The Role of Free Growth in the Differentiation of Provenances of Black Spruce Piceamariana (Mill.) B.S.P.

Abstract

Two distinct phases of needle initiation contributed to the annual complement of needles of 4-year-old black spruce seedlings. The first phase occurred during development of the overwintering bud, and was expressed in predetermined growth. The second phase occurred in the same season as the overwintering bud was flushed, and was expressed in free growth. Ten black spruce provenances were flushed under conditions favorable or unfavorable for free growth. Variation in needle complements for overwintering buds was small and did not correlate with variation in height growth of provenances. Good correlation occurred between growth and needle complements when these included foliage initiated during any subsequent free growth. Fast growth of southern provenances grown at Chalk River, Ont. (46°00′N, 77°26′W), was interpreted as a result of less stringent requirements for free growth. Free growth potential was reduced or disappeared when the local photoperiod was shorter than that at the origin of the provenance. Free growth is characteristic of seedlings only, but advantages thus obtained by southern provenances in the first few years of growth probably establish lasting gains in height.