Phenotypic differences between natural and selected populations of Picea abies. II. Apical mitotic activity and growth related parameters.

Apical mitotic index (MI) and growth of non-juvenile Norway spruce [Picea abies (L.) Karst.] populations growing in northern Sweden (63°54' N) were monitored in 1996. Annual leader shoot lengths and shoot growth components for the period 1990-1997 were measured in 1997. In 1997 populations transferred more than approximately 3° in latitude were found to be shorter than local populations. MI levels were initially high in all populations in mid-April. In spring, populations originating north of 63°30' N showed higher MI levels, and started shoot growth earlier, than populations originating further south. In autumn, MI levels were higher in populations originating south of 63°30' N than in populations originating further north and higher in seed orchard populations than in natural populations of similar latitudinal origin. The number of stem-units (NSU) was correlated with tree height and leader shoot length. NSU and elongation of stem-units appeared to be primarily influenced by summer temperature. Prolonge...