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.
We investigated the methods to promote flower and seed setting in 2-3 years old grafted trees of the hinoki (Chamaecyparis obtusa) clones producing little pollen that have been selected from Chiba Prefecture. As a result, the GA paste (1.5mg) application to the stems of the trees was the most promising method, with little adverse effects on their growth due to leaf die-back. Seed germination rates were from 20 to 69%, when stink bug repellant bags were used, which were sufficient for utilizing the seeds in the forest tree breeding programs. Based on the data acquired in this study, we estimated the area of the miniature seed orchard that can produce as many as seeds for covering the demand in Chiba Prefecture. The estimated area was 0.565 ha, which would be feasible area for the construction of the miniature seed orchard.