Development of flowering and the effect of pruning in a clonal seed orchard of lodgepole pine

Abstract

The development of female and male flowering among 20 clones was studied in a clonal seed orchard of lodgepole pine (Pinuscontorta var. latifolia Engelm.) in central Sweden. Flowering in relation to height, crown volume, and pruning was also studied. Twelve years after grafting (7 years after field planting), female flowering averaged 43 strobili per graft while male strobili were few. Eighteen years from grafting, the number of female and male strobuli were 143 and 142, respectively. The female effective population size was around 80% of maximum and was stable during the whole period. The male effective population size increased from 25 to 68%. Index of monoecy increased from 58 to 81% of maximum. The results indicate that at around 18 years after grafting, female and male flowering were satisfactorily distributed among the clones. There were no clonal correlations between male flowering and female flowering, while correlations between years for those traits separately were strong. Male flowering showed stronger correlation to the size of the graft than female flowering.