Patterns of cone distribution in crowns of young Piceamariana. I. Effect of tree age on seed cones

Abstract

The distribution of seed cones on shoots, on branches, and within the crown was determined for young Piceamariana (Mill.) B.S.P. (black spruce) trees aged 6–18 years. The seed-cone zone was restricted to distal 1-year-old shoots until ages 7 and 8. It expanded with increasing tree age, and in association with increases in cone numbers, to include older branches and a great variety of smaller shoots on those branches. By age 18, about 25, 55, and 20% of the cone crop was borne by 1-, 2-, and 3-year-old branches, respectively; hence, a concentration of cones, typical of the species, was maintained near the tree apex. Order 1 shoots bore all cones up to tree ages 7 and 8, but proportions on such shoots decreased with increasing tree age. By tree age 18, order 1, 2, and 3 shoots bore 27, 72, and 1% of the crop, respectively. Seed cones occurred progressively from proximal to distal and finally terminal positions on shoots of different categories following three patterns of decreasing shoot vigour (length). Medial and distal cones were most common. Terminal cones were located only on the weakest shoots within the seed-cone zone.