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 m aximal pollen release of jack pine (Pinus banksiana Lamb.) in northern Ontario. The base temperature and start date that minimized differenc es between estimated and observed maximum pollen release dates were so ught. Heat sums were calculated for all data sets (n = 26) for a range of base temperatures (1 to 20 degrees C) and start dates (January 1 t o maximum pollen release). The best combination was a start date at Ju lian day 107 and base temperature at 4 degrees C. The heat sum to maxi mum pollen release was 288.58 degree days and the average difference b etween estimated and observed was 2.75 days. Recommendations for opera tional testing are made.