A Heat Sum Model For Loblolly Pine Pollen Development

Catkin development was recorded at 2 to 7-day intervals in February and March of 1988 to 1992 for 90 ramets from 31 families at the Weyerhaueser Company's loblolly pine seed orchard in Lyons, Georgia. Four to twelve clusters per ramet were observed each year and scored for development on a 6-point scale. The timing of catkin development varied widely over the study period. For example, the date when pollen release began (score = 4.0) varied from February 17 in 1990 to March 6 in 1988 for the earliest family and from March 7 in 1990 to March 26 in 1988 for the latest family. A heat sum model was developed to account for this annual variation using the first four years of data from 12 families measured all five years. The model which explained the most variation accumulated heat units above a threshold of 37 °F starting January 17. Different families required different heat sums to reach a given stage of catkin development. The model was validated using development data from 1992. The model predicted the time of 50 % pollen shedding (score = 5.5) within 1 day for 7 families, within 2 days for 3 more families, and within 4 and 6 days for the remaining two families.

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Author(s): W. C. Woodbridge, Floyd E. Bridgwater, David L. Bramlett

Publication: Tree Improvement and Genetics - Southern Forest Tree Improvement Conference - 1995