Reproductive phenology in a Norway spruce seed orchard

Reproductive phenology was studied in a Norway spruce seed orchard, located in southern Finland (62 degrees 13'N, 25 degrees 24'E), consisting of 67 c lones from northern Finland (64 degrees -67 degreesN). Timing of flowering was determined on the basis of data recorded by a pollen catch meter during 1984-1995, and visual observations made on grafts in 1989, 1992, 1993 and 1995. The genetic and environmental factors affecting female and male pheno logy, and reproductive synchronisation were studied. The between-year variation in the timing of flowering was more than three w eeks. However, when it was defined on the basis of the effective temperatur e sum, the variation was smaller. No phenological reproductive isolation wa s found between the seed orchard and surrounding natural forests. The durat ion of the receptive period of the seed orchard varied from 5 to 8 days, an d anthesis determined on the basis of airborne pollen from 5 to 10 days. Th e receptive period started about one day earlier than anthesis, except in o ne abnormally warm flowering period when female and male flowering started simultaneously. In general, the flowering periods of the different clones o verlapped. The clonal differences in the phenology of receptivity were in m ost cases statistically significant, but in pollen shedding they were not. The broad-sense heritability estimates were higher for female than for male phenology. Environmental factors, conversely, had a stronger effect on mal e phenology. A wide graft spacing and a graft position that favoured solar radiation on the lower parts of the crown promoted early pollen shedding an d, subsequently, better reproductive synchronisation between female and mal e flowering.