Genetic Parameters of Growth Traits and Stem Quality of Silver Birch in a Low-Density Clonal Plantation

Abstract

Silver birch (Betula pendula Roth) is productive on abandoned agriculture land, and thus might be considered as an option for profitable plantation forestry. Application of the most productive genotypes is essential. However, information about genetic gains in low-density plantations is still lacking. A 40-year-old low-density (400 trees ha −1 ) plantation of 22 grafted silver birch plus-tree clones growing on former agricultural land in the central Latvia was studied. Although grafted plantations are not common in commercial forestry, the trial provided an opportunity to assess genetic parameters of middle-aged birch. The plantation that had reached the target diameter for final harvest (DBH (diameter at breast height) = 27.7 ± 5.5 cm) had an 85% survival rate, and stemwood productivity was 5.25 m 3 ha −1 year −1 . Still, rootstock × scion interaction and cyclophysis might have caused some biases. Broad-sense heritability (H 2 ) ranged from 0.02 for probability of spike knots to 0.40 for branch angle. Estimated H 2 for monetary value of stemwood was 0.16. In general, the correlations between growth and stem quality traits were weak, implying independent genetic control, though branchiness strongly correlated with diameter at breast height. The monetary value of stemwood strongly correlated with productivity traits. The observed correlations suggested that productivity and stem quality of birch might be improved simultaneously by genetic selection.

Genetic parameters of growth and quality traits in open-pollinated silver birch progeny tests

“…In Scotland, straight stems found to be associated with superior volume growth (Malcolm and Worrell 2001), yet not observed in our study. Similar to previous findings in Sweden and Latvia (Stener and Jansson 2005;Zeltiņš et al 2018), BrD and BrA possessed high heritabilities. However, the substantial negative correlations between BrA and StStr might result in enlarged knot size for straighter logs, thus reducing technical quality (Niemistö 1995a).…”

“…In the Baltic sea region, heritabilities for growth and stem quality of common forest tree species Scots pine and Norway spruce reported to vary from 0.05 to 0.25 (Velling 1982;Haapanen et al 1997;Hannrup et al 1998;Olsson and Ericsson 2002;Jansons et al 2006). In our study, h 2 for growth traits were mainly moderate to high, and genetic correlation among them were strong, supported by earlier findings in Latvia (Zeltiņš et al 2018). Considering that the genes controlling each of growth traits might be strongly correlated (Searle 1961), selection may be based on tree height, which possessed the highest h 2 .…”

“…In contrast, insufficient maintenance, subsequent uneven survival and heterogeneous growth conditions commonly reported to result in low heritability indices with low accuracy, reducing benefits from tree breeding (Haapanen 1996;Mäkinen 1996;Talbot 1997;Nummi 1999;Olsson and Ericsson 2002;Koski and Rousi 2005). Nevertheless, mainly low h 2 for such stem defects as SpKn, Doubl and LostTop (0.04-0.29) coincides with earlier findings (Stener and Hedenberg 2003;Zeltiņš et al 2018), suggesting relatively weak genetic control and strong prevailing effect of such environmental factors as drought, frost or biotic damage (Malcolm and Worrell 2001;Stener and Hedenberg 2003). Stener and Jansson (2005) reported low h 2 and H 2 values (0.09-0.27) for StStr in a series of up to 10 years old silver birch clonal and progeny trials.…”

“…Considering that the genes controlling each of growth traits might be strongly correlated (Searle 1961), selection may be based on tree height, which possessed the highest h 2 . In earlier studies, estimated h 2 and broad-sense heritability H 2 of corresponding traits for silver birch reported to vary widely from low to high (Nepveu and Velling 1983;Malcolm and Worrell 2001;Stener and Jansson 2005;Zeltiņš et al 2018). In Norway, narrow-sense heritability h 2 of six-years-old open-pollinated families estimated to be rather low, i.e.…”

“…In the Eastern Baltic region, breeding activities in combination with appropriate silviculture (e.g. planting density) can result in highly productive silver birch stands for valuable plywood production (Stener and Hedenberg 2003), as confirmed by a clonal birch plantation in Central Latvia ready for harvest at the age of 40 years (Zeltiņš et al 2018). The selection of genotypes must be based on the growth traits and stem quality traits such as stem straightness, desirable branch properties, and apical dominance (Stener and Hedenberg 2003).…”