol; (2) attaining and assessing the identified publications for their specific applicability; (3) collating the results of the resultant study subset in terms of relative height growth gains; and (4) estimating rotational consequences in terms of merchantable productivity via prediction models. The results of the systematic search indicated that documented long-term yield responses to tree improvement were paucity in nature. Specifically, the majority of the published studies consisted of short-term results pertaining to provenance-progeny experiments. Furthermore, studies reporting yield responses to first and second generational selection strategies were practically non-existent. Consequently, expert opinion and unpublished preliminary results derived from ongoing tree improvement experiments were used to augment the limited published information available for these selection strategies. Overall, the results indicated that correct provenance-progeny selection could yield juvenile height growth gains of approximately 15% at 15 years for black spruce, 7% at 21 years for jack pine, 12% at 20 years for white spruce and 8% at 15 years for red pine. Corresponding merchantable productivity (mean annual merchantable volume increment) gains at rotation (50 years) for plantations established at nominal initial densities on medium-to-good quality sites were approximately 17, 15, 26 and 7%, respectively. Preliminary estimates derived from individual case-studies indicated that (1) first generational selection strategies could increase merchantable productivity by approximately 13% at 50 years for black spruce, 28% at 40 years for jack pine, and 20% at 45 years for white spruce, and (2) second generational selection strategies could increase merchantable productivity by approximately 31% at 50 years for black spruce.