Effects of genetic entry and spacing on growth and wood properties in Scots pine

Abstract

In forest breeding, stem volume and sawn timber quality have typically been used as the most important selection traits. Less attention has been paid to wood density and fibre properties. This study investigates the effects of genetic entry and spacing on the growth and yield traits, branch characteristics, wood density traits and fibre properties in 20-year-old Scots pines (Pinus sylvestris L.). Additionally, the phenotypic variation within, and correlations between, different traits and the effects of cambial age, spacing, genetic entry and climatic variables on the ring width and ring density development from pith to bark are studied. Kanerva pine (Finnish plus tree S1101) was the father tree for most of the genetic entries included in this study, whereas the mother trees represented Finnish plus trees with a relatively wide geographical range from northern to southern Finland. The effects of genetic entry (mainly full-sib families) and spacing on the growth and yield traits, wood density traits and fibre properties were analysed (Papers I-II) based on materials, harvested in 2006, from 10 genetic entries grown in a spacing trial in central Finland, with a current stand density range of 2000-4000 trees/ha. Furthermore, additional material was harvested from the same trial in 2008 to study the effects of genetic entry and spacing on the branch characteristics (Paper III) and the effects of cambial age, spacing, genetic entry and climatic variables on the ring width and ring density development from pith to bark (Paper IV). In this study wood density traits show lower phenotypic variation compared to growth and yield traits, regardless of spacing. Wood density traits present from moderate to strong phenotypic correlations among them (Paper I). Spacing affects significantly (p<0.05) all the yield traits, wood density traits and fibre properties (Papers I-II). Furthermore, spacing affects living branch characteristics such as relative average branch diameter and relative cumulative branch area (Paper III). Genetic entry affects tree height, wood density traits and fibre length (Papers I-II). When grouping the Kanerva tree crossings into different geographical origins based on their mother trees, the northern ones have, on average, the largest diameter at breast height and the highest mean wood density, while the central ones have the tallest trees (Paper III). Branch diameter along the stem is affected by branch age, geographical origin group and spacing, while branch angle is affected by branch age and genetic entry (p<0.05). Radial growth and ring density development are both affected by cambial age and spacing, and the latter is also affected by origin group and several climatic variables. The phenotypic correlations between various growth, yield and wood density traits are negative, which suggests that selection for one trait would simultaneously affect the other traits. The phenotypic correlations between different fibre properties are strong, but not well correlated with growth, yield and wood density traits. This kind of information is currently needed for breeders for considering different traits as selection criteria for tree breeding in Scots pine.