The variation of pollination timing in a Cryptomeria japonica miniature seed orchard established in a heavy snow region

Abstract

For the purpose of reducing pollen contamination and improving cross-pollination within seed orchards in regions with heavy snowfall, the pollination dynamics in Cryptomeria japonica was surveyed in its miniature seed orchard for 5 years. We found that if certain climate conditions coincide, it was possible to increase cross-pollination within the orchard due to a delay in the flowering of trees in the orchard. The following conditions could help reduce pollen contamination: (1) deviating the flowering seasons of the trees inside orchard from that of the trees outside the orchard, (2) reducing the variation in flowering seasons between male and female flowers in the orchard and completing the flowering for a short period, and (3) the short-term convergence in flowering of the trees outside the orchard. We considered the continuance of warm weather during the period from the thaw of a large amount of snowfall to the flowering season to be an important climate-based factor. These conditions were met during 2006 and 2008 flowering seasons. In the two years the immigrated airborne pollen when flowering in the orchard made up less than 10% of the total number of immigrated airborne pollen during the whole season, suggesting that airborne pollen contamination in the orchard was low. However, in the years in which the conditions are not met, some kinds of artificial measures are necessary.