Estimating the timing of maximum pollen release from jack pine (Pinus banksiana Lamb.) in northern Ontario

A practical heat sum method was validated for estimating the date of maximal pollen release of jack pine (Pinus banksiana Lamb.) in northern Ontario. The base temperature and start date that minimized differences between estimated and observed maximum pollen release dates were sought. Heat sums were calculated for all data sets (n = 26) for a range of base temperatures (1 to 20 °C) and start dates (January 1 to maximum pollen release). The best combination was a start date at Julian day 107 and base temperature at 4 °C. The heat sum to maximum pollen release was 288.58 degree days and the average difference between estimated and observed was 2.75 days. Recommendations for operational testing are made. Key words: heat sum, phenology, Piuns banksiana Lamb., temperature, pollen, dehiscence, contamination, seed orchard