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 a bies (L.) Karst.] populations growing in northern Sweden (63 degrees 54' N) were monitored in 1996. Annual leader shoot lengths and shoot growth compo nents for the period 1990-1997 were measured in 1997. In 1997 populations t ransferred more than approximately 3 degrees in latitude were found to be s horter than local populations. MI levels were initially high in all populat ions in mid-April. In spring, populations originating north of 63 degrees 3 0' N showed higher MI levels, and started shoot growth earlier, than popula tions originating further south. In autumn, MI levels were higher in popula tions originating south of 63 degrees 30' N than in populations originating further north and higher in seed orchard populations than in natural popul ations of similar latitudinal origin. The number of stem-units (NSU) was co rrelated with tree height and leader shoot length. NSU and elongation of st em-units appeared to be primarily influenced by summer temperature. Prolong ed MI activity in autumn did not result in high NSU but appeared to be asso ciated with a higher risk of frost damage to buds. The results are discusse d in relation to climatic factors, seed transfer, selection and inherent gr owth rhythms.