Growth phenology and crown structure of selected loblolly pine families planted at two spacings

Growth phenology and crown structure of five open-pollinated loblolly pine (Pinus taeda L.) families, planted at two spacings (0.92 and 1.83 m) and grown in pure plots near Summerville, SC, were investigated using a split-plot (main plots = spacing, subplots = genotype) field design. Shoot, branch, and foliage characteristics were quantified during the fourth growing season and related to standing volume. Genotype variation in shoot and branch characteristics was generally small and nonsignificant except for differences in annual height increment (from 135 to 152 cm) and current-year branch production (from 11.1 to 14.0). Significant genotype variation in foliage amount, distribution, and longevity was associated with contrasting growth performances and stage of stand development. Foliage biomass differed by as much as 60% among genotypes (from 4.8 to 7.7 Mg ha-1), with 38% of the variation related to family differences in total height. The large range in foliage biomass was the major contributor to leaf area index differences (LAI; from 7.9 to 13.6 m2 m-2), although significant genotype differences in weighted specific needle area (SNA; from 175 to 199 cm2 g-1) were also a factor. Genotype variation in foliage biomass and LAI was related to the vertical distribution of foliage, and both were significantly correlated with standing volume at age 3 yr (r = 0.64 and 0.59). The best performing families (3, 7, and 49 based on progeny testing) held > 60% of their total foliage biomass in the middle crown third (nonuniform distribution), whereas the poorest families (37 and 138), had < 50% in the same region (more uniform distribution). Compared to the other genotypes, family 37 exhibited reduced foliage longevity, which may have contributed to its low LAI and poor growth performance. Results of this study suggest that foliage display, amount, and duration are the crown characteristics important in conferring differential family performance for loblolly pine.