| dc.description.abstract | Overall tree form ofjack pine (Pinus banksiana Lamb.) growing in natural stands
varies from straight slender trees with compact crowns to broad, limby and even multi-stemed
trees. Jack pine grown in plantations at conventional spacings of 2 m develops
form traits undesirable for forestry utilization. The goal of this study was to investigate
the effects and interaction of spacing and genetic factors on plantation-grown jack pine to
determine the potential benefit of a selection program based on form traits. Ten wind-pollinated
families were collected from each of six natural fire-origin stands from east
and west of Lake Nipigon in northwestern Ontario that had been subjectively rated as
good, average and poor in form. These sixty families making up six form-quality groups,
together with an additional twenty plus tree families making up two more form-quality
groups, were established at two planting sites with contrasting soil texture and fertility at
spacings of 1, 2 and 3 m. Eight tree form quality traits—branch length, branch diameter,
branch angle, branch number, relative branch diameter, relative crown width, number of
crooks, and taper were measured and analyzed together with two growth traits—height
and diameter at breast height (DBH) at age eight. General linear models were used to
evaluate the effects of site, spacing, form-quality group, family and the relevant
interactions on all traits except number of crooks which was not normally distributed. All
jack pine growth and form traits except branch number were greatly affected by spacing.
Most of the change in form traits occurred when spacing increased from 1 to 2 m with
lesser change from 2 to 3 m. This effect was more pronounced at the more fertile test site.
Form-quality groups were significantly different for only two of the form traits—branch
length and branch angle with this effect again being more evident at the fertile test site.
However, the family effect was significant for all seven tested form traits as well as the
two growth traits suggesting that any of these traits would readily respond to family
selection. A definite provenance effect was demonstrated for growth traits and stem
taper; the western sources grew faster with more favourable taper. None of the form quality
group X spacing nor the family x spacing interactions were significant.
Heritabilities and genetic correlations were determined for all traits separately for each
spacing at each test site. Traits height, branch angle and taper had the highest
heritabilities, with individual heritabilities of greater than 0.15, and the traits branch
diameter, relative branch diameter and relative crown width had values less than 0.05.
The two growth traits together with growth-related form traits tended to be strongly
positively correlated with the exception of height and relative crown width. However,
branch angle and branch number showed no strong correlations with any other tree form
and growth traits. Both heritabilities and genetic correlations were more meaningful for
the more fertile test site due to larger components of family variance. | |
