Selection for Improved Growth and Wood Density in Lodgepole Pine: Effects on Radial Patterns of Wood Variation

Changes in growth and wood density traits were investigated across annual rings of 12-year-old trees from four selected subpopulations in lodgepole pine (Pinus contorta Dougl. Ex Loud var. latifolia Engelm) based on X-ray densitometry profile data. Four subpopulations were constructed based on height growth and wood density as follows: 1) fast growth and high wood density (FH); 2) slow growth and high density (SH); 3) fast growth and low density (FL); and 4) slow growth and low density (SL). Annual ring density was initially high, declined with age until age 10, and then plateaued. Significant differences among subpopulations were found for ring density, earlywood and latewood densities, ring width, earlywood width, latewood proportion, and earlywood width after age 6. Wood density decreased less from the pith to the bark in both overall and earlywood densities in the FH subpopulation, resulting in denser, more homogeneous wood than in other subpopulations. This suggests that it may be possible to increase wood density and homogeneity in juvenile wood of this species by selecting FH families. Overall ring density may be better improved by selecting for earlywood and latewood components separately. The earliest age of which families combining fast growth and high wood density can be accurately identified is about 7 years