Selection of Piceamariana for growing space efficiency
In an attempt to select black spruce (Piceamariana (Mill.) B.S.P.) based on growing space efficiency, 398 candidate black spruce trees from a 60-year-old upland stand were measured for various growth and crown parameters. The best 10 trees were selected by two base lines: basal area increment vs. crown area and stem volume vs. crown radius. For comparison 10 trees were also selected by a height vs. age base line and 10 were randomly chosen to serve as a control. Only one tree was selected by all three base lines, but four other trees were selected by two of the three methods. Although discriminant analysis correctly classified 85% of the trees into the four selection and control groups, the high levels of variation associated with the growing-space efficiency base line trees made it impossible to identify a generalized form (crop ideotype) that was associated with either method. Short-term and long-term progeny tests were established to determine the relative gains associated with the different base-line selection methods. A greenhouse test was conducted over one growing season and included light intensity as a treatment; the long-term test was planted in 1984 and included spacing as a treatment. Results of the short-term test demonstrated strong family differences and strong family × light interaction, but no selection method differences or selection method × light interaction. While the long-term test was not yet mature enough to test the effect of spacing, the 2-year height growth results demonstrated strong family differences and no selection method differences. Correlation between the results of the two tests was significant (r = 0.61, P < 0.01), indicating a fairly high level of reproducibility in the juvenile progeny results. A weak, but consistent, trend of slower growth by the progeny of selected parents relative to randomly selected controls was observed. These early results suggest that if black spruce trees selected for superior growing space efficiency have inherent advantages in lower light intensities or more densely spaced situations in mature stands, their open-pollinated progeny do not express these qualities after one or two season's growth.