Plus-tree selection of black spruce in Northwestern Ontario for Superior growing space efficiency

Abstract

Plus-tree selection of black spruce [Picea mariana (Mill.) B.S.P.) based on increment of wood volume per unit of crown (growing space efficiency) has the potential to improve yield per hectare and avoid biased selection of trees that have a competitive advantage in natural stands. In 1981, and again in 1983, 200 and 400 trees from two 60 year-old upland black spruce stands located in Northwestern Ontario were scored for various growth parameters, crown dimensions and competition indices. Regression analysis showed that the competition indices were poorer indicators of basal area increment (b.a.i.) than the crown parameters. The crown parameter that best predicted b.a.i. was crown area (c.a.); r[superscript] 2 values of 0.45 and 0.57 respectively were calculated for the two black spruce stands although the slopes differed significantly. To test the effectiveness of baseline selection of black spruce based on the regression of b.a.i. vs. c.a., the top 10 trees were selected from the second stand by this method and compared to each of the top 10 trees chosen by a height vs, age baseline method and a purely random method. Only one tree was selected in common by each of the baseline methods. Trees selected by b.a.i. vs. c.a. baseline were far more variable in their size than those selected by height vs. age. Scale drawings and statistical analysis of the selected trees did not reveal any easily identified crop ideotype of black spruce plus-trees expressing growing space efficiency. Wind-pollinated seed of the 29 selected trees was collected and used to establish a short-term and a long-term progeny test to investigate heritability of growing space efficiency. The short-term test was conducted in a greenhouse over one growing season and included light intensity as a treatment, while the long-term progeny test was planted in 1984 and included spacing as a treatment. Discriminant analysis of Marks Lake progeny helped to identify a weak trend where the tallest progeny came from short-crowned parents. Results of the short-term progeny test demonstrated strong family differences, strong family x light interaction, but no selection method differences. Some of the family differences in the progeny could be accounted for by the maternal effect of seed weight, although after removal of this effect by analysis of covariance, still no differences could be detected between selection methods. Parent and progeny correlations for height and crown features were weak and often negative, which suggests heritability estimates for characters related to growing space efficiency are likely to be as low as estimates for growth in general. The premature results of this study imply that if trees selected for superior growing space efficiency have inherent advantages in lower light intensities within mature stands, their juvenile progeny do not express these qualities. Characters responsible for growing space efficiency are not heritable or have not yet expressed themselves.